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Solar panels are often compared based on their energy efficiency, and there is a perception that high efficiency is equivalent to high quality. However, there are many other factors to consider when comparing photovoltaic (PV) modules from different manufacturers.
High efficiency alone does not guarantee that a solar panel will also excel in other performance areas. For example, you may find PV modules that have a high efficiency initially, but also a short warranty and a rapid degradation rate.
You can find a wide selection of high-efficiency solar panels in the UK, but in this article we focus on products that also meet the following requirements:
- Product warranty: At least 25 years
- Long term performance: At least 90% of initial capacity after 25 years
- High temperature performance: Less than 0.30% power loss per Celsius degree
The following solar panel product lines meet these requirements, while having a high efficiency:
Solar Brand | Product Line | Energy Efficiency | Additional Features |
SunPower Maxeon | 21.7% – 23.0% | 40-year product and performance warranty 92% capacity after 25 years and 88.25% capacity after 40 years 0.29% power loss per °C Factory-installed microinverters | |
REC (Renewable Energy Corporation) | 20.7% – 22.3% | 25-year product and performance warranty 92% capacity after 25 years 0.24% power loss per °C | |
Panasonic | 21.7% – 22.2% | 25-year product and performance warranty 92% capacity after 25 years 0.24% power loss per °C | |
Canadian Solar | 21.5% – 22.8% | 25-year product warranty and 30-year performance warranty 90.6% capacity after 25 years and 88.85% capacity after 30 years 0.26% power loss per °C |
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These solar panels can generate over 90% of their initial output after 25 years of use, and they can retain their efficiency during warmer weather conditions. They have temperature coefficients of less than 0.30% per Celsius degree, which means a 10°C temperature rise causes a productivity loss of less than 3%.
Thanks to these performance features, the solar brands in the table above offer long-term value and a higher return on investment.
1 – SunPower Maxeon 6 AC Series
Power Ratings Available: 420W, 425W, 435W and 445W
Dimensions and Weight: 1872 x 1032 mm, 21.8 kg
SunPower focuses on premium solar panels: they have above-average prices, but also superior efficiency and one of the longest warranties in the industry. In particular, the SunPower Maxeon 6 AC Series reaches up to 23.0% efficiency, while having a 40-year product and performance warranty.
- SunPower panels lose no more than 2% of their electricity output during the first year, and then 0.25% per year during the rest of their lifespan.
- The Maxeon 6 AC series can operate at 92% capacity after 25 years, and 88.25% capacity at the end of its 40-year warranty.
SunPower panels also have a temperature coefficient of -0.29% per °C. This means a 20°C temperature rise causes a 5.8% loss. Keep in mind this is a temporary effect caused by heating, which does not represent permanent damage to your panels. Having a low temperature coefficient is helpful, given that PV modules are constantly under the sun. Solar panels can heat up even in temperate climate locations such as the UK.
Another advantage of the Maxeon 6 AC panels is having a built-in microinverter, which converts direct current (DC) from PV cells into the alternating current (AC) needed by home appliances.
- Traditional solar panels must be wired in string circuits and then to a common string inverter, since they cannot provide AC power directly.
- This is not necessary when using SunPower Maxeon 6 AC panels, since they have Enphase IQ 7A microinverters with a 25-year warranty.
The microinverter configuration also contributes to higher electricity production. When solar panels are wired in DC strings, and one of the panels is shaded or malfunctioning, all of them suffer a loss of productivity. With microinverters, each solar panel operates independently and their overall productivity is increased.
The other solar brands discussed in this article are also compatible with microinverters, but they are not factory-installed.
2 – REC Alpha Pure-R Series
Power Ratings Available: 400W, 410W, 420W and 430W
Dimensions and Weight: 1730 x 1118 mm, 21.5 kg
Renewable Energy Corporation (REC) is also a premium solar brand with a 25-year product, power and labour warranty. Their Alpha Pure-R Series offers up to 22.3% efficiency, only slightly less than SunPower Maxeon panels. However, REC solar panels have the best temperature coefficient in the industry, tied with Panasonic.
- REC modules only lose 0.24% power output per °C, which means that a 20°C rise only causes a 4.8% power loss.
- Solar panels are constantly receiving solar radiation, and a low temperature coefficient leads to increased productivity over time.
REC Alpha Pure-R panels lose no more than 2% output during the first year and then 0.25% per year. This means you still get 92% of the initial electricity production at the end of the 25-year warranty period.
Traditional solar panels are characterised by their grid-like design. Their frames and blacksheets have clear colours, which results in visible divisions between PV cells. In case you don’t like the appearance of traditional panels, the Alpha Pure-R Series has an all-black design. Their frames and backsheets are painted black to match the colour of PV cells, which results in a sleek and uniform appearance.
Keep in mind that REC only offers the 25-year product, power and labour warranty if your home solar system is installed by one of their Certified Solar Professionals. Otherwise you get a 20-year product warranty and 25-year power warranty, and no labour warranty.
3 – Panasonic EverVolt HK2 Black Series
Power Ratings Available: 420W and 430W
Dimensions and Weight: 1865 x 1040 mm, 21.6 kg
The Panasonic EverVolt HK2 Black Series also offers excellent long-term performance and high-temperature performance, combined with an efficiency of up to 22.2%:
- Panasonic offers a 25-year product and power output warranty, and their panels can still generate 92% of their initial output at the end of this term.
- Thanks to their temperature coefficient of -0.24% per °C, EverVolt HK2 Black modules only lose 4.8% productivity with a 20°C rise.
As you might guess from their name, EverVolt HK2 Black panels have an all-black design with no visible divisions between PV cells. This design can be attractive for homeowners who don’t like traditional solar panels with clear coloured frames and backsheets.
To get the 25-year product and power output warranty, you must register your solar panels with Panasonic within 60 days after being installed. Otherwise, you only get a 15-year product warranty and a 25-year power warranty. You can get a better warranty by hiring a Panasonic authorised installer: in this case the 25-year warranty also covers labour and shipping costs.
Unfortunately, Panasonic announced they will be closing their solar business in Europe. This means the EverVolt solar modules will no longer be available through official retailers in the UK. However, existing warranties will continue to get coverage when Panasonic closes.
4 – Canadian Solar HiHero Series
Power Ratings Available: 420W, 425W, 430W, 435W, 440W and 445W
Dimensions and Weight: 1722 x 1134 mm, 23.0 kg
Canadian Solar also excels in terms of energy efficiency, warranty coverage, long-term performance and high-temperature performance. Their HiHero Series offers up to 22.8% efficiency, closely behind SunPower by a difference of only 0.2%.
- The Canadian Solar HiHero Series has a 25-year product warranty and a 30-year power output warranty.
- The degradation rate is only 1% during the first year and then 0.35% per year, which means you have 90.6% capacity after 25 years and 88.85% capacity after 30 years.
Canadian Solar HiHero panels have nearly the same temperature coefficient as the REC Alpha Pure-R and Panasonic EverVolt HK2 Black series. They only lose 0.26% power output per °C, which means a 20°C temperature rise only causes a 5.2% loss.
Keep in mind that Canadian Solar makes a wider variety of solar panels. While the other brands in this article focus exclusively on high-efficiency panels, Canadian Solar also makes less efficient and more affordable options. This section focuses on the HiHero Series, which is one of their premium solar panel lines.
How we decided on the best solar panels
It’s important to consider that there are panels with better efficiency, better warranties, and sometimes even better longevity.
You can also purchase panels that are as little as half the price of some of the top 10 options listed here. However, we chose the top 5 solar panels in the UK based on a combination of factors designed to deliver value.
For example, we chose low to mid-range panels that offer the most value for the money. Better brands like SunPower offer as much as 5% more efficiency, but the cost is high enough that the extra efficiency won’t make up for the higher investment.
Quality – We are concerned with quality and longevity, so all the panels on this list feature high salt and ammonia corrosion resistance certified by TUV NORD or an equivalent body, a minimum wind load of 2400 Pascal and snow load 5400 Pascal, and a minimum product warranty of 10 years.
Warranty – You want to know that the efficiency of your panels is guaranteed, which is why we set a minimum of a 25-year warranty. These panels are guaranteed at 90% efficiency for a minimum of 10 years and at 80% for a minimum of 25 years.
User Review – User reviews are important for determining the long-term quality of a panel. We only chose panels with reviews that average at 4.5 or higher.
Brand – All our top 10 panels are from Tier 1 solar panel manufacturers. Tier 1 manufacturers have investments with at least 5 major banks, are international players, and are therefore better able to back up their warranties.
Value – Our primary concern was choosing panels that offer a high value in exchange for the money. We looked for models that balance efficiency with cost, so that you can get the most return for your investment. This means that over 25 years, these panels are more likely to provide a better return than either lower-priced models which might not last as long and over high-end models, which have to produce more power just to recoup the cost of purchase.
What Features Should I Look For?
Looking at the length of a solar panel warranty is more useful than looking for a particular solar panel manufacturer. The longer the warranty, the more faith a company has in its product.
Most companies will have a two-part warranty, and your installer will be able to walk you though your exact warranty.
Is Efficiency All That Matters?
You may be tempted to buy the most efficient panels on the market. However, if you have enough roof space, that’s not always the best choice. Using less efficient panels is actually a common practice. Most homeowners only install the more efficient panels when they have a limited amount of space on their roof. That’s because the financial payoff from high efficiency panels does not justify the cost.
For example, Sharp manufactures triple junction panels with an incredible 44.4% efficiency. While these panels are three to five times more efficient than others, they are also prohibitively expensive. The cost is not justified except in the most extreme situations because they cannot pay themselves off.
What Else is Important to Keep in Mind?
The person who installs your system is just as important as the panels you choose. A solar panel system comes with a large upfront cost and you don’t want to trust that project to the wrong hands.
For example, did you know that if a small part of your solar panel is in the shade, the entire panel can stop working? This is similar to how a single broken bulb can ruin a whole strand of Christmas lights.
A good installer will do a thorough shade analysis of your roof. This will be a comprehensive look at the shade zones on your roof and it will take year-round sun exposure into account. By doing this analysis, your installer ensures that your panels will always receive enough sunlight to work properly.
Efficiency Standards for Solar Panels
There are three common types of solar panels. Although all three are made from silicon, they have a different production process which results in varying degrees of efficiency.
Monocrystalline Panels
These are the classic looking black panels. Because of the manufacturing process, and the natural properties of the silicon, the corners are often rounded or cut off. The panels are a uniform colour, which is a consideration for some homeowners.
Monocrystalline panels are made of high quality silicon and have the highest efficiency levels. They are also designed to have a longer lifespan than any other type of panel. In addition, monocrystalline panels are good at generating energy in low light situations.
The downside is that these panels are the most expensive. And, if part of the panel is covered in shade, dirt or snow, the entire circuit can stop producing electricity.
Polycrystalline Panels
Introduced in 1981, polycrystalline panels have been on the market for more than 30 years. Polycrystalline panels use less silicone during the manufacturing process than monocrystalline panels, which makes them more affordable.
These panels have a slightly increased risk of overheating, but this is rare and should only be a concern for people who live in extremely high heat areas. The lower purity silicon used in these panels also means that they aren’t as efficient as their monocrystalline counterparts. Some people may find these panels less aesthetically pleasing because of their mottled blue colour.
Thin-Film Solar Cells (TFSC)
TFSC panels are made from a substrate with several layers of thin photovoltaic material. These solar panels are becoming more popular because they are easy to mass-produce and have a lower price point.
Aesthetically, TFSC have a uniform colour and they can be manufactured to be flexible. This is creating some exciting new opportunities, as it means panels can be installed in different areas. Additionally, TFSC panels are less affected by shade than monocrystalline and polycrystalline panels.
However, they tend to require more space than is ideal for most residential areas. This space requirement also means that the cost of other materials goes up. You’ll end up paying more for products like supports and cables. TFSC panels also tend to break down faster which means they usually have a shorter warranty.
Efficiency Percentages
The efficiency of a solar panel is determined using a standard mathematical formula. That formula is: the maximum power output, divided by the amount of sunlight, times the size of the solar array. This is a consistent formula that gives an accurate and unbiased rating across all manufacturers of solar panels.
While every brand of solar panel is different, most fall into these ranges:
Monocrystalline panels have 15 to 20% efficiency.
Polycrystalline panels have 13 to 16% efficiency.
Thin-Film Solar Cells have 7 to 13% efficiency.
Inverter Efficiency
An inverter is a crucial piece of equipment for any solar panel system. When sunlight hits a solar panel, electricity is produced in a DC current. An inverter takes that and transforms it into an AC current which can be used by your home’s electrical system.
When you look at a solar panel system, one of the factors you should consider is the converter’s efficiency. Most consume about 4 to 8% of the energy they convert, which makes them 96 to 92% efficient.
One of the best inverters on the market is made by SolarEdge Technologies. This inverter loses only 2% of the energy it converts, which makes it 98% efficient. While this is one of the best inverters money can buy, it’s also quite expensive and impractical for most homeowners.
Most inverters last ten years. However, high ambient temperatures, large electrical loads and lightning strikes can all shorten an inverter’s lifespan. Once an inverter ceases to function you will need to replace it. You can do this without replacing the solar panels on your roof as it’s an independent system.
What Solar Incentives Are Available in The UK?
The Smart Export Guarantee (SEG) in the UK is a government-backed measure designed to ensure that small-scale generators of renewable electricity are compensated for the excess power they supply to the national grid. Introduced on January 1, 2020, as a successor to the Feed-in Tariff scheme, the SEG obligates licensed electricity suppliers with at least 150,000 domestic customers to offer a tariff and pay for the renewable energy exported.
Under this scheme, households with solar panels or other renewable technology can earn money for each kilowatt-hour (kWh) of electricity they export back to the grid, essentially turning their homes into small power stations. The export rates can vary between suppliers, but the tariff must be greater than zero at all times, encouraging competition among suppliers.
To be eligible, the installed capacity must be 5 megawatts or less, and the technology must be certified under the Microgeneration Certification Scheme (MCS) or equivalent. The SEG is a step towards a more sustainable energy network and provides financial incentives to encourage the adoption of renewable energy by homeowners, businesses, and communities in the UK.
Eligible Panels
In order for a solar panel system to qualify for the SEG program it must be MCS (Microgeneration Certification Scheme) certified. Most panels made by major suppliers fall under this certification. That includes, but is not limited to, panels made by Suntech, Jinko Solar, Kyocera, Sanyo, First Solar, Sanyo and Yingli.
When you’re ready to put some solar panels on your roof, the person who’s installing them will be able to tell if you the panels you’re interested in are MCS certified.
Finding an MCS Certified Installer
Finding an MCS certified workman to install your solar system is equally as important as choosing the correct panels. Even if you purchase MCS certified panels, if you have an unqualified person install them, you may not be eligible for the FiTs program.
Before you hire someone to install your panels, be sure to ask to see their certification. Search here to find a certified solar panel installer in the UK.
Most 3 bed home installations will cost 6,000 to 11,000 Pounds. The exact amount will depend on the panels you install and the complexity of the project.
Questions for Your Installer
To ensure that you get the best possible value, there are several questions you’ll want to ask your MCS certified workman.
For example, imagine you have a problem with your solar panels. Who pays for the removal of the parts, the shipping back to the company, and then the re installation?
This is an area you’ll want to be very clear on. If the solar panel parts are covered under warranty, but removal and reinstallation isn’t, you could easily end up paying more than a thousand pounds to fix a problem. Be sure to choose solar panels with the most comprehensive warranty possible.
You’ll also want to ask whether the installer will do a comprehensive shade analysis. Also, you can ask what angle the panels will be installed on. If the angle is greater than 15 degrees, the panels will be cleaned naturally by rain.
Compare quotes to get the best solar panel prices
A solar panel system is going to be a great addition to your home. While there is an upfront cost, the long-term benefits make it worth it. You’ll be reducing your dependence on traditional power sources while saving money at the same time.
Studies have shown that a solar panel system is a good investment, even if you plan to sell your home soon. Homes with solar panels sold 20% faster than those without.
Don’t forget to keep in mind, the person doing the installation is just as important as the panels you choose. Be sure that your installer is MCS certified and that he does a thorough analysis of your house. Once you both understand the needs of your home, you can pick a company that makes a product that’s right for you.
The best solar panels offer high efficiency, durability, and a strong warranty from a reputable manufacturer.
Yes, UK weather can impact efficiency; panels designed for lower light conditions perform better in the UK.
Yes, incentives like the Smart Export Guarantee (SEG) pay for surplus solar energy exported back to the grid.
Highly efficient panels yield more energy, essential in the UK’s often overcast weather conditions.
Look for long-term warranties (25 years is standard) that cover performance and manufacturing defects.
