Solar panels

A solar PV panel consists of many cells made from layers of semi-conducting material, most commonly silicon. When light shines on this material, a flow of electricity is created.

The cells don’t need direct sunlight to work and can even work on cloudy days. However, the stronger the sunshine, the more electricity generated.

Solar PV systems are made up of several panels, with each panel generating around 355W of energy in strong sunlight. Typical systems contain around 10 panels and generate direct current (DC) electricity. Because the electricity used for household appliances is alternating current (AC), an inverter is installed along with the system to convert DC electricity to AC. This electricity can be used throughout your home, or exported to the grid.

With any domestic PV system, there will be times when the electricity you generate is more than you can use or store, so the surplus will be exported to the grid to be used by somebody else. If you want to be paid for exporting, you need to make sure you’re getting an export payment. If you were able to claim the Feed-in Tariff (this closed to new applications at the end of March 2019), then you will be getting export payments as part of that. If not, you need to find an energy company that will pay you for this surplus.

Following the closure of the Feed-in Tariff scheme to new solar PV system applicants in March 2019, the Smart Export Guarantee (SEG) was introduced to provide financial support to small-scale renewable energy generators for the electricity they export to the grid. The savings from solar PV with the SEG are considerably higher than without it.

In Great Britain, the Smart Export Guarantee pays you for the electricity you generate.

In Northern Ireland, you can get paid for any surplus you export (ROCs payment) – usually estimated based on how much you generate. Several organisations offer this service, so if you’re interested, we recommend researching their offers to find one that works for you.

The average domestic solar PV system is 3.5kWp and costs around £7,000.

The amount you will pay is influenced by the size of array and will be affected by any difficulty with access to your roof. Some of the installation costs can be shared if you already have scaffolding up for roof repairs or if you are building a new house. Costs are also affected by whether you choose panels or tiles, and whether you opt for building-integrated panels or choose panels that sit on top of your roof. Panels on top of the roof are the cheapest option, while tiles are the most expensive for the equivalent system.

The cost of ground-mounted systems is more difficult to predict, as there are more variables such as the type of mounting frame, and how far away it is from the house.

Costs can vary between installers and products, so we recommend getting quotes from at least three installers.

Most households will use about 15-25% of the energy you generate, though this can change quite dramatically based on:

• Whether you work from home.
• How many people are at home during the day.
• Whether you have an electric vehicle.
• Whether you heat your home or hot water using a heat pump or other electrical heating.
• Whether your cooking is done using electricity.

Instead of sending surplus electricity to the grid, a PV diverter switch can power the immersion heater in your hot water tank, storing hot water for you to use later. On its own, excess solar energy is unlikely to meet all of your hot water needs, but it can help reduce your bills.

Solar PV systems need little maintenance. Keep an eye on nearby trees to ensure they don’t begin to overshadow your system.

In the UK, panels that are tilted at 15 degrees or more benefit from being cleaned by rainfall, which helps to ensure optimal performance. Debris is more likely to build up if you have ground-mounted panels, or if you live in an area with more dust in the air. In these cases, you might need to have the panels cleaned occasionally.

Once fitted, your installer should leave written details of any maintenance checks that you should carry out to ensure everything is working properly. This should include details of the main inverter fault signals and key troubleshooting guidance. Ideally, your installer should demonstrate this to you once the system has been installed.

Keeping a close eye on your system and the amount of electricity it’s generating (alongside the weather conditions) will help you understand what to expect and alert you to when something might be wrong.

The panels should last 25 years or more, but the inverter is likely to need replacing sometime during this period, at a cost of around £800 (depending on system size and the manufacturer). Some inverters have online monitoring functions and can warn you by email if the system fails.

Most inverters have warranties of five years as a minimum, which can often be extended up to 15 years. Speak to your installer about the likely lifespan and benefit of an extended warranty. You might find that a 15-year warranty costs almost as much as a replacement inverter, so consider it carefully.

Consult with your installer for exact maintenance requirements before you commit to installing a solar PV system.

If you live in Scotland, you can read case studies of homeowners who’ve installed solar panels on the Green Homes Network.