Solar panels cost thousands – here’s how to make them pay for themselves

British households are cashing in on high electricity prices and installing solar panels in record numbers. 

Over 130,000 units were sold in the UK in 2022, almost as many as in the previous three years combined, as homeowners looked for smart ways to dodge soaring energy bills. 

The upfront cost can be steep. The average domestic solar panel system of 3.5kW costs around £7,000, according to the Energy Saving Trust.

But if panels are properly installed, maintained and understood, the technology can pay for itself in as little as four years. Here, Telegraph Money reveals how.

Choose the right roof

Solar panels can work well pointing in any direction, except north. In the UK, it often makes sense for solar panels to face due south, as this will expose them to more sunshine throughout the day. East and west-facing set-ups typically yield between 15pc and 20pc less energy than one facing south. 

But Steve Buckley, head of data science and product at Loop, an energy-saving app, says a range of orientations can work well. 

“If your panels point south, you get a big peak at noon,” he said. “Having solar panels installed on both east and west-facing roofs, you get more energy generated in the morning and the evening, but slightly less overall compared to south-facing panels.”

The angle at which the panel is mounted also has a bearing on efficiency. The position that maximises the energy collected by a solar panel in the UK is facing south and tilted at an angle of 35 degrees from the horizontal, according to research by solar panel manufacturer Viridian Solar. 

The slant of your panels matters less than their orientation, according to Mr Buckley.

“The typical roof angle on a UK house is very close to optimal. Pretty much any roof will do,  as long as it’s pointing in the right direction,” he said.

Stay out of the shade

As solar panels require sunlight to generate energy, shade can present a problem. Needless to say, installing panels on a property that’s permanently overshadowed by a neighbouring football stadium isn’t the best idea.

But less obvious sources of shade, such as overhanging branches or a chimney stack, can also slash the performance of your panels.

Panels are connected together in a string of “inverters”, and the performance of the most shaded panel will degrade the performance of all the others.

Inverters act as the gateway between your panels and your home. Any electricity that your panels generate must pass through this corridor before it can be used to power your premises. 

Trimming back foliage regularly is an easy way to keep your panels operating at maximum efficiency. But if the source of the shade is out of your control, it can be worth investing in “microinverters” – small devices that attach to individual solar panels. 

By adding microinverters, shaded panels continue to generate power at their full potential, enhancing overall energy production in partially shaded conditions.

Microinverters usually cost between £100 to £150 per unit, so for a fairly typical 3.5 kW solar panel system comprising 10 350W panels, you would need to spend between £1,000 and £1,500. The extent of the shade coverage will dictate whether the investment is worthwhile. 

Tracking the amount of energy generated with and without shade will help you work out how much you stand to save. Microinverters typically boost efficiency by between 5pc and 15pc, according to renewables firm, MyEnergyGeneration.

Clean your panels 

As time goes by, dust, dirt and debris can accumulate on your solar panels and gradually reduce performance. If you have nesting birds nearby, droppings can also add to the grime. 

Many solar panel manufacturers specify regular cleaning as a condition in their warranty terms, and may even refuse to fix a fault if your panels are dirty.

There are specialist firms that will come out and clean your panels. On average, you can expect to pay around £150 to have your solar panels cleaned; the per panel fee can range from £4 to £15, according to price comparison site MyJobQuote. 

However, as long as you can access your panels safely, you could opt to clean them yourself. 

Checkatrade, an online trade directory, offers the following advice if you plan to do this yourself:

1. Turn off the solar panel system before you start cleaning, with reference to the instruction manual. 
2. Stop if you notice any damaged cabling and report it immediately. The solar panel cabling on your roof will still be live and a potential high voltage risk, so take extreme caution when working around the cabling.
3. Use specialist solar panel cleaning equipment, such as biodegradable soap, a long-handled brush and a solar panel wiper.
4. If possible, clean your solar panels from the ground to avoid having to work up on the roof. 
5. Clean early in the morning or late in the evening during spring and summer. You want to avoid the times of the day when the panels are hot from the sun. Cleaning the panels when they are cool means you can avoid water marks from water evaporating on a hot surface. 

Mr Buckley says that the amount of rain that falls on UK solar panels reduces the need to clean them compared to other countries. 

“Desert conditions mean you can get a layer of sand covering the panels. In the UK this isn’t a problem,” he said. “If the solar panels are on an angled roof, the amount of rain they get means they typically don’t need cleaning very often. 

“If you look at the outputs of the panels after 10 years without cleaning, and the efficiency is still very high.”

Track your usage 

Keeping a close eye on your panel system and the amount of electricity it is generating (and the weather conditions at the time) will help you understand what to expect from your solar panels, and can help you spot when something might be wrong.

Most households use about 15-25pc of the energy they generate, according to the Energy Saving Trust. However, this can vary greatly depending on factors such as whether you work from home, have an electric vehicle you charge from home, or heat your home using an electrical heat pump, rather than a gas boiler.

Knowing what time of day you use the most energy is also crucial to making the most money from your solar panels.

In Great Britain, the Smart Export Guarantee (SEG) allows you to sell electricity back to the grid. But because you pay more for electricity from your supplier than your supplier pays you to buy back electricity from your solar panels, it makes sense to use the energy your solar panels generate as much as you can. 

“Understanding when any spare energy is going out to the grid and working out whether you can use more during that period is really important,” said Mr Buckley. 

One general principle to bear in mind is that running several appliances at once may require more energy than your solar panels can provide, meaning you end up drawing power from the grid instead. Staggering the use of the washing machine and cooker, for example, can smooth out usage and make more efficient use of your solar energy.

There is a wide selection of apps on the market that allow you to track the minutiae of your solar panel usage and performance stats; mySolarEdge, GivEnergy and myenergi are consistently near the top of app review league tables. 

Invest in a battery

If you find that you use most of your energy when your solar panels aren’t generating much electricity, buying a battery could be a smart move. 

Having a battery allows you to store electricity generated until you need to use it, rather than selling it back to the grid at the Smart Energy Guarantee (SEG) rate. 

Solar panel batteries also allow you to choose when to sell electricity back to the grid to take advantage of higher unit prices. 

Batteries are essential for off-grid systems, or areas with unreliable grid connections, as they help ensure you have power when the panels aren’t generating electricity. 

However, you will need to have a good idea of your usage patterns to help you choose the appropriate battery capacity and power rating. 

The capacity of a solar battery is measured in kilowatt-hours (kWh) and indicates the amount of energy it can store. The power rating, measured in kilowatts (kW), determines the electricity the battery can deliver at any given time. 

Battery costs vary significantly depending on the technology, capacity, and brand, but a good quality model can cost around £3,000. The number of years it takes to recoup the investment will depend on the amount of electricity your panels generate and the extent to which you harness variable SEG tariffs.

Comparing upfront costs is a major factor, but the coverage offered by warranties is equally important. Look for a long warranty covering both performance and lifespan.  

The two most common types of battery technology are lithium-ion and lead-acid; some will be compatible with some types of solar panel systems, while others won’t. It is essential that you contact your installer or system manufacturer for guidance on compatibility with your panels before launching into a pricey battery purchase. 

Find the best tariff

SEG tariffs tend to come in two varieties, fixed and variable. It is worth taking time to consider which can save you the most money.

Fixed rate SEGs pay a set amount per kilowatt hour of electricity exported into the grid, regardless of when it’s exported. Most SEG tariffs are fixed-rate.

The best fixed SEG tariff rates on the market have jumped significantly in the last 12 months, after hovering around the 5p mark for years, so it is worth shopping around for the best deal. 

Variable-rate SEGs pay different amounts for exported electricity depending on how valuable the electricity is to the system at the time. 

Some companies offer multi-rate SEGs for electricity exported at different times. For example, whether it is night or day, or the weekend or a weekday.

Octopus Energy, for example, offers an “agile” export rate that changes the amount you are paid for solar-generated electricity every half-hour. 

At around 4pm every day, the rates are published for the next day, meaning you can plan how much you will get paid to export over the next 24 hours. 

Mr Buckley says opting for a variable SEG tariff can be lucrative in the right circumstances. 

“If you have a battery you can choose to sell energy at peak times to get the absolute maximum from exporting energy to the grid,” he explained.

“Over the last 12 to 18 months, throughout the energy crisis, that would have made a solar household a lot more money than using fixed rate tariffs.

“It brings with it a bit more risk. You’re not guaranteed a rate. But over the last couple of years it’s definitely been the way to go.”