Due to the rapid increase in global energy consumption and the diminishing of fossil fuels, the demand for new energy generation capacities and efficient production, delivery and utilization keeps growing. In parallel, the rising number of sensitive or critical loads requires increasing flexibility. The micro grid concept has the potential to solve the major problems arising from the large penetration of distributed energy generation in the smart grid.
Microgrids are an integrated energy system managing interconnected loads and distributed energy resources and capable of operating in parallel with or independently from the existing utility’s grid. Microgrids can operate with and without a connection to the main power network.
Microgrids can provide higher flexibility, energy efficiency and reliability: They are able to run in both grid-connected and islanded mode of operation while their components may be physically close to each other or distributed geographically. Microgrids can offer electrification of rural areas where there is no possible access to grid electricity e.g. due to the inaccessibility of remote areas or insufficient technical skills.
Standardization supports the development of microgrids to meet the rising demand for electricity, and to improve energy utilization, efficiency and reliability, new power generation technologies, including renewable energy, clean and efficient fossil fuels, and distributed generation.
Microgrids – Important parts of the future grid structure
Nowadays, people are very concerned about clean and efficient utilization of energy, as energy related and environmental problems are becoming more and more serious. The electricity generation from renewables such as photovoltaics and wind turbines has some undesirable characteristics such as intermittence and fluctuation. Thus, how to manage them effectively is a key issue to be solved. Microgrids can integrate the undispatchable generation, dispatchable generation, electrical energy storage and loads in a region, and manage them as a whole. They are becoming effective methods to solve the problems outlined above. Microgrids can be divided into isolated microgrids and non-isolated microgrids. Isolated microgrids operate independently and have no electrical connection to the utility grid. Non-isolated microgrids can connect to the utility grid to operate in grid-connected mode, or disconnect from it to transfer to the island mode under certain circumstances.
Where will microgrids be used?
Depending on different purposes, microgrids can be used in the following four scenarios:
- Supplying power to remote areas such as islands or rural areas: For these areas, high power quality is not the most important issue to be considered. The costs to build dedicated lines to supply power from the utility grid are very high. Isolated microgrids which include generators and electrical energy storage are desired to supply power to these areas constantly.
- Ensuring power supply reliability and high-level power quality: For critical infrastructures such as hospitals, non-isolated microgrids with some reliable generators or electrical energy storage can be deployed to improve the power quality. When there is a fault in the utility grid, they can switch to the island mode to avoid power supply interruption.
- Reducing energy costs in regions with abundant renewable energies: In these regions, non-isolated microgrids are used to optimize different kinds of distributed energy resources so as to supply power to loads with low costs. The microgrids can supply additional power to the utility grid and provide ancillary services as well.
- Recovering power supply rapidly after disasters: For the utility grid, the maintenance and repairing time after disasters can take several hours or days. Microgrids can recover power supply to loads much faster. What’s more, they can help to support the “black start” of the utility grid.
Standardization of microgrids
Microgrids, being important parts of the smart grid, should not cause adverse impacts when connected to the utility grid. Where it is necessary, they should also facilitate the operation of the smart grid. Therefore, operational characteristics of microgrids must be standardized. In addition, standardization of microgrids will also pave the way for their commercialization. In 2013, IEC Technical Committee 8: System Aspects for Electrical Energy Supply did establish Working Group 7: General Planning, Design, Operation and Control of Microgrids. The Conveners of WG 7, Prof. Jianhua Zhang from North China Electric Power University, China, and Prof. Zhaohong Bie from Xi’an Jiaotong University, China, are leading the formulation of two technical specifications: IEC/TS 62898-1: Microgrids - Guidelines for Planning and IEC/TS 62898-2: Microgrids - Guidelines for Operation. In the future, more specific standards concerning microgrid protection, energy management, communication etc. will be developed by WG 7.
Microgrids in China
To relieve the energy-related and environmental risks, in recent years, the Chinese government has issued a series of policies to promote the development of renewable power generation. Microgrids play an important role in realizing the goals of the inevitable reformation of the electric power system. In China, renewable energies are widely distributed around the country, and there are thousands of islands in the coastal areas. So the potential to develop microgrids is very huge. At present, over one hundred microgrids of different kinds and scales have been built in China. For example, the microgrid project in Jiaze, Ningxia Hui Autonomous Region，realizes the stable operation under the condition of high penetration of renewable power generations. It can change its topology flexibly to avoid power supply interruption. In Shandong Province, a chain of microgrids were built to supply power to several islands in Changdao County.
What will microgrids be like in the future?
For customers, the energies they need are not only electricity but also heat and cold. To reduce the costs of integrated energy supply, microgrids of the future are not only small electric power systems, they will also supply heat and cold to customers. In addition, with the rapid development of electric vehicles, the charging stations will become indispensable parts of microgrids. Hence, microgrids would link the electric power system, district heating system and district cooling system closely. Microgrids are not only important parts of the smart grid, but they will also become the basic units to build the integrated energy systems in the future.
Prof. Jianhua Zhang:
"Microgrids as effective methods to manage renewable power generations will be important parts of the future grid. The standardization will pave their way to commercialization."
Prof. Jianhua Zhang |
North China Electric Power University |
Convenor of IEC/TC 8/WG 7 |