book_cover_big.gifAlmost every week you can read about efficiency improvements of solar cells. For example on February 25, 2008 the Belgium research organization IMEC announced that they had taken up the efficiency of a single junction GaAs solar cell to a record 24.7 percent conversion rate. As a comparison, mono-crystalline silicon based solar cells (still the mainstream material for PV generated electricity) run at an efficiency of about 20%.

On March 24, 2008 the US Department of Energy’s National Renewable Energy Laboratory reported an efficiency of 19.9 % for a thin film solar cell based on copper-indium-gallium-diselenide material[2]. This comes close  the efficiency silicon solar cells. On April 1, 2008 there was a statement by the Swiss Federal Institute of Technology that the efficiency of so-called Gratzel cells could be improved to 7.2%[3]. That seems to be a low number compared to the ones quoted above. But Gratzel cells are very cheap cells, compared to mono-crystaline silicon and GaAs semiconductors, because they are based on thin film semiconductor materials deposited on low cost glass substrates.

In all these cases the main aim is that the cost of the electricity generated by the PV cells will be lowered and to bring it at parity with fossil based generated electricity. This is quite in line with the discussion in my blog from March 24; where it was argued that PV electricity would reach grid parity around 2015.  The cost per generated kWh is determined by the cost of the PV installation itself and its operational costs. To give you some impression of what makes up the costs of a PV system have a look at the breakdown below.


More than 40% of the total system price is caused by the costs of the PV cells. It is therefore important to have research aiming at improving the efficiency and to look for solar cells that cost much less than the silicon based systems. Today the price of PV electricity in the US is, depending on the solar cell technology used, about 3-4 times as high as the average grid electricity[4]. It is therefore that in some parts of the world governments subsidize solar energy. The best example is perhaps Germany[5]. One of the subsidy measures taken in this country is that of a “feed in tariff”. Owners of roof mounted PV systems can sell their surplus of electricity back to the bulk producers for a generous price that is fixed for 20 (!) years. These kind of measures and others have made Germany the leading country in the world in terms of absolute installed renewable energy capacity (in 2006: 25 gigawatts of which wind is 20 gigawatts and solar about 3 gigawatts). In 2007 6.7% of the total energy need was supplied by renewable sources.

However, there are also critics of PV ever becoming mature (see for instance reference [6]). Main concerns are that PV electricity will never reach grid parity and that as soon as government subsidies stop the PV industry will disappear. Another concern is that the daily rhythm of solar electricity will prevent it from ever providing a substantial part in the overall electricity production.

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 Copyright © 2008 John Schmitz





[4]Steve O’Rourke, Peter Kim, Hari Polavarapu, Solar Photovoltaics, July 2007, Deutsche Bank