Imagine two homes on the same street, with the same-sized roofs, both fitted with solar panels. Yet one home consistently generates more electricity than the other. The difference comes down to solar panel efficiency, or how well each panel converts sunlight into usable power.
Solar panel efficiency is one of the most important factors to consider when designing a system for your home, especially in the UK, where sunlight is limited compared to sunnier countries in Europe. The more efficient your panels, the more power you can generate from every square metre of roof space. In this guide, we explain how solar panel efficiency works, how it’s measured, and how much energy you can expect from today’s systems.
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What is solar panel efficiency?
In simple terms, solar panel efficiency is the percentage of sunlight that a solar panel converts into electricity. So, for example, a panel with 20 per cent efficiency transforms 20 per cent of the sunlight hitting it into usable electrical energy. The average residential solar panel will have an efficiency rating of somewhere between 15-25 per cent, depending on the brand. In our best solar panels guide, for example, the Perlight Black Grid takes our crown for Best for Efficiency, boasting a 26 per cent efficiency rating.
It’s also important to distinguish between cell efficiency – how the individual photovoltaic (PV) cells perform under laboratory conditions – and module efficiency, which measures how the complete panel performs in the real world.
“One of the most important factors to consider when choosing solar panels is the cell technology behind the panel,” says Lloyd Greenfield, founder of installer Glow Green. “Efficiency matters, but so does how long the panel will keep performing.”
Think of solar panel efficiency like fuel economy in a car: the manufacturer’s figure gives you an idea, but your real-world results depend on where and how you drive.
How is solar panel efficiency measured?
Solar panels are tested under Standard Test Conditions (STC), which assume perfect laboratory settings: 1,000 watts of sunlight per square metre, a cell temperature of 25C, and no shading or cloud cover.
Real-world conditions, of course, vary. As panels heat up, their efficiency drops slightly, which is known as the temperature coefficient. Most panels lose between 0.3 per cent and 0.5 per cent of output for every degree above 25C. Orientation, shading, and local weather also affect results.
So while a panel might achieve 22 per cent efficiency under lab tests, its effective efficiency on a UK rooftop will be lower depending on conditions.
What is the average solar panel efficiency in 2025?
Most modern solar panels for UK homes typically achieve between 19 per cent and 22 per cent efficiency. Budget polycrystalline panels can drop to around 15–18 per cent, while premium monocrystalline models can reach upwards of 24 per cent.
Some of the most efficient models on the market include the Perlight Black Grid, SunPower Maxeon 7, REC Alpha Pure, and JA Solar DeepBlue series. These panels use advanced cell technology to boost performance and durability, often at a higher upfront cost.
“We’re biased, but we rate the Perlight Black Grid very highly,” says Greenfield. “The ultra-black aesthetic, a long warranty (up to 30 years), strong efficiency and bifacial options make it one of the best panels in the UK, in our view.”
Higher efficiency is particularly valuable when your roof space is limited. If you can only fit 10 panels on your roof, choosing a more efficient model can significantly increase your total energy generation.
“Where customers sometimes go wrong is being driven purely by price and ending up with lower-wattage or less efficient panels,” Greenfield adds. “If your roof only fits eight panels, going from ~450W to 515–570W per panel in the same footprint can make a big difference to long-term generation and payback.”
How much power does a solar panel really produce?
Efficiency is one thing; total power output is another. The actual energy you produce depends on your panel’s wattage rating, local sunlight levels, and installation quality.
A typical modern panel is rated between 370W and 430W. Under ideal conditions, a 400W panel exposed to four peak sunlight hours would generate roughly:
400W × 4 hours = 1.6kWh per day
Across a year, the same panel might produce 350–400kWh of electricity in much of the UK. Multiply this by 10 panels and you get roughly 3,500–4,000kWh annually, which is about the same as the average household’s yearly electricity use.
If you want to estimate your savings, visit The Independent’s Are solar panels worth it? guide.
Factors that affect solar panel efficiency
Several real-world factors can influence how efficiently your solar panels perform.
Temperature
Solar cells perform best in cooler temperatures. High heat causes a slight drop in voltage and overall efficiency.
Orientation and tilt
In the UK, south-facing roofs set at around a 30–40 degree angle typically capture the most sunlight. East- or west-facing roofs still perform well but may lose around 15 per cent output.
Shading
Even partial shading from chimneys, trees or nearby buildings can reduce an array’s total performance. Microinverters or optimisers can help minimise these losses.
Dirt and debris
Dust, moss, or bird droppings can block light. Cleaning your panels annually helps maintain maximum efficiency.
Age and degradation
All panels slowly degrade over time. Expect an annual efficiency loss of around 0.5–0.8 per cent, meaning the average 25-year-old solar panel still produces roughly 80 per cent of its original output. Some manufacturers, like SunPower and REA Fusion, are now claiming that their solar panels can produce upwards of 90 per cent of its original output even after 30 years. The technology just keeps improving.
Comparing efficiency by solar panel type
Monocrystalline panels now dominate the UK market, offering the best balance between performance, aesthetics and lifespan.
Panel type |
Typical efficiency |
Pros |
Cons |
Monocrystalline |
20–24% |
Highest efficiency, sleek black design |
More expensive |
Polycrystalline |
16–18% |
Affordable and reliable |
Lower efficiency, blue tint |
Thin-film |
10–13% |
Lightweight, flexible |
Shorter lifespan, less power per m² |
How to improve your system’s overall efficiency
Even the best solar panels need good installation and maintenance to perform at their peak. Here’s how to maximise their output:
“Choosing the installer is as important as choosing the panel,” says Greenfield. “Look for MCS and NICEIC/NAPIT accreditations and, ideally, an installer using the EPVS design validation scheme. EPVS independently checks assumptions like shading, pitch and orientation so you get realistic performance and payback numbers.”
“We’re seeing over 95 per cent of our customers take a battery with their installation, and around 10 per cent come back a year later for a second,” notes Greenfield. “Smarter tariffs mean you can buy cheap electricity overnight, charge an EV, and let daytime solar top the battery back up.”
For more, read The Independent’s solar battery storage guide.
The future of solar panel efficiency
As explained above, the technology in solar panels keeps improving every year. Researchers are continuously pushing efficiency boundaries. Perovskite-silicon tandem cells and bifacial panels (which capture light from both sides) have already exceeded 27 per cent in laboratory tests.
These technologies could soon appear in consumer products, promising greater power from smaller panels and lower installation costs over time. Building-integrated photovoltaics (BIPV), such as solar roof tiles and glass, are also on the rise. Meanwhile, the prices continue to fall.
“After the energy crisis, Europe was flooded with panels and prices dropped,” explains Greenfield. “Module wattage keeps rising, so even if list prices look similar, the cost per watt can be better today than a couple of years ago.”
What does solar panel efficiency really mean for your home?
Solar panel efficiency affects how much electricity your system can produce, but it’s only part of the picture. Roof orientation, shading, system design and local climate matter just as much.
“If you’ve got the savings, solar is a good long-term investment. The yield beats bank interest for many households,” says Greenfield. “And it’s peace of mind: you’re future-proofing part of your energy bill.”
Even lower-efficiency panels can deliver strong returns when correctly installed. Focus on total annual output, not just efficiency percentages, to get the best results for your home.
If you’re considering solar, compare quotes to see how different systems perform in real-world conditions. A reputable installer can model your expected efficiency and generation, giving you a clearer idea of how much power your panels will really produce.
