David Hilton is an expert in sustainable building and energy efficiency, and is a director of Heat and Energy Ltd
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When we speak about photovoltaic (PV) panels we always seem to end up discussing efficiency. It’s easy to get confused between all the different figures but in effect we are looking at two different efficiency figures: the first is cell efficiency; the second is panel (or module) efficiency. In the last 15 years, since the introduction of the Feed-in Tariff (FiT), we have seen slight improvements with PV efficiency. The first came by manufacturing the panels with the cells placed closer together, thus eliminating as much wasted space as possible between the cells and maximising panel efficiency.
Another improvement was to the cells themselves. The earlier cells had efficiencies of around 14% for polycrystalline silicone (the blue panels) and around 19% for mono-crystalline (the black panels). This means that for every 1kW of solar energy shining on the panel you will generate from 140W to 190W of electricity. The panels measured around 1x1.6 meters and had a maximum rating of around 240W per panel. Current panels now have a maximum rating of around 340W but the cell efficiency is still only around 21%.