How Do Solar Water Heating Systems Work?

Solar water heating systems collect the heat from the sun with the use of solar collectors. Collectors are generally fitted to the roof (pitched or flat), where they receive the most sunlight. They can also be mounted at ground level or even on a south facing wall, but the best option will always be the location where the collectors are most exposed to the sun. An immersion heater or a boiler can be used as an additional option to increase the temperature of the water when necessary.

There are two types of solar thermal collectors, which mainly differ on their aesthetics but have a very similar performance: flat plate collectors and evacuated tubes.The first type consists of hot water solar panels with a flat glazing which are mounted on a roof and the evacuated tubes consist of several “vacuum tubes” fixed into a manifold mounted onto a roof.

Apart from the collector, you need to route highly insulated pipes from the collectors to a hot water cylinder (either existent, or a new one). Cold water from the bottom of this cylinder is then pumped through the collector, which heats the water and then sends it to the top of the hot water store.

Application of Solar Water Heating System:

  • Solar Water Heating System can heat the water up to 80˚C.
  • Solar water heaters (SWHS) of 100-500 liters capacity are suited for domestic application.
  • Larger systems (above 500 LPD) can be used in restaurants, canteens, guest houses, hotels, hospitals, dairies, industry etc.

 Benefits of Solar Water Heaters

Using solar powered hot water in your home has many benefits. We listed a few of those below.

  • Solar hot water heaters provide hot water all throughout the year.
  • It reduces the utility bills as it can provide a third of your hot water needs.
  • It reduces your carbon footprint by saving between 230 kg and 510 kg of carbon dioxide (CO2) every year.
  • Contrary to other renewable energy solutions, solar water heating has low maintenance costs and high durability, proven by their average warranty of five to ten years.
  • Solar water heating uses the sun’s heat, so once you have covered the initial costs of investing in an installation, there are very little additional costs, besides the amount of electricity needed to run the pump powering the system.
  • The solar thermal system works together with your existing heating or hot water boiler, or even with heat pumps and biomass.
  • Solar water heating is eligible for regular Renewable Heat Incentive earnings for producing energy from renewable resources.

Choose a Solar Water Heating System

Mainly two types of solar collectors are used for residential applications:

Flat-Plate Collector (FPC)

The solar radiation is absorbed by Flat Plate Collectors which consist of an insulated outer metallic box covered on the top with glass sheet. Inside there are blackened metallic absorber (selectively coated) sheets with built in
channels or riser tubes to carry water. The absorber absorbs the solar radiation and transfers the heat to the flowing water.

  • Save up to 70% on your Electricity Bill
  • Eco Friendly, No carbon foot print
  • Low Maintenance with compare to ETC
  • Scale Guard for hard water and best suitable for pressure pump type.
  • Extended life of more than 20 years
  • One time Investment, Lifelong Benefit

Evacuated-Tube Collectors (ETC)

Evacuated Tube Collector is made of double layer borosilicate glass tubes evacuated for providing insulation. The outer wall of the inner tube is coated with selective absorbing material. This helps absorption of solar radiation
and transfers the heat to the water which flows through the inner tube.

  • Capture sunlight better as they have a greater surface area exposed to the sun at any time
  • Are more efficient in transferring heat – up to 163% demonstrated in Indian conditions
  • Can be used in subzero temperatures
  • Are durable and if a tube should be broken, it can be easily and cheaply replaced.
  • Provide excellent performance in overcast conditions
  • Require a smaller roof area than comparable flat plate collectors
  • Do not have the same level of corrosion problems as flat plate collectors

When choosing your solar water heating system, you should consider the following factors to optimise your purchase:

  • That your roof faces the south. Or be sure that you select the best location in your house to fit the solar water heating collectors, which will guarantee their maximum efficiency.
  • That you have the necessary area of south-facing roof available. In the case of flat plate collectors, you will need approximately one square meter of collector area per person living in the building. This is enough to heat up between 30 and 60 litres of water.
  • It is a good idea to have an Energy Performance survey carried out to check if you are maximising the energy use. If you don’t, you should make the necessary changes before installing the solar water heating system and applying for the FiT, which will guarantee a better FiT rate as well.

Maintenance of a Solar Water Heating System

Unlike the initial solar water heating systems cost, the maintenance costs are usually low. As already mentioned, a typical solar water heating comes with a five to ten-year warranty. Once you have installed solar heating panels on your roof, you will not deal with any additional costs.

However, it is important to note that you need to have periodical maintenance checks to make sure that your solar hot water system is working properly. You should have your solar water heating system checked by a professional installer every three to seven years, which is a sufficient time span for the anti-freeze to be checked, topped up, or maybe even replaced to avoid any possible leaks.

Savings on Solar Water Heating

Since there are different types of systems you can choose from, it is hard to estimate the exact solar water heating panels prices. A domestic 100 LPD solar water heater system will generally cost around ₹20,000 and ₹50,000 depending on the features of the system. If you decide to buy solar water heater you could save yourself a great deal on your monthly energy bill.

Cost benefits of SWHS:

  • The most cost- effective way to install a SWHS is to integrate the collector assembly, cold-water supply and piping with the design of a new house under construction. SWHS can easily be installed in group houses and apartments, especially during construction, if adequate provisions are made for piping, collector assembly and cold-water supply. Proper load matching is required to ensure that the capacity of the system installed is optimized to meet the daily hot - water needs of the end-user.
  • Fuel Savings: A 100 liters capacity SWHS can replace an electric geyser for residential use and saves 1500 units of electricity annually.
  • Avoided utility cost on generation: The use of 1000 SWHS of 100 liters capacity each can contribute to a peak load shaving of 1 MW.
  • Environmental benefits: A SWHS of 100 liters capacity can prevent emission of 1.5 tones of carbon-dioxide per year.
  • Life : 15-20 years
  • Approximate cost: Around ₹24,000 (SWHS using Flat Plat Collector) and ₹18,500 (SWHS using Evacuated Tube Collector) for a 100 liters capacity SWHS. ₹110-150 per Liter for higher capacity systems.
  • Payback period:
    • 3-4 years when electricity is replaced.
    • 4-5 years when furnace oil is replaced.
    • 6-7 years when coal is replaced.

Though the initial investment for a solar water heater is high compared to available conventional alternatives, the return on investment has become increasingly attractive with the increase in prices of conventional energy. The pay back period depends on the site of installation, utilization pattern and fuel replaced.