Solar Water Heaters

Solar Water Heater System – how it can help save on electricity bills

Solar  and renewable energy are quite popular these days. Many people want to adopt these technologies but are unaware of what to do and how to get it. So we start with this article on Solar Water Heater systems, providing most of the details one can have questions on.

Using solar hot water is easily integrated into most people’s lifestyles. Once a system is installed and commissioned, it rarely takes any maintenance at all. The three main uses for SHW are:

Domestic hot water is perhaps the best known of solar water heating applications. Nearly every home uses hot water in India. This covers showers, dish washing, and clothes washing. Hot water is stored in a tank for when it is needed. An energy efficient household might use less than half of that amount.

solar water heater
solar water heater

What is solar water heater?

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.

Solar heaters, or solar thermal systems, provide environmentally friendly heat for household water, space heating, and swimming pools. The systems collect the sun’s energy to heat air or a fluid. The air or fluid then transfers solar heat directly or indirectly to your home, water, or pool. Solar water heaters, sometimes called solar domestic hot-water systems, may be a good investment for you and your family. Solar water heaters are cost effective for many applications over the life of the system. Although solar water heaters cost more initially than conventional water heaters, the fuel they use—sunshine—is free. Solar heating technologies can be used in any climate. To take advantage of solar energy


Different types of solar water heaters available in market

There are 2 types of solar water heaters that are available in Indian market:
  1. FPC (Flat Plate Collectors) system: These are metallic type systems and have a longer life.
  2. ETC (Evacuated Tube Collectors) system: These systems are made up of glass and are fragile.

Larger solar panels can also be arranged to provide some contribution to heating your home as well. However, the amount of heat provided is generally very small and it is not normally considered worthwhile.

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 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

  1. If you have ETC system then glass can break, as it is fragile. So the glass may need occasional replacement.
  2. Scaling happens on solar water heaters regularly especially if the water is hard. So the collectors need regular cleaning using acid.
  3. If the outside surface of water heater is painted, then it may need a repaint every 2-3 years to prevent corrosion.
  4. Occasional leakages could happen in the system and local plumbers can repair those.

Sizes of solar water heaters are available in the market

Solar water heaters available in market start from size of 100 ltr per day. The other sizes that are available are 200, 250, 300 and 500 lts per day. The maximum area required for the collectors to be installed on terrace/open area is:

The liter per day mentioned above is liters of hot water at (60-70oC). A 100 liters size is suitable for a family of 4. You can check more on sizing of water heaters in our article: Choose the right sized water heater/geyser for electricity saving.

Capacity (liters per day)

Area in sq. m. for ETC system

Area in sq. m. for FPC system

100

1.5

2

200

3

4

250

3.75

5

300

4.5

6

350

7.5

10

The units used for water heating depend on the amount of water that is heated, so the number of unit increases proportionately as the size increases. You can use our calculator to find out how much do you pay per unit of electricity to evaluate savings: Online Electricity Bill Calculator – For all states in India.

SWH systems are designed to deliver hot water for most of the year. However, in winter there sometimes may not be sufficient solar heat gain to deliver sufficient hot water. In this case an electric booster is used to heat the water.

Savings in annual maintenance of conventional (electric/gas/oil) water heating system
Estimates for individual households and regions. For instance payback period could easily be 7 years