Solar panels: a buyer’s guide

The photovoltaic cells in a solar panel turn sunlight into electricity that can be used to run heating and hot water systems, appliances and lights. Each year, tens of thousands of UK homes install solar photovoltaic (PV) systems.

In 2021 the Microgeneration Certification Scheme or MCS, the national standards organisation for renewables, reported that there had been more than a million PV systems registered in the UK since 2008, when there were just 20 installations (renewingbritain.com).

Exploiting the sun’s energy in this way lowers fuel bills and reduces a home’s carbon emissions. But the kit is costly, so to get the best long-term value, choose the right set-up for your needs before making an investment.

Solar PV unboxed

Most photovoltaic systems are comprised of solar panels, an inverter, connecting cables, a smart meter, and a means of supporting and attaching the panels to a roof. The inverter converts electricity generated by the photovoltaic cells into a type of current that will run appliances. It’s the size of a small box and often lives in the loft. Though panels may last up to 30 years, the lifespan of an inverter is around 10-15 years.

There are three main types of PV technology: mono-crystalline, polycrystalline and thin film. Mono-crystalline is the most expensive and the most efficient, while flexible thin film is the least efficient. ‘Panels usually come in a power range of 300- 400W each and several of them are connected together, often in a series,’ says John Gilham, group technical manager, Green Building Renewables. The power output of the multiple panels that make up a PV system is measured in kilowatts (kW), with the maximum possible output in kilowatt peak (kWp). This is what can be generated when the panels are in bright daylight. A second-generation smart meter (SMETS2) connects to the system, recording how much energy is produced and how much energy is used by the household. It’s fitted close to your fuse box.

Is your home suitable?

Having a south-facing roof is ideal and east- or west- facing are also OK, but a north-facing orientation is not. The idea is to maximise the panels’ exposure to as much daylight as possible, so it’s not great if a roof is shaded by trees or nearby buildings, or even if you live in a part of the country with more overcast days than sunny ones. PVs will still generate electricity under these conditions, but not as much.

The amount of space on your roof will determine how many photovoltaic cells, in solar panels or tiles, will fit and the amount of electricity that can be produced. At least a 20sqm area will be needed for a 4kWp panel system. The Energy Saving Trust has a useful solar energy calculator which lets you input your home’s specific details to get an estimate of the potential performance of a PV system.

Keep to the rules

In many instances, fitting solar panels on the roof falls under permitted development rights (PDR) and you won’t need to apply for planning permission. But there are conditions and limitations that must be satisfied, so check with your local authority before undertaking any work. The installation must comply with Building Regulations – an important factor is the roof structure’s ability to bear the extra weight. The Planning Portal has further details on the rules around PV installation. You can sell any surplus PV power you produce to an electricity supplier, which exports it to the National Grid. But to qualify for payments under the Smart Export Guarantee (SEG), your system and the installer should be Microgeneration Certification Scheme (MCS) certified.

Managing the power

The electricity created by a PV system is only available to use when it is produced. So if you want to turn a light on at night there will be no PV power to run it and you will have to draw electricity from the grid. But any unused PV-generated electricity, such as when no one is home during the day, can be sold to an electricity company of your choosing. The Solar Energy UK website has a table of tariffs offered by suppliers. To be able to exploit more of the power generated by your system you will need to invest in battery storage. A solar battery allows you to draw on the stored electricity whenever you need it. Varying in size from a small panel radiator to a slim chest of drawers, there are battery storage capacities ranging from 3kWh up to 15kWh.

What’s the outlay?

The cost of a PV system will vary depending on the type chosen and its power output. ‘A rough starting price is £1,250 per kW,’ says Kevin McCann, policy manager, Solar Energy UK. ‘So that’s around £5,000 for a 4kW system.

‘You’ll have to add the cost of solar panels installation to this and the outlay for a battery, which is upwards of £2,000 for a 4kW capacity. The greater the battery storage capacity, the more it will cost. Is it possible for all the electricity needs of a home to be met by a PV system on the roof? ‘A 3.5kWp PV system, typically ten panels of 350W each, generates about 3,000kWh of energy per year,’ explains Charlie Clissitt, editor, The Eco Experts. ‘This should be sufficient to supply a well- insulated, three-bedroom, end-of- terrace house. But battery storage is vital – otherwise about 50% of the electricity would go to the grid or be wasted.’

Design advances

Solar panels are quite noticeable and take up a lot of space, but the latest innovations aim to address these issues. ‘Building-integrated photovoltaics (BIPV) such as solar tiles align with the style of your home,’ says Charlie. ‘The downside is they’re often twice as expensive as regular panels and aren’t usually as efficient.’ Another option is clear or tinted solar glass. ‘Transparent panels are great for skylights, greenhouses and conservatories,’ says Charlie. ‘Polysolar has a range that allows you to specify the level of transparency, from opaque to 80 per cent light transmission, as well as tinted colours. Again, the drawback is the price and that they are less efficient than mono-crystalline panels.’