Solar water heaters vary in design, efficiency, capacity and price, but they all replace a good chunk of the gas or electricity used to heat water with clean, free sunlight. The three basic designs all have a way to collect heat, a tank to store hot water, backup heating for when your system can’t keep up and a circulation system.
Batch collector water heaters heat water in tubes or pipes, usually painted black to collect more of the sun’s heat. Cold water can be mixed in periodically to keep water from getting too hot. These heaters are best suited for warmer climates. Where freezing might be an issue, they’ll need to be drained during cold months to avoid damage to the system.
Flat-plate collectors rely on a metal plate, often painted black, to soak up the sun’s heat. Heat travels from the plate to water-filled tubes. The water cycles through heating tubes to and from the storage tank, keeping the stored water hot.
Evacuated tube collectors are the most efficient models out there. Water is heated in a tube that’s surrounded by a larger, vacuum-sealed glass tube. Very little heat is lost because there’s no air between the heating liquid and the outside world.
Solar water heaters can heat water directly or indirectly. In indirect heaters, the sun heats a heat transfer liquid (often a water and propylene glycol mixture), which transfers its heat to water in a tank. Because the freezing point of the heat transfer liquid is lower than that of water, the system can operate in colder climates. For example, evacuated tube collectors can work in temperatures as low as minus 40 degrees Fahrenheit.
Here are some steps before purchasing a solar water heater system.
- Assess your roof: Ensure your roof is in good condition and receives at least five hours of sunlight daily.
- Estimate the size of the heater needed: The size of your solar water heater depends on the number of people in your household and your location. Depending on how much sun you get, a 20-square-foot collector plate is recommended for two people, with an additional 8 to 14 square feet per person. The water tank should be 1.5 to 2 gallons per square foot of collector plate.
- estimate cost: Consider the system’s initial cost, the potential maintenance costs and the savings from the federal tax credit for solar water heaters.
When it comes to solar water heaters, there are two primary types: active solar water heating systems and passive solar water heating systems.
Active solar water heaters use a pump to circulate the heated liquid and can be divided into two types: direct and indirect circulating systems. Active solar water heating systems are generally more expensive.
- Direct circulating systems circulate water directly through solar collectors and are suitable for climates that don’t experience freezing temperatures.
- Indirect circulating systems circulate a non-freezing heat-transfer fluid through a heat exchanger that warms the water, making them ideal for environments prone to freezing.
Passive solar water heaters don’t have pumps to move hot and cold water around. They come in two distinct variations: integral collector-storage systems and thermosiphon systems. Passive solar water heaters are known for their reliability, cost-effectiveness and durability, but don’t allow for some of the finer control of active systems.
- Integral collector-storage systems heat water through a transparent cover on a storage tank from which water is drawn when a hot water tap is opened.
- Thermosiphon systems heat water in a collector on the roof and use the fact that warm water will rise and cold water will sink to keep a flow of cooler water in the path of the sun’s warming rays.
Like any technology, solar powered water heaters have pros and cons.
Pros
- Installing solar water heaters can help you save on your electric bill and reduce your reliance on municipal power for your hot water needs.
- By harnessing the sun’s energy, solar water heaters provide a sustainable energy solution that reduces your carbon footprint.
- Solar water heaters have a long lifespan and can last up to 20 years or more with proper maintenance.
Cons
- The upfront cost of installing a solar water heater can be high, although energy savings can offset this over time.
- Solar water heaters depend on sunlight to function. Cloudy or rainy weather may affect their performance, though pairing them with a conventional water heater can keep the hot water flowing even during a string of cloudy days.
- Solar water heaters need space on your home’s roof to install solar panels. Small homes or shared apartment buildings may not be suitable.
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