Jharkhand Renewable Energy Development Agency

Microgrid and Minigrid

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:-

• 24 V DC up to 1 kWp
• 72 V DC above 1 kWp to 10 kWp

 AC Micro grids:-

• 220 V single phase – up to 10 kWp
• 440 V 3 Phase – beyond 10 kWp

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 :- 

• Households - lighting, mobile charging, TVs, fan and other appliances etc.
• Agriculture – irrigation pumps
• Commercial - shops, telecom towers, ice-makers, battery/ lantern charging and renting etc.
• Productive – milling, rice de-husking, wood/ metal workshops, foundry, small
• Micro industry, village industry, attachakki.
• Social institutions – schools, medical centres, public buildings, community buildings.
• Government or Panchayat Offices.
• Municipal Functions – Street Lights.

There are a lot of opportunities that have been observed with mini-grid systems:

• They can be used to increase the reliability of electricity supply. Due to their small scale in nature and enhanced local level ownership of physical infrastructure or management, power theft which is a commonly associated with centralized on grid systems can be reduced.
• Reliability of supply is generally greater from hybrid mini-grid systems as compared to a single technology. This not only lowers the net costs over the lifetime of a project, but also ensures availability of power when one system is not working.
• There is environmental improvement from the use of mini-grids. This is in terms of efficiency and reduction in carbon emissions. Hybrid mini-grid systems, for example, often incorporate a 75-99% renewable supply.
• Where the grid system is not well developed and there is a vibrant private sector, mini-grids provide opportunities and they are adaptable due to the fact that they can be connected to the grid as they expand.
• Conversely as the cost of fossil fuel increases, mini-grid systems are becoming more economically attractive as the cost of renewable energy resources decrease.

For more   https://mnre.gov.in/file-manager/UserFiles/draft-national-Mini_Micro-Grid-Policy.pdf