The energy yield from wind and solar generators is seasonal, the nature of the variation depends on the climate. In the UK the output of wind farms peaks in winter whilst solar parks make their greatest contribution during summer. Thus supplying a constant load or one with relatively small fluctuations is a challenge. There are two ways of looking at sustainable energy systems, they can either augment fossil/nuclear sources or they can displace them. These two approaches result in different strategies. In the former, fossil fuelled generators act as a back up for wind and solar source, in the UK it seems that at any given time the wind generation accounts for roughly 0 - 20% and on a calm summer's evening the output from PV devices will also approach zero. A combined wind and solar strategy when combined with storage and energy management has the potential to make a group of consumers largely independent of conventional energy sources. Taking the energy economy as a whole it is unrealistic to believe that fossil/nuclear sources will be displace in the foreseeable future, but it maybe possible to build new communities which are based on sustainable sources as an alternative to building additional coal, gas or nuclear fuelled plant.
The graph shows the result of a simplistic simulation of a wind farm and solar park, the parameters were arbitrarily set such that each unit had a peak output of around 1,000 MWh/month. The output of each source shows significant seasonal variation, but when combined the output is more or less constant.
This exercise did not take into account inconvenient issues that might arise from economic considerations.
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