Solar panel efficiency is one of the most important factors to consider when choosing solar panels.
A high solar panel efficiency can allow you to generate as much free electricity as possible. This will result in lower electricity bills and carbon emissions, increased self-sufficiency, and an efficient use of roof space.
According to the Energy Savings Trust, a solar panel system can save up to £600 annually on energy bills and around one tonne of carbon per year, depending on your location and how much solar electricity you can generate and use.
But what is solar panel efficiency, and how does it work? Read on to find out.
Pro tip: Avoid upsells and confusing packages—choose a provider with a clear, fixed-price quote that won’t change. Heatable, a Which?-approved solar installer, offers transparent pricing with no surprises.
What is Solar Panel Efficiency?
Solar panel efficiency measures how much sunlight or solar irradiance hitting the panel’s surface is converted to electricity. Generally, the more efficient a solar panel is, the more of the sun’s energy it can convert to electricity.
For example, if the panel has an efficiency of 19%, it means that 19% of the solar energy reaching the panel becomes electricity, while the remaining 81% is reflected back.
Most of the solar panels on the market have an efficiency of 15% to 22%. Thanks to advances in photovoltaic technology over the years, some models are very efficient and can exceed 22% efficiency. However, these are usually premium solar panels and the most expensive on the market.
How Is Solar Panel Efficiency Measured?
Manufacturers measure a solar panel’s efficiency by tracking its output under standard test conditions (STC).
This involves determining how much solar energy the cells can convert to electricity on a clear summer day by ensuring the temperature is 25°C and exposing the panel to a controlled light source at an intensity of 1,000 watts (W) per m2.
The efficiency rating is the percentage of light the panel turns into solar electricity. However, the maximum efficiency under STC isn’t what the panels will achieve under real-world conditions due to changes in solar irradiance, wind speed, and ambient air temperature.
As a result, some manufacturers also include a performance test conditions (PTC) rating. It offers a more accurate efficiency measure of how the panels perform in various situations and climates.
What Factors Affect Solar Panel Efficiency?
Solar panel efficiency depends on many external factors in the real world. These include:
Solar Panel Placement
The placement of the solar panels on the roof will determine the amount of sunlight hitting them, which can increase or decrease their efficiency.
It’s always recommended that solar panels be installed on south-facing roofs in the UK to get the most sunlight.
The angle or pitch of the roof can also affect the number of sunlight hours your panels receive daily. The best pitch for solar panels in the UK is usually 30-45 degrees for the greatest sunlight exposure.
Shade
Anything blocking the sunlight from reaching the cells will decrease the panel’s efficiency. Shade from other buildings, nearby trees, debris, and dust build-up will have a negative effect. Studies show that even partial shading can decrease efficiency by up to 50% or more.
It’s important to ensure your installer carries out a shading analysis before installing solar panels on your home to evaluate any potential issues from obstructions like trees or chimneys.
Temperature
Like most electrical equipment, solar panels work best when their temperature is as cool as possible.
The panels can temporarily lose some of their efficiency in extremely hot temperatures. Although they won’t stop working, the output will drop as temperatures exceed 25°C.
Type of Solar Panel
There are different types of solar panels, each with varying levels of efficiency depending on the material and how the solar cells are structured. The most common types include:
- Monocrystalline Solar Panels — These are made from a single silicon crystal and are the most efficient and expensive.
- Polycrystalline Solar Panels – These are made up of multiple silicon crystals melted together. They’re less efficient than monocrystalline panels but more affordable.
- Thin-film Solar Panels – These are made by placing thin layers of photovoltaic material on top of each other. They’re the least efficient and degrade faster, but are cheaper, lighter, and more flexible.
Which Are the Most Efficient Solar Panels in the UK in 2024?
Some of the most efficient solar panels available for UK homes include:
REA Fusion Energy Solar Panels
The REA Fusion solar panels are bifacial, meaning they absorb light on both sides. They feature high-efficiency N-type M10 Topcon solar cells and offer a seamless, sleek design in silver or black.
They can achieve efficiencies of 22% to 24% and are micro-inverter optimised to maximise the performance of each panel independently.
Best of all, REA Fusion solar panels can generate electricity even in low light conditions, making them ideal for the UK weather, where cloudy days are more common.
Prices range from £400 to £420 per panel, and they come with a 25-year insurance company-backed product & performance warranty.
SunPower Maxeon 6 AC
The SunPower Maxeon 6 AC solar panels feature an efficiency rating of 22.8% with a powerful output of around 440 watts. They come with a 40-year product warranty and a guarantee that the panels will maintain 92% of their original performance after 25 years.
The Maxeon 6 AC panels are also recyclable, making the product very eco-friendly. However, they can be a bit heavy, with a weight of around 21.8kg.
SunPower Maxeon 3
The Maxeon 3 solar panels from SunPower feature an energy efficiency rating of 22.7% and offer a power output of around 430 watts. It comes with a 40-year product warranty and a performance warranty of 88.25% after 40 years.
The Maxeon 3 is resistant to heat and is an excellent eco-friendly choice since the panels are recyclable.
Each Maxeon 3 panel weighs 21.2kg, and you can expect to pay around £300 to £350 per panel.
Final Thoughts
Solar panel efficiency continues to improve, and researchers are continuously looking to increase efficiency rates to help you make the most of solar power.
Choosing the best solar panels for you is a balancing act between cost, efficiency, aesthetics, and lifespan. However, it’s always recommended to go for panels with an efficiency rating of at least 20%.
Sources and References:
- https://energysavingtrust.org.uk/advice/solar-panels/
- https://www.mdpi.com/1996-1073/16/3/1169