Solar water heater is a system that utilizes solar energy (or the energy from sunlight) to heat water. It has a system that is installed on a terrace or open space where it can get sunlight and the energy from the sun is then used to heat water and store it in an insulated tank. The system is not connected to electricity supply and thus does not have an on-off switch, but it uses the sunlight throughout the day to heat the water and store it in the storage tank. Water from the storage tank can then be used for any application as desired..
Different types of solar water heaters available in market
There are 2 types of solar water heaters that are available in Indian market:
FPC (Flat Plate Collectors) system: These are metallic type systems and have a longer life.
ETC (Evacuated Tube Collectors) system: These systems are made up of glass and are fragile.
Both these type of water heaters come with or without pump. Pump is used to move water from collectors to the storage tank. Those without pump use thermosyphon principle to move water from collectors to storage tank automatically.
How to decide on which type to buy
ETC systems are fragile but are cheaper. They are also very good for colder regions where the temperature is subzero. In place where the water is salty, these systems require regular cleaning due to deposition of salt on the inner surface of glass tubes.
FPC systems are long lasting, as they are metallic. But they are expensive than ETC systems. They can work in colder regions with subzero temperature but will need an anti-freeze solution making the system expensive. In places with salty water a heat exchanger is required with FPC system to avoid scale deposition that can impact the heating capability of the system. System without pump (thermosiphon) is ideal for domestic and small application users (as it is cheaper) provided water does not have high chlorine content. Those with pumps are good for industries.
How does the system perform on rainy/overcast days?
Many people have concerns that solar systems will not work on overcast days. Well a system can still work if the overcast is not long (less than a day or two) as the system works on diffused radiation in the atmosphere. A solar system can also be integrated with an existing electric system that can act as a backup during the days when the overcast is long. The electric system can switch on if the water temperature from the solar water heater goes down below 40oC. Electric backup is not required in solar system if you have an existing electric water heater. In case you do not have an existing water heater, you can install an electric backup. You can also keep the two systems separate and use the electric system only when needed.
Maintenance requirements of solar water heater
If you have ETC system then glass can break, as it is fragile. So the glass may need occasional replacement.
Scaling happens on solar water heaters regularly especially if the water is hard. So the collectors need regular cleaning using acid.
If the outside surface of water heater is painted, then it may need a repaint every 2-3 years to prevent corrosion.
Occasional leakages could happen in the system and local plumbers can repair those.