Can Solar Fuels Avert an Imminent Petroleum Fuels Crisis?

This is a lengthy article, which will be published in the next issue of the journal "Science Progress". A quick summary can be found in the article immediately following this one.

 

The Problem of Energy.

The world population of 7 billion humans uses energy at a mean rate of 16 TW (16 terawatts). This amounts to an annual 504 EJ (504 exajoules = 5.04 x 10²⁰ J), and is provided from fossil fuels (oil, gas and coal), plus nuclear and hydro (hydroelectric) power along with all other forms of renewable energy¹. The breakdown of these various contributions is given in Table 1. Around one third of the total energy used by humans on Earth is provided by crude oil, and close to one quarter each by natural gas and coal, although the amount of coal being burned is rising, particularly in China. Nuclear and hydro-power each contribute around 6% of the total energy mix, while the combination of renewable energy from all sources, wind, wave, geothermal, wood, solar etc. amounts to just a little above 1%. In 2004, humanity used 471 EJ of energy², and while the relative proportion of each contributing energy source has remained modestly constant, it is clear that at a rise to 504 EJ in 2010, the demand placed upon these energy sources is rising relentlessly. This follows not merely a growing human population per se, but an increasingly affluent industrialised consumer society. We need to consider two aspects: firstly, that the CO₂ produced by burning fossil fuels is believed to contribute to global-warming and this may lead to unwelcome or even catastrophic changes to the global climate³. Secondly, and more immediately, the fossil fuels and uranium too (for nuclear power) are in finite supply, and there is compelling evidence that each source will meet its own production peak within the next two decades. Most vulnerable appears to be crude oil (petroleum), world supplies of which are predicted to peak (“peak oil”) probably during the next 5 years⁴. Irrespective of the exact timing of peak oil, there are salient predictions (see below) that a gap will emerge in the supply of oil against demand for it, from the end of this year (2012), rising to a shortfall of 10 million barrels a day by 2015⁵. This situation has been termed “gap oil”⁶, and can only be exacerbated by peak oil, when supply must draw-down against rising demand, thus enlarging the gap from both sides. Thus, in order to curb carbon-emissions and to extend limited resources, alternative and ideally renewable sources of energy are needed.

Liquid Fuels and Transportation.

A simple comparison of the energy content delivered from different energy sources, as is made in Table 1, is somewhat misleading, since it seems to imply that if the production of one of them begins to fail, it can be readily substituted by another. The issue of transportation is a singular example where this is not the case, since practically all the vehicles used in the world – cars, lorries, buses, trains, ships and planes - have been engineered to run on liquid fuels that are refined from crude oil. Therefore the likely consequences of “peak oil”, with dwindling supplies and escalating costs of liquid fuels, are very serious. Ward's, the U.S. based publisher, estimated that as of 2010 there were 1.015 billion motor vehicles in use in the world⁷. This figure represents the number of cars, light, medium and heavy duty trucks, and buses, but does not include off-road vehicles or heavy construction equipment. Between 1950 and 1970, the world vehicle population doubled roughly every 10 years, passing the 250 million mark in 1970, and exceeding 500 million in 1986. It has been estimated that the world's road transportation fleet will reach 2 billion by 2020, of which at least 50% will be cars. China’s and India’s automobile fleets are expected to grow at an annual rate of around 7 or 8%, while in the United States, it will be under 1% a year, and around 1 to 2% in Western Europe, but this depends tacitly on finding an expanding liquid fuel supply, and it is this which is at issue.  Indeed, the International Energy Agency (IEA) has issued a report⁸ to the effect that a shortfall in oil production of 64 million barrels a day (mbd) can be expected by 2030, which represents a loss of 62% of the world supply of conventional crude oil, currently 84 mbd, assuming a demand by 2030 of 96 mbd, a figure significantly downgraded from prior estimates by the IEA of 120 - 130 mbd. At a mean decline rate of 2.9 mbd/year (-3.4%/year) this value accords closely with the prediction in a recent U.S. Army report⁵ that there will be a deficiency of 10 mbd by 2015, following a loss of any spare capacity for crude oil against demand for it by the end of this year (2012).

While it is possible to run cars and other road vehicles on electricity, provided either from batteries or hydrogen/fuel cells, actually converting their number substantially to these alternative energy carriers (neither electrons nor hydrogen being primary fuels, i.e. they must be created from primary sources) would be such a considerable undertaking that the scheme is not feasible. Vehicles can be adapted to run on gas but a peak in natural gas production is expected within twenty years, following oil, and converting them all would take many decades, so this is no solution either. It is, therefore, a new source of liquid fuels that must be sought, since they would be far more compatible with a transportation fleet and distribution infrastructure designed for liquid petroleum fuels. These, ideally, should be “carbon-neutral” in order to reduce carbon emissions, a condition which certainly does not apply⁴ to coal-to-liquids processing (with probably twice the carbon emissions overall that are incurred in the production and burning of diesel or petrol derived from petroleum), nor gas-to-liquids either, unless the CO₂ is captured and stored in some way that prevents it escaping into the atmosphere. Biofuels are attended by a number of vexed issues⁶: the competition for arable land between growing crops for fuel or crops for food, the increased amount of freshwater required to grow fuel crops above that already needed for agriculture, the clearing of rainforest to produce high-energy fuel-crops, e.g. palm-oil, and the fundamental EROEI which for bioethanol may only marginally exceed the overall energy costs of its production, or in some cases not quite break-even. Clearly, some other strategy is necessary.

Table 1. Fuel type: Average power in TW (10¹² W) Energy/year in EJ (10¹⁸ J) (2010 figures), (Data from reference 1).

Oil: 5.4 TW (169 EJ)

Gas: 3.8 TW (120 EJ)

Coal: 4.7 TW (149 EJ)

Hydroelectric: 0.8 TW (26 EJ)

Nuclear: 1.0 TW (33 EJ)

Geothermal, wind, solar, wood: 0.2 TW (7 EJ).

Total: 16.0 TW (504 EJ) (2010).

Solar Energy.

Figure 1 summarises the quantity and fate of solar radiation striking the top of the earth’s atmosphere². We see that 52 PW (10¹⁵ W) is reflected back into space (i.e. 30% of the total). Thus, in outer space, there is more solar energy available to be collected, which has prompted potential schemes to launch photovoltaic arrays into space on satellites², with which to capture the sun’s energy and then beam it back to earth in the form of microwaves for terrestrial applications. At the top of the atmosphere, with the sun directly overhead, the radiation flux provides around 1.4 kW/m² of energy, the “solar constant”². Since the total amount of energy¹ (oil, gas, coal, nuclear, hydro, everything) used on earth by humans amounts to a power of 16 TW, at 174 PW, the amount of radiation striking the exposed hemisphere of the earth is well over 10,000 times that. So if we could capture even a small amount of this bounty, and convert it into useable energy, the imminent energy crisis could be averted. Since the production of solar energy (and renewable energy generally, other than hydropower) has an intermittent quality – the sun doesn’t always shine, or not to the same extent throughout the day, and not at all at night – some method of storing it is essential to its use as a serious energy source, to supplant fossil fuels, and the creation by its means of a chemical fuel (solar fuel) would be the best means to achieve this. Furthermore, and as noted earlier, if liquid fuels could be produced in quantity, they would be entirely compatible with the present world transportation fleet based on liquid petroleum fuels, and a distribution network designed to supply the latter.

Means for capturing solar energy².

Solar energy can be captured by various means, which boil-down to either collecting heat directly from the sun’s rays, or using the wavelengths of the solar spectrum to grow biomass through photosynthesis, or to excite electrons in photovoltaic materials to produce electricity.

(1) Direct heating systems² à on-roof water heating systems; solar furnaces;  concentrating solar thermal power (CSTP) plants etc.

(2) Photosynthesis⁹ (PS) à creates biomass, and a total of 200 EJ of fuel (Shell estimate) could be produced by hydrothermal conversion. PS is 12% efficient as a theoretical maximum, but most plants give 0.1 - 6%. Growing biofuel crops also suffers from competition with food crops for fertile land, hence if we turned all the available arable land in the U.K. over to biofuel crops (i.e. grew no food at all) we could only match ca 17% of our fuel from rapeseed/biodiesel or ca 50% from sugar beet/ethanol as is currently made from crude oil. These estimates assume that all vehicles are first converted to diesel engines, which are more efficient in terms of tank-to-wheel miles than spark-ignition engines, which burn petrol, by about 40%.

(3) Photovoltaics^2,10. In essence, light photons knock electrons into higher energy states in semi-conductor materials such as silicon and cause conduction (electron diffusion), generating electricity. The photo-active material needs a band-gap of < 3.2 eV (i.e. at the edge of the visible spectrum, 400 nm), and ideally down to around 1.0 eV (1250 nm) - which is the “near” IR region. The actual recovered efficiencies for single-junction silicon cells are now approaching the theoretical efficiency of 33%, which is way ahead of that for photosynthesis (6%). In principle, quantum dot (QD) cells might achieve an efficiency of 42% or even 65% as a result of multiple exciton generation², although the record to date is a rather more modest 6%¹¹.

Fuels Made Using Concentrating Solar Thermal Power^12,13.

Those “fuels” that have been most pursued using various solar methods are H₂ and CO, and while each may indeed be used either in fuel cells or combustion engines, a mixture of them (known as synthesis gas or syngas), can be converted to liquid fuels, e.g. methanol, or hydrocarbons, using the Fischer Tropsch process⁴. The latter involves a series of chemical reactions that lead to a mixture of hydrocarbons (C_nH_(2n+2)) (equation 1):

(2n+1) H₂ + n CO → C_nH_(2n+2) + n H₂O                         (1),

where 'n' is a positive integer. It is mainly straight-chain alkanes that are formed and so the product is quite suitable as a diesel fuel. As we now discuss, there are various routes to forming H₂, but CO can be formed essentially either through steam reforming⁴ carbon-containing materials (methane, oil, coal, biomass) – which also yields H₂ - or by dry reforming¹⁴ with CO₂. Now the latter lends the possibility that CO₂, either as a product of steam reforming natural gas or as captured from power stations, might be intercepted from being emitted into the atmosphere and instead converted to useful fuels, in substitution for those presently refined from petroleum.

H₂ by direct thermolysis of H₂O.

Although it is conceptually the simplest process, the thermal dissociation of H₂O to

H₂ and O₂ is difficult to achieve in practice, since very high temperatures are required to attain a reasonable degree of dissociation (e.g. 2725°C for 64% dissociation at atmospheric pressure¹²), and it is necessary to separate the H₂ from O₂ to obviate the build-up of an explosive mixture. Ceramic membranes, such as those made from zirconia, have been tested but even these usually fail to withstand the thermal shocks incurred when exposed to high-flux solar radiation. Rapid-quench methods, in which a cold gas is expanded in a nozzle, or a solar-irradiated target is immersed in liquid water, are straightforward but cause a fall in the energy efficiency which is compounded by significant energy losses by radiation from the extremely hot reactor. Furthermore, the gas mixture is explosive. There are water-splitting multi-step thermochemical cycles which may be performed at significantly lower temperatures (below 950 ^oC), expected to be available in the future either from concentrating solar thermal power or from very high temperature nuclear reactors (VHTR), and which further avoid the necessity to separate H₂ from O₂.The leading candidates are a three-step sulphur iodine cycle (equations 2 - 4)¹³ based on the thermal decomposition of sulphuric acid at 850°C and a four-step UT-3 cycle (equations 5 - 8)¹³ based on the hydrolysis of calcium bromide and iron bromide at 750°C and 600°C, respectively. It is proposed that, in the longer run, a complete substitution of fossil fuels by solar H₂ might be achieved, while the decarbonization of fossil fuels in the medium term creates a link between today’s fossil-fuel-based technology and the solar chemical technology of tomorrow.

2H₂SO₄  → 2SO₂ + 2H₂O +O₂                          850 ^oC          (2)

2HI → H₂ + I₂                                                            300 ^oC          (3)

I₂ + SO₂ + 2H₂O → 2HI + H₂SO₄                      100 ^oC          (4)

2Br₂ + 2CaO → 2CaBr₂ + O₂                           600 ^oC          (5)

3FeBr₂ + 4H₂O → Fe₃O₄ + 6HBr + H₂               600 ^oC          (6)

CaBr₂ + H₂O → CaO + 2HBr                            750 ^oC          (7)

Fe₃O₄ + 8HBr → Br₂ + 3FeBr₂ + 4H₂O              300 ^oC          (8)

H₂ by decarbonization of fossil fuels.

There are principally three solar thermochemical processes for H₂ production using fossil fuels, namely: cracking, reforming, and gasification. In solar cracking, natural gas, oil, or other hydrocarbons are decomposed thermally into H₂ and carbon. The carbon can either be sequestered to avoid the release of CO₂, or used for other purposes. Steam-reforming of natural gas or oil, and steam-gasification of coal and other solid carbonaceous materials furnishes syngas, which may be converted to liquid hydrocarbon fuels, vide supra. The chemical properties of syngas accord principally to its differing content of H₂, CO, and CO₂. The CO content can be reduced in favour of H₂ via a catalysed reaction with steam, known as the water-gas shift reaction (equation 9):

CO_(g) + H₂O_(g) → CO_2(g) + H_2(g)                                                      (9)

CH₄(g) + CO₂(g) → 2CO(g) + 2H₂(g)                          (10)

The product, CO₂, can be separated from H₂, e.g. by using the pressure-swing adsorption technique, which is a method for the separation of a gas from a mixture of gases under pressure, according to particular molecular characteristics and affinity for an adsorbent material (e.g. through differential molecular electric quadrupole moments). Syngas may also be produced by the solar dry reforming of CH₄ with CO₂ (equation 10) and transported to locations to be used as a fuel directly. Stored solar energy is released by the reverse exothermic reaction in the form of heat, which can be used for generating electricity via a Rankine cycle. [The Rankine cycle generates about 90% of all electrical power used throughout the world, including that from virtually all solar thermal, biomass, fossil fuel and nuclear power plants. Heat is supplied externally to a closed loop, which normally uses water. The cycle also provides the fundamental thermodynamic basis of the steam engine]. Similarly, ammonia (NH₃) can be used in a chemical heat pipe to store and transport solar energy. In one system developed by the Australian National University (ANU), ammonia is dissociated in an energy storing (endothermic) chemical reactor as it absorbs solar thermal energy. At some subsequent place and time, the reaction products of H₂ and nitrogen (N₂) undergo an exothermic reaction in which ammonia is re-formed, releasing heat. An industrial demonstration plant has been announced using four of ANU’s 400 m² parabolic dishes¹⁵.

Solar steam gasification.

The steam-gasification of coal and oil shale has been investigated using concentrated solar energy. A conceptual design of a solar reactor for the gasification of carbonaceous materials was created using optical fibres to direct the solar radiation into the reaction chamber. In the project SYNPET¹⁵ (2003–2009), a solar thermal technology for the steam-gasification of petcoke particles was developed, using a 10 kW_th (th = thermal) solar reactor, directly exposed to concentrated solar radiation, with a continuous gas-particle vortex flow confined to a cavity receiver. A scale-up of the vortex solar reactor to 500 kW_th at the Plataforma Solar de Almería is currently being undertaken¹⁵.

Catalysed thermal methods¹⁷ for the production of H₂, CO and CH₄ from H₂O and CO₂.

The cerium(IV) oxide–cerium(III) oxide cycle (CeO₂/Ce₂O₃ cycle) is a two-step thermochemical process based on cerium(IV) oxide/cerium(III) oxide, and is normally employed for hydrogen production.  One advantage of this approach is that the H₂ and O₂ are generated in two distinct steps, and so it is unnecessary to separate the components of a high-temperature gas. The process constitutes a redox system:

Dissociation: 2CeO₂ → Ce₂O₃ + 0.5 O₂                                 (11)

Hydrolysis: Ce₂O₃ + H₂O → 2CeO₂ + H₂                               (12)

In the first step (equation 11), which is endothermic, cerium(IV) oxide is dissociated thermally, under an inert gas atmosphere at high temperatures, into cerium(III) oxide and oxygen. In the second step (equation 12), which is exothermic, cerium(III) oxide reacts at lower temperatures with water to produce hydrogen and regenerate cerium(IV) oxide. The strategy is also applicable to the dissociation of CO₂ (equations 13 - 14):

Dissociation: 2CeO₂ → Ce₂O₃ + 0.5 O₂                                                 (13)

Hydrolysis: Ce₂O₃ + CO₂ → 2CeO₂ + CO                              (14)

If both H₂O and CO₂ are fed into a suitable solar thermal reactor containing a ceria catalyst, which is cycled within the temperature range, 800 ^oC - 1500 ^oC, syngas is produced. Although the yields are low, with only around 0.7 - 0.8% of the solar thermal energy being harnessed by the fuel, it is thought this is only a limitation of the scale and design of the system rather than of the underlying chemistry. Most of the energy is lost as heat through the wall of the reactor, or by the re-radiation of sunlight back through the aperture of the device. But the researchers are confident that efficiency rates of up to 19% can be achieved through better insulation and smaller apertures. Such efficiency rates, they say, could make for a viable commercial device. It is worth noting that of various oxide materials that might be employed as redox catalysts for splitting water or carbon dioxide, ferrite-based oxides show fairly slow reaction rates, whereas oxides such as ZnO and SnO₂ sublime during the decomposition stage and require rapid quenching of gaseous products to avoid recombination. In contrast, ceria is stable to volatility and to sintering (which reduces the surface area and activity), and shows relatively rapid reaction rates. This is thought to be due partly to the presence of nonstoichiometric  oxidized and reduced phases, a high oxygen diffusion rate, and to its thermal structural stability. By impregnating a samarium/ceria catalyst with nickel¹¹, methane was produced, shown to arise from catalytic hydrogenation of carbon particles formed on the surface of the metal by decomposition of CO₂.

Fuels Produced by “Artificial Photosynthesis”.

I have some issue with the accuracy of the term “Artificial Photosynthesis”¹⁷, but it is snappy and sounds very “green” so I think it will stick. As a reminder, natural photosynthesis⁹ is a “water-splitting” process by which green plants and green algae fix CO₂ from the atmosphere to build carbohydrate, and grow. The rate of energy capture by photosynthesis is immense, at approximately 100 TW, which is about six times the entire power consumption of human civilization. Photosynthesis is also the sole source of carbon in all life on Earth, and converts around 370 billion tonnes of CO₂ into 250 billion tonnes of biomass each year, in which is stored almost 4,000 EJ worth of energy. The counterpart product is O₂, and hence photosynthesis is the origin of virtually all atmospheric oxygen, with a roughly 50:50 contribution made by land-based plants and by oceanic phytoplankton. The process may be summarised as follows:

nCO₂ + nH₂O + hν → (CH₂O)_n + nO₂

Production of ONE O₂ molecule requires the transfer of FOUR electrons:

2H₂O → O₂ + 4e^- + 4H⁺

And FOUR electrons are required to reduce ONE CO₂ molecule:

CO₂ + 4e^- + 4H⁺ → (CH₂O) + H₂O

Mechanism.

The energy resulting from light adsorption by the chlorophyll photocatalyst is transferred to a manganese-protein complex called “Photosystem II”, which oxidises water:

H₂O – e^- → [H₂O^+•] → HO• + H⁺

2 HO• → H₂O₂

H₂O₂ – e^- → [H₂O₂^+•] → HOO• + H⁺

2 HOO• → O₂ + H₂O₂

In a broad analogy with this, the label “artificial photosynthesis” is commonly used to describe any scheme for capturing and storing the energy from sunlight in the chemical bonds of a material that might be used as a fuel (a solar fuel). Photocatalytic water splitting converts water into protons (leading to H₂) and O₂, and provides a major research topic in the field. Another important area is “light-driven carbon dioxide reduction” which aims to replicate carbon fixation by natural photosynthesis, and might provide a carbon-mitigation strategy, along with the creation of fuels independent of petroleum and natural gas. In the broad classification of “artificial photosynthesis”, accepting that light can be harvested using external PV cells and converted to electrons, we give due mention to electrochemical processes, which may be photo-assisted or direct. Thus, although the primary reduction product of CO₂ is CO, a direct photoelectrochemical conversion of carbon dioxide and water to methanol using a p-type semiconductor (GaP) electrode has been reported with faradaic efficiencies of 88 – 100%. The process appears highly selective, since other reduction products such as formic acid and formaldehyde were not detected, nor hydrogen.¹⁸ The direct electrochemical reduction of CO₂ has mainly been thwarted by the impractically high overpotentials required to drive the process. In contrast, a direct conversion of CO₂ to CO has been achieved at overpotentials of less than 0.2 volt. The medium uses an ionic liquid (1-ethyl-3-methylimidazolium tetrafluoroborate, EMIM-BF₄) as its electrolyte, which is thought to lower the energy of the CO₂^−• intermediate through the formation of a complex of the type “EMIM⁺-CO₂^−•”.¹⁹ As pointed out previously²⁰, for ionic liquid applications to be used in earnest, they would need to be synthesised on a large scale, and from molecules derived from crude oil. This case is no exception, if it is to provide a source of syngas and hence liquid hydrocarbon fuels, in a quantity that in any way matches the expected loss of petroleum and fuels derived from it. Dye-sensitized solar cells² (DSSC) have been used in H₂ production. A DSSC is a kind of thin-film cell in which a semiconductor, normally TiO₂, along with a coating of an organic or inorganic dye to act as a photosensitizer is coated on the anode, while a platinum catalyst is present at the cathode, where H₂ is generated. Thin-film cells offer the considerable advantage^2,10 over conventional solar cells that perhaps only 1/100^th the amount of conductive material is required in their fabrication, and is thought to be critical both to the rate and scale at which PV technology can be implemented. TiO₂ is the photocatalytic semiconductor material most studied as a potential solar water-splitting catalyst, and yet despite 4 decades of research the process remains inefficient and economically unsound, due mainly to rapid recombination of holes and electrons, the rapid reconversion of oxygen and hydrogen back to water and poor activation of TiO₂ by visible light. The hole-charge recombination can be inhibited by loading the particles at their surface with metals, most commonly platinum, but its limited world supply and high cost imposes a severe limitation on the technology, which is has to be said remains rather inefficient in any case. The implantation of high-energy transition metal ions (accelerated by high voltage) has been shown to modify the electronic structure of TiO₂, so that its photo-response is shifted into the visible region (up to 600 nm), which may prove useful in the development of the “second generation photocatalyst”²¹.

Nocera and his co-workers have developed what they describe as an “artificial leaf”²². In the overall strategy, sunlight can be captured and converted to electricity using a silicon solar PV cell, but the crucial advance lies in the design of the electrode surface to provide a highly efficient anode electrocatalyst (Oxygen Evolving Electrode, OEE) for use in the electrolysis of water employing inexpensive materials. An indium tin oxide (ITO) electrode was immersed in water containing Co²⁺ cations and potassium phosphate (Pi). By application of a voltage to the electrode, cobalt, potassium, and phosphate accumulated on its surface, to form the catalytically active phase, where water is oxidised yielding O₂ and protons¹⁸. By reduction of these protons, H₂ might result, using a suitable cathode, which originally was made from platinum. During the process, the cobalt-based phase decomposes, but is regenerated (“self-heals”) by cobalt, potassium and phosphate being adsorbed from the solution. To reduce the protons to H₂, a cathode made form cheap, readily available (“Earth Abundant”) materials rather than precious metals is required, if a serious scale-up of the technology is to be feasible. To this end, a Co/borate catalyst was deposited on the surface of a triple-junction, amorphous silicon PV semiconductor (which was in contact with a stainless steel plate, to act as the anode (OEE), while a ternary Ni/Mo/Zn alloy was employed as the cathode (Hydrogen Evolving Electrode, HEE)²³. The silicon was passivated (protected) by an ITO layer, which protects it from reactive oxidising species formed at the anode, e.g. HO• radicals. The two electrodes were employed in two configurations: (1) in which they were connected by a wire, and (2) in a wireless mode, where the Ni/Mo/Zn was deposited directly onto the stainless steel backing of the silicon wafer. The efficiencies of the two devices are 4.7% for a wired configuration (1) and 2.5% for the wireless arrangement (2). It is thought that the efficiency of (2) is reduced by the relatively greater distance that the protons must travel to the cathode from the front face of the anode, which imposes substantial ohmic losses in the wireless cell, in comparison with the 1 mm gap between the two electrodes in the wired cell (1). It is proposed that this technology could be adapted from a panel geometry to one based on (nano)particles free in solution/suspension²². However, in the in situ arrangements described, as opposed to standard electrolysers where H₂ and O₂ are generated in different chambers of the device, explosive mixtures of H₂/O₂ would be produced, and need to be separated probably using some form of membrane technology.

          Nocera envisages a widescale future application of such devices for energy production say at the level of individual homes, with H₂ acting as an energy storage medium so that power can be provided even at night (using a fuel cell) when the sun is not shining. He sees the most fruitful regions of the world, for the technology to be developed, as the “non-legacy”(i.e. developing) nations, which are less entrenched by tradition and vested interest in centralised, large-scale power production from fossil fuels and nuclear, than is the case in the “legacy” (developed) nations. Thus, remote communities could be provided with electricity at a local level. In October 2010, Nocera signed with the Tata Group of India to commercialize his research, a country in which there could be great demand for such decentralized, “personal” energy production, which he sees as key to the future of humanity. As we note later, due to the failing supply of crude oil and the absence of other fuels on a matching scale to run the global transportation network, a relocalisation of human civilization and its societies appears inevitable, as access to cheap and extensive personalised transport (mainly cars) will be prohibited both by cost and actual fuel shortages. In such localised communities, small-scale power generation will be necessary, and perhaps Nocera’s invention (or something like it) might contribute to a de-industrializing West, along with sustaining the existing non-legacy nations. However, many daunting challenges remain, including the instability of the cells which lose their activity over periods of hours and that there is a world shortage of indium²⁴ (for ITO), which it is thought may run-out within 5 years, due to other pre-existing demands on it, e.g. for thin-film solar cells and light-emitting diodes (LEDs). Thus, any substantive technology is probably many decades away, along with the putative hydrogen economy itself, if that will ever arise in the full-ascension that some envisage. Meanwhile, we will need to address a more immediate and drastic failing of our energy supply, particularly that from crude oil and natural gas, most likely by transforming from a global village to a globe of villages.

Liquid Solar Fuels Through Industrial Photosynthesis²⁵.

It has been estimated that to match the entirety of 16 TW of energy, as used by humans on Earth, in the form of hydrogen would require splitting some 18 billion tonnes (18 km³) of water annually, using photoelectrochemical methods or other means, e.g. concentrating solar thermal power, all as yet to be fully developed let alone proliferated on this scale. However, there is an established solar technology already available to us, namely photosynthesis. The basis of photosynthesis, as it occurs in Nature, is outlined in the previous section, which captures solar-energy at a rate of around 100 TW. Of the resulting 4,000 EJ worth of stored energy, clearly only a fairly small proportion might be sensibly harvested, and a deliberate growing of particular energy crops is necessary, much as we grow crops for food, while allowing animals to graze on available common land and set-aside pasture. There is, as already noted, competition between the use of arable land for food crops or fuel crops, and to place this into perspective, if in the UK we turned over all our crop-land to growing sugar beet for bioethanol production, and grew no food at all, we might match just half of our national fuel demand as is currently met from crude oil. If we chose rapeseed for the same purpose, a mere one sixth of that demand could be supplied in the form of biodiesel. There is the further issue of the freshwater demand, of which agriculture already struggles to secure enough to meet its needs, and in a sustainable picture of the future, supplies of water appear uncertain against the countenance of climate change. It is in the light of these considerations that algae/algal fuels have begun to look very appealing⁶, especially given the claimed very high yields that can be obtained per hectare as compared say with rapeseed and biodiesel. From a survey²⁶ of the results from different studies, it has been estimated that between 40 – 90 tonnes of biodiesel/hectare can be produced from algae. However, the yields reported have often been extrapolated from growing algae over far smaller areas than a hectare, and there seem to be problems encountered when actual scale-ups are attempted. To date, no one has yet succeeded in producing fuel commercially and at scale, and indeed many small firms that started out to do this have stopped trading, one of which being the MIT spin-off Greenfuel Technologies which closed in 2009 after receiving £44 million  ($70 million) of investment to build its own mini-algae plant. The algae programme of the UK’s Carbon Trust has been scrapped in the wake of the government austerity measures, as it attempts to cut the massive debt incurred in having to bale-out the banks after the 2008 economic crash. One problem is that the algae cannot be grown very densely, because those closest to the surface screen the sunlight from reaching those below. Another difficulty is to actually extract the oil from algae, and it appears that producing highly oil-yielding strains en mass is more difficult than previously thought. There are other means to process algae than by oil extraction/transesterification to biodiesel, including hydrothermal liquefaction²⁶, where the water is not removed (a highly energy intensive process) but the material is heated wet under pressure (perhaps with a catalyst) to decompose it into liquid hydrocarbon fuels and methane. Conventional algae production can be combined with water clean-up strategies^6,24,26, to remove N and P from agricultural run-off water and sewage effluent, both to prevent eutrophication (nutrient build-up in water), which causes algal blooms, and to conserve the precious resource of phosphate, since a peak in world phosphate rock production is expected around 2030²⁴. “Peak phosphate” is connected to “peak oil” since phosphate is mined using oil-powered machinery, and in the absence of sufficient phosphorus, we will be unable to feed the rising global human population, since modern industrialised farming depends on heavy inputs of phosphate, along with nitrogen fertilizers. Pesticides, too, derived chemically from crude oil, are essential, along with oil-refined fuels for farm machinery. It is, nonetheless, doubtful that the world’s liquid transportation fuel requirements can be met through standard methods of algae cultivation entirely, though fuel production on a smaller scale seems thus feasible. I gave an analogy for the latter as growing algae in a “village pond” for use by a community of limited numbers.

Noting the troubles and limitations of growing algae by conventional means and producing fuel from it on a grand scale, a breakthough does appear possible through the use of genetically modified cyanobacteria. The company, Joule Unlimited, Inc., has proposed a new high-productivity solar-to-fuels platform that uses direct product synthesis and continuous production²⁵. The process is claimed to produce 15,000 gallons (US) of diesel/acre/year, to be compared with 3,000 gallons of biodiesel/acre/year. Now, this is hydrocarbon diesel that is being produced, with an energy content of (based on the alkane, heptadecane, C₁₇H₃₆) 47.2 MJ/kg, as opposed to 41 MJ/Kg for biodiesel. Noting that the respective densities of these fuels are 777 kg/m³ and 890 kg/m³, this amounts to 110.7 tonnes/hectare/year compared with 25.4 tonnes/hectare/year for the diesel and biodiesel. When the differential energy content of the fuel is taken into account, it can be seen that the direct, continuous process is almost exactly five times as productive in its energy yield/hectare than the conventional batch method. Through advances in genome engineering, solar energy capture and bioprocessing by the organism, a photosynthetic efficiency of 7.2% is obtained, to be compared with the theoretical limit of 12.1% of available sunlight at the ground being used for photosynthesis. The process is innately less complex in terms of avoiding much of the downstream processing attendant to conventional algae-to biodiesel conversion, and the product, being hydrocarbon diesel, is completely compatible (fungible) with the existing engine and liquid fuel distribution infrastructure. It is stressed that the “platform converts sunlight and waste CO₂ (at a concentration some 50 – 100 times that in the atmosphere, in a closed system) directly into liquid fuels in a continuous process that is not limited by costly biomass intermediates, processing or the use of natural resources. According to the sales-pitch: “this platform can yield renewable diesel fuel in unprecedented volumes with a fraction of the land use incurred by current methods, leapfrogging biomass-dependent approaches and eliminating the economic and environmental disadvantages of fossil fuels.” The technology does indeed sound promising, but it is going to have to be proliferated on a massive scale across the world, and rapidly, if it is to cope year on year with a failing conventional oil supply^5,8 of 2.9 mbd/year. This means that by 2015 – a mere 3 years time – daily production by such unconventional means needs to be around 10 million barrels⁵, and 64 million barrels⁸ by 2030, to offset the fall in conventional crude oil production and meet a projected increase in demand from the current 84 mbd to 96 mbd. It is worth noting that this amounts to a very modest anticipated growth of 0.8%/year. Previous estimates for growth during this period were up to 3%/year, reaching a production of 130 mbd, but this has been reckoned-down significantly.

Overall summary and outlook.

In conclusion, we are faced with an overall serious energy problem, and most pressingly the challenge of how to fill the enlarging hole created by a declining production of conventional crude oil. It appears almost certain that there will be profound efforts made in obtaining “unconventional oil” from shale and in liberating gas from various geological formations by “fracking”; the production of “synthetic crude” from tar-sands will doubtless increase too. Noting that world light crude oil production peaked in 2005, it is increasingly the heavy oils, e.g. from the Orinoco Belt in Venezuela, that will need to be recovered and processed, requiring the building of a new swathe of oil refineries that can handle this kind of material. Thus, not only are supplies of conventional crude oil going to fall, but what is recovered will be increasingly difficult to process. How difficult it is to produce an energy resource is usually expressed by the Energy Returned on Energy Invested (EROEI). Thus in the halcyon days of the Texan “giant gushers”, 100 barrels of crude oil could be recovered using the energy equivalent to that contained in one barrel of crude oil, which gives an EROEI = 100. The figure has fallen since then, and presently EROEIs in the range 11 -18 are obtained for North Sea (Brent Crude) oil, and as low as 3 – 5 for heavy oil and tar sands “oil”.

Oil shale should be distinguished from shale oil, though both are misnomers. Oil shale contains no oil, as such, but a solid primordial material called kerogen, which must be thermally cracked to obtain a liquid  that resembles crude oil. The production and use of oil-shale is hardly environmentally “clean”, taking account of its carbon emissions (both in the retorting of shale and in burning the final fuel) and large water demand (3 – 10 barrels of water to produce each barrel of oil), and as yet there is no serious commercial production. Nontheless, becasue vast resources of oil-shale can be claimed, it is trumpeted in some quarters that the US will become self-sufficient in “oil” by 2020. In contrast, shale oil (the correct term is tight oil) is actual crude oil (petroleum), but is trapped within impermeable rock. The rock is broken open using hydraulic fracturing ("fracking"), which allows the oil to flow out, whereupon it may be refined in the normal way. Current US production of shale-oil is around 0.5 mbd, and which is predicted to rise to 3 mbd by 2020. However, this must be gauged against a loss of conventional oil by 27 mbd across the world. Can solar fuels fill the gap? As we have seen, much of the solar fuel technology is very much at the research stage. Most of what is ongoing aims to produce H₂, but even if half the “new” platinum recovered annually were used to fabricate fuel cells, only something like 1% of the billion road vehicles currently in existence could be so substituted by “hydrogen cars” over the next 10 years. Hence, a global transportation network based on hydrogen/fuel cells, let alone a full-scale solar hydrogen economy, is a pipe-dream. If hydrogen can be made renewably on the grand scale, as an energy carrier (it is not really a fuel, since it must be created from primary energy sources), it will probably need to be used by combustion. The fabrication of electric cars runs into similar resource difficulties, especially in terms of rare earth metals, and so a strategy based on liquid fuels would seem most sensible. Liquid fuels are furthermore entirely compatible with the prevailing transportation infrastructure, in regard to the distribution of fuels and their deployment in internal combustion engines. The Fischer-Tropsch (FT) process is a well-established technology for converting syngas to liquid hydrocarbons, but the means to obtain H₂ + CO on a large scale without using fossil fuels is not. Even when (or if) those clean technologies based on artificial photosynthesis are developed, a whole new generation and scale of FT plants will need to be installed, which at the level envisaged would take decades. Any such timescale must be judged against that for the depletion of conventional crude oil. Of those approaches considered here for the production of liquid fuels, the use of genetically engineered cyanobacteria looks the most promising, but even so, meeting the global demand for them seems to be a bridge too far. Producing millions of electric cars is just not a practical proposition, and the only realistic means to move people around in number using electrical power is with light railway and tram systems. The notion of personalised transport will be relegated to history by massive fuel prices, and an absence of any cheaper “car ownership” option. Our global civilization is underpinned almost entirely by crude oil – as refined into liquid fuels for transporting people and consumer goods around nations; for growing and distributing food; for mining coal, shale and all kinds of minerals, including metallic ores and rock phosphate for agriculture; and as a raw feedstock for the chemical industry, to make pharmaceuticals and to support healthcare. If our stalwart “black gold” is set to abandon us over the next few decades, and it is not possible on that same timescale to produce alternative liquid fuels – “the supply side” - we can only address the problem from the demand side. This means a substantial curbing of transportation and a relocalisation of society, to become more locally sufficient, e.g. in food production, at the community level. Such are the aims of the “Transition Town” movement²⁷. It is likely that energy production will become increasingly decentralized, and done at the smaller scale, to power such communities. Fuel too, e.g. for local agriculture, might be produced from algae at least on a regional scale, as integrated with water treatment schemes^6,24,26 to conserve the resource of phosphate, and to avert algal blooms. Methods of regenerative agriculture, including permaculture, provide means to food production that demand far less in their input of fuels, fertilizers and pesticides, and actually rebuild the carbon content of soil. It is thought that 40% of anthropogenic CO₂ emissions might be sequestered in soil using no-till practices, if practiced across all the Earth’s 3.5 billion acres (14 million km²) of arable land²⁸. Solar energy may also be harvested usefully and directly in the form of heat² (rather than converting it to a fuel), at greater efficiency than through PV, using concentrating solar thermal power plants, roof-based water heating systems, solar cookers, solar stills and water sterilization units, and homes especially designed to absorb and retain thermal energy. Though the foreseeable transition to a lower energy and more localised way of life is unequivocally daunting, we should remain optimistic.

“We act as though comfort and luxury were the chief requirements of life,
when all that we need to make us really happy is something
to be enthusiastic about.” – Charles Kingsley (1819 – 1875).

References.

(1) BP Statistic Review of World Energy 2011. http://www.bp.com/liveassets/bp_internet/globalbp/globalbp_uk_english/reports_and_publications/statistical_energy_review_2011/STAGING/local_assets/pdf/statistical_review_of_world_energy_full_report_2011.pdf

(2) Rhodes, C.J. (2010), Sci. Prog. 93, 37.

(3)http://www.ipcc.ch/publications_and_data/publications_and_data_figures_and_tables.shtml#.T3BFgdWjmeF

(4) Rhodes, C.J. (2008), Sci. Prog. 91, 317.

(5) http://www.marketoracle.co.uk/Article33300.html

(6) Rhodes, C.J. (2009), Sci. Prog. 92, 39.

(7) http://en.wikipedia.org/wiki/Motor_vehicle

(8) http://www.independent.com/news/2012/mar/18/toward-energy-literacy/

(9) Rhodes, C.J. (2011), Sci. Prog., 94, 339.

(10) McIntyre, R.A. (2010), Sci. Prog. 93, 361.

(11) Tang, J. et al. (2011), Nature Materials, 10, 765.

(12) Steinfeld, A. (2005), Solar Energy, 78, 603.

(13)http://www.solaritaly.enea.it/Documentazione/Solar%20Thermal%20Energy%20Production.pdf

(14)https://netfiles.uiuc.edu/mragheb/www/NPRE%20498ES%20Energy%20Storage%20Systems/Carbon%20Dioxide%20Reforming.pdf

(15) http://www.solarpaces.org/Library/docs/Solar_Fuels.pdf

(16) Chueh, W.C. and Haile, S.M. (2009), ChemSusChem. 8, 735.

(17) Styring, S. (2012), Faraday Discussions, 155, 357.

(18) Barton, E.E., Rampala, D.M. and Bocarsly, A.B. (2008), J. Am. Chem. Soc.130, 6342.

(19) Rosen, B.A. et al. (2011), Science 334, 643.

(20) Rhodes, C.J. (2011), Sci. Prog. 94, 211.

(21) Anpo, M. (2004), Bull. Chem. Soc. Jpn. 77, 1427.

(22) Reece, S.Y. et al. (2011), Science 334, 645.

(23) Pijpers, J.J.H. et al. (2011) PNAS 108,10056.

(24) Rhodes, C.J. (2011) Sci. Prog. 94, 323.

(25) Robertson, D.E. (2011) Photosynth. Res. 107, 269.

(26) Rhodes, C.J. in Algal Fuels: Phycology, Geology, Biophotonics, Genomics and Nanotechnology, J.Seckbach (ed.), Springer, Dordrecht, in press.

(27) http://scitizen.com/future-energies/transition-town-reading-_a-14-3716.html

(28) http://www.rodaleinstitute.org/files/Rodale_Research_Paper-07_30_08.pdf

Has the IPCC Outlived its Usefulness?

This is a serious challenge posed by Judith Curry, as can be seen in her interview by Oilprice.

She expresses her concerns for climate science, how climate change is affecting the planet, reasons for the increase in scepticism and why climate scientists have lost touch with the public. As she puts it:

"The IPCC might have outlived its usefulness. Let's see what the next assessment report comes up with. But we are getting diminishing returns from these assessments, and they take up an enormous amount of scientists' time."

Among the questions put to her are:

Q. You have said in the past that you were troubled by the lack of cooperation between organizations studying climate change, and that you want to see more transparency with the data collected. How do you suggest we encourage/force transparency and collaboration?

Q. Do you feel climatologists should be putting more effort into determining the effect of the sun on our climate? As the IPCC primarily focuses on CO2 as the cause of climate change - Is the importance of CO2 overestimated and the importance of the sun is underestimated?

Q. What are your views on the idea that CO2 may not be a significant contributor to climate change?

Her responses are timely and will almost certainly stoke further debate.

The full interview is at: http://oilprice.com/The-Environment/Global-Warming/The-IPCC-May-Have-Outlived-its-Usefulness-An-Interview-with-Judith-Curry.html

The Thorium Age Waits in the Wings.

There is much written to the effect that thorium might prove a more viable nuclear fuel, and an energy industry based upon it, than the current uranium-based process which serves to provide both energy and weapons - including "depleted uranium" for armaments and missiles. There are different ways in which energy might be extracted from thorium, one of which is the accelerator-driven system (ADS). Such accelerators need massive amounts of electricity to run them, as all particle accelerators do, but these are required to produce a beam of protons of such intensity that until 10 years ago the prevailing technology meant that it could not have been done. As noted below, an alternative means to use thorium as a fuel is in a liquid fluoride reactor (LFR), also termed a molten salt reactor, which avoids the use of solid oxide nuclear fuels. Indeed, China has made the decision to develop an LFR-based thorium-power programme, to be active by 2020.

Rather like nuclear fusion, the working ADS technology is some way off, and may never happen, although Professor Egil Lillestol of Bergen University in Norway is pushing that the world should use thorium in such ADS reactors. Using thorium as a nuclear fuel is a laudable idea, as is amply demonstrated in the blog "Energy from Thorium" (http://thoriumenergy.blogspot.com/) to which there is a link on this blog (above left). However, the European Union has pulled the plug on funding for the thorium ADS programme, which was directed by Professor Carlo Rubbia, the Nobel Prizewinner, who has now abandoned his efforts to press forward the programme, and instead concentrated on solar energy, which was another of his activities. Rubbia had appointed Lillestol as leader of the CERN physics division over two decades ago, in 1989, who believes that the cause is not lost.

Thorium has many advantages, not the least being its greater abundance than uranium. It is often quoted that there is three times as much thorium as there is uranium. Uranium is around 2 - 3 parts per million in abundance in most soils, and this proportion rises especially where phosphate rocks are present, to anywhere between 50 and 1000 ppm. This is still only in the range 0.005% - 0.1% and so even the best soils are not obvious places to look for uranium. However, somewhere around 6 ppm as an average for thorium in the Earth's crust is a reasonable estimate. There are thorium mineral deposits that contain up to 12% of the element, located at the following tonnages in Turkey (380,000), Australia (300,000), India (290,000), Canada and the US combined (260,000)... and Norway (170,000), perhaps explaining part of Lillestol's enthusiasm for thorium based nuclear power. Indeed, Norway is very well endowed with natural fuel resources, including gas, oil, coal, and it would appear, thorium.

An alternative technology to the ADS is the "Liquid Fluoride Reactor" (LFR), which is described and discussed in considerable detail on the http://thoriumenergy.blogspot.com/ blog, and reading this has convinced me that the LFR may provide the best means to achieve our future nuclear energy programme. Thorium exists naturally as thorium-232, which is not of itself a viable nuclear fuel. However, by absorption of relatively low energy "slow" neutrons, it is converted to protactinium 233, which must be removed from the reactor (otherwise it absorbs another neutron and becomes protactinium 234) and allowed to decay over about 28 days to uranium 233, which is fissile, and can be returned to the reactor as a fuel, and to breed more uranium 233 from thorium. The "breeding" cycle can be kicked-off using plutonium say, to provide the initial supply of neutrons, and indeed the LFR would be a useful way of disposing of weapons grade plutonium and uranium from the world's stockpiles while converting it into useful energy.

The LFR makes in-situ reprocessing possible, much more easily than is the case for solid-fuel based reactors. I believe there have been two working LFR's to date, and if implemented, the technology would avoid using uranium-plutonium fast breeder reactors, which need high energy "fast" neutrons to convert uranium 238 which is not fissile to plutonium 239 which is. The LFR is inherently safer and does not require liquid sodium as a coolant, while it also avoids the risk of plutonium getting into the hands of terrorists. It is worth noting that while uranium 235 and plutonium 239 could be shielded to avoid detection as a "bomb in a suitcase", uranium 233 could not, because it is always contaminated with uranium 232, which is a strong gamma-ray emitter, and is far less easily concealed.

It has been claimed that thorium produces "250 times more energy per unit of weight" than uranium. Now this isn't simply a "logs versus coal on the fire" kind of argument, but presumably refers to the fact that while essentially all the thorium can be used as a fuel, the uranium must be enriched in uranium 235, the rest being "thrown away" and hence wasted as "depleted" uranium 238 (unless it is bred into plutonium). If both the thorium and uranium were used to breed uranium 233 or plutonium 239, then presumably their relative "heat output" weight for weight should be about the same as final fission fuels? If this is wrong, will someone please explain this to me as I should be interested to know?

However, allowing that the LFR in-situ reprocessing is a far easier and less dangerous procedure, the simple sums are that contained in 248 million tonnes of natural uranium, available as a reserve, are 1.79 million tonnes of uranium 235 + 246.2 million tonnes of uranium 238. Hence by enrichment 35 million tonnes (Mt) of uranium containing 3.2% uranium 235 (from the original 0.71%) are obtained. This "enriched fraction" would contain 1.12 Mt of (235) + 33.88 Mt of (238), leaving in the other "depleted" fraction 248 - 35 Mt = 213 Mt of the original 248 Mt, and containing 0.67 Mt (235) + 212.3 Mt (238). Thus we have accessed 1.79 - 0.67 = 1.12 Mt of (235) = 1.12/224 = 4.52 x 10*-3 or 0.452% of the original total uranium. Thus on a relative basis thorium (assuming 100% of it can be used) is 100/0.452 = 221 times as good weight for weight, which is close to the figure claimed, and a small variation in enrichment to a slightly higher level as is sometimes done probably would get us to an advantage factor of 250!

Plutonium is a by-product of normal operation of a uranium-fuelled fission reactor. 95 to 97% of the fuel in the reactor is uranium 238. Some of this uranium is converted to plutonium 239 and plutonium 241 - usually about 1000 kg forms after a year of operation. At the end of the cycle (a year to 2 years, typically), very little uranium 235 is left and about 30% of the power produced by the reactor actually comes from plutonium. Hence a degree of "breeding" happens intrinsically and so the practical advantage of uranium raises its head from 1/250 (accepting that figure) to 1/192, which still weighs enormously in favour of thorium!

As a rough estimate, 1.4 million tonnes of thorium (about one third the world uranium claimed, which is enough to last another 50 years as a fission fuel) would keep us going for about 200/3 x 50 = 3,333 years. Even if we were to produce all the world's electricity from nuclear that is currently produced using fossil fuels (which would certainly cut our CO2 emissions), we would be O.K. for 3,333/4 = 833 years. More thorium would doubtless be found if it were looked for, and so the basic raw material is not at issue. Being more abundant in most deposits than uranium, its extraction would place less pressure on other fossil fuel resources used for mining and extracting it. Indeed, thorium-electricity could be piped in for that purpose.

It all sounds great: however, the infrastructure would be huge to switch over entirely to thorium, as it would to switch to anything else including hydrogen and biofuels. It is this that is the huge mountain of resistance there will be to all kinds of new technology. My belief is that through cuts in energy use following post peak oil (and peak gas), we may be able to produce liquid fuels from coal, possibly using electricity produced from thorium, Thorium produces less of a nuclear waste problem finally, since fewer actinides result from the thorium fuel cycle than that from uranium. Renewables should be implemented wherever possible too, in the final energy mix that will be the fulcrum on which the survival of human civilization is poised.

Thorium Nuclear Power – A Lesson From Norway.

Norway holds a resource of 170,000 tonnes of thorium, which amounts to 15% of the world’s total of 1.2 million tonnes. There is far more thorium than that within the earth’s crust all told, averaging 8 ppm compared with around 2.8 ppm for uranium, but the above figures refer to richer ores, most commonly monazite sand which contains up to 12% of thorium. There is some opinion that thorium nuclear power might be a better environmental/energy-strategy for Norway than relying on carbon-capture which many consider to be uneconomic. However, the matter of thorium reactors is not straightforward. Professor Egil Lillestol of Bergen University has been pushing thorium for some years now, and thinks that Norway should set the trend in building a prototype accelerator-driven reactor in which a massive particle accelerator converts thorium-232 to uranium-233 by irradiating it with slow (spallation) neutrons generated by the impact of a 1.6 GeV proton beam on a lead target. The conversion is not direct, and involves the initial formation of thorium-233, which decays rapidly to protactinium-233, and then to uranium-233 over a period of about a month. Hence presumably reprocessing is involved in the final stage, since if the protactinium-233 is left in the reactor it will be at least partly converted to protactinium-234, which is not a useful fissile material.

It may well turn out that thorium is the better nuclear fuel as compared with uranium, since it offers the advantages that: (1) it is present in around 3 times the abundance of uranium on Earth, overall, (2) it can be bred into the fissile nuclear fuel uranium-233, (3) far less plutonium and other transuranic elements are produced than is the case from uranium fuel, (4) the thorium fuel cycle might be used to consume plutonium, thus reducing the nuclear stockpile while converting it into useful electrical energy.

However, it is a very big accelerator that will be needed to do the job, and the estimated costs for the project are about 500 million Euros. There are various advantages cited for this type of reactor, including the claim that it can be stopped easily if things get out of hand, and that it produces less long-lived nuclear waste than the uranium-fuelled fission reactors that are currently in common use. However, there are a whole host of scientific and engineering challenges that need to be overcome, and even identified in the first place because nobody has ever built one of these reactors, and hence the plans are still only on the drawing board.

As I have already stressed, it is a very big accelerator that will be needed if the project has any chance of success, so big in fact that there are none with sufficient power anywhere in the world. Some of the suggestions include using molten lead as the coolant for the system, but the reactor would run at a temperature above 700 degrees C. when the material becomes corrosive. A number of countries (including the US, Russia, the UK, France and Japan) have entrenched firm investments in uranium based reactors, and will use them for as long as they can. There are sizeable quantities of uranium on the world market, although the price has recently soared. Nonetheless, there is likely to be resistance to the research and development of a brand-new technology based on thorium, in view of huge costs that will effectively be borne by the Norwegian taxpayer if they go it alone down this unlit path.

The immediate future doesn’t look optimistic for thorium, certainly with the untested accelerator-driven reactors, and yet two thorium reactors have been operated, which were of the far simpler molten-salt reactor kind. Thus it might prove more expedient to invest in this at least tried technology, which could extend the useful lifetime of nuclear power by hundreds of years. The reason is that converting thorium-232 to uranium-233 is a form of “breeder” technology meaning that practically 100% of the thorium can be processed ultimately into nuclear fuel, rather than just the 0.7% uranium-235 isotope that exists in naturally occurring uranium, and which requires enrichment before it can be used. Indeed, the 99+% of uranium-238 can be converted into plutonium-239 and this used in fuel-rods, but there are many negative connotations attached to plutonium, which is almost the “p-word” for the nuclear industry: i.e. unmentionable, certainly in the tabloid press. There are serious issues of terrorism – dirty bombs at the very least, if not an out and out A-bomb detonation involving plutonium. The word alone would swathe a city and the world with fear. Uranium-233 made from thorium is harder to conceal than plutonium, since it is always contaminated with uranium-232, a strong gamma-ray emitter, and accordingly quite easily detected “in a suitcase” than plutonium which is principally an alpha-particle emitter and far more readily hidden.

There is no doubt that we will see a rise in nuclear power and for a number of reasons – cutting CO2 emissions, and securing energy supplies. Most of current thinking is based around using uranium as the fuel to drive it, but thorium could prove a very useful supplement and might power a new generation of reactors when we are short of uranium and do need to “breed” fuel if it proves uneconomic to mine poor quality uranium ores. I maintain my reservations about how long other resources, e.g. oil and gas will last, with which to mine and process either uranium or thorium, but if the latter appears viable in the longer run, I suggest that molten salt (liquid fluoride) reactors would be a better approach than the far more complex (and as yet untested) accelerator-driven systems.

The latter are reminiscent in scale to the putative nuclear-fusion reactors, said to mimic processes in stars, e.g. the sun, of which a working model is not expected for at least another 60 years. No one should forget that we need to make our energy provisions against a backdrop of 10 – 20 years at best, as oil and then gas begin to run short (the “Oil Dearth Era”). We do not want to back a loser now, as it is a one-off bet with the future of civilization resting on the outcome of this particular race.

Related Reading.
www.energyfromthorium.com/ There is also a link at the top left hand corner of this blog.

The Achilles' Heel of Algal Biofuels - Peak Phosphate.

The depletion of world rock phosphate reserves will restrict the amount of food that can be grown across the world, a situation that can only be compounded by the production of biofuels, including the potential large-scale generation of diesel from algae. The world population has risen to its present number of 7 billion in consequence of cheap fertilizers, pesticides and energy sources, particularly oil. Almost all modern farming has been engineered to depend on phosphate fertilizers, and those made from natural gas, e.g. ammonium nitrate, and on oil to run tractors etc. and to distribute the final produce. A peak in worldwide production of rock phosphate is expected by 2030, which lends fears over how much food the world will be able to grow in the future, against a rising number of mouths to feed [1]. Consensus of analytical opinion is that we are close to the peak in world oil production too.

One proposed solution to the latter problem is to substitute oil-based fuels by biofuels, although this is not as straightforward as is often presented. In addition to the simple fact that growing fuel-crops must inevitably compete for limited arable land on which to grow food-crops, there are vital differences in the properties of biofuels, e.g. biodiesel and bioethanol, from conventional hydrocarbon fuels such as petrol and diesel, which will necessitate the adaptation of engine-designs to use them, for example in regard to viscosity at low temperatures, e.g. in planes flying in the frigidity of the troposphere. Raw ethanol needs to be burned in a specially adapted engine to recover more of its energy in terms of tank to wheels miles, otherwise it could deliver only about 70% of the "kick" of petrol, pound for pound.

In order to obviate the competition between fuel and food crops, it has been proposed to grow algae to make biodiesel from. Some strains of algae can produce 50% of their weight of oil, which is transesterified into biodiesel in the same way that plant oils are. Compared to e.g. rapeseed which might yield a tonne of biodiesel per hectare, or 8 tonnes from palm-oil, perhaps 40─90 tonnes per hectare is thought possible from algae [2], grown in ponds of equivalent area. Since the ponds can in principle be placed anywhere, there is no need to use arable land for them. Some algae grow well on salt-water too which avoids diverting increasingly precious freshwater from normal uses, as is the case for growing crops which require enormous quantities of freshwater.

The algae route sounds almost too good to be true. Having set-up these ponds, albeit on a large scale, i.e. they would need an area of 10,000 km² (at 40 t/ha) to produce 40 million tonnes of diesel, which is enough to match the UK's transportation demand for fuel if all vehicles were run on diesel-engines [the latter are more efficient in terms of tank to wheels miles by about 40% than petrol-fuelled spark-ignition engines], one could ideally have them to absorb CO₂ from smokestacks (thus simultaneously solving another little problem) by photosynthesis, driven only by the flux of natural sunlight. The premise is basically true; however, for algae to grow, vital nutrients are also required, as a simple elemental analysis of dried algae will confirm. Phosphorus, though present in under 1% of that total mass, is one such vital ingredient, without which algal growth is negligible. I have used two different methods of calculation to estimate how much phosphate would be needed to grow enough algae, first to fuel the UK and then to fuel the world:

(1) I have taken as illustrative the analysis of dried Chlorella [3], which contains 895 mg of elemental phosphorus per 100 g of algae.

UK Case: To make 40 million tonnes of diesel would require 80 million tonnes of algae (assuming that 50% of it is oil and this can be converted 100% to diesel).
The amount of "phosphate" in the algae is 0.895 x (95/31) = 2.74 %. (The Formula Weight, FW of PO₄^3- is 95, while that of P is 31).

Hence that much algae would contain: 80 million x 0.0274 = 2.19 million tonnes of phosphate. Taking the chemical composition of the rock as fluorapatite, Ca₅(PO₄)₃F, FW 504, we can conclude that this amount of "phosphate" is contained in 3.87 million tonnes of rock phosphate. In fact, rock phosphate is a more impure material than this, and the mineral usually used for fertilizer production is reckoned to contain 29─34% P₂O₅. From the ratio of FW for PO₄^3-/0.5 P₂0₅ (95/71), we may deduce that there are (71/95) x 2.19 million = 1.64 million tonnes of P₂O₅ contained in the above amount of “phosphate”. Taking the range average of 31.5% for the mineral P concentration, reckoned as P₂O₅, this would accord with 5.20 million tonnes of actual “rock phosphate”, a conversion factor of 1.34.

World Case: The world gets through 30 billion barrels of oil a year, of which 70% is used for transportation (assumed). Since 1 tonne of oil is contained in 7.3 barrels, this equals 30 x 10⁹/7.3 = 4.1 x 10⁹ tonnes and 70% of that = 2.88 x 10⁹ tonnes of oil for transportation.

So this would need twice that mass of algae = 5.76 x 10⁹ tonnes of it, containing:
5.76 x 10⁹ x 0.0274 = 158 million tonnes of phosphate. As before, taking the chemical composition of the material as fluorapatite, Ca₅(PO₄)₃F, FW 504, this amount of "phosphate" is contained in 279 million tonnes. Applying the factor of 1.34 as arrived at above, to account for the typical degree of impurity in the mineral, this accords with 374 million tonnes of actual mined rock phosphate.


(2) To provide an independent estimate of these figures, I note that growth of this algae is efficient in a medium containing a concentration of 0.03─0.06% phosphorus; since I am not trying to be alarmist, I shall use the lower part of the range, i.e 0.03% P. "Ponds" for growing algae vary in depth from 0.3─1.5 m, but I shall assume a depth of 0.3 m.

UK Case: assuming (vide supra) that producing 40 million tonnes of oil (assumed equal to the final amount of diesel, to simplify the illustration) would need a pond/tank area of 10,000 km². 10,000 km² = 1,000,000 ha and at a depth of 0.3 m, this amounts to a volume of: 1,000,000 x (1 x 10⁴ m²/ha) x 0.3 m = 3 x 10⁹ m³.

A concentration of 0.03 % P = 0.092% phosphate, and so each m³ (1 m³ weighs 1 tonne) of volume contains 0.092/100 = 9.2 x 10^-4 tonnes (920 grams) of phosphate. Therefore, we need:

3 x 10⁹ x 9.2 x 10^-4 = 2.76 million tonnes of phosphate, which is in reasonable accord with the amount of phosphate taken-up by the algae (2.19 million tonnes), as deduced above. This corresponds to 4.87 million tonnes of Ca₅(PO₄)₃F, or by applying the 1.34 “impurity factor” to 6.53 million tonnes of rock phosphate.


World Case: The whole world needs 2.88 x 10⁹ tonnes of oil, which would occupy an area of 2.88 x 10⁹/40 t/ha = 7.20 x 10⁷ ha of land to produce it.

7.2 x 10⁷ ha x (10⁴ m²/ha) = 7.2 x 10¹¹ m² and at a pond depth of 0.3 m they would occupy a volume = 2.16 x 10¹¹ m³. Assuming a density of 1 tonne = 1 m³, and a concentration of PO₄^3- = 0.092%, we need:

2.16 x 10¹¹ x 0.092/100 = 1.99 x 10⁸ tonnes of phosphate, i.e. 199 million tonnes. This corresponds to 352 million tonnes of Ca₅(PO₄)₃F, or 472 million tonnes of rock phosphate.

This is also in reasonable accord with the figure deduced from the mass of algae accepting that not all of the P would be withdrawn from solution during the algal growth.


Now, world rock phosphate production amounts to around 140 million tonnes (noting that we need 472 million tonnes to grow all the algae), and food production is already being thought compromised by rock phosphate resource depletion. The US produces less than 40 million tonnes of rock phosphate annually, but would require enough to produce around 25% of the world's total algal diesel, in accord with its current "share" of world petroleum-based fuel, or 118 million tonnes of rock phosphate. Hence, for the U.S., security of fuel supply could not be met by algae-to-diesel production using even all its indigenous rock phosphate output, and significant imports would still be needed. This is in addition to the amount of the mineral necessary to maintain agriculture.

The world total of rock phosphate has been reckoned at 8,000 million tonnes (Mt) and that in the U.S. at 2,850 Mt, using a Hubbert Linearization analysis [4]. The total world reserve, as expressed in terms of P₂O₅ content, is estimated to be in the range 3,600─8,000 Mt [5]. However, as is true of all resources, what matters is the rate at which it can be produced, and that once the peak is reached, what remains will be inexorably harder (of diminishing EROEI) to recover. The peak in world oil production will impact on the peak in phosphorus production, since rock phosphate, and all other mineral substances, is mined and recovered using machinery powered by liquid fuels that are refined from crude oil.

I remain optimistic over algal diesel, but clearly if it is to be implemented on a serious scale its phosphorus has to come from elsewhere than mineral rock phosphate. There are regions of the sea that are relatively high in phosphates and could in principle be concentrated to the desired amount to grow algae, especially as salinity is not necessarily a problem. Recycling phosphorus from manure and other kinds of plant and animal waste appears to be the only means to maintain agriculture at its present level beyond the peak for rock phosphate, and certainly if additionally, algae are to be produced in earnest. In principle too, the phosphorus content of the algal-waste left after the oil-extraction process could be recycled into growing the next batch of algae. These are all likely to be energy-intensive processes, however, requiring "fuel" of some kind, in their own right. A recent study [6] concluded that growing algae could become cost-effective if it is combined with environmental clean-up strategies, namely sewage wastewater treatment and reducing CO₂ emissions from smokestacks of fossil-fuelled power stations or cement factories. This combination appears very attractive, since the impacts of releasing nitrogen and phosphorus into the environment and also those of greenhouse gases might be mitigated, while conserving precious N/P nutrient and simultaneously producing a material that can replace crude oil as a fuel feedstock.

It is salutary that there remains a competition between growing crops (algae) for fuel and those for food, even if not directly in terms of land, for the fertilizers that both depend upon. This illustrates for me the complex and interconnected nature of, indeed Nature, and that like any stressed chain, will ultimately converge its forces onto the weakest link in the "it takes energy to extract energy" sequence. It seems quite clear that with food production already stressed, the production of (algal) biofuels will never be accomplished on a scale anywhere close to matching current world petroleum fuel use ( > 20 billion barrels/annum). Thus, the days of a society based around personalized transport powered by liquid hydrocarbon fuels are numbered. We must reconsider too our methods of farming, to reduce inputs of fertilisers, pesticides and fuel. Freshwater supplies are also at issue, in the complex transition to a more localised age that uses its resources much more efficiently.

There is a Hubbert-type analysis of human population growth which indicates that rather than rising to the putative "9 billion by 2050" scenario, it will instead peak around the year 2025 at 7.3 billion, and then fall [7]. It is probably significant too that that population growth curve fits very closely both with that for world phosphate production and another for world oil production [7]. It seems to me highly indicative that it is the decline in resources that will underpin our demise in numbers as is true of any species: from a colony of human beings growing on the Earth, to a colony of bacteria growing on agar nutrient in a Petri-dish.

Related Reading.
[1] http://www.resourceinvestor.com/2010/10/26/peak-phosphate-spells-end-of-cheap-food
[2] “Making Fuel From Algae: Identifying fact Amid Fiction,” BY C.J.Rhodes, in Algal Fuels: Phycology, Geology, Biophotonics, Genomics and Nanotechnology, J.Seckbach (ed.), Springer, Dordrecht, in press.
[3] "Chlorella" - Wikipedia.
[4] http://www.energybulletin.net/node/33164
[5] http://www.imphos.org/download/jena/cisse_prb-15.pdf
[6] “Environmental Life Cycle Comparison of Algae to Other Bioenergy Feedstocks,” By Andres F. Clarens, Eleazer P. Ressurreccion, Mark A. White and Lisa M. Colosi, Environ. Sci. Technol., 2010, 44, 1813.
[7] "Algae to Biofuel Conversion; Survival in the Oil Dearth Era," By C.J.Rhodes, Science Progress, 2009, Vol. 92, 39.