Solar PV for Electricity

Since its introduction as a viable option for homeowners in the 1970s, take up of solar PV (photovoltaic) technology has been spasmodic — affected mainly by fluctuating oil prices. Since the early 1990s, and the realisation that cheap 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 monocrystalline 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 third 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 socalled organic PV as an alternative to silicon-based cells. Silicon crystals 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 suggests that thin-film technology can reduce the price to 1 Euro (70p) per watt by 2018.

But even this is only second-generation technology. A company in Cardiff, G24 Innovation (g24i.com), has developed a new, third-generation technology. In November 2007 it shipped the first of its ‘dye-sensitised thin-film’ PV systems. The raw materials used in this process are a closely guarded secret, but are said by G24 Innovation 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 five years.

The production process for dye-sensitised thin-film PV uses a high-speed and environmentally friendly, ‘roll-toroll’ 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.

Above left: Solarcentury’s c21e roof tiles are designed to minimise architectural impact (solarcentury.com); Above right and main image: Third-generation PV solar technology, developed by Welsh company G24 Innovation, uses a process whereby a light-sensitive material is sprayed onto a synthetic film (rather like an inkjet printer) and converts light to electricity through molecules. It’s currently used on smaller applications such as for charging mobile phones, but is likely to be incorporated for domestic uses within five years.

A History of Solar PV

The very first solar electricity was produced in France in 1883; the first usable silicon cell was created 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 expensive and inefficient. Elliot Berman, working in the USA in the 1970s, improved efficiency and production methods to make solar PV commercially viable.

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 metre (W/m²). In the UK, with PV technology as it currently stands, we can harvest less than 30W/m² as electricity. This may not sound much but it compares to a maximum potential of 56W/m² at the equator.

Integrated solar systems ( as shown in the clip below) 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.

PV in Zero Carbon Homes

With the requirement that all new homes in England and Wales have zero net carbon emissions from 2016 (2011 in Wales), it is difficult to see how PV will not enjoy a 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 and 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, that 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.

Homes that use Solar Power:

• A Green House in the Garden
• An Eco-friendly Self-build with Sails
• A Sustainable Self-build in Devon

Further reading:

• Solar PV: From Specification to Installation
• Solar Panels for Hot Water
• A Guide to Green Technology: Solar PV
• Feed-in Tariffs Explained