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Harnessing Variable Renewables. A Guide to the       Balancing Challenge. Paris : IEA, 2011, 200 p.http://www.oecd-ilibrary.org/content/book/9789264111394-enPower systems must be actively managed to maintain a steady           balance between supply and demand. This is already a complex           task as demand varies continually. But what happens when           supply becomes more variable and less certain, as with certain           renewable sources of electricity like wind and solar PV that           fluctuate with the weather? To what extent can the resources           that help power systems cope with the challenge of variability           in demand also be applied to variability of supply? How large           are these resources? And what share of electricity supply from           variable renewables can they make possible? (© IEA)There is no one-size-fits-all answer. The ways electricity is           produced, transported and consumed around the world exhibit           great diversity. Grids can cross borders, requiring           coordinated international policy, or can be distinct within a           single country or region. And whether found in dispatchable           power plants, storage facilities, interconnections for trade           or on the demand side, the flexible resource that ensures the           provision of reliable power in the face of uncertainty           likewise differs enormously.(© IEA)Written for decision makers, Harnessing Variable             Renewables: a Guide to the Balancing Challenge sheds           light on managing power systems with large shares of variable           renewables. It presents a new, step-by-step approach developed           by the IEA to assess the flexibility of power systems, which           identifies the already present resources that could help meet           the twin challenges of variability and uncertainty. (© IEA)