Solar electricity (photovoltaic) panels
On this page:
The technology of solar electricity panels is easy to understand. The panels are installed on a sloping surface (probably your roof), and connected by a wire to an inverter (a box, positioned e.g. in your loft, to convert the lower voltage direct current to mains voltage (250 V) alternating current), which is connected via a meter to your mains junction/fuse box. There are no moving parts. When electricity is generated by the system, it goes to power anything in your home that is drawing current, and any excess is exported to the mains. A monitor gives the power currently being generated, the total for the day, and so on.
The hard part is understanding the government subsidy system introduced in April 2010 (the feed-in tariffs). Most people expect that they get paid for what they export to the mains. In fact this is just a small rate (generally 3p per unit), and the main financial return is the tax-free payment by the government initially 41.3p for every unit that is generated by the system whether you export the electricity or use it in your home. The meter between the inverter and the fuse/junction box has to be installed by an accredited installer, and it will be read at intervals, and people will receive cheques from the government via their electricity company according to the energy generated. It is estimated that most people will use about half of the electricity that they generate (which saves them about 14p per unit), and export the other half (which earns them 3p per unit). Initially it seems that many electricity suppliers will merely estimate the amount of electricity exported, but some are installing an export meter to actually measure it.
From spring 2011, the feed-in tariff increased to 42.3p per unit, but is due to decrease for new installations to 21p per unit from December 2011.
Systems are rated in kilowatts according to the peak output (i.e. in bright sunshine, in the middle of the day, in the middle of summer). The total annual energy generated is estimated to be this figure times approximately 800 hours. Outputs are obviously best for angled roofs facing south, and are less for east or west facing roofs.
• 14 panels on a south-facing roof
• total area: 16 sq metres
• rated peak output: 3.2 kW (kilowatts)
• estimated annual energy generated: 2,600 kWh (kilowatt-hours i.e. units of electricity)
(the average UK household uses 4,800 kWh per year)
• total cost: £12,000
• estimated government payment (feed-in tariff): 2600 kWh @ 41.3 pence per kWh: £1074
• estimated annual saving on electricity bill: 1300 kWh @ 14 pence per kWh: £182
• estimated annual earnings on exported electricity: 1300 kWh @ 3 pence per kWh: £39
• estimated annual return on investment: £1,300, i.e. 11% (tax-free)
• estimated annual C02 saving: 1.48 tonnes
Some Wirral installations
We are grateful to three Wirral residents who have given us their experiences of solar electricity systems. The following is a summary of what was installed and so on.
1. Nine Mitsubishi 185 watt polycrystalline modules
2. Seven Sanyo panels, total 1.5 kW
3. Fourteen Yingli panels, total 3.22 kW peak output
1. SMA SB1700 inverter
3. SMA SB3000 inverter
1. Sunny beam personal display.
3. SMA Sunny beam personal display.
1. Northern Solar of Liverpool (www.northernsolar.co.uk). The customer told us "As a result of my email, I recieved an email quote, and no further contact till I rang a few weeks later (no pestering). I was then given the phone numbers of two homes in the area which they had installed with PV panels. I rang one and visited the other: both were highly complementary about Northen Solar, as am I."
2. Eco Environments Ltd, based in Crosby (www.eco-environments.co.uk). The resident told us that they took a tape measure onto the roof and adjusted the layout to fit in seven panels (which would generate the minimum needed to be eligible for a grant); and that "From our experience we can recommend them highly. They have a very informative website and, being local, they were easy to access and talk to. They were happy to visit and talk the issues through - and absolutely no hard sell nor pressure. They have a close working relationship with experienced roofers and electricians - again local to Merseyside. The installation took only a couple of days."
3. Northern Solar of Liverpool (www.northernsolar.co.uk) - as case 1 above.
Other suppliers not chosen
• A local company gave a quote which was said to be a special offer, and had to be signed for immediately, but was no cheaper than Northern Solar's. The company also pestered subsequently.
• An out-of-area company which would have added the cost of two overnight stays
• A company based in the south of England, which had been recommended by a power company (they all have to promote micro-generation in their areas). "We were frustrated having to work at arms length with them. They even determined that our roof was too small for the installation we wanted by measuring it from Google maps! But they gave us a quote anyway."
1. Total cost £8,447 inc. 5% VAT, reduced to £5,947 by a £2,500 grant (no longer available).
2. Total cost £9,000, reduced to £6,500 by a grant (no longer available).
3. Total cost £12,080 inc. 5% VAT.
The projections for electricity generated are
1. 1,300 kWh per year
2. 1,200 kWh in a year.
3. 2,603 kWh in a year.
This compares with the average UK electricity usage per household of 3,600 kWh per year.
The systems were installed between winter 2009/2010 and May 2010. The latest reports are that all seem to be on course to meet their projected annual outputs.
Experience so far:
1. In December/January, average generated: 1.2 kWh per day, with maximum of 3 kWh in a day
2. In January, on a sunny day with a few scattered clouds: 2.5 kWh in a day. Even on a cloudy day in December, electricity was being generated.
3. The maximum output so far has been 3.1 kW (for a system rated as 3.2 kW peak)
Guarantees / Warrantees
1. A 5 year guarantee on the panel with + 10 year guarantee of 90% of Pmax power output + 25 year guarantee of 80% of the Pmax level.
Northern Solar gives a 2 year warranty on parts & workmanship.
3. Yingli give a warranty on their panels of 90% of the rated power output at 10 years, and 80% at 25 years.
Installing solar panels is normally a permitted development not requiring planning permission. If you live in a listed building, a conservation area or a world heritage site then you may need permission.
Long term considerations
• The technology is tried and tested, and installed extensively in Germany where feed-in tariffs have applied for years.
• There are no moving parts in the panels and so there is not much to go wrong.
• no maintenance is needed
• The government feed-in tariffs are guaranteed for 25 years and are index-linked.
• If electricity prices were to increase markedly, it seems likely that the price paid for exported units would also increase, so that people are likely to be protected from large price increases.
Energy Saving Trust: an excellent and comprehensive source of information on capital grants, recognised installers etc.
Good FAQ section
See also the links on the main home energy page
|Last updated: 08 Dec 2011|