SOLAR PHOTO-VOLTAIC PANELS

The basic technology has been around a long time: the action of light on a silicon wafer sandwich causes electrons to flow within the sandwich, and the 'potential' can be harnessed. It is always DC so has to be altered through an Invertor in order to power any AC equipment, this involves percentage losses unless the invertor is of very high quality and expense. A cheap low power invertor as is commonly available gets hot in use -- this represents a loss of useful energy.

Although the manufacture of solar cells is now very big business the demand outstrips supply and my view is that the cost as an alternative electricity supply is still too high. For remote locations or where no grid supply is available it's an obvious choice provided the amperage required is not too high.

Three variations of PV cells exist:

• Polycrystalline, which have a characteristic mottled blue appearance and are the most common type
• Monocrystalline, which are more grey in appearance and less mottled
• 'Hybrid' cells which are thought to have advantages from both other types

Monocrystalline cells seem to be regarded as about 15% more efficient at converting light into power, but they cost more. Hybrid cells are claimed to be more efficient than polycrystalline but less expensive than monocrystalline cells. So far few makers produce them.

PV Panels are normally costed per 1Kw peak power capacity but the actual amount of power produced rarely reaches peak capacity. Current suggested cost is around £3500/KwP., with a full installation costing in the region of £8500. Approved Grants are set at a maximum of £2500 per household or 50% of the installed cost, whichever is the less.

Inclination to the sun, colour temperature of the sky and measured light value all affect output. Some French systems have automatic sun tracking, unsurprisingly named 'Girosol' but need small amounts of power to operate. Many houses in Germany (where the possible income from micro-generation is much higher than in UK) now have roofs almost covered with PV panels and one of the houses at the Building Research Establishment in Watford has a roof composed of solar tiles. It is important that a PV panel is not shaded by trees or other buildings.

Rectangular framed panels are not the only form of PV available: 'Solar Tiles' resemble roof tiles but produce electricity and Solar Façades have solar cells embedded in glass panelling, thus providing a dappled light into entrance halls below. Solar Glass is a fast-growing industry for commercial and office use.

SUMMARY

• Well-established technology with little or no maintenance required
• Careful positioning required for optimum output
• DC output needs altering to AC for domestic use, unless used for low voltage DC lighting and fans
• Can be connected to National Grid with possibility of income, but capital cost of equipment for this is quite high
• Initial capital cost for a useful amount of power is high, running costs negligible
• Basic manufacturing methods have not changed over 20 years or more, a breakthrough to low-cost methods is needed
• The obvious choice for a carbon-negative house achieving CSH Grade 6, but energy produced aver a time cycle will still need to exceed consumption in order to qualify
• UK Govt. grants are at present higher for PV installation than for Solar Thermal collectors, perhaps reflecting the capital cost imbalance

LINKS

Solar Century:    www.solarcentury.co.uk

Solar Energy Alliance:    www.solarenergyalliance.com

+ many of the sites concerning Solar Thermal technology also deal with Photo-Voltaic systems

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