Tuesday, December 04, 2007

Cheap "Organic" Solar Power?

To use current silicon technology at the thickness (200 microns) that it is employed in the present generation of solar cells is not feasible on the grand scale. The main problem is how quickly high grade silicon wafers can be fabricated and I calculated previously that we would need around 100 times the present production capacity to be installed over 20 years to make a real dent in the anticipated shortfall of future world electricity production. Thin-film cells, which use perhaps 100 times less materials, and in more accessible amorphous forms rather than crystalline wafers, would represent a considerable advantage in terms of raw material requirements, but this technology needs further refinement.

In contrast to such devices based on "mineral", inorganic, semiconductor materials, there is the possibility of organic cells, which instead are made from carbon molecules. A conventional photovoltaic (PV) cell consists of a silicon wafer of thickness 200 microns (one fifth of a millimeter), to be compared with a human hair which is around 70 microns thick. This is treated with other materials to form a double-layer structure which is known in electronics as a p-n junction. Photons of light are absorbed by the silicon causing a flow of electrons and a hence a small electric current. In an organic cell, the double layer is made from two ultra-thin (100 nanometer or 0.1 micron) films of organic conducting polymers, embossed onto glass.

A prototype organic cell has been developed by Neil Cavendish at Cambridge University, and one about the size of your hand can produce enough electricity to run a pocket calculator. Most standard solar cells operate with a light-to-electricity conversion efficiency of around 10 - 15%, but organic cells have proved so far much less efficient, perhaps only 3 - 4%. However, they are much cheaper to produce. Indeed, Paul O'Brien at Manchester University thinks that solar cells need be no more expensive to make than high-performance self-cleaning glass. He said: "We're very interested in solar cells where we take an organic layer that's printable or sprayable containing an inorganic mineral like lead sulphide which will actually do the photon capture."

Indeed, lead sulphide can be fabricated into minute "nanorods", perhaps 100 nanometers in length and 20 nanometres in cross section, and can be dispersed in the semiconducting polymer, hence releasing electrons within the material, which can then conduct them carrying an electric current. All researchers in the field stress the need to move away from carbon-based fossil fuels in order to mitigate climate change, or in my view, more urgently to use less of the cheap oil and gas that we are running short of. In principle, cheap solar cells could be incorporated into the walls and roofs of buildings in the form of building integrated photovoltaics (BIPV), as a means to bear the burden of costs yet further. O'Brien reckons that the new solar cell technology might cost as little as one hundredth as much as silicon cells, and that will surely provide an incentive for further development.

Nonetheless, the clock is ticking away toward the Oil Dearth Era, and any such technologies need to be installed quickly, if we are to avoid a massive energy crunch, especially if electricity is implemented in various strategies to keep transportation running. There is also the issue of other materials such as platinum, which will be needed on a massive scale to underpin such innovations - another potential bottleneck in the shifting schemes of potential "solutions" to the impending and unavoidable energy crisis.

Related Reading.
"How solar power could become organic - and cheap," By Michael Pollitt, The Independent, 29-11-07.


Anonymous said...

Plan A: Shelter

The old farm house sits on a rather flat rock of about 20 x 20 feet. I wondered why the first settlers built it there. It seems the rock provides natural cooling, while the wood stove was burning the then plentiful wood.
The elevated position also allowed for quick drainage of rain water (sometimes torrential) and an effective kitchen and bathroom drain away from the building.

The cooling during the summer makes living on the ground floor bearable, while the wood stove needs to be replaced. But with what? Firewood prices are increasing every year. Storing solar or other sources of heat during the bitter winters becomes a matter of survival. If plans such as these don't work, I would have no choice but to rebuild. I'm even thinking of placing hollow, elongated oval-like structures and stuffing them with snow (easily available from the roof). If snow is good enough for the huskies up north, it might be an asset. A wind break is of limited value because the house sits in the hollow of a valley between two unequal ridges.

I'm constantly studying the technological possibilities of "outliving" Peak Oil. Trouble is, the run-up to Peak Oil brought with it consumption of many other resources. Peak Everything is a more apt expression for those of us who still want to "sneak" through to a technologically sustainable future. In keeping things as simple as possible, my budget won't get exhausted keeping up with the Jones'. I have to choose my extras with considerable care. May God help us!

Anonymous said...

You can grow your own trees, and rather than cut them down, you pollard them. Cutting off the branches that grow. Leaving a tall stump. That way you can harvest lots of wood, save the wood factory for generations. You don't need to cut large tree trunks, or have heavy chain saws. Pruning shears will do for much of the growth. Insulate the home, and use passive solar heating etc. There are many helpful energy conservation measures.

Professor Chris Rhodes said...

Yes, photosyntheisis is probably the most efficient and sustainable use of solar energy. Just one question - could pollarding provide enough biomass to make sufficient fuel to run Europe, say? I ask the question as I am curious about how much diesel can be made using BTL technology given the amount of wood we can produce. I will work this out and post something about it.Please see my posting about permaculture and the running theme that we will return to smaller communities provided for by local farms etc.