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Energy Systems and Technologies for the Coming Century ...

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In general, in power systems with less controllable, limited predictable, stochastic <strong>and</strong>intermittent power generation – like wind <strong>and</strong> solar – power balances can be achievedthrough combinations of <strong>the</strong> following means – see Figure 2:flexible generations;flexible consumptions;local storage;dynamic import / export;conversions to / from o<strong>the</strong>r energy carriers.Figure 2: Means of power balancing.Flexible generation: The fluctuating power generation from wind <strong>and</strong> solar mayto some extent be compensated by flexible power generation, provided bycontrollable power generation units.Flexible consumption: Some energy services based on electricity may provideflexibility in <strong>the</strong>ir consumption, e.g. by shifting part of <strong>the</strong> load in time – fromminutes to days, depending on <strong>the</strong> actual application. Examples are electricalheating or cooling services with <strong>the</strong>rmal capacities <strong>and</strong> / or temperatureflexibility.Storage: Local dedicated electricity storage can act as both (temporary) flexiblegeneration <strong>and</strong> (temporary) flexible consumption. Requirements to power,energy, efficiency <strong>and</strong> response time depends on <strong>the</strong> actual application.Import / export: Local power balance may be obtained by exporting orimporting power to / from <strong>the</strong> remaining power system – as far as possible. Thisoption is limited by bottlenecks in <strong>the</strong> power system <strong>and</strong> by <strong>the</strong> extent of <strong>the</strong>power system. E.g., isl<strong>and</strong> systems will not have this option.Conversion: Power may be converted to o<strong>the</strong>r energy carries – like heat orhydrogen. Conversion to heat may be part of combined power <strong>and</strong> heatgeneration (CHP) <strong>and</strong> as such with an overlap to flexible generation. Conversionto hydrogen may be reversible <strong>and</strong> as such with an overlap to storage.All <strong>the</strong>se means could in principle solely be able to provide <strong>the</strong> full power balances in allpower system nodes. However, <strong>the</strong> most economic solution involves a combination of allavailable means. The more flexibility <strong>and</strong> controllability in generation <strong>and</strong> dem<strong>and</strong>, <strong>the</strong>better.Many of <strong>the</strong> new small-scale distributed power units – providing energy services likeheating / cooling, pumping or battery charging – can with minor modifications changestatus from being passive power units to become active power units that to some extentRisø International <strong>Energy</strong> Conference 2011 Proceedings Page 177

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