If you took Detroit and covered it in solar panels you would have enough energy to power the entire USA. If solar panels were 100% efficient a city five times smaller like Miami or Newark would be enough. So why are solar panels so inefficient?
The reason why solar panels are inefficient is mainly because of the inherent limitations of the technology they use to convert sunlight into electricity.
What are these limitations? In this article, we will dig into some basic physics and how it applies to solar to explain why we can’t have 100% efficient solar panels. We will also look at some of the other limitations of solar energy.
Is Solar Panels Inefficient?
Only a partial amount of the energy a solar panel absorbs can be converted into usable electricity. Solar panels have an average efficiency of around 22%. The remaining percentage of energy not converted is lost.
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It’s impossible to explore solar panel efficiency without looking into how solar panels work. Let’s take a look at the photovoltaic process and how it relates to efficiency.
The photovoltaic effect
Solar panels convert sunlight into energy through the photovoltaic effect. This is a process through which particles of energy are absorbed and converted into electricity.
A solar panel consists of two layers of silicon. The top layer or N-Type layer is chemically altered or “doped” with phosphorous to give it more electrons. The excess electrons make the silicon more electrically conductive.
The bottom layer or P-Type layer is doped with Boron to give it fewer electrons. When sunlight hits a solar panel, photons charge the electrons creating a movement between the layers. This creates the electric current that finds its way to your battery or appliances.
Ona side note, find out: Where Do The Electrons Come From In A Solar Panel? Will They Ever Run Out !
This is a simplified explanation of the process of energy conversion in a solar panel. But why is the process inefficient and can it be improved?
Can Solar Panels Be 100% Efficient?
Solar panels cannot be 100% efficient as there are limits to the energy conversion process. However, all energy conversion processes are inefficient with fossil fuels and even nuclear energy having energy losses.
There will always be some loss when you convert energy from one form to another regardless of the process used. But compared to traditional electricity generation methods, solar is the least efficient.
| TYPE OF ENERGY | EFFICIENCY (%) |
|---|---|
| Nuclear | 92.5 |
| Geothermal | 74.3 |
| Natural gas | 56.6 |
| Hydropower | 41.5 |
| Coal | 40.2 |
| Wind | 35.4 |
| Solar | 24.9 |
Why Is Solar Inefficient? (Factors Listed)
Several factors limit the efficiency of solar panels.
Recombination
Recombination is the reversal of the process that creates electricity in a solar cell. Recombination is when the electrons in a solar panel recombine with electron holes or impurities in the crystal structure. This prevents the creation of an electrical current in the cell.
Recombination is the primary reason why solar panels cannot reach 100% efficiency and why the theoretical maximum efficiency solar cells can reach is about 30%. This limit is known as the Shockley–Queisser limit after the scientists who discovered it.
Inefficient light absorption
Not all of the light that hits a solar panel is absorbed. Some of it is lost through reflection and refraction while some of it passes right through the solar panel. This is why solar panels have an anti-reflective coating applied to them to reduce reflection.
Light shines in a spectrum that consists of 53% infrared light, 43% visible light, and 4% ultraviolet light. A limitation of existing solar panels is they convert mostly visible light and half of infrared light into electricity. Only a small portion of UV light is converted.
Can Solar Panel Efficiency Be Improved?
Several routes are being pursued with the view of improving solar cell efficiency. Most of them are still in the lab and are yet to reach the mass production phase.
Bifacial solar panels
Traditional solar panels have solar cells on the front and a metal underside or backsheet. Bifacial solar panels are two-sided solar cells that absorb light from the front and back. This allows the solar panel to capture far more light and improves the overall efficiency of the panel.
The improved efficiency comes at a steeper price, however. Bifacials are 10% more expensive than conventional solar. They are more commonly used for commercial applications and utility-scale solar farms. Source
Multi-junction solar panels
Multi-junction cells are engineered to absorb a wider spectrum of light. This is achieved by combining different types of semiconductors that absorb different wavelengths to create a solar panel that absorbs more light.
One way to do this is by combining silicon solar cells with thin film solar cells. Multi-junction solar cells have reached efficiencies of up to 45%. The drawback of this technology is that fabrication is far too expensive. While impractical for residential use it is used in space where the costs can be better justified.
Emerging solar cell technologies
There is also research into technologies like organic solar cells and perovskite solar cells. These technologies could push efficiencies up to 30% if the challenges faced by them are solved. Source
What Are The Two Main Disadvantages Of Solar Energy?
The two biggest disadvantages to solar are the high upfront cost of solar panels and that they are weather dependent.
Cost of solar
The average cost of solar in the U.S is around $20,000. Federal tax credits and solar incentives can reduce the costs by up to 30%. The payback period of solar is around 8 to 10 years.
While the cost can be steep, it can be worked around in a few ways. One effective way to go solar without breaking the bank is to start with a smaller system that you can expand over time rather than trying to build a large system at once.
For example, you can build a system that has solar panels but no batteries at first and then add batteries later if you decide you need energy storage. In most systems, energy storage isn’t necessary. This is important since batteries are the most expensive part of a solar system.
Unreliability of solar
Solar panels rely on the sun to produce energy. Some days solar panels will produce less energy than others if it’s cloudy. In winter your solar panels will have less output than in the summer. This is a major reason why some homeowners opt for battery storage and even generators. This is to compensate for the inherent unreliability of solar.