Solar thermal systems, or active solar systems, have taken a back seat to solar PV technology in most building applications. As the price of solar technology drops lower and lower, however, home and business owners are investigating solar thermal systems as a way to supplement or replace their current heating and hot water systems.
Given that space heating accounts for the biggest chunk of the energy we use in our homes (35-50 percent in the U.S., according to the Center for Climate and Energy Solutions), it makes a lot of sense to explore renewable energy for residential heating. Given that the second largest use of energy is hot water heating, at 18%, the potential to offset energy costs through solar thermal becomes enormous.
Let’s explore whether that potential could pay off for you.
First Off, How Do Solar Thermal Systems Work?
Unlike solar PV systems, which convert solar radiation into electricity, solar thermal technology turns that radiation directly into heat.
It does this by using solar collectors. Solar collectors are flat plates or vacuum tubes that contain pipes filled with a transfer medium. The collectors absorb energy from available sunlight and use it to heat the medium. The heat can be distributed immediately through pumps or fans, or it can be stored for later use.
Liquid Heating Systems
Liquid systems (i.e. systems that uses a boiler, or radiant heating), pump a transfer fluid through pipes to a heat exchanger inside a storage tank. The fluid heats the water in the tank before being pumped back up to the solar collector for reheating. In radiant floor systems, the heat from the transfer fluid can also be stored in the floor slab.
Systems feature a controller that activates the pump when the temperature in the tank drops to a certain degree below the temperature in the collectors.
Forced Air and Other Heating Systems
Forced-air heating systems can also work with solar thermal. That’s true for new builds and also for retrofits. In these systems, a liquid to air heat exchanger transfers heat to the air as it returns to the furnace.
Solar air heating systems can also be used for space heating. These systems use air as a transfer medium. Air is less efficient, and it’s much more difficult to capture heat from to store it, though. So at this point, these systems are typically used just for room heating.
Solar air collectors feature a dark-coloured, glazed metal plate that absorbs heat from the sun. A fan moves air from the room into the collector, where the plate heats it. The heated air is then moved back into the room. Larger air collectors for multiple rooms will use ducts to transfer the air to the collector and back.
How Much Energy Do They Save?
The amount of energy a system will save is variable. Savings depend on factors such as location, the energy source being replaced and the efficiency of the building. Just to name a few. Here, however, are some ballpark figures.
Natural Resources Canada estimates that a “typical solar hot water system will reduce annual energy costs by 40 to 50 percent. You can expect that a solar water heater will provide you with 1500 to 3000 kWh of energy per year, depending on your hot water usage and regional climate.”
According to the U.S. Department of Energy, solar water heaters can slash your water heating bill 50-80%. Ecohome tells us that a solar thermal system can provide “60% or more of your heating and hot water in the winter and almost all your hot water needs in the summer.”
How Much Does a Solar Thermal System Cost?
Costs, too, will depend on a variety of factors, including the size and type of system you purchase. The smallest-scale units can be very cheap. Energy.gov says that a “simple window air heater collector can be made for a few hundred dollars” if you DIY it.
Again, to ballpark, the U.S. Renewable Energy Hub estimates a price tag “between $2,500 for a pool solar heater and from $7,700 for full solar thermal installations.” For our British friends, that’s between £3,000 and £6,000, including installation for a solar thermal hot water system, according to The Renewable Energy Hub U.K.
David Dodge and Dylan Thompson at Canada’s Pembina Institute state that it costs “$8,000-$10,000 to install a solar hot water system in a home, but expanding on this basic system can cost as little as another $5,000-$6,000 to turn your hot water system into a home heating and hot water system.”
The upfront costs of a solar thermal system also depend on the renewable energy incentives available in your area. Many levels of government in many countries offer rebates, grants, loans and other incentives for renewable energy projects.
If you’re considering this type of renewable energy system, find out about the grants that are available to you.
Solar thermal collectors are efficient—much more efficient than solar PV panels (70% efficient, compared to an average of 12% for solar panels). Since they’re more efficient, they can also take up less space on your roof than solar panels. With these additional advantages, solar thermal could become more popular as the price of the technology drops and energy storage becomes more innovative.
If your hot water needs (and bills) are high, however, or if you’re looking for ways to decarbonize your fuel source, the existing technology could make a real dent in the fossil fuels you consume every month. If not replace them completely.