Renewable Energy - Solar Water Heaters

How do Solar Water Heaters work?

A solar collector collects the heat of the sunlight and heats water which is stored in an insulation tank. The water from the insulated tank is mixed with cold water before being delivered to the tap. The quantities of cold/hot water can be adjusted using a valve.

Are there different types of solar collectors used in Solar Water Heaters?

There are two common types of solar collectors used in solar water heaters: evacuated tubes and flat plate collectors.

Flat plate collectors have pipes attached to flat plate absorber plates. Sunlight heats up the absorber plates and the heat is transferred to the liquid in the pipes.

Evacuated tube collectors have glass or metal tubes, containing the fluid, encased in another glass tube with vacuum between the two tubular surfaces. The vacuum prevents heat being lost from the fluid.

Evacuated tube collectors are lower in capital cost but Flat plate collector water heaters are more popular. Evacuated tube collectors are considered somewhat more fragile compared to Flat plate collectors.

What sizes are solar water heaters available in?
  • For commercial applications, typical capacities come in 1,000-10,000 LPD (liters per day).
  • For industrial applications, capacities range from 1,000 LTD to 1,10,000 LTD.
  • For domestic applications, the capacity range is about 100-500 LTD.
  • For capacities greater than 2,500 LPD, a pump is required to circulate the water.
What are the benefits of installing solar water heaters?

The benefits of implementing solar water heaters are immediately applicable as there are negligible operating costs. In the case of a solar water heater with a pump to force the circulation of water, the electricity consumption of the solar water heater is about 3-5% of an equivalent conventional water heater.

The capital cost of typical solar water heaters is about Rs. 1,20,000 to about Rs. 1,80,000 (for 1000 litres per day capacity ) and Rs. 10,00,000 to Rs. 14,00,000 (for 10,000 litres per day capacity). The capital cost depends on the type of solar water heater (ETC/FBC) but also on parameters such as materials, finishing, type of tank used and so on. Payback periods range from 2-3 years, depending on the fuel that is being replaced (coal, gas, LPG, electricity...)

Solar Water Heaters typically heat water upto 80 degress Celsius and meets about 60-70% of the heating needs of commercial establishments like hotels and hospitals and industrial units.

What are some of the questions that potential customers ask?

Q. The water in my area is hard. Can I still use solar water heaters?

Hard water is a risk for all water heaters. For total hardness above 500 ppm, you are strongly advised to ensure regular de-scaling. In areas where the water is very hard, an ion-exchange softener is used and/or an indirect solar water heater is used. Indirect water haters use a heat exchanger that separates the water from a heat-transfer fluid that circulates through the collector. After being heated in the panels, the HTF travels to the heat exchanger, where its heat is transferred to the potable water.

Q. Can I use solar water heaters for an existing building or an apartment?

It is always better to plan for the installation of solar water heaters at the time of design and construction. In general, it is always fairly simple to install a solar water retrofit where a central water heating system exists. In these cases, the solar water heating system replaces the water boiler. However, where individual rooms and apartments are fitted with geysers, the plumbing associated with a new solar water heating system becomes challenging.

Q. What is the typical warranty or guarantee the vendors provide?

Vendors typically provide 1 year product warranty against manufacturing defects and a 5 year performance guarantee.

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