A ‘Mini Grid’ is a system having a RE based electricity generator (with capacity of 10KW and above), and supplying electricity to a target set of consumers (residents for household usage, commercial, productive, industrial and institutional setups etc.) through a Public Distribution Network (PDN). A ‘Micro Grid’ system is similar to a mini grid but having a RE based generation capacity of below 10KW. Micro and mini grids generally operate in isolation to the electricity networks of the DISCOM grid (standalone), but can also interconnect with the grid to exchange power. If connected to grid they are termed as grid connected mini/ micro grid.
The generator of a mini grid can be powered by RE sources such as solar, biomass, wind, small hydro or other notified sources and can have diesel-based generator as a backup. Hybrid systems using a combination of resources like those that of solar-wind, solar-biomass, solar-hydro etc. can also be deployed to improve system reliability and for back up. While the use of conventional fuels like diesel and kerosene to enhance the reliability of RE mini grids is allowed as a back up in rare cases, the Ministry strongly discourages the same. The Public Distribution Network of a mini grid can be designed to carry either Alternating Current or Direct Current (AC or DC). AC is intrinsic to rotating generators (wind, hydro, diesel etc.), while solar photovoltaic (PV) generates DC. The decision of AC or DC influences the cost of project, appliances that can be used, and interconnection conditions. DC distribution is acceptable for low power applications (like lighting, radio, mobile, and household appliances like fans, TVs etc.) and that too in a limited geographic area based on voltage levels and it is also not suitable for interconnection with the DISCOM grid. AC distribution can also support high power applications (by using single or three phases) and can interconnect with the grid. (The policy is neutral towards either AC or DC systems.) A combination of AC & DC in mini-grids is also possible. DC Micro grids are recommended where loads are closely located. The recommended levels are as follows:-
DC Micro grids:-
AC Micro grids:-
A mini grid can provide the electricity service to consumers for various purposes. Few of the consumer categories and potential service applications are listed below. These will be the 7 categories for fixing tariff/billing :-
There are a lot of opportunities that have been observed with mini-grid systems: