Solar Hot Water for Your Home
posted in Home Solar Power |To create hot water using solar thermal energy, the sun’s heat is used to heat water directly without converting it into electricity. The most common use of solar hot water in North America is heating swimming pools, but solar thermal’s potential goes far beyond this.
Solar thermal is commonly used for water heating and for heating houses. The cost of heating by a solar thermal system is usually lower than the cost of an equivalent amount of electricity supplied by photovoltaics because solar thermal is on average 3x more efficient at converting the sun’s heat into energy, although the savings depend on the type of solar thermal technology used. Solar thermal systems are also low maintenance.
Types of Solar Water Heater
1) Collector (solar hot water panel) Types
There are three main collector types: flat plate, batch, and evacuated tube. Evacuated tube technology is generally more expensive than flat plate and batch because it is mechanically more complicated.
2) System Type: Passive or Active
Active systems include a pump; passive systems do not. Passive systems are less expensive and may be more reliable but are less efficient (Energy Savers: Solar Water Heaters).
Passive Solar Water Heating
Batch Heater
A batch heater is the simplest type of solar water heater available. They are also sometimes known as breadbox heaters, since the tank of water on the roof is often about the size of a breadbox. If you wish to build your own solar hot water system, a batch heater is probably your best bet. Being water-based, they are not suitable for winter use in climates where freezing weather can be expected. They also have the disadvantage that hot water cools overnight and usually isn’t hot early in the morning. The Florida Solar Energy Center has a free set of plans and instructions for building one, which can be found here. They give the materials cost as being US $70.00.
Thermosyphon
This design tends to be more expensive than batch heaters. However, because there is an insulated storage tank hot water is available at all times of the day or night, unlike the batch filter. This design is actually the world’s most popular solar water heater (Homepower.com). It may be closed loop or open loop. If it is a closed loop system, glycol can be used. This modified design is suitable for using in climates with freezing temperatures.
Active Solar Water Heating
Drainback Heater
This type of heater is more complex, being a closed loop system where the water in the collector does not mix with the house’s water. A heat exchanger is used to move the heat from the liquid in the collector to the house’s water. Like most active systems, it is more expensive than a batch heater. On the other hand, this system can be used in the winter in climates with freezing temperatures if the pipes are adequately sloped to ensure drainback occurs quickly.
Glycol-based Solar Thermal Systems
Systems containing glycol are primarily used in areas which have freezing temperatures during winter. This is because they continue to work and provide hot water during such weather, unlike most systems that use water. Water-based systems may also suffer damage when the collectors freeze that will then need to be repaired. Glycol-based systems are more expensive than systems that use water, but in a cold climate this disadvantage is outweighed by their resistance to freezing (Homepower.com).
Overall, solar thermal hot water is a technology that is economical to install and run by renewable energy standards and can be used almost anywhere. It has excellent potential for home use and should be perhaps the first alternative energy technology considered by a homeowner wanting to reduce dependence on the electricity grid.
Sources:
Build Your Own Solar Batch Water Heater. Florida Solar Energy Center Retrieved June 12, 2009.
http://www.builditsolar.com/Projects/WaterHeating/FSECFS36Batch11349.pdf
US Department of Energy. Energy Efficiency and Renewable Energy. Energy Savers:Solar Water Heaters. Retrieved June 12 2009
http://www.energysavers.gov/your_home/water_heating/index.cfm/mytopic=12850
Homepower.com
http://www.homepower.com/basics/hotwater/