Can My Heating System Run with Solar Energy?
Heating systems are fundamental for homes and apartments during winter, and their operating costs can be high in the coldest months. However, there are many ways to use solar energy in space heating and domestic hot water applications, reducing your heating expenses.
- Unless you live in a remote location, electrical engineers will normally recommend a grid-tied solar power system.
- This improves reliability, and your appliances can rely on the power grid when solar panels are not productive.
The effectiveness of solar-powered heating will depend on the equipment used and its configuration. For example, an ENERGY STAR heat pump offers electricity savings of over 60% compared with a resistance heater. While a resistance heater can only deliver one kWh of heat for every kWh of electricity, a heat pump can produce 2-4 kWh of heat per kWh of electricity.
Save on heating costs during the winter months with solar power.
Even if your heating system uses a fuel like natural gas, propane or oil, it will have electrical components like air handlers or hydronic pumps. Solar panels cannot reduce the direct heating cost in these cases, but they can provide power for electrical components of the heating system.
Combining Solar Panels with Electric Heating Systems
Ideally, solar panels should be combined with a high-efficiency heat pump, since this maximizes the heating achieved per kilowatt-hour. A resistance heater converts electricity into heat less efficiently, which means two things:
- You will need more solar panels to offset your heating costs.
- You must rely more on local utility services, since solar energy is used less efficiently.
Assume you live in a city where the residential electricity tariff is 16 cents/kWh. If you consume 1,000 kWh with an electric resistance heater, you are billed 160 and you get 1,000 kWh of heat. However, a heat pump will produce over 2,500 kWh of heat for that same cost and consumption. This same heating output would have cost 400 with a resistance heater.
The same applies with solar panels: an output of 1,000 kWh only saves you 160 if you use an electric resistance heater, but your savings are increased to 400 when combining solar panels with an efficient heat pump.
What is a solar water heater?
Unlike traditional water heaters, solar water heaters don’t use energy from the grid to heat water. Instead, these high-efficiency appliances use dedicated solar collectors on your rooftop to draw power from the sun. The solar energy collected is then used to heat the water in your home.
Solar water heaters have been extremely popular in the past because they cut down your electric bill and allow you to heat up your water with clean energy. The solar collectors directly heat your water and do not provide any other solar energy to your home.
recently, people have been opting for electric heat pump water heaters, which are coupled with home solar panel systems. Electric heat pumps use grid energy to heat your water, however, when paired with a home solar system, they are able to still run on solar electricity.
If you aren’t able to install a full home solar system, or if you have an off-grid home, a standalone solar water heater can be a great option.
How do solar water heaters work?
Solar water heating systems can produce enough hot water to fulfill most of your daily domestic hot water needs.
There are two main types of solar water heaters available for residential and commercial use:
Each of these works differently and consists of different equipment.
Active solar water heaters
Active solar water heaters use a pump to circulate hot water from the solar collectors, or absorbers, to your home. These are usually installed in areas with colder climates, as the water gets stored in a tank that can be kept indoors to prevent freezing.
There are two different types of active solar water heaters:
- Active direct systems, where the water is heated directly in collectors and is then sent to your faucet and showerheads. The solar collectors are usually metal or glass tubes.
- Active indirect systems, in which a heat transfer fluid, like propylene glycol, is heated up within the solar collectors, and then transfers the heat to the water supply with a heat exchanger in a closed-loop system. Some heat loss occurs while the transfer fluid circulates the system.
Passive solar water heaters
Passive solar water heaters do not use circulating pumps to move hot water. Instead, they rely on convection as the circulation system, where hotter water rises to the surface and cold water sinks, in order to circulate water.
Passive solar water systems are usually cheaper than active ones, as they don’t require special equipment to pump the water.
There are two main types of passive solar water heaters:
- Integral collector solar water heaters are large, black water storage tanks that are built into an isolated box with a top that lets sunlight through. The sunlight heats the water directly in the black tanks, which then flows into your plumbing system when you need hot water.
- Passive thermosyphon systems use metal flat plate collectors to heat small batches of water on your roof. When you open your hot water valves, hot water in the top of the batch collector flows down from your roof to your faucets. These usually are designed to contain 40 gallons of water.
Many passive systems include a tankless heater as a backup energy source, which can either be gas or electric.
What are the most popular brands of solar water heaters?
As solar technology continues to find new applications in our daily lives, more companies are manufacturing solar heaters. These are some of the most popular models on the market today.
- Duda Diesel manufactures machinery that uses biodiesel and other alternative fuels. They offer a range of solar water heaters for residential and commercial use.
- Sunbank Solar produces collectors, pumps, plates, and other components for solar water heating systems.
- SunEarth offers a range of solar energy solutions for homes and businesses, including solar water heating systems and elements.
- Apricus and Rheem are two of the more popular solar water heaters.
How much you spend on a solar hot water heater depends on what kind of system and what size system you get.
Smaller passive solar water heater systems could cost around 3,000, while a larger active system could run you more than 10,000.
How to select the right solar water heater
Each type of solar water heating system works best in different environments.
- Direct systems work best in areas that don’t often see temperatures below freezing. In cold climates, indirect active systems are more resistant to freezing damage.
- Want your solar heating system to do double duty? Invest in an indirect circulating system. The heating fluid can be redirected to heat your swimming pool or spa in between working to supply your home with heated water.
- Families that use more warm water during daylight hours benefit from integral passive systems. By producing multiple small batches of warmed water, family members won’t have to worry about having enough hot water for morning showers.
- Have more roof than ground space? A thermosyphon solar water heater fits on your roof, which leaves you more space in your living area.
- Integral collector storage systems can weigh over 400 pounds, so you have to make sure your roof can support the weight of a heavy water tank.
You also have to consider how much sunlight your property receives, how much hot water you use on a daily basis, and your budget.
When shopping for solar water heater options, look for ratings from the Solar Rating and Certification Corporation (SRCC). SRCC ratings allow you to easily compare different brands and models using expert third-party data.
Every property is unique, so you should also seek expert guidance to ensure you choose the perfect system for your home. Talk to an installer in your area to learn more about suggested equipment for your project.
Find the best solar installer in your area
Solar Water Heaters: What You Should Know
Types, components, and pros and cons of solar water heaters.
Starre Vartan is an environmental and science journalist. She holds an MFA degree from Columbia University and Geology and English degrees from Syracuse University.
Using a solar water heater can save a household significant money and help reduce local and regional emissions that cause air pollution. Although they do require a higher initial cost for both the system and installation (compared to replacing an existing electric or gas-powered water heater), they will save 50% to 80% of the costs for heating water over time, according to the Department of Energy.
Depending on what system you buy, and how much hot water your household uses, this means they could pay for themselves in a couple of years. And you may also get a tax deduction for installing one.
What Is a Solar Water Heater?
Solar water heaters work by using the sun’s energy to either directly heat water that can then be used in the house for hot-water needs, or by using solar energy to heat another fluid that’s then used to heat the water. They can be active or passive, and all systems require a storage tank.
Solar water heaters can work in cold climates, less sunny places, and in a variety of conditions, though less effectively than in sunnier locales. But even if you live in a place where your solar water heater only preheats the water a little bit in winter, somewhat in fall and spring, and plenty on summer days, you will still save money and reduce emissions.
At night and on cloudy days, if you don’t have enough warm water stored, you will need an additional heating element to raise water temperatures. Most people with solar water heaters in mixed or seasonal climates use them in conjunction with an on-demand water heater to raise the water temps a little further. Since these devices are warming already warmed water, they work even faster and more efficiently than if they were heating cold water.
Usually, solar water heaters are placed on the roof, facing south, so they get the best quality direct sunlight. However, they can also be placed in a garden, meadow, or other areas where they receive direct sunlight.
Types of Solar Water Heaters
Active Solar Water Heaters
An active solar water heater can be direct or indirect. In the direct system, water is circulated via pumps through the solar collectors (usually on a roof) where it’s warmed by the sun and then sent to a well-insulated tank for storage. These are useful in climates where it rarely freezes.
An indirect active solar water heater uses a special non-freezing heat-transfer fluid that’s heated by the sun, which then warms stored water. These are useful in places where it freezes seasonally.
Passive Solar Water Heaters
Passive systems are simpler and cheaper than active systems, but less efficient. There are a couple of different kinds, with some using hot-cold water differentials to move water around rather than pumps. The other kind simply uses whatever heat energy is available from the sun to preheat water and then uses a traditional water heater to raise the temperature to what’s needed.
Parts of a Solar Water Heater
Every solar water heater must include at least two elements: a collector to gather the sun’s energy and a storage tank. After that, other parts of the system depend on the type of solar water heater being used.
Solar Collectors
The primary components of any solar water heating system are one or more collectors to trap the sun’s energy and a well-insulated storage tank. There are, of course, several types of solar water heating panels.
Flat plate collector panels have a glass or polymer cover with a dark plate underneath. As the sun shines on the panel, its heat is absorbed by the plate (and the dark piping that the water flows through) and transferred to the water.
Integral storage systems are black tanks filled with water that are kept inside a clear box that’s well-insulated. This system is often used to preheat water that’s then fully heated to desired temperatures for bathing or household chores by an additional system like a tankless water heater.
A third type, evacuated tube collectors, contain clear tubes with metal inside and are mostly used for commercial applications.
Storage Tanks
Solar water heater storage tanks can vary depending on the size of the home, the number of solar collectors, and the amount of hot water needed in the home. Typically, most systems have a large-capacity tank—80-gallons (or more)—which allows for warm water storage on overcast days. Some systems include two tanks, so there’s one for immediate use and another one just for storage.
Pros and Cons of Solar Water Heaters
- The significant energy savings means most households that have an appropriate setup or placement for a solar water heater will save money on their utility bills quickly.
- Homeowners aren’t subjected to price hikes for home heating oil or gas. Once a system is installed, it only requires maintenance (and electric or gas-burning water heaters need maintenance, too).
- They are relatively simple systems to install and maintain, compared to solar panels that generate electricity.
- In the summer season, solar thermal heaters generate a lot of energy—when you’re less likely to be taking a hot shower or bath—and storing that energy over a long period of time isn’t practical. (Compared to solar panels that generate electricity, which you can sell back to the power company in the summer months or use for air conditioning).
- Solar thermal systems are fairly simple, but they have pipes and pumps (for active systems), which can fail and take the whole system offline.
- It may be the case that with increasing efficiency, it makes more sense to use electricity-generating solar panels on your roof rather than using that space to heat hot water.
Solar water heaters do work in the winter, but they’re least efficient when the sun’s radiation is weakest. Short days reduce solar thermal input, and cold outdoor temperatures make it hard for water to remain hot. Most solar water heaters include freeze protection, which helps keep snow and ice from accumulating around them.
No electricity or electrical components are needed to run a solar water heater. Instead, these systems use solar collectors that draw energy directly from the sun.
Solar water heaters heat water during the day, when the sun is shining, and keep it hot in insulated tanks overnight. This could be difficult in frigid temperatures, but how well your solar water heater keeps water heated in the winter depends on the quality of the system.
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But it’s solar PV that has exploded into the global electricity sector, thanks to manufacturing innovations and strong government support. Leveraging economies of scale, the price of solar PV panels has dropped by over an order of magnitude in the past decade. In California, additional boosts came from government-instituted solar feed-in tariffs, cheap financing plans and private-sector investments. And, in a major coup for the industry, California mandated solar PV on new residences up to three stories starting 2020.
On the other hand, California’s residential solar water heater industry finds itself in a vicious cycle of low consumer demand and high prices. As the CSI-T report notes, “In contrast to conventional gas and electric water heaters, which are typically installed by plumbers, solar water heaters are installed by a range of firms and public entities.” In other words, consumers must actively seek out solar water heaters by relying on nonstandard sales channels.
This additional friction reduce s consumer demand among all but the most motivated consumers. leading to higher marketing costs that drive up the customer’s bottom line. in California are further exacerbated by past industry failures, which have led to strong, self-imposed regulations in the name of consumer satisfaction, says Murray. For example, after many cheaper solar water heating systems froze during the unprecedented 1990 freeze in California, only more expensive systems were allowed through the CSI-T program.
All told, the cost of the average solar water heater sold in California through the CSI-T program was US7,400, compared to less than US450,000 for a fossil fuel alternative. By contrast, a solar water heater in Israel can cost as little as US700.
Rather than embracing the growing portfolio of technologies available to solve the carbon emissions problem, going all-in on one satisfies the very human need for “magic bullets.”
Today, drumming up excitement for solar thermal remains difficult. According to CSI-T report interviews with solar water heater adopters, “Some interviewees remarked that it seemed tough to get others interested, theorizing that PV was so dominant in neighbors’ minds that solar water heating hardly registered.”
“It’s just the sizzling, sexy PV [that] really captivates the audience,” says Murray.
Portfolios, Not Magic Bullets
Entrepreneurs routinely caution, “Fall in love with the problem, not the solution.” In this case, the problem is carbon emissions, and, against entrepreneurial advice, individual governments have tended to fall in love with just one solution. For Israel, Cyprus, Hawaii and others, solar water heaters were that solution. For California, it’s solar PV.
By committing to a specific technology, governments fall prey to a conceptual error that science journalist Ed Yong recently referred to as a “ monogamy of solutions . ” (Interestingly, he argues this fallacy also shapes the government’s response to Covid-19.) Rather than embracing the growing portfolio of technologies available to solve the carbon emissions problem, going all-in on one satisfies the very human need for “magic bullets.”
Europe’s Green Deal may model such a “portfolio” approach for the rest of the world, according to Bärbel Epp, a German physicist-turned-journalist with nearly two decades of experience studying the global solar thermal market. According to Epp, representatives from the European solar thermal market have lobbied the European Commission for over a decade to use solar thermal technologies to decarbonize the heating sector. “It took [the solar thermal industry] I don’t know how many years, at least 10, of just continuously repeating the sentence that heat is 50% of our final energy consumption in Europe. … It was hard to lobby in Europe, but it’s now obvious that we have to do something for heat.” Whether these efforts will succeed in providing solar thermal a seat at the table remains to be seen.
To Grossman, solar water heaters are the first piece of Israel’s portfolio. As Israel struggles to meet its Paris Agreement goals, Grossman says he believes solar PV panels will take their place alongside solar water heaters on Israel’s rooftops.
Back in Sacramento, Murray is still battling for solar thermal. This year, he’s lobbied the California legislature to extend the state’s recently expired solar thermal subsidy program for one more year, citing Covid-19 as a barrier. The legislature hasn’t budged, but Murray vows he’ll keep going. He may be a lot older than he was in 1978, but the idealism is still alive.
Editor’s note: Dina Berenbaum and Manoshi Datta wrote this story as participants in the Ensia Mentor Program. The mentor for the project was Peter Fairley.