PV Solar Collectors
Photo voltaics or PV is the direct conversion of the sun’s energy into electricity. (not to be confused with thermal plate solar collectors which heat up the domestic hot water ) This is usually achieved by a complicated process of coating glass with a silicon material which responds to sunlight by creating a DC current of electricity from two wires connected to the glass coating. By connecting multiple panels together the voltage can be raised to a level where it can be put through an inverter and used like mains electricity in the house.
Further information on the Solarserver site
Feed in tariffs
Some countries have reverse metering with a generous feed-in tariff and this has driven the growth in PV. There are rumours here that the government may bring in something similar with anything between 35p and 50p per kWh. This would move things along a bit provided the total amount was not capped and was held constant long enough for the whole process to gather momentum.
Value for money
The money spent on PVs would normally be much better spent on saving energy in the first place through better insulation or the use of more efficient appliances (and when that has been done then on other environmental lifestyle aspects such as transport, food etc). However it is important to keep an eye on market developments. Both Germany and the US are much cheaper for PV than is the UK and things could change quickly here. A recent BBC news item suggests that costs might reach grid parity for most of Europe by 2020.
Given that money is usually a limited commodity it makes sense to calculate where that money is spent. PV should not be incorporated at the expense of insulation or air tightness so if there is a conflict then go for these two first. There is then the option to make the house PV ready so that when prices drop PV can be added later. Being PV ready involves several design factors.
- Having an area (probably of roof) which is built so that
- it is facing in the right direction
- is at the correct pitch
- has a covering which can be modified to take the supports for PV
- has some easy means to run cables indoors
- is, ideally easily accessible
- Having an area set aside where the control gear can be housed
The hope over the last 30 years or so has been that through mass production the rather high price of these PV panels would tumble to the point where everyone would have them on their roofs. Due to the inherent difficulties of manufacturing the panels this has never happened although some people are predicting that it could begin to happen soon. It now looks like costs are dropping at the rate of about 5%/year.
The price has almost halved over the past decade. At present the cost is about £3.50/watt for the panels and maybe roughly the same again to mount and control them. So to generate a kilowatt of electricity (during bright sunlight) would cost say £7000.00 in investment. However, in the US state of California, where a certain amount of solar installation is mandatory it looks like a 2kW solar array fitted to a new house roof will soon be costing about £6000 (ie £3000/kW).
The conditions under which the use of PV makes the most sense are -
- In an extremely sunny climate and where the orientation is correct and shading is minimal. To establish whether there is sufficient sunshine throughout the year you can use a sun calculator
- If the location of the building is so remote that there is no connection to mains electricity
- If it is possible to use the solar panels as the roof and/or wall covering and thereby save costs on other materials. This has been done successfully on several new industrial buildings and houses in the UK
It depends exactly where you live in the UK but there are only a few hours of bright sunlight per day on average and the electricity generated drops to about 25% if the sky is only bright rather than sunny (or when the collector is not pointing fairly directly at the sun). With an average of about 3 hours of sunlight per day this would give a return of £164 p.a. so it would take 43 years to pay for the initial investment. (And this is without including any interest repayment on the capital expenditure). Extremely poor by any standards. Worse than this is the fact that the lifetime of such panels might be 20 - 30 years and they may not even recoup the energy involved in making them during their life time.
Here is one family who converted their existing house to include PV and changed their life style. Useful figures on solar panel performance.
The BRE’s Green Book Live web site contains lists of microgeneration companies specialising in PVs.
There may be government grants available to help with installing PVs.
