The future of solar PV
Is it the renewable energy option to watch?
There is nothing new under the sun, and certainly not electricity from photovoltaic (PV) cells. The very first solar electricity was produced in France in 1883. The first usable silicon cell in 1954 and silicon-based PV still accounts for 96% of the world market. Satellites have used solar PV since 1958. At that time PV cells were very expensive and relatively inefficient. Elliot Berman, working in the USA in the early 1970’s, improved efficiency and production methods to make solar PV commercially viable.
Since then the take-up of solar PV technology has been spasmodic – affected mainly by fluctuating oil prices. Since the early 1990’s, and the realisation that oil will end and we have to find an alternative, PV has enjoyed steady growth, in research, investment and product take up. Recently the UK has seen a 25% year-on-year growth in the industry.
Silicon crystal PV technology, the monocrystaline or polycrystalline systems on domestic roofs, street lights, road signs, etc., is still the main player but is becoming a bit old-hat. These fairly large systems are considered first generation technology and we are now moving to a 3rd generation. The future is considered to be something other than silicon and Shell, the oil giant, recently sold its interest in a silicon cell manufacturing company and switched its investment to thin-film technology.
In January 2008 the Carbon Trust launched a £5m research and development programme with Cambridge University on a new technology, with the aim of making solar energy cost-effective for the building industry in 10 years. The project involves unlocking the potential of so-called organic PV as an alternative to silicon-based cells. Silicon crystal are difficult and expensive to produce and need sawing into wafer thin slices, which is also expensive and wasteful. The current price of silicon based PV cells is around £2 per Watt (which equates to around £5 per Watt for an installed system). The Carbon Trust suggest that thin-film technology can reduce the price to 1 euro (70p) per Watt by 2018.
But even this is only 2nd generation technology. A company in Cardiff, G24 Innovation, has developed a new, 3rd generation technology. In November 2007 they shipped the first of their “dye-sensitised thin film” PV systems. The raw materials used in this process are a closely guarded secret, but said by G24i to be inexpensive and almost limitless. At the moment they are only available as small systems, useful for charging mobile phones and the like, but plans are in place to have systems large enough for domestic property available in 5 years.
The production process for dye-sensitised thin film PV uses a high speed and environmentally friendly, "roll-to-roll" process, similar to inkjet printing, that sprays layers of light sensitive material on a metalised or synthetic film. Electricity is produced by a process similar to photosynthesis, in which a molecule is coated in a light absorbing dye (similar to the dye in blackberries). This molecule passes the particles excited by the light to another molecule that converts them to electricity and in turn passes them to a third molecule which conducts the useful electricity away. The finished product is less than 1mm thick, robust and highly flexible.
If you need convincing that this new technology works, have a look at www.youtube.com/watch?v=YYJe12X6T50 for a 2 minute movie of thin film roof covering being installed.
PV in the UK
The sun may not be our most plentiful commodity right now, but there is still enough solar energy falling on this country to make a significant contribution. The “solar constant” – the amount of solar energy hitting the planet – is around 1,300 Watts per square meter. In the UK, with PV technology as it currently stands, we can harvest less than 30 Watts / m² as electricity. This may not sound much but it compares to a maximum potential of 56 Watts/m² at the Equator.
Building integrated solar systems (as shown in the movie mentioned above) have a lot going for them. They replace the roof or wall covering (and its cost) with a productive layer with a known life in excess of 40 years.
Zero Carbon Homes
With the requirement that all homes in England and Wales have zero carbon emissions from 2016 (2011 in Wales), it is difficult to see how PV will not see significantly greater take-up. Certainly the self-builder looking to design a zero carbon house will need to give serious consideration to solar energy. It is the only renewable energy that can be installed virtually anywhere, and the only fit-and-forget technology.
At £5,000 per kW installed (and a low energy house will need 3kW to 4kW capacity) PV in the UK is still expensive. But it is another “rip-off UK” product, with prices in Mediterranean countries as little as half what we have to pay. Increased supply, innovatory products, greater awareness of what is happening in the rest of Europe, should all help to put downward pressure on UK retail prices.
But consider, even at those inflated costs, investment in a domestic PV system will fix the price of the householder’s electricity at 12p to 15p per kWh for the next 40 years. And that is a deal you won’t get anywhere else.