Last Updated: Feb 10, 2021
About a year ago, we here at Rise published an interview and home feature with Justin Allen, a dog-musher and homestead. Allen built his own off-grid home in the woods of New Brunswick, Canada. Even though a solar PV setup entirely powers his home, Allen mentioned in the interview that he was installing a small household micro-hydro renewable energy system. This system would increase the efficiency of his renewable energy needs. Rivers and streams run 24 hours a day and seven days a week (assuming no prolonged droughts). In contrast, solar panels can only produce electricity when the sun is shining. On top of that, most solar panels are surprisingly inefficient at converting sunlight into usable energy for the homes we inhabit.
Today's average commercial solar panel converts between 17 and 19 percent of the light energy it receives into electricity. On a positive note, this is up from 12 percent just ten years ago, a huge improvement. However, most experts in the solar industry consider that solar panels can continue to increase their efficiency. If we could boost the efficiency of commercially available solar photovoltaic (PV) panels to 30 percent, we could almost double the amount of renewable energy produced on millions of rooftops around the country. In today's article, we will analyze and detail some of the most exciting and promising developments in solar panel technology's efficiency revolution.
When shopping for the best solar panels for a residential installation, potential buyers might be confused and overwhelmed by the different efficiency ratings. These ratings refer to the portion of energy from the sunlight that photovoltaics can successfully convert into electricity by the solar cell. The higher the efficiency rating, the more annual renewable energy output will be possible.
When most people think about renewable energies, we conjure up images of solar panels dotting the roofs of homes across the nation, and for a good reason. Today, there are well over two million residential solar panel installations across the United States. Despite the impressive growth of the solar industry, most of the United States' renewable energy comes from hydropower and wind. Seventeen percent of US energy generation comes from renewables, and hydropower and wind account for about 80 percent of that energy. Why isn't solar energy more of a player in the renewable energy market?
Though several factors affect the solar power industry's growth, one of the main limiting elements is the solar panel's relative inefficiency. As we mentioned above, most solar panels that are available today convert less than one-fifth of the sun's energy that hits the panel into usable energy. Of course, cloudy days, shading, snow, and darkness also limit solar panels' energy production capabilities.
Some variables that can affect the efficiency of solar systems include:
The two main types of solar panels available today are monocrystalline and polycrystalline. Because monocrystalline panels use the highest-purity silicon, this generally makes them the most efficient type of panel on the market for homeowners.
If your home, rooftop, and yard receive a significant shade during the day, your solar panel system's efficiency will also suffer. Fortunately, micro-inverter technology can help avoid losses in efficiency if partial shade only affects a part of your solar setup. Without micro-inverters, even a small shadow on the corner of one panel would change the entire system.
Almost all residential solar installations should go on rooftops or mounting racks that face in a southward direction in the northern hemisphere. Especially during the shorter winter months, the sun passes low on the southern horizon. Only a south-facing roof can capture enough light to produce a significant amount of renewable energy from solar panels. As an added benefit, south-facing homes can incorporate passive solar heating principles to reduce heating and cooling needs. Check out this Rise article for more information on passive solar design. You might also consider investing in solar trackers. These simple devices are attached to the system and allow the panels to shift as they follow the sun's trajectory. While trackers will increase the efficiency of your panels, they are prohibitively expensive at the moment.
Though it might confuse some homeowners, extremely high summer temperatures can reduce the efficiency of solar panels. When installing in an area with long, hot summers (think Phoenix), the right installer will ensure that the panels receive natural airflow for cooling.
As solar panels age, they also tend to lose efficiency. As a rule of thumb, most experts agree that even the best solar panels lose about 0.5 percent of their total potential power output each year. Make sure to check the guarantee on the solar panels you purchase. Many companies will guarantee a minimum power output (usually between 80 and 85 percent) over a 20 to 25 year period.
A few essential maintenance tips can also help keep your solar panels functioning at optimum efficiency. Wiping off any dust is critical, especially in areas with dry summers.
Even the best commercially available solar panels only convert about one-fifth of the sun's light into energy. This might seem, well, inefficient. A 100 percent efficient solar panel isn't possible due to complex physics, such as the Second Law of Thermodynamics and Carnot's Theorem. Fortunately, the relative inefficiency of solar panels is offset by the fact that the sun sends enormous energy to the earth.
Every commercially sold solar panel will announce its official efficiency rating. However, if you want to measure your panels' efficiency at home, look for the "incident radiation flux" in your area (check here for an NREL solar radiation database). Multiply that number by the area of your panel in square meters. Take that number and divide it by the maximum wattage of your panel, and you will get your efficiency rating.
As research and development in the solar industry continue, photovoltaic panels' efficiency ratings should continue to rise. Today, the most efficient solar cell is called a multi-junction concentrator. This panel can convert an impressive 44 percent of solar energy into electricity. The problem is that these panels cost hundreds of thousands of dollars and are not commercially available. For the North American market, the most efficient solar panel currently being sold is the SunPower SPR-327NE-WHT-D. This 327-watt panel has a module efficiency of 20.1 percent, which is significantly higher than the average 17 to 18 percent of competing models.
For homeowners who have already invested in a solar panel system, upgrading to a better system with slightly higher efficiency ratings is probably not a financial possibility. Fortunately, a few things can be done to improve the efficiency of your existing solar panel system. First, you can prune any trees or other vegetation on your property that create shade on your rooftop or wherever your panels are located. It might make sense to place your panels on a garage, shed, or some other building in some cases. While the distance from the house might nominally increase installation costs, a south-facing shed in a sunny part of your backyard will allow the panels to produce much more electricity than the shady, west-facing roof of your home.
You might consider upgrading to a micro-inverter system. String inverters or central inverters are generally only built to last between 5 and 10 years. In contrast, your solar panels will hopefully last for at least 25. If you do need to change your inverter, micro-inverters don't only last longer. Still, they can also increase the system's overall efficiency by reducing the adverse effects of partial shading on the system.
The leading causes that decrease solar panel efficiency include:
Heat buildup can lower solar panel efficiency because as the solar panel temperature rises, the output increases while the voltage output is linearly reduced. To avoid this decrease in efficiency, proper airflow and spacing can keep the panels cooler. Of course, cloud cover is an element affecting solar power efficiency that homeowners have no control over. According to some estimates, solar PV panels' efficiency can drop anywhere between 10 and 25 percent on cloudy days. Again, micro-inverters can play a significant role in increasing efficiency even during dark days.
Relative humidity can lower the efficiency of panels because water vapor can accumulate on the solar PV units. This excessive humidity reflects sunlight away from the solar cells. Similarly, improper maintenance can lead to dust buildup that also reduces efficiency due to obstruction of sunlight.
Physics dictates that we will never see 100 percent efficient solar panel technology. Even 50 percent efficiency is probably never going to happen. The Shockley–Queisser limit estimates that maximum solar conversion for a single p-n junction photovoltaic cell is around 33 percent. More recent findings have stated that the maximum possible efficiency might be closer to 44 percent for this solar cell type.
As more money and resources flow towards research and development in the solar panel industry, significant efficiency gains are fortunately expected. Some experts estimate that more than 2.8 trillion dollars will be invested in solar energy R & D in the coming years. Not only will this make solar panels cheaper and much more widespread, but it will also lead to significant advances in efficiency, with commercially-available panels perhaps even pushing the 40 percent efficiency barrier.
Tobias runs an agroecology farm and a natural building collective in the mountains of El Salvador. He specializes in earthen construction methods and uses permaculture design methods to integrate structures into the sustainability of the landscape.