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Storage requirements for a power-supply with renewable energies

The necessary capacity requirements of storage power plants in order to equalize the difference between a weather dependent production and the requested power, can be calculated, for Europe, from available data of wind speed and solar radiation. In the form of “load divergence” and “storage emptying curves” suitable calculation methods were developed for this purpose. The good availability of data in Germany makes it possible to compare the actual wind and solar power feeds with the calculated values. Thereby the calculations could be validated.

If every country produces its own average consumption plus a certain reserve from wind- and solar power stations, then the storage requirements to equalize the difference between power production and consumption would require a storage load from a few days up to some months of the average consumption. This huge difference is caused by several influences. On one hand by the continental distribution and cross linking of renewable power production, which enables considerable equalizing effects between temporary overproduction and deficits, because high- and low-pressure areas move across the continent and provide different regions of weather. Furthermore strong winds occur in Europe mainly during winter time. An optimized combination of power production using wind- and solar energy on the other hand reduces the need to balance dramatically in comparison to a mono structure using only wind- or only solar power stations.

Considerable influence also has the capacity factor of wind power stations. It tells the amount of average power output compared to the rated power. Wind power stations in Germany in the year 2010 have a capacity factor of about 20%. This value proves unfortunate to the intended increase of wind power to the total power supply. The equalizing and storage needs could be drastically reduced by using wind power stations with an efficiency of 50% for example.

A further strong lever to reduce the equalization needs is the power production reserve. A bigger reserve will reduce the time where storage power is required and will accelerate the refilling of an emptied storage plant.

A skilled tuning of all parameters allows a secure power supply what will meet the demands with a storage capacity of only a few days. The storage capacity needed would be much more than available in the year 2010. Ringwallspeicher as a new type of pumped-storage power plants are introduced. They could be built in all countries and could close the gap of missing storage capacity.

A secure power supply, only using wind-, solar- and storage power plants in Europe is therefore a real option.

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