Building-Integrated Photovoltaics (BIPV) is is a version of photovoltaic technology which is being increasingly incorporated into the fabric of both commercial ind domestic buildings as a major or augmenting source of electricity. The essential idea of BIPV is that a cost-reduction is possible for a PV system which is effectively made by fabricating solar-cells within the structure of a building element, e.g. a roof-tile, roof-membrane or a facade-panel. The BIPV modules are thus made component parts of the roof or walls of a building using normal construction techniques, but with the need for additional electrical connections. In Japan the technology has been encouraged in the form of government incentives for PV generally, and this has allowed a significant number of new houses to be fitted with BIPV; however, elsewhere, the relatively high cost of BIPV modules or their limited availability has restricted their use.
In some countries, extra incentives are offered for BIPV over PV but only in France is that differential sufficient to be of significant service. France currently makes around 80% of its electricity from nuclear power, having very little in the way of natural resources, and so as part of a strategy of being as independent as is possible on gas, oil and coal, an investment in solar-power might be expected, and particularly BIPV if it is the most cost-effective version of the latter.
I was reminded of BIPV by a recent e.mail promoting investments in the technology, and which among all the lush information about financial growth expected in the sector, were given some cornucopian figures to the effect that the sunlight hitting the Earth amounts to 174 petawatts of energy per day. In fact that is the amount impinging onto the upper atmosphere, and which is filtered to some extent but in anybody's terms it is an awful lot of energy. This can be broken down into tasty chunks, e.g. 1 petawatt is enough to keep New York City running for 3,846 days. It is claimed that installation of BIPV systems on a mass scale could eventually produce in a single month more energy than Saudi Arabia will in the next 50 years.
It all sounds great, but like is not being compared with like. All resources of energy are not the same in how they are used to release that energy. Most of Saudi's "energy" is oil, and that is used mostly to fuel transportation. More oil is used in the US for space heating and electricity generation than is the case in Europe, but the vast bulk of world oil goes to run cars and planes etc. However, the direct production of electricity from PV (and BIPV since it is cheaper to install as a part of the overall costs of a building) is a special case, and it would be used to power the latter only in the form of a huge (electric) vehicle infrastructure which would need to be installed within probably a couple of decades to keep the cars on the road, even if it could still keep all the lights on.
My final concern is over the resources necessary to collect the sunlight and turn it into electricity by BIPV or indeed any form of solar technology. Conventional silicon solar-cells are presently used in BIPV and this is probably too resource-intensive for widescale exploitation, or at least so on the world-scale that is needed to offset the fall in other energy resources expected. However, "thin-film" technology uses perhaps just 1% of the resources of silicon or cadmium sulphide, gallium arsenide etc. semiconductor materials currently required to make solar-cells, and might provide the lynch-pin of success, although much of it remains to be rendered commercial. As is true of many technologies (including new generations of nuclear reactors) proposed to produce energy into the future, if we are serious about them, we should be going hell-for-leather to install them as soon as possible, otherwise there will be nothing in place to meet our energy needs in the next couple of decades when oil is running short, and demand on gas supplies is relentless.
The fundamental equation seems to include both the actual amounts of resources available and how quickly we can both recover these and fabricate them into practical devices; and also whether we have enough energy remaining from other sources to do all of this by the time such action begins. Either way, time is of the essence.