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July 3, 2024

How Efficient Are Solar Panels?

Solar panel efficiency

Solar technology gives us free, renewable electricity that cuts energy bills and combats climate change. Financial and carbon savings depend on the efficiency of your solar panels – how well they convert sunlight into electricity.

Find out here what you should know about the energy efficiency of solar panels.

What Is Energy Efficiency?

Energy efficiency means using less energy to generate the same amount of power. No energy system is 100 percent efficient. This would contradict the basic principle of thermodynamics: energy cannot be created (or destroyed); it can only be transferred.

Electrical energy is produced by movement of electric charges called electrons. Electrical energy efficiency is the proportion of usable electricity you get from a given electrical input. All energy systems lose energy to some extent. However, advances in technology have made solar panels increasingly energy efficient in recent years.

Solar Panel Efficiency

Solar panels contain silicon cells that release electrons and produce an electric charge as they capture tiny packets of sunlight called photons. 

A solar inverter converts this direct current (DC) into an alternating current (AC) compatible with household electrical systems.

Solar panels lose some energy as electricity makes its way to your home via various parts of the system. Solar efficiency is calculated as the percentage of solar energy input turned into usable electricity.

Solar panel output is measured in watts (w) and is the amount of power that can be produced. Panels with a higher wattage rating produce more usable electricity.

Typical efficiency levels of residential solar panels range from 15 to 23 percent. More costly solar arrays can achieve 40 to 50 percent energy efficiency. A higher solar panel efficiency means more free electricity for your home. This results in bigger savings on energy bills and is key in decarbonisation to combat climate change and achieve net zero CO2 emissions.

What Affects Solar Panel Efficiency?

Solar panel efficiency and power output have increased significantly in recent years. The more efficient the panels, the fewer you need to power your home. 

Several considerations are important when it comes to solar energy efficiency. These include: 

  • Type of solar cells in the solar panels. 
  • Surface area of the panels.
  • External factors such as air temperature and roof orientation and incline.

Types Of Solar Cells

The main factor that determines solar panel efficiency is the type of solar cell it has. Solar cells – also known as photovoltaic (PV) cells – are typically made with silicon and convert sunlight into electricity by absorbing electromagnetic radiation from the sun. 

Two types of solar cells are mainly used for homes: monocrystalline and polycrystalline. Thin-film solar cells are also available but are used mainly in large-scale commercial applications.

Monocrystalline Solar Cells

Monocrystalline solar cells, made of high-purity single silicon crystals, have the highest energy efficiency – 15 to 24 percent. This means monocrystalline solar panels need less space than panels with other types of PV cells. They’re the most expensive but last the longest and perform better in low levels of sunlight.

Monocrystalline solar panels are immediately identifiable by their deep black colour.

Polycrystalline Solar Cells

Introduced in the early 1980s, polycrystalline solar cells consist of bonded fragments of silicon crystals. They’re 13 to 16 percent efficient. This lower level of energy efficiency makes polycrystalline solar panels less space efficient than monocrystalline panels, so they require more roof space. However, they’re cheaper than monocrystalline solar panels.

Polycrystalline solar panels react to light to create a shimmering dark blue colour.

Thin-Film Solar Cells

Thin-film solar cells have multiple slim layers of semiconducting material placed on top of one another. Efficiency rates vary from 7 to 13 percent and are expected to increase as the technology evolves.

Thin-film solar panels can easily be mass-produced, which makes them potentially cheaper than crystalline solar panels. But they have a shorter lifespan and aren’t ideal for residential use because they take up too much space.

Solar Panel Surface Area

Solar panels with a larger surface area and more solar cells output more power. That said, a smaller panel with more energy-efficient solar cells can produce the same amount of power as a larger panel with less efficient cells.

Solar panels are expected to get smaller with better efficiency as the technology advances. They should also become more affordable, a trend which has already started to take effect.

Air Temperature

Some people assume solar panels only work in direct sunlight. That’s not the case. While they perform best on clear, sunny days, they also work in partial shade and in overcast conditions and during winter.

In fact, less direct sunlight can be beneficial. The semiconducting silicon in solar panels is sensitive to high temperatures, which can reduce the energy solar panels capture by up to 25 percent. The optimal temperature for solar panels is 25C.

Roof Orientation And Incline

Most homes in the UK have a roof suitable for solar panels. Solar panels are most efficient when installed at a 35-degree angle on a south-facing roof, where they will get the most sunlight. But they will still produce power on a west- or east-facing roof, at an angle from 10 to 60 degrees.

Solar panels also work efficiently on flat roofs provided they face the right direction and are angled in the right position.

Do Solar Panels Become Less Efficient Over Time?

Solar panels are considered to have a useful life of 25 to 30 years but may continue generating electricity for much longer. However, they gradually degrade with time, producing less electricity from the same amount of sunlight. This happens through factors such as wear and tear and the effects of the weather.

Over 20 years, solar panels lose around 10 percent of their original efficiency levels. After 25 years, they typically lose around 20 percent efficiency.

While these solar panels still produce electricity, output is reduced and they may need more frequent maintenance or replacement of parts. Long-term solar panel efficiency could improve in the future as manufacturers strive to reduce the degradation rate of their products. 

Meanwhile, solar panel degradation remains inevitable. However, you can lessen its impact and prolong the life of your solar panels by choosing a reputable, professional solar panel installer and scheduling periodic maintenance checks.

Solar Panel Battery Storage

Adding battery storage to a solar panel system improves its overall efficiency by preventing energy from being wasted. Households generally use more power during the evenings, but solar panels don’t produce electricity after sunset. Without a battery, solar energy that isn’t used during the hours of daylight goes into the national grid.

When you can store this energy for later use, you won’t need to pay for as much expensive mains electricity when energy demand peaks after dark. Solar batteries are highly efficient. They charge fast and store large amounts of electricity.

With a solar battery, you can use 20 to 40 percent more of the electricity produced by your solar panels. This can reduce electricity bills by up to 90 percent – 20 percent more than solar panels on their own.

Types Of Solar Batteries

Two types of solar batteries are commonly used with residential solar panels: lithium-ion and lead-acid.

Lithium-ion (li-ion) batteries are the most popular choice for household solar panel systems.They cost more than lead-acid batteries but store more energy, are more efficient, more reliable, and last longer. They take up minimal space and last 10 to 20 years with little maintenance.

A lead-acid solar battery may provide a solution as a small off-grid energy storage system that’s seldom used. Li-ion batteries typically achieve a 95 percent efficiency rate or higher. This compares with lead-acid battery efficiency of around 80 to 85 percent.

What Are Bifacial Solar Panels?

Solar panels traditionally have solar cells on one side. Unlike these monofacial panels, bifacial panels have solar cells on both sides. This makes them more efficient. Double-sided solar panels have been developed following the introduction in the1960s of passivated emitter and rear contact (PERC) technology.

They address the issue of loss of efficiency in conventional solar panels. They generate more energy because they absorb reflected light and diffuse light as well as direct sunlight. This can result in up to 30 percent more power output. Bifacial solar panels have reflective backsheets or dual panes of tempered glass that capture light at the back of the panel as well as at the front. 

They’re installed on an elevated racking system around four metres from the ground. The front of the panel is exposed to direct sunlight while the rear side gets direct sunlight reflected off the ground and diffuses sunlight from overhead and reflected off the ground.

Monitoring Solar Panel Efficiency

Monitoring capabilities are now commonly incorporated in solar panels to track and analyse performance. These systems tell you how efficiently your solar panels are working. They gather real-time data on energy production, so any problems can be identified and fixed early.

You’ll be able to see when your panels are at peak performance. This can help you manage your energy use to further reduce reliance on the grid. Solar panel monitoring systems often include mobile apps or user-friendly interfaces so you can access the data remotely.

Modern solar panels commonly have built-in solar inverter monitoring. This collects data as the inverter converts direct current electricity into alternating current. External solar monitoring systems are also available that work independently of solar inverters and often provide more detailed data.

Alternatively, you can monitor the efficiency of your solar panels via your solar meter, which will confirm how much energy they’ve generated.

If your solar panels are underperforming, contact the installer, who can determine what’s going wrong and address the issue. Tampering with solar panels yourself can damage the system and invalidate your warranty.

Benefits Of Solar Panels

Solar panels give households both financial and environmental benefits. Generating your own, free energy lessens reliance on expensive mains electricity while reducing your carbon footprint. Advances in technology in recent years have made solar panels more efficient and more cost-effective to boot.

A 4kW solar array with 10 panels, suitable for the average, three-bedroom home, costs around £7,000. It cuts energy bills by an average of £730 a year, paying for itself in less than 10 years and saving more than 900 kg of CO2 each year. And you can expect your solar panels to last 25 to 30 years.

A further benefit of solar panels is that you can sell surplus solar energy back to the grid under the Smart Export Guarantee (SEG). SEG payments for 2022-23 totalled more than £7 million.

Installing solar panels can also increase the value of your home and help you sell it faster. According to some sources, properties with solar panels can sell for as much as 20 to 25 percent more than comparable homes without them.

Furthermore, solar panels can help extend the lifespan of your roof and reduce the need for frequent repairs. They shield it from damage from rain, direct sunlight, and other environmental factors. 

VAT on solar panel installation is zero-rated until April 2027, and you may be eligible for a government grant allowing you to install solar panels for free or at a heavily discounted cost.

Solar Panel Grants

Various government-backed grants are available that cover up to 100 percent of the cost of installing solar panels.


ECO4 is the fourth and final phase of the Energy Company Obligation. It’s scheduled to run until the end of March 2026, with £4 billion of funding available. The programme is aimed at relieving fuel poverty and reducing carbon emissions in England, Scotland and Wales.

The scheme includes funding for solar panels to power electric heating. It’s open to households who get a means-tested benefit and whose homes are energy-inefficient. 

ECO Flex

More households can access Energy Company Obligation funding through ECO Flex. Also known as LA Flex (Local Authority Flexible Eligibility), this initiative widens ECO4 eligibility criteria.

Local councils have their own eligibility requirements, and you don’t have to be receiving a means-tested benefit to qualify.

Home Upgrade Grants

The Home Upgrade Grant (HUG2) provides solar panel funding for lower-income households in England with no access to mains gas for central heating.

HUG2 will run until March 2025, with grants up to £10,000 on offer to households in economically disadvantaged areas.

Nest Scheme In Wales

Part of the Welsh government Warm Homes programme, the Nest scheme provides free solar panels for low-income households

You may qualify for this funding if your home is energy-inefficient and you get a means tested benefit. Nest is also open to lower-income households where someone has a chronic medical condition.

Solar Panels Vs Fossil Fuels

Fossil fuels produce energy by burning coal, oil, or natural gas. Solar technology converts sunlight into electrical energy and lowers the amount of carbon dioxide emissions your home produces. 

According to the United Nations, fossil fuels produce 400g of carbon dioxide per kilowatt hour of power, compared with the 25g to 32g of CO2 per kWh of electricity that solar PV panels produce.

Solar Panel Maintenance

Durable construction and lack of moving parts means solar panels need little maintenance. They self-clean when it rains. Any remaining dirt or debris can be washed away by hosing down the roof.

An annual service will help ensure optimal solar panel performance and efficiency over many years.

Final Thoughts

Solar panels are an incredibly efficient way to power your home and ensure you’re making savings on sky-high energy bills. With that said, the exact nature of their efficiency can be impacted upon by a number of different factors. One of which, and probably the most key, is the spec of the solar panels themselves. 

Pay more for your panels, and you’ll likely notice increased efficiency with it. Still, you don’t have to pay through the nose to switch to solar and enjoy reduced energy bills and carbon emissions with a thoroughly efficient system. 

Find out how with our solar experts at Effective Home today.

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Justine Effective
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