Making the most of the sunshine: What is solar power efficiency?
How efficient are solar panels? Learn about factors that affect solar panel efficiency, different rates per type and how it can be increased with our guide.
Solar panels have come a long way since they were invented seventy years ago. While the basic idea is still the same — turning sunlight into energy using photovoltaic cells — the amount of power that panels can generate has dramatically increased.
As more of us move toward cleaner, greener energy, solar power efficiency is becoming a hot topic. Whether we’re just starting our solar journey or already getting energy from the sun, we all want to generate as much power as possible in as little space as possible—so it’s important to understand how panels work and what affects their efficiency.
In this guide, we’ll break down everything you need to know about solar panel efficiency and share tips to help you get every possible drop of power from the sun.
What is solar panel efficiency?
The efficiency of a solar panel is the percentage of light it can convert into usable electricity. The higher the efficiency of a solar panel, the less space it needs to take up. But how do solar panels convert sunlight into electricity?
It’s all down to the tiny particles that make up sunlight, called photons. When photons hit a solar panel, its photovoltaic (PV) cells, usually made of silicon, react in different ways. They either reflect the photons off, pass them through, or absorb them into the panel. Only absorbed photons can create electricity. The more photons a solar panel can absorb, the higher its efficiency.
When enough sunlight is absorbed, electrons get knocked loose from the material’s atoms. The front of the solar panel is designed to attract these electrons. When electrons move towards the front this creates an electrical charge difference between the front and back, like the positive and negative sides of a battery. Finally, the metal grid-like lines on the panel collect the electrons and allow electricity to flow when connected to a circuit.
Does the UK weather affect solar panel efficiency?
We all know how haphazard the UK weather can be. And lots of people worry about how well solar panels can work in a country that’s not exactly famous for sunshine.
But there’s good news: solar panels actually rely on daylight or atmospheric light to work, not heat from the sun. And while panels will generate less electricity on the shortest days of the UK winter, they can still generate the power you need.
How is solar panel efficiency measured?
Solar panel efficiency is measured under standard test conditions (STC) that mimic a sunny day with a solar panel tilt of 37 degrees. The three STC conditions for measuring solar panel efficiency are:
1. Temperature at 25°C: Did you know solar panels become slightly less efficient with every degree they heat up beyond 25°C?
2. Sunlight intensity of 1000 W/m²: A sunlight intensity of 1,000 watts per square meter (W/m²) is the power of sunshine on a sunny day.
3. Air mass of 1.5(AM): Air mass is the distance that sunlight travels through the atmosphere to reach the Earth’s surface. When the sun is lower in the sky, sunlight has further to travel so less of it reaches solar panels. 1.5AM matches the typical atmospheric conditions when the sun is at an angle of about 48° from the horizon.
There are other factors that can affect solar panel efficiency too, like the age of the panels and how much shade they have on them. But one of the biggest factors affecting solar panel efficiency is what type they are.
What are the average efficiency rates for different types of solar panels?
Ever since early solar cells in 1954 which were very small, and limited to the lab, solar panel efficiency has steadily improved across the decades. Where the first solar panels had a 6% efficiency rate, today’s best panels reach an average of 15-22%, as well as being more cost-effective, requiring less roof space and lasting longer.
There are two most common types of solar panels currently available: monocrystalline and polycrystalline solar panels. Here’s what you need to know about both of them.
Monocrystalline solar panel efficiency
Monocrystalline solar panels are known for their high efficiency, typically ranging from 15-22%. They’re better at converting sunlight into electricity than other types like polycrystalline and thin-film solar panels. They are made from one, continuous crystal of pure silicon.
Monocrystalline panels are easily identified by their uniform black colour. But their pure silicon structure isn’t just for aesthetics; it allows electrons to easily flow through the cell with less resistance and energy loss. This means they can generate more electricity in a smaller area compared to other types.
Monocrystalline solar panels are ideal for smaller rooftops where space is limited and you want to maximise power output. But because they’re more complicated to manufacture, they tend to be more expensive than other types. Their average lifespan is 30-40 years.
Polycrystalline solar panel efficiency
Polycrystalline solar panels typically have an efficiency range of 15-17%. As the name suggests, polycrystalline panels are made from many fragments of silicon rather than one crystal. They’re easier and cheaper to produce than monocrystalline panels. However, their mixed structure creates more resistance to electron flow so reduces their efficiency.
If you’ve got a large roof with lots of space and a lower budget, polycrystalline panels might be the most cost-effective option despite their lower efficiency. Their average lifespan is 25 to 30 years.
How does solar panel efficiency change over time?
Solar panels are designed to perform reliably for decades, with only a minor efficiency adjustment of about 0.5% per year due to natural exposure to the elements, as noted by the National Renewable Energy Laboratory. And with a 20-year guarantee, you can be confident in enjoying clean, sustainable energy with minimal impact on performance over time.
Ironically, daylight and high temperatures wear down a solar panel’s materials over time. Extreme temperature swings can cause potential cracks. Humidity, salty sea air and getting hit by hail or debris can also damage solar panels. Monocrystalline solar panels are the most durable type and tend to last the longest.
What are the factors that affect solar panel efficiency?
Broadly speaking, solar panel efficiency is determined by the quality of the materials used to make the panel, and the amount of direct sunlight the panels get. There are few elements to consider when looking for solar panel efficiency – we’ve broken them down for you here:
Silicon purity: Monocrystalline solar panels are far purer than polycrystalline panels which improves electron flow and their efficiency.
Manufacturing technologies: Advanced manufacturing techniques like bifacial and passivated emitter rear contact (PERC) technologies help solar panels absorb more light that can be converted into electricity. Solar panels that combine these technologies can be up to 18% more efficient than standard monocrystalline panels, according to research published in the scientific journal Materials Today.
Geographic location: Solar panels near the equator get more sunlight, which boosts energy output. However, solar panels don’t work as well in high temperatures over 25°C. The best place for solar panels is somewhere sunny and cool.
Obstructions: Dust and animal droppings on solar panels can block sunlight and make them less efficient. Objects like trees and buildings casting shadows can have a similar effect. Even minimal shading can make a big difference to their output.
Seasonal changes in daylight: Long summer days are ideal for maximising the amount of sunlight on solar panels. Shorter winter days are less good.
Weather conditions: Panels work best in cooler temperatures. High heat and extreme weather like heavy rain or snow reduce efficiency and may damage the panels.
How to increase solar panel efficiency
Here are several strategies to increase solar panel efficiency. Some of these are best left to your installer, but others you can do yourself.
Panel positioning: Panels should be south facing if you live in the northern hemisphere to get the most sunlight throughout the year. Your installer will typically angle your solar panels between 30 and 45 degrees.
Different angles for different seasons: Adjust the tilt of your solar panels depending on the season. In winter, a steeper angle can capture lower sun angles, while a flatter tilt works better in summer.
Use solar trackers: Solar trackers automatically adjust your solar panel's angle to follow the sun throughout the day. They can boost electrical production by up to 35%, according to the Eco Experts. But because they’re expensive, they may only be worthwhile if you’re going for a larger installation.
Install a solar battery: Store any excess energy you produce during peak sunlight hours, to use at night or when it’s cloudy. Plus you can earn money back by selling any solar energy you don’t use back to the grid.
Keep them clean and maintained: Regularly removing dirt, dust or debris from your solar panels allows them to capture the most amount of sun.
New technologies advancing solar panel efficiency
There are a bunch of cutting-edge solar panel efficiency technologies worth getting excited about. Here are the main ones:
Better solar batteries: Lithium-ion and solid-state batteries are becoming more efficient and affordable. They allow solar power to be used when there isn’t any sunlight. New flow batteries have longer lifespans and higher storage capacities making solar energy more reliable.
Perovskite-on-silicon tandem cells: Tandem cells are made up of lots of solar cells stacked on top of each other. Each layer responds to a different part of sunlight so they can capture a broader range of the solar spectrum. According to the Energy Institute, Oxford PV’s latest perovskite-on-silicon solar panel set a record high of 26.9% efficiency and made its first commercial sale in September 2024.
More bifacial solar panels: Bifacial panels can absorb sunlight from both sides. This boosts their energy output by 30% compared to traditional single-sided panels. They work really well in places where sunlight bounces off things like rooftops or snow.
The future’s bright for solar panel efficiency
Thin-film solar panels
Solar panels have come a long way. And in the future, they’ll be even more powerful. One developing technology that might one day have big applications is thin-film solar panels. These are made from lots of layers of photovoltaic materials on top of a base layer of either glass, plastic or metal. This will make them flexible, lightweight and more mobile than other types. Their simpler manufacturing process means that they could become a cheaper option. However, right now, they are much less efficient than more widely-used options.
But in the long term future, we can look forward to technology that radically improves solar panel efficiency. MIT researchers have developed an even thinner, paper-like solar cell that can turn almost any surface into a source of green, renewable energy. Not only are these solar cells 100 times lighter than traditional ones, they can generate 18 times more power per kilogram!
The really exciting thing is that they’re made using printable electronic inks, so they’re easy to produce at scale. The solar cells are attached to a strong, flexible fabric, which makes them both durable and bendable. Imagine wearing solar panels on your clothes or using them on tents in remote emergency areas where traditional solar cells just wouldn’t work.
The only thing that’s stopping them from hitting the shelves today is the material they’re encased in. Researchers are still looking for a material that protects the cells from the environment without compromising their unique properties. These super-thin solar cells have incredible potential and open the possibility of solar power being used in more versatile ways.
What’s your next solar step?
We hope this guide has given you a better picture of solar panel efficiency. If you’re ready to start generating your own free, greener energy from the sun – as well as storing what you don’t use and even selling energy back to the grid – it’s simple to get started with Hive.
We can help you choose the right panels, get them installed, and start shrinking your energy bills – as well as your carbon footprint.
Just get in touch.
