Solar net-metering explained:
In grid-connected solar PV systems the solar energy produced by the solar panels is converted to AC (alternating current) by a solar grid inverter. The output of the solar grid inverter is connected to the distribution board switch board of the building. The electrical energy flows to the loads of the buildings (lights, fans, appliances etc.). If the solar energy produced is more than what the building loads consume, the surplus energy will automatically be exported to the TANGEDCO distribution network (the grid). If there is less solar energy than what the loads of the building require, the shortfall will be drawn from the grid (energy import).
The Service Connection Meter:
For solar net-metering to be implemented the existing TANGEDCO service connection meter needs to be replaced with a meter that can measure both energy import (from the grid to the consumer) and energy export (from the consumer to the grid). These meters are known as bidirectional energy meters or import-export energy meters.
The Electricity Bill with Solar net-metering:
With solar net-metering the Consumer pays for the difference between import and export energy (the net-metered energy). Example: a Consumer imports during a billing cycle 900 kWh (units) and exports 500 kWh. The electricity bill will be for 400 kWh. If the export energy exceeds the import energy, the excess of import kWh will be carried over to the next billing cycle. During a 12 months period (the Settlement Period) the maximum of energy export that will be credited by TANGEDCO is 90% of the energy import. Example: During the settlement period there is a total import of 5,000 kWh and a total export of 6,000 kWh. Of the 6,000 kWh exported 4,500 kWh is eligible for adjustment with the import kWh (90% of 5,000 kWh).
Solar PV System Capacity:
The solar PV system capacity shall not be more than the sanctioned load of the service connection. It is also advisable to have a solar PV system size that has an annual estimated generation of not more than 90% of the estimated consumption.

Q.No.1 What is Solar Water Heater?
Ans. A Solar Water Heater is a device which provides hot water for bathing, washing, cleaning, etc. using solar energy. It is generally installed at the terrace or where sunlight is available and heats water during day time which is stored in an insulated storage tank for use when required including mornings.
Q. No. 2 How does it work?
Ans. A Solar Water Heater comprises of an array of solar collectors to collect solar energy and an insulated tank to store hot water. Both are connected to each other. During the day time, water in solar collectors gets heated which is either pumped or flown automatically on thermosyphon principle to the storage tank. Hot water then stored in the tank can be used for various applications.
Q. No. 3 What are different types of Solar Water Heaters?
Ans. Two types of Solar Water Heaters are available; one based on flat plate collectors and the other based on evacuated tube collectors. Flat plate collector (FPC) based systems are of metallic type and have longer life as compared to Evacuated tube collector (ETC) based system because ETCs are made of glass which are of fragile in nature.
Both these systems are available with and without heat exchanger. They can also work with and without pump. Systems without pump are known as thermosyphon systems and those with pump are known as forced circulation systems.
Q. No. 4 What is the approximate cost of solar water heater?
Ans. Cost of solar water heater depends on size and type of system installed.
Smallest size of a system is 100 liter per day, which means that it can deliver 100 litres of hot water in a day at 60 C. A 100 lpd capacity system is sufficient for a family of 3-4 members and it may cost Rs. 15,000 to Rs.22,000 in plains depending on the type of system. In hilly & N-E region, the cost may be 15 to 20% more.
The system cost does not include the cost of cold water tank, & its stand which is required if overhead tank is not installed in a house/ building. Cost of hot water insulated pipe line also, may be extra if number of bathrooms is more than one. Additional cost towards all these components may increase by 5 to 10%.
The cost, however, does not increase linearly with increase in capacity; rather it comes down proportionately as we go for higher capacity system.
Q. No. 5 Is there any subsidy available from Government?
Ans. No. The subsidy scheme has been discontinued w.e.f 12.08.2014 onwards.
Q.No. 6 Why should I go for a Solar Water Heater? What do I save from it?
Ans. A 100 litre per day capacity system suitable for 3-4 people can save up to 1500 units of electricity in a year depending on the amount of hot water used. It can also save around 140 litres of diesel in an establishment using oil fired boiler besides reducing greenhouse gas emissions in the atmosphere. Higher capacity systems will save higher amount of electricity/fuel oil besides reducing higher amount of GHG emissions.
Electricity is expensive and is not available due to power cuts in many areas when required for heating water. Solar Water Heater, since it stores hot water in an insulated tank, provides water all the time when required. Fuel oil is also expensive and creates pollution. Storing the fuel oil for long term use in commercial establishments is another problem.
Q.No.7 What happens on cloudy/rainy day? Do I still get hot water?
Ans. On cloudy days also, if it is for a day or two, you still get warm water as water gets heated due to diffused radiation available in the atmosphere. The system, however, is either connected to an electric geyser in the house or an electrical back-up is provided in the storage tank of the system which is switched on when water is not sufficiently hot. So, you get hot water all the time even on rainy days.
Q.No.8 How do I decide about the size/capacity of the system to be installed?
Ans. For a house with one bathroom and 3 to 4 members, 100 liter per day capacity system should be sufficient. For more numbers of bathrooms, the capacity will increase accordingly due to pipe losses & more number of family members. Generally the capacity is decided based on hot water required in mornings for bathing. If the usage is in evening & at other times also, the capacity is decided accordingly.
Q.No.9 Are there any maintenance requirements?
Domestic solar water heating system do not need significant maintenance requirements. Occasional leakages in the plumbing could be easily repaired by common plumbers. In case quality of water is hard, scale deposition in the collectors may result over the years. This may require de-scaling with acids for which it is best to contact the suppliers. Broken glass may also have to be replaced by the suppliers. If outside exposed surfaces are painted, the paint may have to be redone every 2-3 years to prevent corrosion of the surfaces.