Solar Water Heaters
Solar water heaters — also called solar domestic hot water systems — can be a cost-effective way to generate hot water for your home. They can be used in any climate, and the fuel they use — sunshine — is free.
HOW THEY WORK
Solar water heating systems include storage tanks and solar collectors. There are two types of solar water heating systems: active, which have circulating pumps and controls, and passive, which don’t.
Active Solar Water Heating Systems
There are two types of active solar water heating systems:
- Direct circulation systems
Pumps circulate household water through the collectors and into the home. They work well in climates where it rarely freezes.
- Indirect circulation systems
Pumps circulate a non-freezing, heat-transfer fluid through the collectors and a heat exchanger. This heats the water that then flows into the home. They are popular in climates prone to freezing temperatures.
Passive Solar Water Heating Systems
Passive solar water heating systems are typically less expensive than active systems, but they’re usually not as efficient. However, passive systems can be more reliable and may last longer. There are two basic types of passive systems:
- Integral collector-storage passive systems
These work best in areas where temperatures rarely fall below freezing. They also work well in households with significant daytime and evening hot-water needs.
- Thermosyphon systems
Water flows through the system when warm water rises as cooler water sinks. The collector must be installed below the storage tank so that warm water will rise into the tank. These systems are reliable, but contractors must pay careful attention to the roof design because of the heavy storage tank. They are usually more expensive than integral collector-storage passive systems.
STORAGE TANKS AND SOLAR COLLECTORS
Most solar water heaters require a well-insulated storage tank. Solar storage tanks have an additional outlet and inlet connected to and from the collector. In two-tank systems, the solar water heater preheats water before it enters the conventional water heater. In one-tank systems, the back-up heater is combined with the solar storage in one tank.
Three types of solar collectors are used for residential applications:
- Flat-plate collector
Glazed flat-plate collectors are insulated, weatherproofed boxes that contain a dark absorber plate under one or more glass or plastic (polymer) covers. Unglazed flat-plate collectors — typically used for solar pool heating — have a dark absorber plate, made of metal or polymer, without a cover or enclosure.
- Integral collector-storage systems
Also known as ICS or batch systems, they feature one or more black tanks or tubes in an insulated, glazed box. Cold water first passes through the solar collector, which preheats the water. The water then continues on to the conventional backup water heater, providing a reliable source of hot water. They should be installed only in mild-freeze climates because the outdoor pipes could freeze in severe, cold weather.
- Evacuated-tube solar collectors
They feature parallel rows of transparent glass tubes. Each tube contains a glass outer tube and metal absorber tube attached to a fin. The fin’s coating absorbs solar energy but inhibits radiative heat loss. These collectors are used more frequently for U.S. commercial applications.
Solar water heating systems almost always require a backup system for cloudy days and times of increased demand. Conventional storage water heaters usually provide backup and may already be part of the solar system package. A backup system may also be part of the solar collector, such as rooftop tanks with thermosyphon systems. Since an integral-collector storage system already stores hot water in addition to collecting solar heat, it may be packaged with a tankless or demand-type water heater for backup.
SELECTING A SOLAR WATER HEATER
Before you purchase and install a solar water heating system, you want to do the following:
- Estimate the cost and energy efficiency of a solar water heating system
- Evaluate your site’s solar resource
- Determine the correct system size
- Investigate local codes, covenants, and regulations.
Also understand the various components needed for solar water heating systems, including the following:
- Heat exchangers for solar water heating systems
- Heat-transfer fluids for solar water heating systems
INSTALLING AND MAINTAINING THE SYSTEM
The proper installation of solar water heaters depends on many factors. These factors include solar resource, climate, local building code requirements, and safety issues; therefore, it’s best to have a qualified solar thermal systems contractor install your system.
After installation, properly maintaining your system will keep it running smoothly. Passive systems don’t require much maintenance. For active systems, discuss the maintenance requirements with your system provider, and consult the system’s owner’s manual. Plumbing and other conventional water heating components require the same maintenance as conventional systems. Glazing may need to be cleaned in dry climates where rainwater doesn’t provide a natural rinse.
Regular maintenance on simple systems can be as infrequent as every 3–5 years, preferably by a solar contractor. Systems with electrical components usually require a replacement part or two after 10 years. Learn more about solar water heating system maintenance and repair.
When screening potential contractors for installation and/or maintenance, ask the following questions:
- Does your company have experience installing and maintaining solar water heating systems?
Choose a company that has experience installing the type of system you want and servicing the applications you select.
- How many years of experience does your company have with solar heating installation and maintenance?
The more experience the better. Request a list of past customers who can provide references.
- Is your company licensed or certified?
Having a valid plumber’s and/or solar contractor’s license is required in some states. Contact your city and county for more information. Confirm licensing with your state’s contractor licensing board. The licensing board can also tell you about any complaints against state-licensed contractors.
IMPROVING ENERGY EFFICIENCY
After your water heater is properly installed and maintained, try some additional energy-saving strategies to help lower your water heating bills, especially if you require a back-up system. Some energy-saving devices and systems are more cost-effective to install with the water heater.
Best Solar Water Heater Systems
By reducing your reliance on the electrical grid, the industry’s best solar water heater systems can help you to save money and the environment. These innovative systems use thermal energy to heat water and can be used in lieu of traditional gas or electric hot water heaters.
They don’t require costly solar panels or overly technical installation and can be a great first purchase for homeowners looking to try out alternative energy.
Solar water heater systems come in a variety of shapes and sizes. Some can heat your shower to the perfect temperature while others can extend the swimming season by heating your pool. Whatever your needs and level of investment, there’s a solar water heater system out there for you.
6 Solar Water Heating Systems
Best Overall: Duda Solar 200L Active Split System
- Gallons: 53
- Type: Active (indirect)
- The High Points: Great for cold climates as it’s winter resistant.
- The Not-So: May not be great for those who travel frequently.
Duda is known in the solar water heating industry as being a reliable and high-quality brand. They are SRCC-certified and can be used for federal or state tax credits and exemptions, which is a great incentive for on-the-fence homeowners to commit to a solar water heating system.
The 200L Active Split System is great because it allows homeowners to heat their water on the roof or other sun-heavy location and store their water in a protected tank close to where it will be dispensed.
This prevents major heat loss by keeping the water warm even with the ambient air temperature is low. The system also utilizes a single copper heat exchanger coil that’s placed near the upper part of the tank to strategically heat the water as it’s being used, so the cold water at the bottom of the tank can be heated later.
What Do Reviewers Say?
Reviewers are generally happy with the efficiency of the Duda solar water heating system. Using the Duda 20 tube solar collection rack, homeowners have reported that they can heat water quickly with only a few hours of direct sunlight and partial shading.
Others have concerns about the rise in temperature that may occur when the homeowner is away from the system. The expansion tank regulates the excess hot water but it cannot withstand more than a few days. This may be a problem for those who travel frequently during the summer months.
Features & Considerations
Duda Diesel’s popular solar water heater comes in a variety of sizes, but the 200-liter (53 gallon) system is the best for residential use.
Its water tank rivals standard electric or natural gas systems but eliminates the need for costly energy consumption as it’s equipped with a solar water heater collector. The storage tank itself consists of food grade stainless steel.
It also includes an 8-liter expansion tank to help prevent failures in the system due to stagnation. This means your solar collectors won’t be damaged if the amount of solar energy exceeds the amount of water you’re heating at any given time. There’s also a thermostatic mixing valve to prevent scalding.
The solar collector is fitted with twenty 14mm solar tubes on a 45-degree stand, which can easily be exchanged for a 37-degree or slope roof stand if you plan on mounting it elsewhere.
The solar collector transfers the heat of the sun to your water pump through an indirect circulation system. The Duda kit includes the necessary two gallons of food-grade inhibited propylene glycol used in the process.
The kit also includes a solar water heater working station which regulates the split pressurized system by connecting the collectors, storage tanks, relays and sensors. It uses a circulation pump, pressure gauge, pressure relief valve and check valve.
Other safety systems include an automatic air vent for purging air from the top portion of the system, and a submersible water pump for the initial air purge and charging of fluid into the system.
Runner-Up: Sunbank 40 Gallon Solar Water Heater
- Gallons: 40
- Type: Passive (thermosyphon)
- The High Points: Requires virtually no maintenance.
- The Not-So: Not as efficient as an active system.
The Sunbank 40-gallon solar water heater is a no-frills integrated system that can be easily installed and maintained by any homeowner.
The passive water heating is great for small households living in mild climates that receive a lot of sunlight. With no-moving parts or extra pieces, the Sunbank system is a great starter kit for those who may be intimidated by more intricate and advanced solar heaters.
With a SRCC certification, the Sunbank is a cost-efficient way to cut down on expenses. Their affordable price point and 10-year warranty guarantee financial security. By using a passive solar system, homeowners can save as much as $600 per year in energy costs.
What Do Reviewers Say?
Most reviewers are pleased with their Sunbank systems as they are efficient and reliable. One reviewer even claimed that the water is too hot. In general, homeowners have been able to easily assemble and install the systems on their own.
However, several homeowners have purchased dual 40-gallon systems to increase the capacity of their hot water tanks as a single system is not enough to service an entire family.
When buyers had concerns about their water intake or configuration, the Sunbank staff were eager to assist and advice on the best setup. For those DIYers with a big household, a dual Sunbank system may be the best option.
Features & Considerations
The Sunbank system includes a tank, evacuated tube collectors and bracket. The 40-gallon tank is made with stainless steel.
The high-density polyurethane insulation also provides heat retention to prevent extra heat loss in low ambient temperatures. The size of the tank is adequate for small households of one to three people. Those with larger families may want to consider an 80-gallon tank instead.
Sunbank’s system is passive, rather than active, so it doesn’t require pumps, glycol heating fluid, or any moving parts. This makes installation much more convenient for novice plumbers or DIY homeowners.
Passive systems are also cheaper than their active counterparts and are a great “starting point” for those looking to enter the solar market.
Since the system doesn’t use pumps, it’s pressurized. The system relies on municipal or well water pressure to move the water in and out of the tank. Once a faucet is turned on, the cold water is pushed into the hot water tank, which then pushes the hot water to your faucet.
The 15 evacuated solar tube collectors are mounted on a corrosive resistant aluminum bracket. Each tube can collect 92-96% of the sun’s energy in prime conditions.
The tubes can be used as a pre-heater for an existing system or as a stand-alone unit. They are best suited for roofs that receive an adequate amount of sunlight.
Best for Camping: Sportneer Solar Shower Bag
- Gallons: 5
- Type: Panels
- The High Points: Allows for temperature control.
- The Not-So: Can only provide enough hot water for a few short showers.
As far as portable showering is concerned, Sportneer’s Solar Shower Bag ticks all the boxes. With a durable design and host of features, campers can now have a hot shower even in the wilderness. However, this bag is not a substitute for indoor showering or advanced solar water heating systems.
The design of the Sportneer is simple: a small, integrated solar panel heats up the water which is held in an insulated PVC bag. With a 5-gallon capacity, the bag can provide enough showers for a solo outdoorsman or a small crew. It also comes equipped with a temperature bar, shower head, storage pockets and a carrying case.
What Do Reviewers Say?
Buyers are pleased with the convenience the Sportneer Solar Shower Bag provides. They claim that it’s great for camping or outdoor activities as it’s portable and durable. One complaint that seems to be common among buyers is that the shower head is too small.
Some have tried unsuccessfully to use it as an at-home product, but it is not really a suitable alternative for a normal shower. However, some use it as a backup for power outages or other emergency situations.
Features & Considerations
The Sportneer Solar Shower Bag is the perfect accessory for avid campers. The bag is made of durable PVC material and comes with a hook for temporary installation on a tree, wall or car.
On the front of the bag are two net pockets that can be used to store bath products. It only weighs 1.2 pounds and can be easily rolled up and stowed in its mesh carrying case during outdoor excursions.
With a built-in solar panel, the shower bag can heat water in direct sunlight in as little as 3 hours. It includes a temperature indicator on the back so campers can add cool water if the bag exceeds comfortable levels. With a 5-gallon capacity, the bag can hold enough hot water to last a few short showers.
Attached to the bag is a shower hose with nozzle that simulates a real shower experience. The hose is connected to a water inlet with a sealed cap to prevent leakage. If the hose does manage to leak, the kit includes cable ties that can be used to prevent further leaks by closing off the connections.
Best for Swimming Pools: SunQuest 3-2X20 Solar Swimming Pool Heater
- Gallons: N/A
- Type: Flat-plate (unglazed)
- The High Points: Can raise the temperature of a swimming pool by up to 10 degrees.
- The Not-So: Can’t be used for residential purposes.
The SunQuest Solar Swimming Pool Heater is a great option for those with a pool at home. During off-seasons, like spring or fall, the SunQuest can keep your pool at a comfortable and ambient temperature. With a maximum 10 degree increase in temperature, you can swim at any time of year.
The system works by pumping the water through unglazed tubes that heat the water before it’s returned to the pool. It requires very little installation or maintenance and can be used for above or below ground pools. Even better, the sleek black heating pad won’t be an eyesore in the back garden.
What Do Reviewers Say?
Buyers are happy with the effectiveness of the heater. A standard pool pump works well with the system. However, the pool will not be very warm during cloudy days or cool nights.
One note is that a pool skimmer will not work properly when you use both at once. It’s a good idea to use a diverter valve to bypass the heater while the filtration system is operating. Overall, the system is a great value and can help to extend swimming season for the family.
Features & Considerations
The SunQuest system is unique in that it heats both in-ground and above-ground pools through an integrated unit. It works with the pool’s pump to push water through the heated coils and back into the pool, raising the temperature by up to 10 degrees.
It’s a very cost-effective way of extending the swimming season when spring or fall temperatures drop below comfortable levels.
The kit comes with two 2 by 20-ft. panels that you can simply place on the ground or a rack near the pool. The system is UV protected and won’t be damaged by the sun. It also comes with a “MAX-FLOW” design that improves the water circulation.
You will need to purchase additional piping to complete the installation. This will connect from your pool to the heating pads. The system comes with standard connectors to attach to flexible or rigid pipes and hoses.