Would you like to generate your own solar electricity, but don’t know where to start?

The information team at the centre of alternative technology have the answers to some common questions.

Is my roof suitable for solar panels?

A house roof is usually an excellent site for solar electric (PV) panels – they will perform well if they face anywhere between south-east and south-west, at an angle of 20 to 50 degrees. A PV array that faces due east or west will give about 20% less energy than one facing due south.

Look for a site that’s largely free of shade, particularly between spring and autumn, to maximise sun exposure. Roof mounted panels are usually a ‘permitted development’, so you won’t normally need planning permission.


How much electricity could I generate?

The ‘rated output’ or ‘rated capacity’ is a key figure to use when you compare PV systems. This is the peak power in kilowatts (kWp or just kW) that a PV array gives in bright summer sunshine. Domestic PV systems are commonly between 3 and 4 kW, taking up 20 to 30 square metres of roof.

Of course it’s not sunny all the time, and the output of PV panels will drop a little under cloud or on winter days, when the sun is weaker. Where you live will be a factor – for example Cornwall receives 30% more solar energy that northern Scotland.

In average UK weather conditions, you can expect one kW of PV panels to generate between 700 and 900 units of electricity per year. So a 3.5kW south-facing domestic system will produce about 3,000 kWh per year.

What’s the environmental benefit?

Generating about 3,000kWh from solar instead of from a gas fired power station will save about 1.2 tonnes of carbon dioxide emissions. The energy used during the manufacture of PV panels is far less than they will generate through their lifetime. Even with the UK’s levels of sunshine, PV panels will ‘pay back’ this energy cost in less than 3 years – and most PV panels come with a guarantee that they will still be giving something like 80% of their maximum output after 25 years.


How much does solar PV array cost?

A 3.5kW array (which would cover about 25 square metres) is likely to cost about £6,000.

Ongoing maintenance costs will be very low because there are no moving parts and the panels should last for decades. The only major part that will require replacement every 10 years or so is the inverter, at a cost of perhaps £500 to £1,000. The inverter converts the low voltage DC output of the panels into the 230 volts needed in your home.

A domestic PV system will be particularly economic if you’re renovating a roof, or building a new house as the panels can be used in place of roof tiles, and many of the associated costs (such as scaffolding) will be incurred when roofing anyway.


Could I eligible for the feed-in tariff?

The feed-in tariff (FIT), a government scheme whereby housefolders were paid for electricity generated, closed to new installations from April 2019. We don’t yet know what payment may be available under a proposed Smart Export Guarantee (SEG). This would require a suitable type of smart meter that is able to measure exported electricity (which many first generation smart meters cannot do).


Should I go off-grid?

You can connect a PV system to a battery to provide off-grid electricity generation and storage, but if your house is already wired to the grid then we would recommend staying connected.

If you’re connected to the grid, you can sell your excess electricity and buy it back when you aren’t producing enough, effectively using the grid as a battery. When you calculate the energy a battery can store over its lifetime, the cost per unit of electricity is more expensive than buying electricity through the grid.

In environmental terms, batteries have negative impacts in manufacture and disposal, whereas if you feed the excess electricity from your PV system into the grid you will help reduce the need to generate electricity from fossil fuel power stations.


About the Centre for Alternative Technology

The Centre for Alternative Technology (CAT) is an environmental education centre specialising in practical solutions for sustainability. CAT provides information, advice and courses, including postgraduate degrees, on renewable energy, green buildings and a wide range of other topics related to greener living. Find out more at www.cat.org.uk.


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