Solar Water Heater System – Comprehensive report and Buyer’s guide

What is a solar water heater system? After talking about a Gas geyser and an Electric geyser, I am excited to introduce you to the grand benefits of a Solar water heater system / Solar geyser. If you want to go with an electric geyser instead, read about the top 10 best geyser in India here.

This report aims at providing comprehensive information about the solar water heater system. Right from its types; parts; working ; price etc. to a useful buyer’s guide that enables you to select the right solar water heater for your home. To begin with, let’s start with the answer to the question that we saw at the very beginning- what is a solar water heater system?

solar water heater system
Solar Water Heater System

A solar water heater system is a water heating device that works on the principle of heating water by absorbing energy from the sun’s rays. 

These geysers also come equipped with an electrical heating element to facilitate heating the water with electricity. The heating element provision proves helpful in lousy weather when there isn’t enough sunshine to heat the water by radiation. But when operating through sun rays, a solar water heater system turns to be the cheapest way to get hot water in a large quantity compared to an electric geyser or gas geyser. A solar geyser can raise the temperature of cold water to 100deg centigrade or even more than that, depending on which type of solar water heater system you are using.

Solar Water Heater Geyser
Solar Water Heater Geyser

Hot water for use in the bathroom or kitchen is usually found satisfactory at a temperature of 65 deg centigrade. In India, many solar geyser manufacturers claim that a solar geyser takes about 5-6 hours of a sunny day to give hot water with a 65 deg centigrade temperature. It means if you fill up your solar geyser at 9:30 am, you can get the hot water to the desired temperature, as stated above, by 3:30 pm. You can store this water and use it in the morning with a slight temperature drop. The temperature dropped in the night is usually small. The extent of temperature drop depends on the coldness during the night hours and the insulation thickness of your solar water heater/ geyser storage tank. So, the buyer should check the manufacturer’s insulation thickness before buying a solar water heater/ geyser. There are other factors to check before buying a solar geyser, which we will discuss later in the article.

Types of a Solar Water heater/ Geyser?

Solar geysers are available in two types.

  1. Natural circulation thermosyphon Solar water heater system – In this system, heat transfer occurs on natural convection; water transfer from the collector to the storage tank takes place without any external aid. The hot water, due to its lightweight, rise above the cold water and is obtained at the user end.
Natural circulation thermosyphon system
Natural circulation thermosyphon system
  1. Force Circulation solar water heater system– In this type, the hot water gets transferred to the storage tank using a mechanical pump. A controller governs the pump operation. It powers the pump on, only after the water in the collector attains a specific preset temperature.
Forced circulation  solar water heater system
Forced circulation solar water heater system

Based on the method of heating, solar geysers are available in two types:

  1. Direct heating Solar geyser: Direct heating solar geysers are best suited if you stay in a moderate temperature region i.e., where the temperature does not fall below 4 deg centigrade or if the water you use is not hard. Coldwater gets heated by direct sunlight falling on the collectors. The hot water rises above the cold water for its property and available for use at the faucet.
  2. Indirect Heating Solar geyser: In contrary to the above, if you are using hard water, or if you stay in a region where the temperature falls below 4 deg centigrade and the water freezes. It would be best if you used indirect heating solar geysers. An anti-freezing liquid or distilled water is circulated through the collectors, which collects heat from the sun, moves to the heat exchanger in the storage tank, and heats the water. This system is more efficient but is expensive as it has a heat exchanger also. The user has to top up the anti-freezing liquid at regular intervals as it gets evaporated.

Parts of a solar water heater system

A solar system has three main parts:

  1. The storage tank– The storage tank collects water from the primary storage tank of the house by gravity. It comes in different materials like SS( Stainless steel), Glass-line, Mild steel, Galvanized Iron. You need to select the tank according to the nature of water ( how hard the inlet water is?) you are using. The outside of the storage tank comes covered with insulation. The insulating method can be of PUF (Polyurethane foam) or Glass-wool/Rock-wool. Most manufacturers provide a 50 mm thick insulation. The outermost part of the tank is G.I Sheet covering painted with enamels to fight rust.
  2. The collector– The collector is the part where water absorbs sun rays and gets heated. 

The collectors come in two types:

  • The Evacuated Tube Collector (ETC), and
  • The Flat Plate Collector (FPC)

Let’s understand them briefly.

ETC ( Evacuated tube collector)

ET Collectors consist of the glass tube in which the water circulates and gets heated by solar energy. The length of glass tubes varies according to the manufacturer’s product standard. It is available from 1.8 Meters long to 2.1 meters long. It is named “Evacuated Tube” because it consists of two glass tubes, One inside the other and sealed at the open end. The space between the tubes is free of any air. This evacuation increases its efficiency as it’s emission loss becomes low. The inner tube is silicone coated to maximize heat-absorbing capacity. In case of breakage, the user can replace the broken tube with a new one. The installation of this collector is straightforward, and even a single person can do that.

Solar water heater system ET Collector
Evacuated tube collector

 FPC (Flat Plate Collector)

This collector comes in a framed structure, insulated from all other sides except the top one. The top of this collector has a flat transparent glass, mounted above a plate to which copper or aluminum tubes are connected. The space between the glass and plate has a vacuum to maximize heat absorption. Water flows through the tubes and gets heated by conduction. There are two header type pipes attached at the top and bottom of the collector; one for inlet water and the other for outlet water. The hot water rises for its property into the tank in a thermosyphon system, whereas transferred through a pump, as explained in the solar geyser’s forced circulation type.

Solar water Heater system
Flat Plate Collector
  1. The structural frame – The structural frame is made of MS angle or can be of MS channels. Whatever be the material of construction, the frame comes galvanized and enamel painted to fight rust and corrosion. The load on the structure has a uniform distribution. A user must ensure good quality of frame structure to withstand the high-speed winds and rains.

Apart from these three, a solar geyser has two more important parts, which a buyer should check before buying a solar geyser.

  1.  Heating element– Heating element is provided as an option to heat the water electrically. It proves very useful in bad weather when there is no sunshine. The heating element provided for electrical heating of water comes along with a thermostat. The thermostat helps set a preset temperature at which it will cut off the power to the heating element and avoid the condition in which the hot water turns into steam and develops pressure inside the tank. Another recommendation is to check if the geyser has this heating element installed in it. Also, it will be much safer f your geyser has two thermostats, One automatic and One manual rest based. You can refer to our article on the electric geyser, which explains in detail the function of two thermostats.
  1. Sacrificial Anode– Sacrificial anode plays a vital role in the safety of the storage tank. It absorbs hard water particles, thereby avoiding their attack on the body of the container. Due to the attack of hard water particles, these anodes sacrifice themselves and need to be replaced at regular intervals.

What is the difference between Evacuated tube collector (ETC) and Flat plate collector (FPC)- ETC Vs FPC

  • An evacuated tube collector (ETC) has a broader crossectional area, so the heat-absorbing capacity increases. It raises the temperature of water fast as compared to FPC.
  • The heating extent is greater for ETC than to FPC. An ET Collector can heat the water to 100 deg centigrade. In contrast, the FPC is useful if you want temperature up to 70 – 80 deg centigrade.
  • The maintenance of ET collectors is not much complicated. You can clean the scales, due to hard water, inside the tube whereas, any such maintenance is challenging in FPC.
  • The installation is straightforward for ET collectors; a single person can do it. FPC collectors are massive and need a team to install in a safe/secure manner.
  • ETC gives better performance in freezing conditions than FPC because their emissive losses are low.

solar water heater working principle

Solar water heater working
Solar water heater working

Solar water heaters/geysers have collectors (ETC/FPC) that absorb the sun’s rays and make the water hot. The hot water, being lighter in weight, rises above the cold water and moves to the storage tank. The hot water in the storage tank moves out through the outlet pipe to the user’s end. The heat transfer in these geysers occurs through natural convection. The hot water transfer from the collector to the storage tank can be natural (as in the Thermosyphon system) or a forced transfer (as in forced circulation system), depending upon the type of solar water heater system you are using.

Solar Water Heater Price in India

If we talk of the solar water heater price in India- it is high compared to an Electric geyser or a gas geyser. But when it comes to using a water heater for an extended period- the merits of a solar water heater system in terms of savings, the volume of water, etc., outperforms the other formats of heating the water. 

Its initial purchase price in India starts from 15,000 INR and goes in lakhs. The cost varies as to the type and the storage capacity that you choose to buy. The storage tanks with capacity from 100 Litre to 1000 liter are available in the market. A tank with a capacity above 1000 liter can also be made available by placing an order to the manufacturer.

How hard water affects the life of a storage tank?

As we know, hard water contains lots of dissolved solids; these dissolved solids form scale on the body of the storage tank, creating corrosion and developing leakages in the tank. Hence, the user should check the hardness of inlet water and choose the storage tank’s materials accordingly.

The scale formation also reduces the efficiency of the collector, and the user should clean the collector tubes periodically. However, cleaning of tubes is only possible with ETC as they come with a larger diameter. The FPC comes with small dia tubes that are challenging to clean, and hence the FPC system is not recommended for use with hard water.

Benefits of using Solar water heater/ Geyser?

A solar geyser requires little maintenance as compared to an electric geyser or a gas geyser. Also, the nature of maintenance is quite simple. You do not have to change or replace a part frequently unless it suffers some physical damage.

This geyser is very cost-effective and safe when compared to an Electric geyser or a Gas geyser, and gives you good saving after some years. Most manufacturers claim to recover these geysers’ purchase cost in three to four years or even less than that, depending on how long in a year you use this geyser. You can check an estimated saving calculation here.

Can we get hot water in the morning from a solar Water heater/ Geyser?

There have been questions on the availability of hot water in the morning from a solar geyser. A solar geyser can give hot water in the morning. The temperature of hot water may fall to some extent depending upon the outside temperature in the night and the thickness of insulation used around the storage tank. Still, it remains hot enough to use in the morning for bathing or washing need.

How much you save using a solar Water heater/ Geyser?

As we have discussed in the article above, a differential temperature of 40 deg centigrade makes the water suitable for use in the winter season. The saving depends on the quantity of water heated. 

For illustration, let us suppose that you are using a 150 ltr capacity solar geyser, and you raised the temperature by 40 deg centigrade. It means you used 150x 40= 6000 kcal to heat the water. If we relate it with KWh, It will become around five (05) units of electricity. Now for one month, it becomes 5x 30 = 150 Units. If you use it for six (06) months in a year (say from mid-October to mid-March), you save 150 x 6 =900 Units of electricity in India. In this way, the total cost of your solar geyser can be recovered in 4-5 years. Rest after that period; it’s an overall gain for you.

What should you check before buying a solar Water heater/ Geyser?

Buying a geyser may be an easy idea, but selecting which one to buy is something that swallows your time and energy. Here are some points a buyer, we recommend, should check before finalizing one.

  • The first question to answer is- what is the storage tank capacity you should choose? The answer depends on your family size or the volume of water you need to meet your daily needs. The government has set some guidelines according to which 25 liters of water per person are enough to meet his/her daily needs. You can make a similar assumption to select a tank capacity you need.
  • The second point to consider should be the climatic condition in your region. As guided in the article above, you can select a geyser that best suits your area’s weather.
  • The third point to consider is what hotness of water you need. You can select an ETC or an FPC collector accordingly. Please refer to the collector sections to understand the suitability in detail.

Other checks a buyer should look out for are:

  1. Check the insulation thickness around the storage tank.
  2. Choose a geyser according to the hardness of the water in your area.
  3. Check for the presence of an electrical heating option in the geyser.
  4. Ensure that the mounting structures are capable enough to withstand high-speed wind or rain and the system does not topple down.


With the information about solar water heater system above, it is obvious that a solar water heater system is useful and economical when the volume requirement of hot water is large; or at places where the electricity reach is not consistent.

The space requirement for installing a solar water heater system may further be a reason to abort the decision to purchase it.

But if the conditions are favorable and the volume requirement of hot water is enormous- one should prefer a solar water heater/ geyser to an Electric Geyser or a Gas Geyser.

Thanks for reading the article. You may please leave your comment, suggestion, or queries in the comment section below. We will try answering your queries in a possible early time.

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