Energy is an important material foundation necessary for the development of the national economy and people’s lives, and it is also a driving force for promoting social and economic development and improving people’s living standards. However, with the development of society and the increasing demand for energy by mankind, the reserves of primary energy are depleting day by day. A recent report issued by the Swiss Bank pointed out that the world’s oil reserves are approximately 1.8 trillion barrels. According to the current level of oil consumption, the world’s oil can be exploited for 46 years. After half a century, the earth’s oil and natural gas will be exhausted, and there will be no coal to be mined in 200 years. In China, this situation is not optimistic. According to statistics, in 2016, China’s coal consumption was 3.91 billion tons (t), a decrease of 2%, and its share of primary energy consumption dropped from 64% to 62.4%; apparent oil consumption was 556 million tons (t), an increase of 2.8%. Energy consumption accounted for 18.1%, which was the same as in 2015. Net oil imports amounted to 356 million tons (t), and foreign dependence reached 64%; natural gas consumption was 204 billion cubic meters (m3), an increase of 6.5%, accounting for an increase in the proportion of primary energy consumption. To 6.2%, according to relevant research predicted by the China Energy Research Society and other industry organizations, the peak of China’s coal consumption will come around 2020, and the demand for natural gas will reach 400 billion cubic meters (m3). The mining, transportation and use of fossil energy will cause serious pollution to the air and human living environment. At the same time, large-scale greenhouse gas emissions make the earth’s surface temperature rise year by year. If the world does not control CO2, emissions, and the greenhouse effect, the icebergs in the north and south poles will melt, causing sea levels to rise, and 1/4 of human living space will be greatly threatened.
Therefore, with the increasing shortage of primary energy and serious environmental pollution today, countries around the world have begun to pay attention to environmentally friendly, efficient and flexible power generation methods-distributed generation/generator (DCG; or Distributed Resourses, DR). The development of distributed power sources can not only reduce energy shortages and reduce environmental pollution, but also improve the efficiency, reliability and power quality of the existing power system, reduce system constraints, and reduce power transmission costs.
The concept of distributed power was promulgated by the U.S. Public Utilities Management Act (PURRA) in 1978 and has since been widely used. Due to different national policies, different countries, even different regions of the same country, have different understanding and definitions of distributed power sources. So far, there is no uniform and strict definition of distributed power sources. Regarding the maximum capacity of distributed power sources, access methods, voltage levels, power properties and other relevant definition standards, there is no universal authoritative definition in the world.
The International Energy Agency (International Energy Agency, IEA) defines distributed power sources as power stations that serve local users or local power grids. Including internal combustion engines, small or micro gas turbines, gas batteries and photovoltaic power generation systems, as well as energy comprehensive utilization systems capable of energy control and demand side management.
The Institute of Electrical and Electronics Engineers (IEEE) defines distributed power sources as power generation equipment or energy storage devices connected to the local distribution network. Germany defines distributed power sources as power sources located near users and connected to the low- and medium-voltage distribution network, mainly photovoltaic power generation and wind power.
Based on the standards defined by developed countries, industry organizations and the characteristics of China’s power grids, distributed power sources can generally be defined as: use of distributed resources, small installed capacity, located near users, access to renewable energy at voltage levels of 10 (35) kV and below, Multi-generation facilities that realize comprehensive utilization of resources and cascade utilization of energy, and can independently output electrical energy. These power sources are owned by the power sector, power users or third-party organizations to meet the specific needs of the power system and users. It mainly includes wind power, solar power, biomass power, hydropower, tidal power, ocean power and other renewable energy power generation, as well as power generation using waste heat, pressure and exhaust gas, and small-scale natural gas cooling, heating and power cogeneration.