Metering Requirement for a roof top solar system
Metering is required to measure the following energy transactions besides measurement of DC battery voltages, DC current, AC system voltages and currents , frequency etc
- Solar Gross Generation
- Consumer load consumption
- Export of energy to the Grid
- Import of energy from the Grid
- Export from DG to Grid
There are two basic philosophies of metering prevalent in the world when utility grid is connected with solar generating source and feed the load.
- Net metering or Market rate net metering
- Feed in tariff metering
Net metering is an electricity policy for consumers who own (generally small) renewable energy facilities, such as wind, solar power or home fuel cells. Net metering means measurement of net energy consumption by the load from a system. If a consumer load is connected to two generating sources and one is infinite grid and other is a small generating source such as solar described above their may be following options depending upon the size of the small source and time of use
Generated power by the small source is in excess of the load at a particular moment. In this case surplus power from this source will be fed into the grid if it is a grid interactive system.
Generated power by the small source is less than the power required by the load. In this case the extra power to meet the consumer load will be taken from grid.
At the end of month the billing of the consumer by the distribution company is done based on the net energy import from the grid. Under net metering, a distribution company receives credit for net energy supplied to the consumer load in case it is import and pays to the developer of the small source if there is net export to the grid.
Currently, Feed in Tariff is only available in Gujarat under the new GERC solar Tariff order 2012-2015. Similar solar feed-in-tariff policies are under process of being released in Delhi and other states. It is means of promoting solar power and will serve to meet hour demand in the cities of India. with spot prices of conventional power reaching new highs of round Rs.9 during peak load hours, it makes a lot of sense to include a reliable and clean source such as solar into the energy mix to meet peak demands in cities across India.