The two main solar thermal products are

  • Solar Cookers
  • Solar Water Heaters

The two emerging products are

  • Solar Dish Concentrator for process heating
  • Solar Air Conditioner

Solar Cookers

Solar cookers are a form of outdoor cooking and are often used in situations where minimal fuel consumption is important, or the danger of accidental fires is high. The different types are

Box Type Solar Cookers

These are most widely used type of solar cookers. They can be rectangular or circular in shape. There are two types

  • Direct heating of food by sunrays
  • Mini greenhouse, using a black coated inner surface

Although box cookers are slow they provide even heating of the food. Box types of solar cookers are easy to make and use, safe, and cheap. Cost varies from Rs. 2,500-5,000.

Dish Type Solar Cooker

This uses a parabolic dish with manual tracking to concentrate sunlight. Temperature achieved at the bottom of the vessel is 250-400° C – enough to boil 3 litres of water in 30 minutes. Cost is about Rs. 7,000/m2 of concentrator area

Solar Steam Cooking

Designed for large scale cooking in community kitchens, this system uses multiple parabolic concentrators with tracking systems to provide large quantities of steam. Cost varies from Rs. 18,000-22,000/m2 of concentrator area depending on whether single- or dual-axis tracking is used. 5 pairs of 9.5 m2 concentrators can supply a 500 person cooking system.

Solar Water Heaters

Usually the form of solar energy that most people are familiar with, solar water heaters can be seen on rooftops across the country and have been in use for a long time. Solar water heaters are a Rs. 200 Crore market in India; the country currently has 8.8 million m2installed solar collector area and is targeting 20 million m2 by 2022. They are mandatory in new buildings in some cities like Bengaluru, where a solar water heater is necessary to receive a power connection.

Solar water heaters use a collector to absorb heat from the sun which is concentrated to heat water. There are several different types

  • Flat Plate Collectors (FTC) – They can heat water up to 60° C and last longer than ETCs
  • Evacuated Tube Collectors (ETC) – They can heat water up to 70° C but are fragile and have shorter lifespan than FTC. This is the more popular technology worldwide
  • Enhanced Evacuated Tube Collectors (EETC) – Variation of ETC that achieves higher temperatures by passing the liquid through multiple tubes

Water quality is a concern in India as hard or acidic water damages the collectors. A heat exchanger is required where water quality is poor, but increases the cost and reduces efficiency. Solar water heaters may be gravity fed (cheaper, less efficient) or pump fed (more expensive, more efficient, and flexible layout).

A 1,000 LPD (Litres Per Day) gravity fed water heat with heat exchanger costs about Rs. 1,75,000 while a pump fed water heater with heat exchanger is about Rs. 2,80,000.

Solar water heaters are most famous for domestic water heating but they are used in the industrial and commercial sector as well, such as pre-heating boiler water.

Large Area Solar Dish Concentrator for Process Heat

Industrial process heat is a huge market in India – about 15 million tonnes of fuel oil is consumed ever year for applications below 250° C. In India, the Arun-160 dish is an indigenously developed Fresnel paraboloid concentrator with dual-axis tracking that has been used by several industries. It can heat water up to 250° C. Further innovation (such as making the system lighter to be mounted on metal roofed industrial sheds) may see wider adoption.

Solar Thermal Air-Conditioning

Air-conditioning through solar can be achieved through driving conventional air-conditioners (particularly inverter air-conditioners) through solar PV but this process is considered to be inefficient and expensive.

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An emerging technology is solar thermal air-conditioning – using the sun’s heat to drive a cooling system. Similar to conventional air-conditioning, a refrigerant evaporates to produce a lowering of temperature. This evaporated refrigerant is then absorbed by another liquid. The refrigerant-saturated liquid is heated using the solar thermal plant to extract the refrigerant which is then cooled through a heat exchanger to regain its liquid form before being returned to the evaporator for another chilling cycle.

Solar thermal air-conditioning is at very early stages of commercialisation with very few installations in India. A lot of development is still required in the product, making it unsuitable for many entrepreneurs.

Market Status of Solar Thermal Products

While the solar thermal industry is much older than the solar PV industry, with solar water heaters lining rooftops over 20 years back, its growth has not been that well noticed in the last 5 years as has been that of solar PV. However, as you will see in this section, the solar water heater sector has been growing quite well in the period 2010-15. The same however cannot be said about many other sectors within the solar thermal industry.

Installed Capacity

Solar Thermal

  • 72 million m2 of solar water heating collectors were installed during the year for a total of 8.82 million m2 cumulative capacity
  • 6,89,493 solar cookers, representing 1,95,833 m2 of collector area or 39.2 MW equivalent is the cumulative capacity for solar cookers
  • 160 Concentrated Solar Thermal units, representing 45,000 m2 of collector area or 18 MW equivalent is the cumulative capacity for CST units.

Solar Water Heaters

Solar Water Heaters (millions of m2 of collector area)

The withdrawal of subsidy has affected the growth of this sector, but we believe that solar water heaters will continue to have a growing market as more and more states mandate them for various categories for consumers. The withdrawal of subsidy (because it is no longer necessary) means this sector is no longer subject to variation in government policies; the business case for solar water heaters is well established.

Box Type Cookers

No. of Box Type Solar Cookers

This sector has witnessed slowly growth over the last few years. We do not expect the rate of growth to increase in the near future.

Dish Concentrator & Solar Thermal Air Conditioning

These two products are in nascent stages and do not yet have established markets.

Related Articles

1. Emerging Opportunities in Solar Thermal – Refrigeration & Air-Conditioning
2. Business Opportunities in Solar Thermal – Heating Applications
3. Business Opportunities in Solar Thermal – Power Applications
4. Solar Off-Grid Applications and Products
5. Market Status of Offgrid Solar Products in India