Solar water heaters are a clean and lucrative source of energy, since they collect energy from sunlight and use it to heat water for showers or swimming pools. As compared with Tesla’s solar tiles, they use less space and can be more efficient and cheaper. This is especially true if water heating is your main concern (e.g. having a swimming pool at home). The information provided in the infographic and below can help you determine the system most suitable in your home.
Normally, solar thermal water heaters can be classified into either active or passive systems, as diagrammed in the infographic above.
Passive systems are normally cheaper than actives ones since they don’t have pumps. They are not as efficient as active ones but might last longer. They have 2 basic types:
- Integral Collector-Storage Passive Systems. Cold water pass through collector directly and then to backup heater or storage tank. They meet with the need of large hot-water supply but is prone to freezing in cold climates.
- Thermosyphon Systems. Collector installed below storage tank so hot water would rise to storage tank automatically. Expensive but reliable. They are very heavy thus require very solid roof.
Active systems have 2 basic types as well:
- Direct Circulation Systems. Pumps circulate household water through the collector then back home. They work great but might freeze in cold climates.
- Indirect Circulation Systems. Pumps circulate non-freezing, heat-transfer fluid through collector then to heat exchanger, where the fluid transfer the heat to household water loop. Popular in areas with freezing climates.
Most solar thermal water heater systems have solar collector and storage tanks. There are 3 types of solar collectors commonly used:
- Flat-plate collectors. Frequently used in active systems for shower needs or solar pool heating.
- Integral collector-storage system. Also called batch collectors. They are very reliable and frequently used in passive systems, but cannot be used in severe cold weather.
- Evacuated-tube solar collectors. Most frequently used for U.S. commercial applications.
For more detailed information about solar thermal water heaters, please refer to this link: https://energy.gov/energysaver/solar-water-heaters
There is also a newly developed type of solar collector, which is the cylindrical solar collector. According to published scientific research (Madani, 2006), this type of solar collector has similar efficiency as compared with flat-plate collectors while using significantly less space on the roof. The research also suggested that this type of solar collector is economically cost effective as compared with flat-plate collectors. Below is a photo example of this type of collector in the article. (Madani, 2006)
credit to Madani, 2006For detailed information about cylindrical solar water heaters, please refer to: Madani, H., (2006). The performance of a cylindrical solar water heater. Renewable Energy 31(11), 1571-1763.
There is also a newer type of water heater called PV water heaters, since it utilizes solar electric (PV) technology. This type of water heaters collects energy from sunlight and transform the energy into electricity to heat water directly or to power air-to-water heat pumps. The advantages and disadvantages of PV water heaters are listed in the infographic.
For more detailed comparison between solar thermal water heaters and PV water heaters, please refer to: http://www.renewableenergyworld.com/articles/2013/09/solar-hot-water-which-is-better-pv-or-thermal.html