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 fusebox.

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.