China sets aggressive goals to develop high penetration of renewable energy but also suffers from the large scale of curtailment due to the lack of power system flexibility. The electric power, gas, and heat systems work on different but complementary time and space scales. Multiple energy systems (MES) increase the efficiency and flexibility of both energy supply and consumption. Integrating multiple energy systems is viewed as an effective way to accommodate the high penetration of renewable energy in China. Different regions of China have different resource endowments and energy demands, thus facing different challenges or bottlenecks to fully accommodate renewable energy. Different forms of multiple energy systems integration have been taken in different regions as important measures to promote the integration of high penetration of renewable energy. In this blog, four most typical trials are introduced in the following.
- Electric-Heat Coupling in Northeastern China
Northeast of China is the worst-hit area for renewable energy curtailment. This area has the highest density of heat demand. The percentage of Combined Heat and Power (CHP) in coal-fired units is higher than 70%. However, the output power of CHP is determined by heat demand, which makes the CHP units less flexible and leads to huge wind power curtailment.In 2013, the National Energy Bureau of China issued a “Notice on the Wind-powered Heating Projects” to encourage the utilization of wind power in space heating. Since then, there have been a lot of wind-powered heating demonstration projects in Jilin, Heilongjiang, and Inner Mongolia. Electric boilers (EB) and heat storage have been widely adopted in this area to reduce wind power curtailment. The interaction between CHP, EB and heat storage expands the flexible operation region of the whole electric-heat system. The capacity of EB for each project ranges from 10 MW to 40 MW. Take a project in Jilin as an example, where 1.2 million square meters of clean heating area in Baicheng was converted from coal based boilers to electric boilers to solve the problem of wind power curtailment in 2013. The accumulated wind power consumption for heating in the project reached 78.92 GWH by the end of 2016, of which 85.04% were consumed in the low valley period. It was estimated that the project saved 42.52 million RMB and 9699 tons of standard coal.
- District MES in Southeastern China
Southeastern China is the energy demand center of China. The integrated planning and construction of MES has become popular in southeastern China, especially for high load density areas such as Jiangsu and Guangdong. The integration of heat pump, absorption chiller, CHP, and ice storage air conditioning systems, etc., improves the overall end-use energy efficiency by introducing high efficiency energy convertors and realizing increased efficiency of energy utilization. The district MES is either as small as a single building or as large as an industrial park. In addition to energy efficiency, district MES also provides flexibility to accommodate distributed renewable energy such as rooftop PV.There are a lot of MES towns that have been constructed in China. More and more MES towns are under construction or in the planning stage. Meanwhile, the push for distributed renewable energy integration has never stopped. The planning and operation of district MES need methodology and technology innovations such as standardized matrix modeling, integrated planning, MES operation sequential simulation, etc. An increasing number of researchers are focusing on this promising area.
- Concentrated Solar Power in Northwestern China
Deserts and sandy regions in northwestern China are ideal locations for Concentrated Solar Power (CSP) installation. In 2015, China launched a series of CSP demonstration projects in Gansu and Qinghai provinces with a total capacity of 1 GW. A feed-in tariff of 1.15 RMB/kWh is provided.The integration of heat storage enables the CSP to provide both renewable energy generation and operational flexibility. Specifically, a part of the collected solar energy is used to drive a steam turbine directly, while the remaining energy is stored in the heat storage which will be used to generate electricity at night or during cloudy weather. Chinese engineers and researchers are uncovering both the “energy value” of the solar power itself and the “flexibility value” to accommodate intermittent renewable energy. Even though the capital cost of CSP is high, investing in CSP is still economic in China from a social cost-benefit perspective. This is due to its external benefit of accommodating wind power and PV as a virtual storage that leads to lower cost over time in power system operations. CSP is a unique way of accommodating renewable energy using renewable energy.
The research of the Electrotechnical Institute of China Academy of Sciences and the General Electric Power Planning Institute shows that the cost per kilowatt of solar thermal power generation in China will drop to 12000~14000 RMB/kW in 2020 and to 9000~11000 RMB/kW in 2050. The levelized cost of CSP will reduce to 0.67~0.76 RMB/kWh in 2020, and 0.50~0.56 RMB /kWh in 2050. China plans to achieve 5 GW and 180 GW by 2020 and 2050, respectively. We will see a rapid development of CSP in the near future.
- Power-to-Gas in Southwestern China
The capacity of hydropower in China is about a quarter of the whole capacity in the world. Even through hydropower is a controllable renewable energy source, it also has great seasonal variation and thus results in curtailment during the high flow season in several provinces in China such as Sichuan and Yunnan.In the Sichuan “13th Five-Year” Energy Development Plan, the government of Sichuan province will launch several demonstration projects about hydrogen production and utilization based on surplus hydropower. By installing a hydro-electrolytic hydrogen producer and injecting the hydrogen fuel into the natural gas system, the power-to-gas solution is able to provide a seasonal storage for the curtailed hydro power. The hydrogen can also be used in industry processes or by vehicles. It is interesting that there are two hidden benefits of power-to-gas: producing heat and facilitating carbon recycling in the energy system. The methanation reaction will use CO2 that may come from the carbon capture and storage (CCS) and produce large amounts of heat which can be used for building heating.
As you can see from these four examples of energy systems integration, there are numerous opportunities throughout the country to improve the efficiency of energy supply and utilization. All of these efforts will increase system flexibility and assist in the integration of very large amounts of renewable energy in China.
Ning Zhang, Yi Wang & Chongqing Kang
Department of Electrical Engineering
Tsinghua University, China