Power Transmission over HVDC Lines

By 2050, according to our scenario, transmission lines with a capacity of 2.5 to 5.0 GW each must be able to transport around 700 TWh of solar energy per year from 20 to 40 dif­ferent locations in the Middle East and North Africa to the major centers of consumption in Europe (Table 9), thus supplying ca. 15 % of the European power requirements. The cost of these imports is based on low production costs of ca. 0.05 12000-ct./kWh and a high flexibility for base-load, balancing power and peak-load operation (see below). Since our present AC grids would have overly high trans­mission losses at such high power levels and long trans­mission distances, it will be necessary to employ HVDC transmission lines. HVDC is available as a mature technol­ogy and is becoming increasingly important for the stabi­lization of large-area power grids. It contributes to the strengthening of equalization effects between local and dis­tant energy sources and to containment of operational in­terruptions in larger power plants by utilizing back-up ca­pacity from far away.

In mid-2010 in China, a nearly 1500 km long HVDC transmission line was put into operation. It connects sev­eral hydroelectric plants with the large cities Guangzhou, Hong Kong and Shenzen with a transmission capacity of 5000 MW. This corresponds to the output power of five large plants.

Power will be transported over sometimes long dis­tances throughout Europe and the MENA countries and then fed into the conventional grids. Analogously to a mo­torway network, a future HVDC grid will have only a few inputs and outputs, which connect it to the conventional AC grids. In this analogy, the present AC grids are compa­rable to the local and municipal street networks. They will carry out the local distribution of electrical energy, just as they do now. The energy loss in the HVDC lines over a dis­
tance of 3000 km will be about 10 %, in contrast to more than 45 % for transmission over conventional AC lines.

There is a widespread misconception that for every wind farm or photovoltaic installation, a fossil-fueled back­up power plant of the same generating capacity must be built. In contrast, a model of the hourly time evolution of the energy supply systems of selected countries showed, in accordance with our scenario, that even without addition­al energy-storage capacity, the balancing power from the ex­isting peak-load plants suffices to equalize fluctuating de­mands. This holds so long as the fluctuating portion of the sustainable sources is smaller than the existing peak-load ca­pacity, which is the case in our scenario.

In fact, the need for conventional base-load power plants will decrease step by step as a consequence of the grow­ing proportion of sustainable energy sources (Figure 9). Base-load power will be generated using coupled heat and power plants burning both fossil and biomass fuels, by

Подпись:Подпись:Подпись:image171"runoff-river hydroelectric plants and by wind and photo­voltaic plants. Balancing power will be taken from more readily storeable sources such as hydroelectric plants with reservoirs, biomass or geothermics. This combination of en­ergy sources will not completely meet the daily demand variations, but will approach them closely. The remaining peak-load capacity (or, more correctly, balancing power ca­pacity) will be provided by pumped-storage plants, water reservoirs, solar-thermal plants and peak-load plants burn­ing fossil fuels [6]. The generating capacity based on fossil fuels that is still in operation by 2050 will serve exclusive-

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1 11 21 31 41 51

61 71 81 91 101 111 Hours in winter weeks

121 131 141 151 161 171

■ Hydrogen storage

Desertec

■ Comb. gas/steam

■ Pumped-storage plants

■ Norwegian imports

plants

Gas turbine plants

■ Geothermal plants

■ Coal power plants

Phovoltaics

■ Energy-yield crops

■ Nuclear power

Wind offshore

■ Biomass

■ Soft coal plants

Wind onshore

■ Flowing-water hydro

□ Electric load

Fluctuating and balancing power from various sources in a typical summer and winter week in Germany, from a model scenario with 90 % sustainable energy by the year 2050. Installed generating capacity: Wind power, 65 GW; Gas turbines, 60 GW; Photovoltaics, 45 GW; Solar imports, 16 GW; Biomass, 8 GW; Pumped-storage plants, 8 GW; Runoff-river hydroelectric, 6 GW; Hydroelectric imports from Norway,

6 GW; Geothermal, 5 GW.

ly for load equalization or combined heat and power gen­eration.