Buying solar panels means researching your options and one of the things that you should come across fairly quickly is solar panel efficiency. Efficiency is typically used as a quality indicator for homeowners because it directly indicates how much sunlight your panels can convert into energy. That’s important, because it can greatly affect the performance of your panels.
While high efficiency solar panels are more expensive than low efficiency models, they can pay themselves off by collecting more energy, so that you buy less electricity, and receive more from the Feed in Tariff. However, it is important to consider that very high end models, which are high efficiency, might not offer a significant cost to earnings ratio, so rather than buying the most efficient solar panel, you are better off researching to see which offers the most return on your investment.
What is Solar Panel Efficiency
Solar panel efficiency is quite simply the measurement used to determine how much of the available electricity the panel can absorb from a ray of sunlight. To understand that, you have to know a little bit about how solar panels work.
The sun generates electromagnetic radiation which travels in waves that we see as light. These waves travel in different wavelengths ranging in size. As you may remember from school different wavelengths show up as different colours of light. This is important, because solar panels only absorb waves between 380 and 750 nanometres, in the spectrum of red to violet light. That makes up about 7% of all total light, including daylight with no sun.
When the light hits your solar panels, the electric field scatters electrons from their bond with the electromagnetic radiation. These electrons are then trapped between the positive and negative layers in the solar cell and pushed into the conductors attached to the cells, which creates an electric current. This process happens constantly, anytime there is light on any of the solar cells.
So, where does solar panel efficiency come in? Most solar panels are rated with an efficiency rating, typically between 11 and 21%. This rating measures how much of the 7% of all total light that the solar cell can convert into electricity. This affects you in a couple of different ways. A 21% efficiency solar panel can collect nearly twice the energy over its lifetime than an 11% efficiency panel. Unfortuantley, it’s not quite that simple, because a number of other factors affect what you will get out of the panels. Most panels are rated by their maximum output. For example, you’ll see panels rated between 50 and 385 watts. This is the maximum power output of the panel, taking efficiency into account. What’s the most important thing to remember? A high efficiency panel produces more energy in a smaller or same-size package.
Different Types of Solar Cells
Different types of solar cells are more or less efficient, because they can trap different types of energy. The most efficient cells are made of layers of silicon, stacked together like wafers, where each layer is optimized for trapping one wavelength of light, so that you catch as much of the spectrum as-is possible. You also have different types of solar cell technologies, and this affects your efficiency and the output of the cell as well.
Polysilicon – Polysilicon or polycrystalline silicone cells are created using poured silicone, which is made up of multiple silicon crystals. These cells can typically achieve efficiency rates of 11-15%, and can be recognized by their distinct flaky appearance. Polysilicon solar panels make up roughly 80% of the panels available on the market.
Mono Silicon – Mono silicon or monocrystalline silicone cells are high quality cells constructed of a single piece of silicone. These cells are able to achieve higher efficiency than polysilicon because they do not have imperfections or spaces between the silicon. However, mono silicon cells are more expensive to produce, which is why they high efficiency solar panels typically cost more. Mono silicon cells are solid, with no flakes in the cell.
Thin Film – Thin film solar panels are very cost effective panels but are typically less efficient than crystalline silicone cells. Thin film panels literally feature a thin film of silicon over electrical components, which helps to reduce costs. However, while the maximum efficiency of thin film solar cells is 21.7%, most panels on the market achieve an average of 12% efficiency.
Why Your Solar Panels Might Be More or Less Efficient Than Listed
Temperature – Solar panels lose efficiency at high temperatures because the heat affects the conductors and wiring in the panel. While this is rarely a large problem in the UK, where the weather is moderate, it does mean that you won’t be achieving maximum efficiency on very warm days. Why? You can generally estimate that the inside of your solar panels is twice the temperature of the air because the glass over the silicon works to increase the heat. This means that if it’s 30 degrees, it’s likely to be 60 inside the panel in direct sunlight. Luckily, most solar panels compensate for this, because they’ve usually been tested in conditions that don’t expose them to the maximum amount of sunlight. So, if it’s 30 degrees and very sunny, you could actually be generating more wattage than the maximum listed output, despite the offset.
Condition – Dirty, shaded, or broken solar panels are significantly less efficient than clean panels. Even a fine layer of dust building up over the glass can greatly reduce the efficiency of cells by preventing light from reaching the silicon. Regular cleaning is crucial to maintaining your solar panels, especially if they are ground mounted.
Direction – The direction of your solar panels will expose the panels to more or less light. Ideally, you would be able to slightly re-adjust your solar panels to follow the sun throughout the day to collect the most light, sort of like a sunflower. However, while these systems exist, they don’t typically allow you to collect enough extra energy to offset the extra costs. Instead, most solar installers will point your solar panels where they will be most efficient at noon, when you can collect the most power.
Construction – Many solar panel manufacturers list the efficiency rating of the solar cell. The entire panel might have a much lower efficiency rating, because of the conductors and wiring. However, this doesn’t change how much energy your panels will be able to generate. If it’s listed at 200 watts, it will still produce 200 watts.
Conversion – Solar panels produce DC energy but your home and the grid use AC. Unfortunately, you will typically lose about 20% of your total power when converting DC energy into AC. This doesn’t affect your production, because it’s already been taken into account.
If you want to get the best idea of what your solar panels are capable of, look for Performance Testing Conditions (PTC) or System Performance Testing Conditions (STPC). These tell you the panel or system (including inverter) performance in testing conditions that are closer to what you will see on your home.
The Most Efficient Solar Panel
The world’s most efficient solar cells actually achieve double the efficiencies of the best solar panels on the market. In fact, the world record was in 2014 at the Fraunhofer Institute for Solar Energy Systems ISE and it sets a remarkable precedent of 46% efficiency. Unfortunately, we don’t yet have the technology to create that kind of efficiency in an actual solar panel. Solar cells lose efficiency when they are connected to each other, and when paired with conductors, placed behind glass, and when placed in less than ideal conditions or at higher temperatures.
In fact, the Shockley Queisser limit or solar efficiency cap is a calculation that suggests that modern single junction silicon solar cells are only capable of 33% efficiency. And, the world record is held by a double junction cell. Currently, there are no double junction cells on the market, and there likely will not be for over a decade, due to the cost of producing them.
The highest efficiency solar panel on the market is produced by SunPower, who actually produce 17 of the 20 most efficient solar panels on the market. SunPower’s record is 24.1% efficiency, but their highest efficiency panel on the market is the SunPower X21 which achieves an average of 21.5%.
Choosing the Best Solar Panel for Your Needs
In most cases, you should pay less attention to getting the most efficient solar panel and more to getting a panel that offers the most return on your investment.
How Much Electricity You Use – Check how much electricity you use every year. Most homeowners in the UK use between 2,000 and 4,900 kWh per year, or an average of 3,600 kWh per year. Your system should be able to supply anywhere from 10-30% of your total energy.
When You Use Electricity – You can use your electricity bill to check your peak usage hours, or just check to see when you have the most devices on. If you frequently use electricity between 12 and 4 in the afternoon, more efficient solar panels are likely a great investment. If your peak hours are after 6 PM, you’re mostly using electricity off of the grid. Why is this important? You earn about half the rate from Fit and Export tariffs as you do from using the energy yourself.
The current average electric rate in the UK is 11 pence per kWh. The FIT rate is only 4.3, plus the 4.8 Export tariff. So, you will earn less if you aren’t using the extra energy anyway. Considering this is important if you want to make sure that your panels are paying themselves off.
The Cost of the Panels – In some cases, a panel will cost more than the extra efficiency warrants. It’s important to consider if you’re getting the same or more energy production for the money. For example, if you have the space, you might actually be able to get more lower efficiency panels to create the same size system to collect the same amount of power.
Cost Per Watt – The cost per watt should be your primary decision maker unless you have a limited amount of roof space. Cost per watt is an easy way to see if you’re getting a good value for the panels. For example, the SunPower X21-345 offers 21.5% efficiency and produces 345 watts in a 1559 x 1046 x 46 panel. The Hanwha 250 watt offers 15% efficiency and produces 250 watts in the same size panel. Except, the Hanwha starts at £242.86 while the SunPower costs twice that much. That’s a big difference in what you’re paying per watt, which means that the extra efficiency won’t likely pay off unless you are in a very sunny area. On the other hand, you might pay £350 for the Kyocera KU265-6MCA 250 watt panel (16% efficiency) and £170 for the Canadian Solar CS6P 250 watt panel (15.545 efficiency). Because they both have comparable efficiencies, the Canadian Solar is the clear choice because you’re paying almost half the rate per watt, which will add up considerably for an entire system. How much? The average 4kW solar system includes 28 or more panels, which means you can save £5,000 by choosing the lower efficiency panel.
In other cases, the more expensive panel will pay off, because it will offer more for your money. But, it is always important to look at the cost per watt, to decide if it offers enough value.
How Much You Will Earn – If you need help deciding how much you will earn with your solar panel array, you can use our free solar rate calculator. It will do the math for you to tell you how much you are likely to spend on a solar array and how much it will earn you over a 25 year period.
The Best High Efficiency Solar Panels for Homeowners
The following include the best high efficiency solar panels that offer a good cost to efficiency ratio, so that you can get the most out of your money. While there are more efficient solar panels available, they typically cost more than the extra investment warrants, which means that you will not likely earn a return. The following solar panels offer efficiency and affordability
1. SunPower E-Series – The SunPower E-Series Residential is one of the most expensive options on this list, but with an efficiency rating of 20.1%, is also one of the highest performing. SunPower’s guarantee states that these panels produce up to 36% more energy than some other leading panels, and they back that with a 25 year guarantee.
2. Yingli Solar YLM 60 Cell – The Yingli Solar 60 Cell solar panel offers a performance of up to 17.8% conversion efficiency, with panels available from 270 to 290 watts.
3. JA Solar Mono Percium – JA Solar’s Mono Percium line is available with panels ranging from 270 to 315 watts, at an average of 16.5% efficiency. The panels are backed by a 25 year guarantee and a 10-25 year power guarantee.
4. Canadian Solar CS6P-P – The Canadian Solar CS6P-P solar panel offers 15.54% efficiency and comes in a 260 watt panel for the 60 cell or 320 watts for the 72 cell. The panels come with a 10 year limited product warranty and a 25 year power output warranty.
5. SolarWorld Sunmodule Plus – The Sunmodule Plus offers 17% efficiency for 285 watt panels with prices starting at just £183.00 per panel. The panels come with a 25 year performance warranty, and a 10 year product warranty.
6. Sharp – Sharp offers a number of solutions ranging from design to high efficiency, at a range of prices. Their mid-range panel, the NURJ285 offers 17.4% efficiency for a 285 watt solar panel, with a 10 year product guarantee and a 25 year power output warranty.
In many cases, your best option will be to check which high efficiency solar panels your local solar installers can supply, so you can compare your available options to get the best for your home. If you want to get the best deal on any solar panels, including high efficiency ones, your best option is to compare installer quotes so that you can choose the best rate and get the lowest price.
If you’re ready to get started, use our free comparison tool to find the lowest rates in your area. We will send you the lowest quotes from top rated installers in your area, so you can choose your favorite. And, there’s absolutely no obligation.