Yuan Dongming

Research Report No 080, 2004

China’s power supply-demand situation is still very grave in 2004. It is estimated that the country’s total installed capacity of power generators will reach about 410 million kilowatts, and the shortage will be about 30 million kilowatts. At present, the coal stock of many thermal power plants could only sustain 1-3 days, and many places have no choice but "suspend production to avoid the power consumption peak" or even have to "resort to blackouts" in order to cope with the power shortage, and this has led to huge economic losses. To fundamentally solve the current problem of power shortage, in addition to expanding the installed capacity of power generators and to speeding up the power grid construction, it is a must to actively develop the distributed power architecture (DPA) and to optimize the mode of power supply. At present, the distributed power sources are realized mainly through the combined supply of cooling, heat and power has become an international trend, breaking away from the traditional concept about power sources that "small means non-economical." After the California power crisis in the United States and the "September 11" terrorist attacks all counties are paying greater attention to power supply security, and are considering the DPA as an important part of their electric power planning.

I. Distributed Power Architecture: Features and Prospect

The DPA is a new model of power supply, which is completely different from the traditional centralized power supply model. It is distributed around the users in a distributed method, and its power rate is usually several kilowatts to 50MW. It is relatively independent from the public power grid, applies natural gas, methane, and biomass gas and light oil as fuel and realizes the combined supply of cooling, heat and power. Compared with the traditional power architecture in which power is transmitted in long distance to the load center, the DPA is directly installed in the power distribution network where the power load is needed, the transmission through power grid is made unnecessary, and it concurrently supplies power, steam, hot water and heating directly to the designated areas through the pipelines and cable system.

In terms of energy conservation, environmental protection, investment, power supply safety and satisfying the diversified needs of customers, the DPA supply method has its unique advantages.

1.Good effect in energy conservation

The DPA is not simply a "small thermal power plant" or a "small-capacity

generator" for power generation, it is a power generation mode which, through the comprehensive utilization of quality energies, provides heat, cooling and power at the same time, and its energy utilization rate could reach as high as over 80%, doubling that of the conventional coal thermal generating units [1].

2.Little negative impact on environment

The DPA applies clean energy as natural gas, light oil and renewable energy as

fuel, and boosts good property in terms of environmental protection. Generally speaking, compared with the conventional coal-burning generating units, the SO2 and solid waste discharge from the DPA using natural gas as fuel is virtually zero, the discharge of CO2 is reduced by more than 50%, the discharge of the NOx discharge is reduced by 80% and the discharge of Tsp is reduced by 95%[2].

3.Falling into the category of "power generation by all"

The DPA needs small investment, occupies less land and has a short construction period,and it is therefore conducive to solving the power shortage problem in a short term.The investment for a 5MW small DPA power plant is only over 20 million yuan whereas a 135MW thermal power generation unit,the minimum capacity allowed in China, will cost as high as more than 700 million yuan[3].

4.Saving investment in the power grid, transmission and distribution facility construction

The loss of electricity for centralized transmission and distribution is usually about 10%, and even as high as more than 15% in China [4]. Under the DPA mode, because the power architecture is located close to the load center, there is no need to construct the expensive transmission and distribution grid, neither is it necessary to construct power distribution stations, furthermore, the loss of electricity in power transmission and distribution is very low, or even naught. Compared with purchasing electricity from power grids at a high price and simply using natural gas for power supply, the DPA mode has high economic benefits.

5.Satisfying the diversified needs of customers

The DPA mode could provide heat, power and cooling at the same time, and could, according to the special needs of customers, provide heat and cooling at different levels of temperature.

6.High reliability in power supply

The DPA mode applies advanced small and medium-sized, or mini generating

units that are convenient to start or shut down, easy to operate and flexible to adjust the load. Furthermore, the power plants are relatively independent, this would be convenient for customers to control the units and could avoid massive power supply accident from happening.

DPA is suitable for power, heat and cooling supply to commercial centers, residential areas, industrial parks, hotels, schools, airports and subway stations. As proven by the experiences of the developed countries, the combination of the public power grid and the DPA is a major method to save investment, reduce energy consumption and improve the safety and flexibility of the power system. In Japan, the amount of power generated through the DPA accounts for 25%-33% of customers’ total power consumption[5], and the remaining portion is supplied by the public power network, and both are inter-dependent. After the "September 11" terrorist attack, the developed countries all sped up the pace in the construction of DPA for the safety of power supply. To date, Britain has built more than 1,000 DPA power plants, and the United States has constructed more than 6,000 DPA power plants. According to the US government plan, 20% of newly constructed commercial or office buildings by 2010, and more than half of such buildings by 2020 will use DPA power supply, and by 2020, 15% of the existing buildings will also be transformed to use DPA power supply[6].

II. DPA Is a Constructive Supplement to the Centralized Power Architecture, and Is Helpful in Improving the Security Level of Power Supply

1. DPA is more economical and effective in dealing with peak power load

DPA and big power plants and power network share a mutually supplementary relationship, not an antagonistic relationship, DPA is a constructive supplement to and a strong guarantee for the public power network. As a relatively independent power supply system, DPA could be connected to a big, public power network to make it safer.

By relying on the construction of large generating units and power network to meet the power needs during the peak period, it calls for huge investment and the utilization rate of equipment is also low. The equipment would be operating under capacity during the non-peak period after satisfying the needs for power supply during the peak period, and the rate of capital utilization is also very low. In addition, power supply relying on big power grids would not only mean a big loss of electricity in the long-distance transmission, the power supply safety would also be a grave problem. The fundamental solution to this problem is to transfer part of power supply load to DPA, and at the same time, to make DPA and the public power grid be coordinated and supplement each other. DPA is an independent power plant, the customers could control it and it is easy to operate. Because fewer systems are involved and it is swift to start or shut down the DPA plant, it is highly reliable and could help improve the reliability and stability of the public power system.

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* Wang Zhenming, adviser to the Heat and Power Specialized Committee of China Society of Electrical Engineering, offered great help to the writing of this paper.

[1] "Ladder Utilization of Natural Gas" in the "Collection of Theses of the Seminar on DPA Heat, Power and Cooling Joint Production," by Zhao Zhiyi, Li Mingyuan, etc., P38

[2] Data source: Meeting minutes of the 2003 DPA Heat, Power and Cooling Joint Production Seminar.

[3] "Optimizing the Utilization of Natural Gas, Vigorously Speeding up the Construction of DPA Plants" from the "Energy Policy Research," 2003, by Hua Bi, Lai Yuankai, P40-46.

[4] "Vigorously Developing the Gas Turbine Power-generating Industry" from the "Collection of Theses of the Seminar on DPA Heat, Power and Cooling Joint Production," P1. by Jiao Shujian

[5] "Discussion of Several Questions on the Design of Distributed Power Architecture," by Han Xiaoping, www.china5e.com

[6] "Optimizing the Utilization of Natural Gas, Vigorously Speeding up the Construction of DPA Plants" from the "Energy Policy Research," 2003, by Hua Bi, Lai Yuankai, P40-46.