Solar water heating systems are one of the most cost-effective solutions to generate hot water for your home. Solar hot water systems can be used in any climate and since the fuel they use comes from the sun, the energy used to heat your water is absolutely free. Solar water heating uses the sun to heat either water or a heat-transfer fluid in the collector and the heated water is then held in the storage tank ready for use.
Heating water represents the biggest energy use in your home and unlike traditional solar photovoltaic (PV) panels, solar thermal panels are less expensive, which means that you will get your return on investment much more quickly with solar water heating.
Solar Water Heating Systems
With the installation of a solar water heating system, you will lessen your family's environmental impact through reducing carbon emissions, by reducing the amount of fossil fuels needed to be burned to supply electricity to do the same thing solar water heating does. You will also save money on a monthly basis with the free hot water generated by the sun. The best part of a solar hot water system is that it's relative simplicity and durability.
Solar hot water systems have two main parts, the first being a solar collector and the second being a storage tank. There are three types of solar collectors available, the most common collector used in solar hot water systems is the flat-plate collector, the other options include evacuated-tube solar collectors and integral collector-storage systems. Solar water heating works by using solar collectors that are installed on the roof of your home, which heats the water in the collector and then once heated, the water is stored in a well insulated storage tank.
Solar water heating works by using a process called thermo-siphoning which continuously cycles the water to keep it hot and can save the average household up to 75% of their hot water energy requirements. Since hot water rises naturally in the tank, it remains at the top of thank to be made available to the house when needed through either a gravity feed or a pump. The colder water stays at the bottom of the storage tank and travels back into the collector to be reheated in a continuous cycle to keep hot water available. Solar water heating systems can be either active or passive, with the most common being active systems.
Solar water heating systems almost always require a backup system for cloudy days and times of increased hot water use. Conventional storage water heaters usually provide backup and may can be part of the solar system package you purchase. 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 conventional backup water heater.
Active Solar Water Heating
Active solar water heating systems rely on the use of electric pumps and controllers to circulate water, or other heat-transfer fluids through the collectors. There are three types of active solar water heating systems available, which are:
Direct-circulation systems use pumps to circulate pressurized water directly through the collectors and into the home. These systems are more suited in areas that do not freeze for long periods and do not have hard or acidic water.
Indirect-circulation systems pump a non-freezing, heat-transfer fluid through collectors and a heat exchanger. Heat exchangers transfer the heat from the fluid to the water. Some indirect systems have "overheat protection," which is a means to protect the collector and the glycol fluid from becoming super-heated when the load is low and the intensity of incoming solar radiation is high.
Drainback systems are a type of indirect system which use pumps to circulate water through the collectors. The water in the collector loop drains into a reservoir tank when the pumps stop. This makes drainback systems a good choice in colder climates. Drainback systems must be carefully installed to assure that the piping always slopes downward, so that the water will completely drain from the piping.
Passive Solar Water Heating
Passive solar water heating systems are typically less expensive than active systems, but they are usually not as efficient. Passive solar hot water heaters rely on gravity and the tendency for water to naturally circulate as it is heated. Because they contain no electrical components, passive systems are generally more reliable, easier to maintain, and possibly have a longer work life than active systems. The two basic types of passive systems are:
Integral-collector storage systems consist of one or more storage tanks placed in an insulated box with a glazed side facing the sun. These solar collectors are suited for areas where temperatures rarely go below freezing. They are also good in households with significant daytime and evening hot-water needs. They however, do not work well in households with predominantly morning draws because they lose most of the collected energy overnight.
Thermosyphon systems are a more economical and reliable choice, especially in new homes. These systems rely on the natural convection of warm water rising to circulate water through the collectors and to the tank which is located above the collector. As water in the solar collector heats, it becomes lighter and rises naturally into the tank. The cooler water naturally flows down the pipes to the bottom of the collector, enhancing the circulation. Though the tank is normally placed on the roof, it can be placed in the attic of the home to conceal it from view. With the use of a glycol fluid in the collector loop, indirect thermosyphons can be installed in freeze-prone climates if the piping in the unconditioned space is adequately protected.
