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About Photovoltaics
Overview
Rather than having just a handful of ageing and polluting power stations we now have the possibility of decentralisation; millions of small generators producing power where it is needed, solving the problem of large energy losses during transmission.
Although photovoltaics work better in direct sunlight, they are not reliant on it. They only need daylight to produce electricity.
PV's are silent and unobtrusive, they are designed to withstand the elements and weather very little with age.
PV's have no moving parts and are very reliable. Most PV modules are guaranteed for 20/25 years, with a life expectancy far exceeding this. Maintenance requirements are negligible.
Solar PV produces electricity, not hot water. Please see our solar thermal page for information on thermal systems.
Terminology
Module
A PV (photovoltaic) panel, which is made up of a number of 'cells',each of which produces a small electrical charge under light.
kWp (kilo-watt peak)
The number of thousand watts a photovoltaic system will produce in peak conditions.
kWh (kilo watt hours)
A unit of electricity. This is defined as power of 1000 watts (being consumed or produced) over the period of one hour. e.g. 2000w over 1/2 hour or 100w over 10 hours.
For example:
A PV module could have a rating of 200 Wp (produces 200 watts in peak conditions). 12 modules are connected together on a roof to form a 2.4 kWp array (200 * 12 = 2400 Wp or 2.4kWp).
Module Types and Efficiency
Solstice Energy can supply and install any PV module accredited for use in the UK, such as Sanyo, Sunpower, Sharp, Kyocera, BP or any others. If you have a particular requirement or preference for any reason please let us know.
People often confuse efficiency with quality, but all it means is that high efficiency modules can generate the same amount of power as lower efficiency modules in a smaller area. For example, 210Wp Sanyo hybrid and Sunpower monocrystalline modules are almost the same dimensions as 170Wp Sharp polycrystalline modules. Our design team tends to recommend the (proportionally more expensive) high efficiency modules for smaller roof areas or where a client really wants to maximise output, and less expensive polycrystalline modules for large roof areas.
Despite some manufacturers claims, we have found that hybrid, mono and polycrystalline all give the same kWh yield / kWp over the year. Quality and guarantee periods are similarly high with all the common brands available for use in the UK.
Electricity Produced
Daylight levels in the UK mean that PV will produce an average of 780 kWh of electricity per kWp system size, per year (South-facing & un-shaded). This figure is reached by Standard Assessment Procedure, and forms the basis of our predictions. In reality, for South-facing & un-shaded systems in the SE of the UK, that figure is found to be more like 950kWh.
An average UK household uses around 3000 kWh per year (so a 1kWp system would supply a quarter of the yearly use). Simple energy efficiency measures in the building will increase the proportion of energy coming from the PV's.
Roof Suitability
Positioning
The PV array will usually be mounted on a Southerly facing, pitched roof.
The "solar sundial" below shows that a fair bit of deviation in the positioning of the array will still yield a large percentage of the energy expected from an optimum orientation (a pitch of 30/40 degrees facing due South).
Shading
Whenever shading decreases the power output of any one module in an array, then the output of the whole array is similarly decreased. It is therefore very important to avoid shading (from trees, other buildings etc) when siting a PV array. However, if, for example, the shading only occurs late on winter afternoons then it will have less impact on the annual output of the array than shading that occurs every morning until 12:00.
For complicated shading situations, our designers can plot the PV array and the surrounding objects and run a PVSYST simulation to show predicted output throughout the year.
Roof Area Required
Allow approximately 8m2 of pitched roof area (16m2 of flat roof) for every 1kWp of PV. Obstructions like dormer windows and roof vents need to be considered when surveying the site.
Planning Permission
Planning permission is not normally required unless it is a listed building or in a conservation area - please see the Town and Country Planning Amendment of April 2008. If in doubt, check with your local council, and if you do need to make a planning application we will advise you and supply all the drawings, photographs etc that you need for a successful outcome.
Exporting Your Electricity
There are two ways of storing the electrical energy produced by a photovoltaic array. One is by using batteries in a stand alone system (the remote house, boat, caravan etc); the other is by connecting to the national grid.
In a grid connect system, the grid works in effect as a battery. During the day the PV array might produce more energy than is required by the building it serves. This excess will be exported to the building next door or down the road via the mains. In the evening, or any other time of high use / low sun, electricity is drawn in the usual way from the grid, and supplemented by the PV system. This all happens automatically due to natural ebb and flow of electricity as it finds the shortest route to a load. Grid-connect PV is often referred to as ‘fit and forget' because of the lack of user interaction or maintenance required.
At times of high production / low use the excess electricity that flows back to the grid can be recorded on an export meter, for which you can expect payment. Electricity suppliers getting their chequebooks out for their customers is a photovoltaic phenomenon! The electricity companies all run different buyback schemes that suit different patterns of use. We have collated all of these deals, and can advise you on your options. You can switch electricity supplier to get the best deal at any time before or after our installation.
Grant Funding
There are grants available for domestic and community installations. Please see the relevant page on this site for details, as well as financial case studies of previous installations.
On the 15th of July the UK Government announced illustrative feed in tariffs (also known as ‘Clean Energy Cashback’) for small wind turbines and photovoltaic solar panels. The rates are:
| Size & nature of system | Payment / kWh generated |
|---|---|
| <4kWp New build | 31p |
| <4kWp retro-fit | 36.5p |
| 4 – 10kWp | 31p |
| 10 – 100kWp | 28p |
These tariffs will replace the existing grant and Renewable Obligation Certificate system, and are intended to be incentive enough for people to install renewable energy without grant funding. Payments will begin on 1st April 2010, but all small wind and solar systems commissioned from now on will be eligible for both LCBP grants and the new feed in tariff.
There really isn't a better time to install a solar PV system!
There are grants available for domestic and community installations. Please see the relevant page on this site for details.
A PV installation will also be an addition to the value of the building.
One must assume that fuel prices will rise in the next 100 years. Fuel prices have gone up 40 per cent this year alone, with a further rise on the way this winter. When you take into account the rapid decline in North Sea gas reserves, an increasing global demand for liquefied gas and the willingness of Russia to play politics with its fuel reserves, prices are highly likely to rise for the foreseeable future. The era of cheap fuel is over, even the politicians say so.
Extract from Martin Hickman article