Projected impact of climate change on hydropower production in China
Hydropower productions consume large amounts of water due to evaporation in dammed reservoirs. It accounts for the predominant share of water consumption for power productions in China. From 2002 to 2010, hydropower's water consumption in China grew substantially from 6.1 to 14.6 billion m3, which represented some 80% of the power sector's total water consumption (Liao et al., 2018). As described in Chapter 2, water consumption at reservoirs differs substantially in different places, depending on local geographical, hydrological and climatic conditions. According to Liu et al. (2015), average water consumption intensity for hydropower production in China amounts to 12.86 m3 per MWh of electricity produced. As shown in Figure 7.8, Liu et al. (2015) examined 209 hydropower stations in China, and their water consumption intensity ranges from 0.0036 to 15121.43 m'7MWh. There is a general trend of relative lower water consumption intensity at upstream and larger water consumption intensity at downstream within a river basin. Hydropower production's water consumption intensity is particularly high in the arid and semi-arid northern regions where local climatic and land surface conditions (e.g. high wind and little vegetation) contribute to high evaporation rates in reservoirs.
It should be noted that although hydropower stations have much larger consumptive water losses than coal power plants, water consumption for coal power productions should not be overlooked since their impacts on water resources are site-specific and depend on local water scarcity levels. While large hydropower stations are often developed at large waterways because they depend on sufficient flows to generate electricity, coal power plants are often built close to coal mines to save coal transportation cost
Figure 7.8 Water consumption intensity for hydropower production in China’s 209 hydropower stations
Source: Liu et al., 2015.
and are much less concerned about water availability or impacts on water resources. Since China’s coal reserves are mostly endowed in water-stressed areas, for instance, the Yellow River Basin is endowed with merely 2% of China’s renewable water resources, but with almost 50% of the country’s total coal reserves, growing coal power generation imposes increasing pressures on scarce water resources. Furthermore, many coal power plants him to groundwater resources if sufficient surface water supplies are not available, which leads to deteriorating groundwater over-exploitation issues.
Based on multi-model hydrological projections by the Inter-Sectoral Impact Model Intercomparison Project (ISI-MIP) (Warszawski et al., 2014), Liu et al. (2016) investigated the impacts of future climate change on China's gross hydropower potential as well as on the existing hydropower facilities. They found that the gross hydropower potential of China is projected to largely decrease in southwestern China and south-central China, especially in the summer period, while increasing in most areas in northern China. However, because the existing hydropower facilities are mostly located in southwestern and south-central China, the usable capacity is expected to decrease by about 2.2% to 5.4% from 2020 to 2050 and decrease by 1.3% to 4% from 2070 to 2099. Their results are consistent with the global findings by Van Vliet et al. (2016). Despite that global hydropower potential is projected to increase, the usable capacity is expected to decrease because most existing facilities are located in regions where reduced water availability is projected.
Water constraints on concentrated solar power
Besides hydropower, potential water limits may pose constraints on the large deployment of concentrated solar power (CSP). CSP typically uses large arrays of ground mirrors to concentrate sunlight to transfer heat through a medium (e.g. oil, water or salt) and then to generate steam to spin a turbine to generate electricity. CPS technology uses water in the steam cycle and cooling process. Moreover, CSP also requires water for cleaning the mirrors, especially in dry areas. As illustrated in Figure 7.9, Macknick et al. (2012) have conducted a review study of electric power plants in the US and consolidated the values of water consumption of different generating technologies and energy sources. CSP with tower cooling technologies require similar amounts of water inputs as coal power plants per unit of electricity generated.
It can also be seen from Figure 7.9 that theoretically dry cooling technology is able to reduce water use for CSP significantly. However, as air has a much lower capacity to dissipate residual heat than water, a large number of cooling fans need to be deployed, which results in large amounts of
Figure 7.9 Operational water consumption factors for different types of electricity productions
Source: Macknick et al., 2012.
Note: IGCC: Integrated Gasification Combined Cycle; CCS: Carbon capture and sequestration; CSP: Concentrated solar power. Upper and lower ends represent maxima and minima, respectively; Red Cross represents median values.
auxiliary electricity demand with reduced conversion efficiency. Especially during the summer, while electricity demand is particularly high, CSP using dry cooling technology has low thermal efficiency due to the high air temperature. As a result, researchers were unable to identify any large-scale CSP facilities around the world that use dry cooling systems (Carter and Campbell, 2009).
China’s CSP development is in the early stage but is projected to grow rapidly. In 2011, China’s National Development and Reform Commission issued an ’Industry Structure Adjustment Catalogue', which has given high priority to CSP development as one of the newly encouraged energy resources. China’s first MW-class CSP power plant, ’Dalian’, entered into operation in 2012. China National Energy Administration launched the first batch of CSP pilot projects in 2016 including 20 projects with a total capacity of 1.35 GW. According to IEA estimates (2018), China is expected to overtake the US to have the world’s second-largest CSP installed capacity by 2023, with 1.9 GW coming online, following 2.3 GW in Spain. From 2017 to 2018, China has further completed a feasibility study for another 24 projects with a total capacity of 3.05 GW. In 2019, 57 projects with a total capacity of 14.9 GW have been submitted for the application of China’s second batch of CSP demonstration projects (CSP Focus, 2019).
China’s most promising CSP sites are located in dry northern regions where water availability is low. As can be seen from Figure 7.10, there are mismatches between China’s water resources (Tu et al., 2016) and potential solar power locations. While China’s solar energy sites are mostly endowed in the northwestern regions, water is less abundant in those regions. The largest five provinces for CSP development are Qinghai, Gansu, Hebei. Inner Mongolia and Xinjiang, which have made plans for developing CSP to, respectively, 20, 5.6, 6, 16 and 20 GW by 2030. Among these provinces, in 2018. Hebei’s annual water withdrawal (18.24 km3) already exceeded its annual water availability (13.83 km3). The water Withdrawal-to-Availability (WTA) ratio in the other four provinces are 0.63 (Xinjiang), 0.42 (Inner Mongolia), 0.34 (Gansu) and 0.02 (Qinghai) (National Statistic Bureau. 2019). Except Qinghai, all of the other four provinces are facing different levels of water stress. Future CSP development may face potential water constraints in those provinces, which needs to be further studied.
