IEC_Elctrical Energy Storage.pdf

131 more renewable energy less fossil fuel on grid

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1.3.1 More renewable energy, less fossil fuel On-grid areas In on-grid areas, the increased ratio of renewable generation may cause several issues in the power grid (see Figure 1-2). First, in power grid operation, the fluctuation in the output of renewable generation makes system frequency control difficult, and if the frequency deviation becomes too wide system operation can deteriorate. Conventionally, frequency control is mostly managed by the output change capability of thermal generators. When used for this purpose thermal generators are not operated at
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13 full capacity, but with some positive and negative output margin (i.e. increases and decreases in output) which is used to adjust frequency, and this implies inefficient operation. With greater penetration of renewable generation this output margin needs to be increased, which decreases the efficiency of thermal generation even more. Renewable generation units themselves in most cases only supply a negative margin 3 . If EES can mitigate the output fluctuation, the margins of thermal generators can be reduced and they can be operated at a higher efficiency. Secondly, renewable energy output is undependable since it is affected by weather conditions. Some measures are available to cope with this. One is to increase the amount of renewable generation installed, i.e. provide overcapacity, so that even with undependability enough power can be secured. Another is to spread the installations of renewable generators over a wide area, to take advantage of weather conditions changing from place to place and of smoothing effects expected from the complementarity of wind and solar generators. These measures are possible only with large numbers of installations and extension of transmission networks. Considering the cost of extra renewable generation and the difficulty of constructing new transmission facilities, EES is a promising alternative measure. Off-grid areas In off-grid areas where a considerable amount of energy is consumed, particularly in the transport sector, fossil energy should be replaced with less or non-fossil energy in such products as plug- in hybrid electric vehicles (PHEVs) or electric vehicles (EVs) (see Figure 1-2). More precisely, fossil fuels should be replaced by low-carbon electricity produced mainly by renewable generation. The most promising solution is to replace petrol or diesel-driven cars by electric ones with batteries. In spite of remaining issues (short driving distance and long charging time) EES is the key technology for electric vehicles. 1.3.2 Smart Grid uses EES is expected to play an essential role in the future Smart Grid. Some relevant applications of EES are described below. First, EES installed in customer-side substations can control power flow and mitigate congestion, or maintain voltage in the appropriate range.
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