Solar water heaters come in three basic designs, although all have a method of collecting heat, a tank to store hot water, backup heating when your system can't keep up, and some kind of circulation system.
Bulk collection water heaters heat the water in the tub or pipes, usually painted black to capture more of the sun's heat. To prevent the water from overheating, cold water can be added periodically. These heaters are best for warm climates. If freezing might be an issue, they will need to be drained during the colder months to avoid damaging the system.
Flat-plate collectors rely on metal plates, usually painted black, to absorb heat from the sun. Heat is transferred from the plates to the water-filled tubes. Water is circulated in and out of the storage tank through heating pipes, maintaining a hot water supply.
Evacuated tube collectors are currently the most efficient model. The water is heated in a tube surrounded by a larger vacuum-sealed glass tube. Since there is no air between the heated liquid and the outside world, very little heat is lost.
Solar water heaters can heat water directly or indirectly. In an indirect heater, the sun heats a heat transfer liquid (usually a mixture of water and propylene glycol), which then transfers the heat to the water in the tank. Since the freezing point of the heat transfer liquid is lower than that of water, it can operate in cooler climates.
Water needs to be circulated through the system so that warm water can be stored and new water heated. This happens in one of two ways. Passive systems rely on hot water rising and cold water sinking. The natural movement of water circulates the water through the system. Alternatively, the system can actively circulate the water using a pump.
buy solar water heater
Before you buy a solar water heater, you need to do some research.
First, your roof (where solar water heaters are most common) needs to be kept in good shape and get enough sunlight. If you need to replace the roof, do so first. Depending on the system, you can get by with more or less sunlight, but a recommended metric is at least six hours of sunlight on clear days throughout the year. Roofs facing directly south (in the northern hemisphere) are best, but the water heater can move 45 F in either direction and still perform well enough.
Second, like any bulk purchase, you should get multiple quotes. An installer with local knowledge can give you a better understanding of how your water heater will perform in your area's climate.
Are solar water heaters easy to use?
How quickly a solar water heater can pay for its energy savings depends on local energy costs, whether you're heating your water with gas or electricity, or even using hot water. (Moving showers, dishes, or laundry into the evening, when plenty of solar hot water is available, requires less backup energy than doing these things earlier in the day.) You can find detailed instructions for calculating the payback period , but replacing natural gas with solar water heaters will take longer to pay for itself than replacing electricity. If your hot water costs are high, you can recoup your bills in a few years, much faster than if a solar water heater ran for 20 years or more.
A more cost-effective way to get solar energy might be to run an electric water heater with solar panels that generate electricity on the roof. Solar panels are getting cheaper, and they can replace not only the electricity needed to heat water, but any of your other household electricity needs. Rooftop solar arrays are sized to meet the needs of an electric water heater, and depending on the efficiency of the water heater, only a slightly larger solar array may be required.