With over a million solar panels installed across the UK, lots of homeowners are harnessing the power of sunlight to generate clean electricity. But panels don’t effectively use all of the sunlight that hits them. In fact, they are far from 100% efficient.
It’s an important point to consider. For example, two similar solar arrays with just a small difference in panel efficiency can serve up significantly different levels of generated electricity.
In this article, we’ll take a look at solar panel efficiency, explore the range of standards currently available and the factors that affect how efficient they are.
How efficient are residential solar panels?
When talking about solar panel efficiency, we’re referring to the percentage of incoming sunlight that a single panel can convert into usable electricity. It’s a key measure of a panel’s performance, but the numbers might actually surprise you.
The best residential solar panels on the market today have an efficiency of 22% and over. It’s very rare to find a panel that has an efficiency of 24% in real-world conditions. This means that even the most efficient solar panels are only converting less than a quarter of the sunlight they receive into electricity.
At the lower end of the spectrum, you might find panels with efficiencies as low as 15%. The average residential solar panel typically falls somewhere in the middle, with efficiencies ranging from 17% to 21%.
In controlled laboratory conditions, things are slightly different. A world record-breaking solar panel reached 47% efficiency in the lab, and an impressive 40% in simulated real-life conditions. This special panel consisted of six different layers that absorbed differing light wavelengths. These scientific tests offer a glimpse into the future potential of solar technology.
Why is greater solar panel efficiency good?
There are plenty of benefits to increased solar panel efficiency. Most obviously, more efficient panels generate more electricity from the same amount of sunlight. This means you can produce a greater amount of power from a smaller area, which is a particular advantage for crowded cities and homes with limited roof space.
Higher efficiency also translates to a faster return on investment. By generating more electricity, efficient panels can help you recoup your initial spend more quickly through reduced energy bills and potential feed-in tariff payments.
With the average power rating of a solar panel increased over the past decade from around 250 watts to 370 watts, even a few extra percentage point increases in efficiency can make a huge difference to the electricity generated.
Efficiency is certainly an important factor but it’s not the only one when selecting the right solar panel. Manufacturing quality and warranty conditions are also considerations to bear in mind. A slightly less efficient panel from a reputable manufacturer might outperform a more efficient panel of lower overall quality in the long run.
How has solar panel efficiency changed?
The trajectory of solar panel efficiency over the past decade or so has been one of steady improvement. Five years ago, top-performing panels were achieving around 19% efficiency. Today, that figure has climbed to about 22%, representing a 10% increase in electricity production per panel. This is significant and will only improve in the future.
This progress is the result of ongoing research and development in solar technology. Manufacturers continually refine their production processes, technology and materials used to squeeze ever more power from each ray of sunlight.
To measure and compare solar panel efficiency, manufacturers use carefully controlled Standard Test Conditions (STC). These conditions include a cell temperature of 25°C, solar irradiance of 1000W/m2 and an Air Mass of 1.5. Under these standardised conditions, a panel’s efficiency is calculated by dividing its power rating (in watts) by the total panel area (in square metres)
This standardised approach allows for fair comparisons between different panels and manufacturers, helping consumers make informed decisions when investing in solar technology.
Factors affecting solar panel efficiency
There are a number of factors that influence the real-world efficiency of solar panels. Understanding these can help you maximise the performance of your solar installation. Let’s take a look.
Type of solar panel
Broadly speaking, there are three main types of solar panel: monocrystalline, polycrystalline and thin film solar panels.
Monocrystalline panels are generally black in colour and made from a single silicon crystal. They typically have the highest efficiencies, ranging from 18-23%. However, they often come with a higher price tag.
Polycrystalline panels usually have a blue colour and are made up of multiple silicon crystals. This decreases the efficiency, with numbers generally hitting 15-19% . This makes them more affordable.
Thin-film panels are much less efficient with numbers around 7-13%. These flexible, lightweight panels are both cost-effective and versatile. This makes them ideal for using on the likes of campervans, boats and other non-stationary residential units.
Sunlight intensity
The measure of the sun’s intensity, more scientifically known as solar irradiance, can directly affect panel output. Solar panels perform best under strong, direct sunlight. This changes with the time of year, atmospheric conditions and geographic location.
Temperature
Under the Standard Test Conditions, panels are measured at a cell temperature of 25oC. However, in full sunlight in the real-world, cell temperature often rises well above this. The impact is a decrease in efficiency and power output.
Mild or cold conditions actually suit solar panels the best. A temperature range between 1oC and 20oC is ideal.
Shading
If you want your solar panel to work efficiently, you don’t want it to be in shade. You want your array in full sunlight. You might think this is obvious. But did you know that even partial shading can significantly impact a panel’s performance. This is because solar panels are connected in series and ‘strings’, so shading one string can impact the next.
Panel orientation is important here too. In the UK, south-facing panels at a tilt of around 30-40 degrees capture the most sunlight throughout the year.
Cleanliness
Regular cleaning can prevent dust and debris from blocking sunlight and reducing efficiency.
Age and degradation
Solar panels gradually lose efficiency over time. The National Renewable Energy Laboratory estimates a degradation rate of about 0.5% per year. At this rate over 20 years, a panel will generate power at around 90% of its original output.
Over this time, you’ll want to make sure your panels remain relatively clean. And by clean we mean free from dust and dirt. The rain, especially the regular amounts we receive here in the UK, will do most of the job for you but it’s worth keeping an eye on. A quick clean once a year should be enough.
Improving solar panel efficiency
Whilst the true efficiency of your solar panels is primarily determined at the point of manufacture, there are a few steps you can take to ensure they perform at their best.
- Optimal installation – Work with your installers to make sure your panels are positioned for maximum sunlight exposure throughout the year.
- Consider microinverters – Newer technologies such as microinverters can help to reduce the impact of shading. These tend to be available on new installations.
- Regular maintenance – Keep your panels relatively clean and free from high levels of dust. An annual clean can help maintain peak performance.
- Monitor performance – Use your system’s monitoring tools to track output and identify any unexpected drops in efficiency.
Solar technology is an ever changing field as companies compete to launch the next best, most efficient panel. Researchers are currently exploring multi-junction cells that can capture a broader spectrum of sunlight, whilst perovskite solar cells offer the potential for higher efficiencies at lower costs. As well as improvements in solar panel efficiency, we’re seeing big changes in other areas of the residential renewable energy industry. Significant strides are being made with solar battery storage and heat pump technology, which will all eventually work together in all new homes.
