Mini Grids

Overview

A mini grid, also sometimes referred to as a "micro grid or isolated grid" can be defined as, a set of electricity generators and possibly energy storage systems interconnected to a distribution network that supplies electricity to a localized group of customers. This power delivery architecture can be contrasted to a single customer system such as in the case of a solar home system (SHS). Where there is no distribution network interconnecting customers it can be connected to a centralized grid systems, where electrical energy is transmitted over large distances from large central generators where local generators are generally not capable of meeting local demand.

Mini-grids have a unique feature as they can operate autonomously without being connected to a centralized grid. However the mini-grid may be designed to interconnect with the central grid which means it operates under normal conditions as part of the central grid with disconnection occurring only if power quality needs to be maintained. For instance in the case of a central grid failure. Alternatively, a mini-grid may be designed to operate autonomously in a remote location with the option to connect to a central grid when grid extension occurs.

A mini-grid can be supplied by all sorts of energy resources and power plants, however most of the time a mini-grid will use low AC voltage (220-380V) with a centralized production and a storage system and will have an installed capacity of between and 5 and 300kW even though bigger systems exist.

Implementation of mini-grids have proved to have a positive social impact by fostering and improving the local governance structure through the involvement of the community in the decision making process linked with the energy system. There are hundreds of diesel-based isolated grids worldwide which lend themselves to be retrofitted with renewable energy technologies. Sharing limited resources and power among users in a mini-grid requires rules and a tariff structure that ensures sustainability in the operation. In general, mini-grids involve intense preparation to ensure the systems operation and maintenance will be sustainable.

Opportunities

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.
  
• Economic assessments indicate that of the renewable technologies available, biogas, geothermal, wind and micro-hydro systems costing US¢6-15/kWh are the potential least-cost generation options for mini-grids in developing countries, this however assumes that sufficient renewable energy resources are available. Biogas digesters and biomass gasifiers are particularly promising from this economic perspective; this is because of their high capacity factor and availability in size range matched to mini-grid load. Geothermal on the other hand also appears economically viable for countries that have geothermal resources although it is limited to larger grid connected systems.
  
• For countries 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. However subsidies are still required for the different schemes but they are a smaller percentage of the investment than on-grid subsidies
  

Challenges

Despite the opportunities with mini-grids, their penetration remains low in most developing countries. Progressive development in mini-grids has been greatest in China where there is an estimated 60,000 schemes, and in Nepal, India, Vietnam and Sri Lanka which have 100-1000 mini-grids each. Majority of the schemes however use diesel or hydro power generation and are run and maintained by the government.

Technological failure may arise from the implementation of the scheme. Common reasons of such failures include:

• Lack of maintenance or the use of poor quality or untested technology. This could be as a lack of sufficient funding to sustain the project over its lifetime or the shortage of local skills for maintenance of the mini-grid.
  
• Insufficient primary energy resource, in bio gasification projects for example, there are challenges in finding sustainable sources of biomass and operating effective supply chains for biomass feed stocks. Similar challenges can affect diesel powered mini-grids in remote locations where infrastructure is not adequate, thus most of these schemes remain in their pilot stages (e.g. in Zambia).
  
• Poor assessment that is mostly compounded by lack of data on the local physical parameters that affect the power output and economics including:
  
  • Population density within the location of the mini-grid, This will have an influence on the load factor as well as the overall economics of the mini-grid.
    
  • Type of terrain, this will have an impact on the various resources required for the mini-grid i.e. the cost of infrastructure, fuel cost (for diesel systems) as well as the operation and financing of the system.
  • Seasonal resource fluctuations- This includes solar isolation, wind speed fluctuations and river flows.
  • Future policies- This policies are important in determining the future investment capacity in renewable energies, as an example it should include suitable sites and an ambitious rapid rural electrification programme.
• Development of schemes without attention to developing supplementary programes dealing with issues such as market access, small medium enerterprise (SME) development and working with local financing institutions, has contributed to a lack of demand and inability to sustain the schemes.

Further Information

• Basic Energy Services - Overview
  
• Grid Portal on energypedia