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Solar PV: still FiT for purpose


Since 1971, the price of a single watt of solar power has fallen from £63 to just 0.67p, thanks partly to government incentives to ramp up the adoption of domestic solar power generation. Homeowners that install solar panels score wins all-round under the Feed-in Tariff scheme; as well as slashing energy bills by generating your own power, you’re also paid for all the electricity you generate – even if you use it yourself. Anything left over can be sold back to the National Grid, so the cash flows in whether you use the power or not.

The FIT rate – or the sum you’re paid for the energy you generate – started off pretty high when the scheme launched in 2010; at 41.3p per kilowatt hour (kWh), you could expect an average-sized solar PV system to pay for itself in 10 years. But when the rate dropped to just 21p/kWh at the end of 2011, the payback time stretched out to around 18 years. Last July the rate was shaved again, and those installing solar PV systems now will be paid 14.9p/kWh.

While solar installation might be starting to feel more like a risky gamble than a sure-fire income generator, don’t be put off just yet. The rate you receive is fixed from the point of installation and guaranteed for the next 20 years; while rates might drop in the future, the earlier you get in, the better off you’ll be.

The falling rates are testament to the solar boom’s success, and the solar PV market is being forced to respond to increasing competition. From small flexible panels to large ground-mounted tracking stations, the market has differentiated itself to provide power for all sorts of situations, making solar generation a possibility for everyone. So while FIT rates may have dropped, innovative new ways to harness the sun are appearing – and they’re carrying lower price tags than ever before. Here’s a rundown of the technology available and information to help you decide which system would work best for you.

Amorphous Silicon

Amorphous panels usually consist of a glass or plastic panel coated with a thin film of amorphous silicon. This particular form of silicon doesn’t have a crystal makeup and, due to its disordered structure, produces efficiencies in the region of 6-9%. Amorphous silicon panels tend to take up more space than other options and also cost more to install – but the panels themselves are relatively cheap, which tends to balance things out. Interestingly, amorphous silicon can be coated onto plastic sheets in order to make a flexible solar panel, and can even be made transparent to certain wavelengths of light. These designs can act as both a window and solar panel simultaneously. One such example of transparent solar panels is brought to us by Polysolar ( of Cambridge in the UK.

Polycrystalline Silicon

Companies like Sharp have been making polycrystalline panels since 1963. This type of panel comprises many small crystals which have been fused together and cut into a wafer. This is in contrast to monocrystalline panels, which consist of one large continuous crystal. Polycrystalline panels typically have efficiencies of 12% in standard test conditions, meaning they’re twice as efficient as amorphous silicon options. As a result they require half the roof space, which reduces installation costs. The typical installation process involves attaching a racking system through the roof tiles and into the rafters of the building. The panels are then mounted to this frame. To install a 2kW solar array will cost around £2,000 in equipment costs and £1,800 in installation costs.

Monocrystalline Silicon

Monocyrstalline panels from companies such as Hyundai are the most efficient form of conventional solar panel, with efficiencies reaching 17%. Monocrystalline silicon is grown into one large single crystal, stretching 30cm in diameter and 2m in length. This is then cut into incredibly thin wafers for use as solar cells. Due to the excellent crystal structure, monocrystalline cells use more of the energy that falls onto their surface – but due to increased manufacturing costs, this tends to be a more expensive option for the homeowner. Monocrystalline and polycrystalline panels share similar installation costs; for this reason many solar installers recommend opting for monocrystalline panels for their higher lifetime efficiencies.

Concentrating Photovoltaic

Research into concentrating photovoltaic panels began in the USA’s Sandia National Labs in the 1970s. The concept is to reduce the amount of silicon required for construction by concentrating sunlight through a series of mirrors or lenses. It’s possible to concentrate the sunlight one thousand times onto a focused point, which contains a very small but highly efficient solar cell, typically one or two centimetres wide. This reduces the number of silicon cells required by up to 95%. Through clever reduction of the expensive silicon components, CPV panels come very close to the price point of monocrystalline panels.

Due to the reduced use of silicon and the increased use of glass mirrors and framing, the vast majority of CPV panels can be recycled again and again as technology improves. Another major benefit of CPVs is that they typically require 40% less space than the most sophisticated monocrystalline panels. Less material taking up less space results in a reduced environmental impact for each watt of power generated, making concentrated solar power very attractive when used in the correct application.

This type of panel functions best in direct sunlight, so CPVs are typically ground-mounted and attached to a single or dual axis tracking system, designed to follow the path of the sun throughout the day. This adds an additional cost, but single axis tracking alone can improve efficiencies by approximately 20% over a fixed panel. This means that concentrated solar power is ideally suited for use in large-scale solar power stations; the increased weight makes their use prohibitive for roof-top installations.

CPV efficiencies can reach 36%, which even outstrips coal- and oil-fired power plants (which have efficiencies around 33%). This is just another feature of concentrated solar panels that makes them very attractive for large power generation projects.

For updates on FIT rates, including when they’ll expire and kick in, have a look at the OFGEM website.

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