A large number of interconnected, intermittent generation sources operating over a large spatial scale may effectively smooth out the variability between individual generation sources. But, still variation will occur in output in the short and longer term.
Coupling intermittent renewable sources to a number of electricity production and storage sources could be used to meet the energy demand of a given facility or community, known as a hybrid power system. The power sources used depends upon the local geographical and temporal constraints, and can be used to meet demand from remote applications such as communication stations, military installations and rural villages. Full renewable power hybrid systems are in operation and have been mainly applied to remote hybrid systems in China. One of the most cost effective hybrid systems for a microgrid, a small-scale grid, is a photovoltaic array and a micro hydro turbine.
Therefore, more or less electricity is generated than meets demand. Excess electricity can be exported; dumped; stored as another form of energy and/or other electricity sources feeding into the grid can be modified accordingly. An electricity deficit can be met by electricity imports, ramping up or turning on of other electricity generating sources (backup power); and use of stored energy. Another option is to use demand management to balance supply and demand imbalances.
Storage is one of the more expensive options to balance supply and demand, but is increasingly more attractive in order to meet high renewable energy penetration targets. Another way countries are balancing their energy generation and consumption is by expanding the reach of their networks through imports and exports.
The potential for exporting and importing electricity depends upon the grid infrastructure, interconnections with other grids and the ability for the importers to absorb surplus electricity generated and exporters to meet any shortfalls in the importers electricity demand. For example, excess electricity generated from wind turbines in Denmark is exported to Norway, Sweden and Germany through grid interconnections.
In Norway and Sweden, the imported electricity is absorbed by reducing output from the countries’ hydro power plants or by using the electricity to pump water to higher elevations in a pumped storage plant. Electricity is also exported from Denmark to Germany. Although, with the expansion of wind power in Germany, it is unlikely that electricity will continue to be imported and exported in roughly equal quantities between the two countries.