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Frequently Asked Questions - Solar Water Heater FAQs

What are the benefits of using a solar water heater?

A solar water heater is a technically proven and commercially viable solution to meeting the daily hot water needs of a residential household. It offers the following benefits:

      • Availability of hot water throughout the year 

With a solar water heater you are assured of reliable hot water supply throughout the year and these systems if properly installed & maintained have a lifespan of 15 years and more. With the abundant supply of sunshine throughout India (most parts of India have on an average 300 sunny days per year), these systems can meet your daily hot water needs on most days and even on cloudy days there is usually enough radiant heat available to provide you warm water. 

      • Significant savings on water heating costs 

An average household with an electric water heater spends about 25% of energy costs on heating water and the use of a solar water heater has the potential to reduce this cost annually by about 50% to 85%. The smallest solar water heating system with a capacity of 100 lpd (litres per day) can replace a 2 kW electric geyzer and save upto 1500 units of electricity per year

      • It’s also an environmentally friendly option

Reduce your hot water carbon footprint: Each unit of electricity consumed by an electric water geyzer leads to an effective coal consumption of 1.5Kg at the power plant used to produce this electricity. A 100lpd solar water heater thus offsets an equivalent coal burning of about 1500 Kgs per year.

Saves water: Each unit of electricity produced at a power plant consumes on an average 3 litres of water for cooling purposes. Thus a 100 lpd solar water heater can also save around 4500 litres of water every year.

      • They are reliable 

As long as the sun is shining, hot water will continue to flow through your pipe & plumbing fixtures. The reliability of solar water heaters is further enhanced by the fact that there are no moving parts and the system is very easy to maintain, requiring no more care than a standard water heating system. Most of the solar systems available today simply require an annual checkup and a system flush to ensure that the system stays operational. Further, warranties are available from manufacturers for the entire system and for the individual parts (tank and the collector).

How does a solar water heater work?

A solar water heater uses heat energy available from the sun to heat water. The basic configuration of solar water heaters used in residential applications consists of:

  • A solar collector that absorbs the sun’s heat energy and transfers the heat absorbed to a working fluid. Collector technologies are of two types: Flat Plate Collectors (FPC) and Evacuated Tube Collectors (ETC) 
  • A means of transferring the heat energy absorbed by the working fluid to the water that needs to be heated. 
  • An insulated water tank that stores the water heated for future use
What are the different type of solar water heater technologies available?

Solar water heaters differ in terms of the collector technologies used and the design & construction of the system to suit specific applications.

Classification based on Type of Collector:

Basic solar water heaters are of two types depending upon the collector technology used: Flat Plate Collector (FPC) type and Evacuated Tube Collector (ETC) type.

  • Flat Plate Collector (FPC) based solar water heater


Fig1: FPC Solar Water Heater System                                                                         Fig2: Flat Plate Collector


Operating Principle: (refer Fig 1) Cold water enters the storage tank, fills it up and then flows to the collector through the bottom header and into the riser tubes, until all the absorber tubes and the header at the top are full. When the sun shines, the heat energy is absorbed by the absorber and transferred to the water in the riser tubes. The heated water being lighter than the cold water rises and via the top header pipe flows into the storage tank. More cold water flows into the collector, gets heated and rises to the top, and so on. This process known as the “Thermosyphon process” continues until the temperature of the water in the storage tank and the collector equalizes. Hot water is stored in the insulated storage tank and is available for use as and when required.

The Flat Plate Collector (refer Fig 2) consists of an insulated metallic box covered on the top with toughened glass. The metallic box contains an absorber sheet (normally made of copper) that is coated with a selective coating to increase the absorption of solar energy. Vertical tubes made of copper, known as riser tubes are attached to the absorber and carry the water to be heated. The riser tubes are connected to two horizontal tubes called headers, one placed at the bottom and the other at the top. The bottom header is used for flow of water into the collector whereas the top header is used to take out the heated water.

  •  Evacuated Tube Collector (ETC) based solar water heater


Fig3: ETC Solar Water Heater System                                                     Fig4: Evacuated Tube Collector


The Evacuated Tube Collector (ref Fig. 4) consists of two co-axial glass tubes fused at both ends with air between the tubes evacuated to create vacuum that works as insulation. The outer surface of the inner tube forms the collector area and it is selectively coated to increase the absorption of solar energy.

Operating Principle: (ref Fig. 3) Cold water enters the storage tank, fills it up and then flows into the individual tubes until all the tubes are full. When the sun shines, the heat energy is absorbed and transferred to the water in the inner tube. The heated water being lighter than the cold water rises and flows into the storage tank. More cold water flows into the collector, gets heated and rises to the top, and so on. This process known as the “Thermosyphon process” continues until the temperature of the water in the storage tank and the tube equalizes. Hot water is stored in the insulated storage tank and is available for use as and when required.     

In addition, in both these types of technologies variants are available that suit specific applications:

Classification based on Type of Application:

  • Normal systems: These systems are the basic models (available in both ETC & FPC type systems) and are used when the water hardness is typically below 200ppm & the system is operating under atmospheric pressure (i.e. there are no pressure pumps being used to pump water out of the storage water tank). ETC type Collector based systems, because of the collector design can typically withstand water hardness upto 600ppm, compared to the FPC type collector where due to water flowing through the narrow copper tubes the collector is able to withstand water hardness upto only 200ppm (water with higher hardness levels would lead to quicker clogging of the tubes).
  • Pressurized systems: These systems can withstand the higher operating pressure that exists due to the use of a pressure pump in the water circulation system. Pressurized systems are suitable when:
    • The height of the overhead tank carrying cold water is less than 7 ft above the terrace
    • High pressure hot water flow is required for various uses like jet showers, shower panels etc
      • The number of hot water points are more than normal

The pressure rating of these types of systems varies from 3 bar upto 8 bar.

  • Heat-exchanger type systems: This type of system is used in cases where there is  hard water or where the ambient temperatures are low enough to cause water freezing. In such cases, distilled water is used as the heat transfer medium and is circulated in a closed loop system through the solar fins or tubes and goes back into the top of the outer tank where it transfers its heat to the cold water in the inner tank.   

The water hardness tolerance level for the different type of systems varies from 600ppm to 1200ppm.

Optional features

The following optional features are available with all kinds of water heaters:

  • Electrical back-up heater: Most solar water heaters come with the provision of an electrical back-up heater that can be used to heat water on cloudy days when enough sunshine is not available to heat the water to the desired temperature.
  • Sacrificial anode: The sacrificial anode rod made of Aluminium/Magnesium is screwed to the storage tank and protects the tank against galvanic corrosion. For long life of the storage water tank it is advisable to replace the anode rod from time to time. Magnesium anodes are in general preferable to Aluminium anodes as they provide better protection to the tank. 
What is the maximum temperature the water will be heated to?

Solar water heaters depending upon the technology and efficiency heat the water up to 60 to 80 degrees.

Which type of solar water heater is better, FPC or ETC?

The choice of an FPC or ETC type of solar water heater depends upon the location, seasons and other external factors.

In general, FPC type solar water heaters have better performance in hot climatic conditions whereas ETC type solar water heaters perform better in cold climatic conditions. A detailed comparison between the two technologies in the context of providing domestic water heating is as below:


Comparison between FPC & ETC type solar water heaters

Heat generation

ETC has better heat generation in colder climates and under cloudy/low sunlight conditions

Heat insulation

ETC has lower heat loss at night as the vacuum inside the tubes offers better insulation

Pressure endurance

In case of non-pressurized systems, FPC can withstand higher pressure compared to ETC

Water hardness

In case of non-heat exchanger type systems, scaling due to hard water leads to a higher loss in efficiency in case of FPC compared to ETC


FPC systems can last for 15 years or more without major maintenance whereas ETC systems can last for 5 years or more without major maintenance.

Operations & Maintenance

  • The tubes in case of ETC are prone to breakage and in case of breakage of one of the tubes the entire system gets drained and hence is not usable. However, the cost of replacement in case of ETC is lower as the broken tube can be replaced whereas in case of FPC the entire glass needs to be replaced
  • Corrosion is not an issue in case of ETC as it is made of glass
  • ETC systems cannot be exposed to solar radiation when there is no water inside the tubes as thermal shock could lead to cracking of the tubes



Does the solar water heating system work on cloudy days?

Yes the system works on cloudy days as even under cloudy conditions there is usually some radiant heat available to heat water though this to a lesser extent compared to a sunny day. An optional back-up heater is normally provided in most systems so that it can be used to further heat this water to the required temperature.

What is the life of the solar water heating system?

Good quality solar water heaters are generally expected to last around 15 years or more and FPC type systems are in general more durable than ETC type systems. If the system is maintained properly and water quality is not a problem the systems can actually last for upto 30 years and there are already a few installations in India that have been operating for so long.

What are the regular maintenance requirements?

The surface of the collector must be periodically cleaned to remove dust from the top surface to get optimum output from the system. Occasional observation of the solar water heating system to eliminate any plumbing leakages may help. The exposed metal surfaces may be examined for any damage to paint etc after monsoon period to avoid further damage. Some rubber or plastic components may not last beyond 10 years and may require replacement. The back-up water heater might not last through the life of the solar water heater and will require replacement.

What are the guarantees on solar water heating systems?

All solar water heating system are guaranteed by manufacturers for one year. Some manufacturers provide guarantee of 5 years also. A large number of installers take annual maintenance contracts for larger systems for a fee, on mutually agreed terms.

What are the certifications available for solar water heaters sold in India?

The Bureau of Indian Standards (BIS) specifies the standards for solar collectors for certified products in India. In addition, the Ministry of New and Renewable Energy (MNRE) has certified the performance of all products sold by certified manufacturers and provided a rating for approved manufacturers.

All products sold on Glowship are from MNRE approved manufacturers with the solar collectors conforming to BIS standards. The rating provided by MNRE to each manufacturer is also provided on Glowship.

What is the rating provided by Ministry of New and Renewable Energy (MNRE) for solar manufacturers/system integrators?

MNRE has commissioned one of the following rating agencies – CRISIL, ICRA, CARE, FITCH to rate the solar manufacturers/system integrators as per the below matrix:

Is it necessary to have a south facing shadow free area for installation of solar system?

Solar systems perform best in winter when installed facing south, angled at the latitude of the location. However, deviations of 30 degrees on either side of solar south and plus or minus 15 degrees in angle from the latitude will only cause a small loss in performance. 


What kind of solar water heater should I install and what capacity is the right capacity?

Please use the Glowship solar water heater wizard, it helps you determine

  • The right system capacity
  • The type of solar water heater (technology, model) that best suits your requirement.



How do I purchase a solar water heater using the Glowship product selector?

It’s simple! Please follow the steps below:

  • Open the Glowship solar water heater product selector
  • Answer the questions in the product selector
  • Click on “View Recommended Products” to see the products that match your requirement
  • Select the product you like and add it to your shopping cart
  • Make the payment online
  • The solar water heater will be delivered and installed at your residence
Why is it important to use the product selector before making a purchase on Glowship?

The product selector will help you select the specific models of solar water heaters that are best suited to your requirement. Solar water heaters are long-term investments and choosing the right model will ensure that you consistently get the requisite amount of hot water throughout the life of the system.


How does the Glowship product selector determine the right product for me?

The Glowship product selector estimates the capacity of the solar water heater system required by you based on your hot water usage data and recommends the appropriate technology & models to you taking into account the water quality, type of application, climate and site specific information shared by you.

How does the product selector determine the exact solar water heater system capacity required by me?

The product selector will take into account the type of residential unit you live in, your location, average statistics for water usage (published by United Nations Development Program, UNDP and Ministry of New and Renewable Energy, India, MNRE), expected heat losses to calculate the capacity of the solar water heater system that is appropriate for your usage.

Why does the product selector ask me to pick the place that is closest to my residence?

The hot water output for the same system capacity varies from place to place depending upon environmental conditions. The Ministry of New and Renewable Energy in India (MNRE) has compiled exact data for the hot water output for specific locations in India. The hot water output of the solar collector for your location is extrapolated from the same and is expected to within 10% of the above exact data. The Glowship product selector takes into account the hot water output for an average clear day in December (for plane areas) and in April (for hilly areas) so that the required capacity is calculated for the period when you need hot water the most. 

How does the product selector recommend the technology and model of solar water heater to me?

The product selector takes into account the type of water (hard water or soft water), climatic conditions, type of application (whether you are using pressurized applications such as shower jets etc.) and other site specific details provided by you to recommend the appropriate technology and model of solar water heater to you.

What are the benefits of buying solar water heaters on Glowship?/ What is the Glowship PentaVantage?

PentaVantageTM is the biggest reason to buy from Glowship! The advantages are described below:

  • We help you select the Right Product: The Glowship Product Selector & Glowship Knowledge Central combines to help you choose the product that best fits your requirements.
  • We carry only Genuine, Reliable products: Glowship brings to you genuine and high quality products at the best prices from manufacturers approved by the Ministry of New and Renewable Energy (MNRE)
  • Make a Trusted purchase from Verified Dealers: Glowship carries listings from only verified dealers and is the first marketplace to provide comprehensive ratings on service & delivery for each dealer thereby offering you the flexibility to make a purchase from the dealer of your choice
  • We offer you a One-stop Solution: All dealers selling on Glowship offer you free installation & hot water plumbing service at a nominal cost thus offering you the convenience of a high quality, one-stop solution, so, you don't need to look anywhere else!
  • Glowship Asset Management: Purchasing from Glowship offers a free subscription to Glowship Asset ManagementTM that allows you to monitor the health of your system, provides warranty claims management and other services to ensure you maximize the return on your investment.