Solar energy has been heralded as one of the technologies that will revolutionize the way we get our energy and help mitigate the damage traditional energy use has done to the planet. It does have many environmental and economic benefits, but how efficient is solar energy compared to other renewable energy sources? And how big of a difference does that really make?
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What Is Efficiency?
Before we discuss solar energy’s efficiency, let’s define the term. We can define efficiency as the amount of energy potential that becomes electricity.
For example, a device with 100 percent efficiency would convert all the fuel that goes into it — whether it’s coal, geothermal, wind or solar energy — into useful electricity. A device with 50 percent efficiency would convert half the input into useful electricity and lose the rest of the energy potential, typically in the form of waste heat.
Most energy resources, however, have a lower efficiency than that. Combined-cycle natural gas plants can get up to an efficiency of just over 50 percent. Coal plants typically have between 30 and 40 percent efficiency. The most efficient wind turbines can make it up to 55 percent. Hydropower is one of the most efficient generation resources, with as much as 90 percent.
Most commercially available solar panels have an efficiency of between 14 to 16 percent, while the most efficient on the market reaches around 22.5 percent.
Recent innovations have resulted in solar panels with efficiencies of up to 44.5 percent, which researchers achieved by stacking multiple materials that each absorb different parts of the solar spectrum. When technologies like this become commercially available, the efficiency of solar panels will improve substantially.
How Much Does Efficiency Matter?
Efficiency is just one factor to consider when determining how effective an energy resource is. Some of the differences between solar and other generation technologies mean, in some sense, efficiency is not the most useful measurement when comparing solar’s efficiency with that of other resources.
If you’re comparing solar energy to a fossil fuel or nuclear plant, it’s important to remember sunlight is free, while natural gas and coal are not. Once you install your solar panels, you do not have to pay for sunlight to fuel them. You don’t lose any money when some of the solar energy turns to waste heat. You just lose energy potential.
You have to pay for fossil fuels, though, whether or not they produce electricity. In effect, you only get electricity from about half the natural gas you pay for, because the other half becomes waste heat.
When you compare solar energy to wind and other renewable resources, though, it does lag behind in terms of efficiency. The water that powers hydropower plants and the wind that powers turbines are free as well, so you don’t lose money when you lose energy potential.
Another important thing to consider when discussing the efficiency of energy resources is the capacity factor, which is how much electricity a resource generates, compared to the maximum possible amount it could generate in a year.
The sun doesn’t shine all the time or always shine enough to generate the maximum potential amount of energy, so the capacity factor for solar panels is usually somewhere between 15 and 25 percent. This capacity depends on several factors, including where you’re located and whether the panels move to follow the sun. In 2016, the capacity factor for utility-scale solar photovoltaic generation was around 25 percent.
During the same year, wind farms had a capacity factor of around 35 percent, and hydropower reached 38 percent. Offshore wind farms have a capacity factor that can be as high as 77 percent.
For comparison, nuclear power typically has a capacity factor of close to 90 percent because it needs to run all the time to remain economical. Coal plants typically have about 50 percent, and natural gas plants often have a factor of only about 10 percent if they only generate electricity when demand is especially high.
Advantages of Solar
So, wind and hydroelectric have an advantage over solar power when it comes to efficiency and capacity factor. Does solar have other renewable energy resources beat in any other relevant categories?
Well, for one, solar is much less location-dependent than hydropower and wind. Dams need very specific conditions to make any sense: namely, a body of water and a large area that can act as a reservoir. Wind farms also need large open spaces.
Solar panels, on the other hand, are sensible to put anywhere the sun will hit them. Homeowners can install them on their roofs or on the ground without taking up too much space. By contrast, few homeowners have room for a wind turbine or a dam on their property.
Solar panels are one of the few energy resources that allow customers to take control over their electricity generation, which can save them large amounts of money. Having your energy source so close to where you’ll be using the energy — for example, on your rooftop or elsewhere on your property — means there aren’t any energy losses during transmission and distribution, as there are in most other cases.
Research and development in the field of solar energy are far from over. Solar technologies are always advancing and becoming more efficient. As mentioned earlier, researchers have developed a solar panel design with an efficiency of as much as 44 percent.
We’ll see solar energy gradually become more efficient over the coming years, and may even see a large leap in efficiency if researchers make big discoveries. Granted, the efficiency of other resources, especially wind power, will also likely improve.
Solar energy might not technically be the most energy-efficient resource, but it does have advantages over other generation technologies in other areas. It’s also important that the electric grid of tomorrow will be diverse and consist of many different types of electricity generation sources, of which solar will be one.
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