Many homeowners turn to renewable energy such as solar power to try to cut down on their utility bills and be more eco-friendly. One of the more daunting aspects of taking on this type of upgrade is the cost. Though solar solutions have come a long way in recent years toward being more affordable, they can still cost quite a bit of money to put in and take years to pay for themselves. It is, therefore, expected that the potential solar system owner will want to shop around and determine what product has the best efficiency both in their home and wallet.
There are two major types of solar installations that can be used in the home. The first and most simple type is thermal solar energy. These systems are a replacement for the traditional hot water system that uses electricity or gas. Instead, a system of pipes runs through a heat collector panel on the roof and down to the water tank to transfer the heat collected from the sun’s light to the water that is used in your home. The second type of solar system that is actually more prevalent is the solar electric system. These systems use photovoltaic panels to convert the sun’s rays into electricity that can be used directly in the home, stored in batteries or sold back to the utility company and sent to the electric grid. For more on how these systems work, check out this article for thermal solar panels and this one for photovoltaic systems.
Thermal Solar Panels
There are two types of thermal solar panels that can be used in this system. The more basic model is the flat panel. These collector panels are made of a box with a thick glass top and a metal interior that work together to amplify light and trap the resulting heat, like a solar oven. A series of pipes run through the box and liquid runs through the pipes to absorb the heat in the collector box. This liquid then travels down to the water tank and passes its heat on to the water in the tank before traveling back up to the roof to get reheated.
The second type of thermal solar panel is called an evacuated tube collector. This is made up of a series of empty tubes that trap light and turn it into heat like tiny greenhouses. The heat is then transferred to a collector medium where the solar system liquid receives it and carries the heat to the tank.
There are many ways for energy to be lost in this system, such as through the pipes as the heated liquid travels from the collector to the tank, and in the pump that must keep everything moving. Even the type of liquid that is used in the system can impact the overall efficiency. As for the efficiency of the panels themselves, both the flat panel and evacuated tube style collector tend to be between 60–80% efficient. Both can lose heat due to several factors, but the main one is the temperature of the outside air. There is some evidence that evacuated tube thermal solar panels are more efficient than flat panels, but they are also more likely to have failures and a shorter life expectancy. This tends to balance the overall monetary efficiency between the two types of panels.
Photovoltaic (PV) Solar Panels
In the same way that there are two primary types of thermal solar panels, there are two primary types of PV panels based on the material. These are Monocrystalline and Polycrystalline panels, which you can probably tell by the prefixes are differentiated by their crystalline structure. Both are made of silicon but polycrystalline panels have impurities that are almost non-existent in polycrystalline panels. This directly affects the efficiency of the panel, with monocrystalline panels being more efficient. Polycrystalline panels are around 13–16% efficient, while monocrystalline panels are around 15–20% efficient.
This seems like quite a major difference from the efficiency of solar thermal panels, but one needs to realize that they are producing two different types of energy. This also means we have a lot of room to improve PV panels and further drive down the price to make them more affordable. As an aside, the difference in efficiencies between these two types of panels can also translate to a size trade-off. Monocrystalline panels that have the same power ability as a polycrystalline panel are smaller because they do not need as much surface area to put out the same amount of output. This means if you have enough surface area you can go with the cheaper polycrystalline panels and disregard the lower efficiency.
To defend the efficiency of PV panels, 13–20% efficient panels can still be plenty to fully power a house in the right situation. To put this efficiency into perspective, power plants that run coal and fossil fuels only have efficiencies in the mid 30% range. The most efficient plants do not even get to 50% efficiency, so compared to these professional industrial operations, 13–20% efficiency in a home application starts to not look so bad. This is even better considering this power is being produced by a clean and passive method. For more on relative efficiencies, UCSD has published this article that explains expected efficiencies in a very relatable manner. All this is to say, don’t let the current efficiency numbers scare you away from installing a home solar system if it is something you are interested.
As with any energy-generating process, solar energy is not and will never be a 100% efficient process. It is important to know what you can expect to get in terms of efficiency out of your panels so you can properly plan your system and compare products when it comes time to make a purchase. This is an exciting time in solar power as we are starting to be able to improve the efficiency and size of panels at a more rapid pace every day. Even if you do not think the current systems are that energy efficient and can perform at the level you need, it will not be long before they get there—and ensure that you are constantly using renewable energy to reduce your carbon footprint!