IEC_Elctrical Energy Storage.pdf

31 present status of applications in this section

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3.1 Present status of applications In this section, those cases are described which have already been implemented by electric utilities and consumers. These are respectively time shift and investment deferral for the former, and emergency supply and power quality for the latter. 3.1.1 Utility use (conventional power generation, grid operation & service) 1) Reduce total generation costs by using pumped hydroelectricity for time shifting, which stores electricity during off-peak times and provides electricity during peak hours. 2) Maintain power quality, voltage and frequency, by supplying/absorbing power from/into EES when necessary. 3) Postpone investment needed by mitigating network congestion through peak shift. 4) Provide stable power for off-grid systems (isolated networks). 5) Provide emergency power supply. Utility use of pumped hydro storage for time shift and power quality Pumped hydro storage (PHS) has historically been used by electric utilities to reduce total generation cost by time-shifting and to control grid frequency. There are many PHS facilities in different countries, and they have the largest proportion of total storage capacity worldwide. A conventional installation cannot function as a frequency controller while pumping, but an advanced variable-speed-control PHS (Figure 3-1) can do so by varying the rotational speed of the motor. Figure 3-1 – Variable-speed PHS operated by TEPCO (TEPCO)
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43 Utility use of compressed air energy storage for time shift and power quality Today only two diabatic compressed air energy storage (CAES) power plants are in operation worldwide. In 1978 the first CAES power plant was built in Huntorf, Germany (Figure 3-2). It works as a diabatic CAES plant with a round-trip efficiency of roughly 41 % [rad08]. It consists of a low-pressure and high-pressure compressor with intercooler, two salt caverns (2 x 155 000 m³ usable volume, 46 - 72 bar pressure range), a motor-generator (60 MW charging, 321 MW discharging) and a high-pressure (inlet conditions: 41 bar, 490 °C) and low-pressure turbine (13 bar, 945 °C). The second CAES plant is in McIntosh (Alabama, USA) and was commissioned in 1991. It has a net electrical output of 110 MW and is also based on a diabatic CAES process, but additionally a recuperator is used to recover heat from the exhaust at the outlet of the gas turbine. Therefore a higher round trip efficiency of 54 % can be achieved. Both systems use off-peak electricity for air compression and are operated for peak levelling on a daily basis. Worldwide several CAES plants are under development and construction. In Germany for example a small adiabatic CAES plant is scheduled for demonstration in 2016 (project ADELE), which will achieve a higher efficiency in comparison to a diabatic CAES [rwe11]. Figure 3-2 – CAES plant in Huntorf (Vattenfall, IEC MSB/EES Workshop 2011)
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44 S E C T I O N 3 Markets for EES Utility’s more efficient use of the power network As one of the examples of EES for utilities, a Li-ion battery can provide the benefit of more efficient use of the power network.
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