Distributed generation refers to the deployment of small generating units (generally below 30MW) at or near user sites to meet the needs of specific users, support the economical operation of existing distribution networks, or simultaneously meet both requirements. These small units include fuel cells, small gas turbines, small photovoltaic power generation, small wind-solar hybrid power generation, or hybrid units of gas turbines and fuel cells. Proximity to users improves service reliability and power quality. The combined effect of technological advancements, public environmental policies, and the expansion of the electricity market has made distributed generation an important energy option in the new century.
Depending on the primary energy source used, distributed generation can be divided into fossil fuel-based distributed generation technology, renewable energy-based distributed generation technology, and hybrid distributed generation technology.
I. Distributed power generation technology based on fossil fuels
Distributed power generation technology based on fossil fuels mainly consists of the following three technologies:
1. Reciprocating Engine Technology: Reciprocating engines used in distributed power generation employ four-stroke ignition or compression ignition systems, using gasoline or diesel fuel, and are currently the most widely used method of distributed power generation. However, this method can cause environmental impacts. Through technological improvements, noise and exhaust emissions have been significantly reduced.
2. Micro Gas Turbine Technology: Micro gas turbines refer to ultra-small gas turbines with a power output of less than several hundred kilowatts, using natural gas, methane, gasoline, or diesel as fuel. However, compared with other existing power generation technologies, micro gas turbines have lower efficiency. Their efficiency at full load is only 30%, and at half load, it is even lower at only 10%–15%. Therefore, they are often used in residential combined heat and power (CHP) systems to utilize waste heat energy from existing equipment to improve efficiency.
3. Fuel Cell Technology: A fuel cell is an electrochemical device that directly converts chemical energy into direct current electrical energy under isothermal conditions. Fuel cells do not require combustion and do not pollute the environment; their electrical energy is obtained through an electrochemical process. Hydrogen-rich fuel is passed through the anode, and air is passed through the cathode, with the two substances separated by an electrolyte. The only byproducts in the process of obtaining electricity are heat, water, and carbon dioxide. Hydrogen fuel can be produced from various hydrocarbon sources through steam reforming under pressure or through oxidation reactions. Therefore, it is a promising clean and efficient power generation method, often referred to as a distributed power source for the 21st century.
II. Distributed generation technology based on renewable energy
Distributed generation technology based on renewable energy mainly consists of the following technologies:
1. Solar Photovoltaic Power Generation Technology: Solar photovoltaic power generation technology directly converts solar energy into electrical energy using the photoelectric effect of semiconductor materials. Photovoltaic power generation has advantages such as not consuming fuel, not being limited by geographical location, flexible scale, no pollution, safety and reliability, and simple maintenance. However, this distributed power generation technology is very expensive, so current solar power generation technology still needs technological improvements to reduce costs and make it suitable for widespread application.
2. Wind power generation technology is a technology that converts wind energy into electrical energy. It can be divided into two categories: stand-alone and grid-connected. The former consists of micro or small wind turbine generators with a capacity of 100W to 10kW, while the latter typically has a capacity exceeding 150kW. Wind power generation technology is advancing rapidly, and technologies with a single unit capacity of less than 2MW are already quite mature.
III. Hybrid Distributed Generation Technology
Hybrid distributed generation technology typically refers to the combination of two or more distributed generation technologies and energy storage devices to form a composite power generation system. Various forms of composite power generation systems have been proposed, one important direction being the multi-objective distributed energy supply system of combined heat, power, and cooling (CHP), often simply referred to as a distributed energy supply system. This system can provide heat energy or simultaneously meet heating and cooling needs while generating electricity. Compared to simple power supply systems, distributed energy supply systems can significantly improve energy efficiency, reduce environmental pollution, and improve the system's thermal economy.
