Solar Water Heating
With the average household spending a quarter of it's home energy costs on water heating it makes economical sense to consider running costs when purchasing a new system for heating your water.
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Solar water heaters are not only environmentally friendly they can be cost efficient over the life of the unit with the savings made from the conservative use of power. The heated water is stored in a tank akin to the conventional tank we are used to. It uses the sun's energy to heat the water directly or a heat transfer fluid like water glycol antifreeze. You will require a regular backup system in most climates but the system's effectiveness is also influenced by the temperature of the water that feeds into the system. Paradoxically the colder the water the more efficiently the system will operate. |
There are ways of assisting the effectiveness of the system by making your home itself more energy efficient. Insulate piping and setting the thermostat on the water heater to around 120°F (49°C) will help, as will flow restriction devises on your taps and showerheads.
Have your local solar heater merchant do a solar site analysis to ensure you have a site suitable to house the system and that the position you choose does not contravene any local ordinance.
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A flat-plate collector is the most common of three types of collectors. It is a weatherproof and insulated box that has a dark absorber plate under at least one see-through cover. Another collector is the evacuated-tube, which is made up of rows of parallel glass tubes. The tubes consist of a glass outer tube and an inner tube covered with a special coating that absorbs solar energy while inhibiting radiative heat loss. The system forms a vacuum by withdrawing air from the space between the tubes thus eliminating conductive and convective heat loss. The third collector is the concentrating collector. |
These are usually parabolic troughs using mirrored surfaces to focus the energy from the sun onto an absorber tube. Containing a heat-transfer fluid. The absorber tube is sometimes called a receiver.
A sound insulated storage tank is mandatory for most commercially available solar water heaters. A system may use converted electric water heater tanks or run the solar storage tank in sequence with the conventional water heater. They may also use pumps to recirculate warm water from storage tanks through collectors and exposed piping which protects the pipes from freezing when outside temperatures drop below freezing point.
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Solar water heaters can be either active or passive. An active system uses electric pumps, valves, and controllers to circulate water or other heat-transfer fluids through the collectors and a passive system does not have a pump. Because their storage tanks do not need to be installed close to or above the collector, an active system is usually easier to retrofit. They are more efficient than passive systems but are also more costly and usually more expensive than passive systems but because they use electricity, they will not function in a power outage. Passive systems do not use electricity and are generally more reliable as they have no electric components to ware out or break. |
They move household
water or a heat-transfer fluid through the system without pumps so they
will still operate in a power outage.
Plumbing
The temperature of the water from a PSWH depends on many variables. The amount of sunshine, ambient air temperature, the amount of insulation used, the temperature of the supply water as well as the hot water demand all effect outlet temperature. Under ideal weather conditions, and no hot water used since morning, the water temperature at 5 pm can exceed 180 degrees F. You may consider installing a tempering valve which allows you to set the temperature for the water before it reaches the faucet.
How much of your hot water demand will be met by your PSWH varies depending on a number of factors. Have you installed low-flow shower heads and aerators? Have you installed a water heater blanket and set the thermostat to 120 degrees F? When do you use the most hot water? If you normally wash clothes/shower etc. in the evening, there probably won't be any solar water in the morning. If someone is normally home during the day and clothes washing is scheduled for around solar noon, you can stretch your solar water. After normal water use in the am, the sun heats the water all morning and then that water is used for the laundry (if necessary). This schedule allows time for the water to heat up again during the afternoon.