Solar technology is one of the best renewable energy sources in the world and one of the most rapidly growing industries. This technology allows homeowners, businesses, industries, and grid-level utilities to harness energy from the “big fusion reactor in the sky called the sun” and convert it into electrical power. Aside from being convenient and practical, solar technology is fairly easy to install.
While solar panels are highly popular, the technology has its limits regarding solar cell efficiency. Solar cells are the fundamental component in the overall construction of a solar panel. Thankfully, there is no need to worry. The solar industry might be on the brink of a breakthrough, and the future could give way for solar panels with efficiencies reaching 30 – 47%.
In this article, we will explain everything you need to know about solar cell efficiency, why the value is so low in the present, what the future holds for solar technology, and many interesting facts about it.
What Does Solar Cell Efficiency Mean?
Before diving into the concept of solar efficiency, let us understand a little about solar radiation and how it is measured. Every place on Earth receives a certain amount of solar radiation or irradiance, real-world testing conditions consider the daily energy radiation, but laboratories tests tend to consider the radiation per second. This solar radiation is measured in kilowatt-hour per square meter per day (kWh/m2/day).
Now that we know about solar radiation, we can dive into the concept of solar cell efficiency. The efficiency for a solar cell is the ratio of energy you get at the output of a solar cell, considering the input energy coming from the sun or another radiating light source. In other words, solar cell efficiency is the percentage of solar radiation per square meter (m2) that is converted into electrical power.
The efficiency of a solar cell is measured in laboratories by using the Standard Test Conditions (STC). These conditions consider an irradiance of 1,000 W/m2 per second, subjecting the PV modules to a 25ºC temperature. For instance, testing a silicon multi-crystalline solar cell considering a 22.3% efficiency under these conditions, PV modules will produce around 223W/m2. The efficiency of each PV module, combined with an array of external factors, affect how much energy a solar panel can produce.
Why Is Solar Cell Efficiency so Low?
The solar industry has made amazing breakthroughs in the last few decades for solar technology, but there is still one major flaw to work on: the low efficiency of solar panels. Commercial silicon solar panels can reach efficiencies ranging from 15 – 22% in real-world conditions, but as you will see in the table below, silicon solar cells under STC have reached efficiencies of 26.7% and other technologies up to 28.8%.
The highest silicon solar cell efficiency reported by this table has reached 26.7% efficiency, this means that 73.3% of the solar radiation energy is lost in the conversion process. But converting solar radiation into electricity is not that easy, especially since many factors are affecting the efficiency of panels. Some of these factors are recombination, spectrum losses, temperature, and reflection.
Solar cell efficiency fluctuates depending on the amount of sunlight a solar panels are exposed to, as well as the quality of solar panel cleaning and maintenance being carried out. And whilst solar panels can function on cloudy days, they require optimal conditions to achieve their highest possible solar cell efficiency. Of course, that efficiency is dictated on its most basic level by the technology behind the cell in the first place.
Actually, the low efficiency of solar panels is not something entirely surprising. The maximum efficiency for solar cells using a single p-n junction (a single material) was calculated by William Shockley and Hans-Joachim Queisser at the company Shockley Semiconductor in 1961, around 60 years ago. This theoretical limit known as The Shockley-Queisser limit sets a maximum conversion efficiency of 33.7%. Considering this limit, there is still some room to grow for the efficiency of solar cells.
Has Solar Cell Efficiency Reached Its Maximum Limit?
According to the Shockley-Queisser limit, the maximum theoretical efficiency for a single p-n junction solar cell is set at 33.7%. Since the solar industry has reached up to this point a maximum tested solar cell efficiency of 26.7%, this means that there is still room for increasing the efficiency by 7.0%. While 33.7% is a great efficiency for solar panels, this still means losses of around 66.3% for solar technology.
Another material with a promising future for the solar industry is Perovskite. This is a material composed of the same structure as calcium titanium. Up to date, Perovskite solar cells have reached a solar cell efficiency of 25.6%. This material combined with a silicon tandem cell can reach a theoretical cell efficiency limit of 43%.
While silicon alone can only reach a conversion ratio of 33.7%, when combined with Perovskite this limit is increased by 9.3%, which is a long way to go for solar efficiency. Since the theoretical cell efficiency can be surpassed by combining different materials, does this mean that there is a greater future for the solar industry than just reaching the Shockley-Queisser limit?
What Is Required To Make a Breakthrough for Solar Cell Efficiency?
While the industry so far has been trying to reach the Shockley-Queisser limit, the future might offer more opportunities to surpass this limit by combining several materials, which could give room for more efficient solar cells.
A group of scientists at NREL successfully created semiconductors that Gave life to III-V solar cells. The first III-V solar cells, contained aluminum indium phosphide (AlInP) and aluminum gallium indium phosphide (AlGaInP), with the name deriving from the fact that each of the materials used for the semiconductors falls under groups III and V of the chemical periodic table. III-V solar cells, show great promise for the future of the solar industry. Using a concentrated sunlight focus, multijunction III-V solar cells can reach efficiencies of 45%.
Another great experiment shining a light on the future of solar cells is the creation of Transmissive concentrator multijunction (TCMJ) solar cells. Laboratory experiments using these six-junction solar cells achieved ground-breaking results that prove solar cells can reach efficiencies of 47.6%.
It seems that the future of the solar industry lies in multi-junction solar cells. This technology is still being developed, but there is nothing to prove that we will not be able to see solar panels with rated efficiencies of 45% or more in real-world conditions, considering that laboratory tests are already showing promising results.
The best thing about multijunction technology is that it is not entirely attached by the Shockley-Queisser limit, since it is comprised of several junctions, and can be developed further in the future.
Conclusion: Present and Future of Solar Cell Efficiency
In 1961, the theoretical limit for the maximum solar cell efficiency using single p-n junctions was calculated. This calculation known as the Shockley-Queisser limit sets the maximum solar cell efficiency at 33.7%. With the current technology, the solar industry reached tested efficiencies of 26.7% for silicon solar cells, showing the groundbreaking technology already developed in the present.
Even though the current technology has not reached the 33.7% solar cell efficiency limit for single-junction solar cells, this limit is still fairly low. Multijunction technology has proved to be the way of the future for the solar industry. III-V solar cells have the potential to reach efficiencies of 47.6% and maybe even more. This technology is quite new, which is why the future for the solar industry might shine brighter than the present state.
Frequently Asked Questions
How Does the Temperature Affect the Efficiency of Solar Panels?
Temperature affects the efficiency of solar cells in real-world conditions. The ideal temperature for panels is 25ºC (77ºF), which is the one used for STC. For crystalline solar panels, the temperature varies the efficiency of PV modules by -0.35 – 0.55%/ºC differing from the 25ºC STC. This means that solar panels at an external temperature of 35ºC (95ºF), would have an efficiency reduced by 3.5 – 5.5%.
Reflection is one of the main factors affecting solar cell efficiency, this efficiency can be increased depending on how much light the panel reflects and absorbs. To minimize light reflection, manufacturers coat their cells with anti-reflection materials, which is why most solar cells seem black or dark blue. Solar cells without this coating can reflect more than 30% of the light.
While you cannot increase the efficiency of solar cells, there are some things you can do to increase your solar panel production:
–Keep your panels away from shading. Check if your panels are being shaded by a tree or any other structure. If this is the case, look for a way to eliminate the problem or relocate the installation.
–Consider installing a cooling system. Some large solar installations, increase the efficiency of their panels by reducing the temperature of the module and therefore reducing thermal losses.
–Perform regular maintenance on your solar panels. Solar panels get dirty with time, this dirty film ends up obstructing the light, and therefore reducing the efficiency of your modules. Perform maintenance once or twice a year to keep your panels in top shape.
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