Can you run a water heater on solar power?
Solar water heaters can be more efficient than traditional electricity (and can reduce fuel consumption by up to 70%). For this reason, they’re fairly popular in other parts of the world — Cyprus and Israel, for instance, have solar hot water mandates, with 90% of homes using solar heating systems — and they’re slowly taking hold in the U.S.
If you're considering a solar water heater, be sure to have your roof inspected by a qualified professional to make sure it can handle the weight of the system.”
These systems do have a few unique requirements, though. Most notably, your roof needs an abundance of sunlight throughout the day. This means you’ll need a large, unshaded area that faces either south, southeast, southwest or west. For optimal performance and to ensure your investment is as safe as possible, your roof should also be relatively new and built with durable materials, such as asphalt.
“If you're considering a solar water heater, be sure to have your roof inspected by a qualified professional to make sure it can handle the weight of the system,” said Alan Duncan, the founder of Solar Panels Network USA, a company that helps educate individuals on renewable energy installations.
To help determine whether your home can handle a solar water heater, review the U.S. Department of Energy’s guide for siting a solar water heating system.
Types of solar water heating systems
Homeowners can choose from active or passive solar water heaters. Active solar water heaters have several components that help move water through a system — and thus have a more complex installation. Passive systems don’t use any sort of water-moving technology and have a less complex and expensive installation.
Active solar water heaters
Active solar water heaters use pumps and controllers to move water or heat-transfer fluid between the solar panels and a storage tank. This makes them more efficient and reliable than passive systems, albeit more expensive. They’re ideal for homes or businesses that need steady hot water or larger volumes. Benefits include faster heating, consistent supply, and flexible installation, making them a good choice for anyone looking for dependable solar water heating.
Passive solar water heaters
Passive solar water heaters use gravity or natural convection to circulate water between the collector and storage tank, so no pumps or controllers are needed. Their simple design makes them reliable, low-maintenance, and durable. They work best in sunny areas and for homes with modest hot water needs. Advantages include lower upfront costs, energy savings, and straightforward installation.
What is an integral collector storage (ICS) system?
An ICS system is a simple type of passive solar water heater that collects and stores cold city water in a tank. Three sides of the tank are insulated, and one side is glazed. The glazed side faces the sun and collects the heat; the sun’s rays pass through this side to heat the water inside. These are best for warm or hot climates because heat can easily be lost through the large plate.
(A thermosyphon system) relies on the fact that hot water rises and cold water falls, so no external pump is needed to move the heated water around.”
What is a thermosyphon water heater?
A thermosyphon water heater is a type of passive solar water heater that separates the collector and the storage tank. With this system, the storage tank is located higher up than the collector, with gravity pushing colder water into the collector and warm water rising by convection to the storage tank.
“(A thermosyphon system) relies on the fact that hot water rises and cold water falls, so no external pump is needed to move the heated water around. This makes thermosyphon systems a very efficient way to heat your home's water supply using renewable energy sources,” said Ryan Collier, director of Heat Pump Source, a company that works with heating installation and repair in London.
Breakdown of solar water heater components
Understanding a solar water heater’s main components is helpful when buying or maintaining your system. Each part plays a role in capturing sunlight, transferring heat, and keeping your water reliably warm.
Collectors
These panels capture sunlight and turn it into heat. Flat-plate and evacuated-tube collectors are common, and efficiency depends on size, angle, and sun exposure.
Heat transfer fluid
Usually water or a water-antifreeze mix, this fluid moves heat from the collector to the storage tank. Active systems use pumps, while passive systems rely on natural convection.
Storage tank
The tank stores hot water until you need it. Well-insulated tanks keep water warm for hours, even after sunset. Some tanks sit separately, while others are integrated with the collector.
Controller
Found in active systems, controllers monitor temperatures and regulate pumps to keep the system running efficiently and prevent overheating or freezing.
Backup heater
Electric or gas backup heaters ensure hot water is available when sunlight is limited, such as at night or on cloudy days.
Valves
Valves control flow, prevent backflow, and allow maintenance. Check valves, mixing valves, and pressure relief valves are all critical for safety.
Insulation
Pipes and tanks are insulated to prevent heat loss, boosting efficiency and reducing energy costs.
Piping
Durable pipes, usually copper or PEX, connect the system. Proper installation ensures reliability and prevents leaks.
Sensors
Sensors track temperatures in the collector and tank, sending data to the controller to optimize performance and protect the system.
Do solar water heaters work in winter?
If you live in an area with long winters, your home may not be the best candidate for a solar water heater, especially if you already have budget concerns. This is also true for homes in foggy or rainy climates (like in the Pacific Northwest). Without a significant amount of direct sunlight, solar water heaters aren't as effective.
If you do opt for solar in these climates, you should install a backup water heater that can pick up the slack during the colder months.
What are the disadvantages of a solar water heater?
While solar water heaters can save some homeowners big money long-term, there are some downsides to purchasing and installing these machines. For starters, they’re expensive, usually costing somewhere between $2,000 and $6,000 to install (compared with $1,000 to $3,000 for a traditional water heater). Solar installation may be eligible for certain tax incentives, however.
You can expect to spend from $2,000 to $6,000 upfront on a solar hot water system.
Solar water heaters also require more maintenance, including annual pump and antifreeze checks and regular scaling prevention efforts. For some, like a reviewer from Arizona on our site, the added cost and headache of maintenance can be too much to handle.
“I had solar years ago in California,” he said. “I had one for my water heater and it never worked. … I said I'd never do solar again.”
Depending on the size of your household and your habits, a solar water heater also might not be suited to your needs. If you have a house full of people who regularly shower at night, for example, it might not make sense — these heaters create energy during the day, when the sun is out, and store whatever is left, which means nighttime hot water usage should be kept to a minimum.
Solar water heaters vs. home solar systems
You can also heat your water with a traditional photovoltaic home solar system. Rooftop solar panels convert sunlight into energy, which you could then use to run a water heater. Home solar systems are relatively inefficient when it comes to powering water heaters, though, because traditional heaters require so much electricity. A total home solar system is also significantly more costly.
» LEARN: How do solar panels work?
Solar water heaters, on the other hand, only have one job, which makes them more efficient and cost-effective for heating a home’s water supply. Plus, they require much less rooftop room than a full home solar system.
That said, if you already have plans to install a home solar system, it could be worth testing powering your electric water heater with the solar energy your system creates. If you’re only hoping to cut down your hot water costs, however, a solar water heater is a much smarter investment.
» MORE: How much do solar panels cost?
FAQ
Are solar water heaters worth it?
Solar water heaters are worth it if you live in a sunny climate and your house faces adequate sunlight. Though they cost more upfront than traditional water heaters, they typically pay for themselves within a few years through lower energy bills and tax incentives. They’re also an eco-friendly way to reduce reliance on traditional power sources.
How does a solar water heater work at night?
At night, water heaters don’t generate heat,but they store hot water in insulated tanks for later use. Many systems also include an electric or gas backup to keep water warm when sunlight isn’t available. This ensures steady hot water even after dark or on cloudy days.
How to check if a solar water heater is working?
To see if a solar water heater is working, start by checking if the water is noticeably warmer than usual during sunny hours. Inspect the panels for dirt, damage, or shading that could reduce performance. You can also check any system gauges or indicators to make sure water is circulating properly.
Article sources
ConsumerAffairs writers primarily rely on government data, industry experts and original research from other reputable publications to inform their work. Specific sources for this article include:
- Project Drawdown, “Solar Hot Water.” Accessed June 1, 2022.
- U.S. Department of Energy, “Estimating the Cost and Energy Efficiency of a Solar Water Heater.” Accessed June 1, 2022.
- National Renewable Energy Laboratory, “Solar Water Heating.” Accessed June 1, 2022.
- U.S. Department of Energy, “Solar Water Heaters.” Accessed June 7, 2022.
- Energy Star, “Federal Tax Credits: Solar Energy Systems.” Accessed June 7, 2022.
