Solar water heating

Figure 1. A solar water heater.[1]

Solar water heating or SWH is the process of converting sunlight into energy that can then be used for domestic water heating. This heated water can be used for washing in the home, radiant floor heating, or to heat swimming pools.[2]

Solar water heating systems use a large number of different technologies and these technologies can be used almost anywhere in the world. Each of these systems include two main components - storage tanks and solar collectors. Additionally, there are two main types of solar water heating systems: active systems with circulating pumps and passive systems without pumps.[3]

Currently, China is the world leader in solar water heating technologies, with more than half of the 100 GW of solar water heating capacity occurring in that country.[4]

Types of Systems

Generally speaking, solar water heating systems are composed of two main pieces: storage tanks and solar collectors. The collectors serve the purpose of collecting and retaining heat from the Sun. Once the collectors capture the energy from the Sun, this heat is transferred to a liquid known as the heat transfer fluid. If this fluid is water it takes the heat from the collector and moves the warm water for use or storage. However if this fluid is not water, heat exchangers are used to transfer the heat from the heat exchange fluid to a home's water supply.[5] Pumps are sometimes used in active heating systems to control what temperature the water gets to and how quickly it moves.

Passive

Passive solar water heating, in general, is less expensive than active solar water heating as it does not require a pump. Additionally, this makes maintenance of the system easier. However, they are usually less efficient although they may last longer. The two main types of passive water heating systems are:[3]

  • Integral Collector-Storage Systems: These types of systems work better in areas that rarely fall below freezing, or in households with significant daytime or evening hot water needs. These systems include one or more black tanks in an insulated box. Cold water passes through the solar collector, heating the water. The slightly warm water then moves to a backup water heater, providing a reliable source of hot water. These are used in areas that do not freeze as sub-zero temperatures could result in the pipes freezing.
  • Thermosyphon Systems: Fluid movement in this system occurs when warm water rises and cool water sinks. When the water is heated, hot water flows into the storage tank. These are usually more expensive as roof design must be taken into account because of the heavy storage tank.

Active

There are two distinct types of active solar water heating systems that utilize pumps. They are:

  • Direct circulation systems: In these systems, pumps circulate water through collectors and into the home. These systems work well in climates where it doesn't reach freezing temperatures or else the water could freeze and break the system.
  • Indirect circulation systems: These systems pump a non-freezing heat-transfer fluid through collectors and into a heat exchanger. This heats the water that then flows into the home. They are popular in climates prone to freezing temperatures as the fluid will not freeze and break the system.

Benefits

Using the energy from the Sun to heat water can save homeowners significant amounts of money in the long run. If solar is used to replace all or part of the heating in a home, there are significant savings on the homes energy bill. Although solar-electric is popular, it does not save as much money as compared to the investment as solar water heating. Savings for solar water heating can be as high as 50%-100% of a homeowners bill.[6] As well, the original investment can be returned in as little as three years, although five years tends to be the average payback time. This depends largely on how much the Sun shines where the collector is located. As well, the use of these solar water heaters can result in provincial, state, or federal tax credits or utility rebates.[6]

The fact that energy used is reduced with the use of solar water heaters is also beneficial to the environment. Currently, most energy people use comes from burning a variety of fossil fuels. This combustion of fossil fuel resources is associated with a wide array of environmental impacts including climate change, acid rain, and global warming associated with carbon dioxide emissions.[6] The use of solar water heating reduces energy use from these fossil fuel sources, benefiting the environment in the long run.

References

  1. Wikimedia Commons. (August 17, 2015). Solar Water Heater [Online]. Available: https://upload.wikimedia.org/wikipedia/commons/5/5e/Solar_water_heater.jpg
  2. CANSIA. (August 17, 2015). What is Solar Water Heating [Online]. Available: http://www.cansia.ca/solar-energy-101/what-solar-water-heating
  3. 3.0 3.1 Energy.gov. (August 17, 2015). Solar Water Heaters [Online]. Available: http://energy.gov/energysaver/articles/solar-water-heaters
  4. David JC MacKay. (August 17, 2015).Sustainable Energy - Without the Hot Air, 1st ed. Cambridge, England:UIT Cambridge Ltd, 2009
  5. Home Power. (August 17, 2015). What is Solar Water Heating? [Online]. Available: http://www.homepower.com/articles/solar-water-heating/basics/what-solar-water-heating
  6. 6.0 6.1 6.2 Home Power. (August 17, 2015). Why Use Solar Water Heating? [Online]. Available: http://www.homepower.com/articles/solar-water-heating/basics/why-use-solar-water-heating

Authors and Editors

Jordan Hanania, Kailyn Stenhouse, Jason Donev