Storage Required

In order to calculate how much storage would be required for each percentage level of wind penetration, it was necessary to analyse daily electricity consumption profiles, typical wind profiles and agree on a 'worst case-scenario' strategy. The worst-case scenario would take place in the winter when consumption was high and would involve several days with little or no wind.

Worst Case Scenario 

Consumption profiles for England and Wales were examined (since they are more readily available than those for Scotland) and were then scaled down to represent typical Scottish consumption. Scottish consumption is, however, only around 70% of generation as 18% is exported and around 12% is accounted for by transmission losses and 'own use' by electricity generators. The consumption figures were then scaled up to include the export figure but not the losses. This would ensure the stability of the export market. A further scaling was applied to represent a 1% per annum increase in usage and provide a projected figure for the year 2020. After comparing data for several winter days, it was calculated that Scottish electricity consumption (including export) for a typical winter day in 2020 could be represented by the following graph.  

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The red line shows the winter base load which is approximately 60% of the peak demand. The green line represents 80% of peak demand. If 20% of electricity were generated from the wind then all consumption above the green line would come from wind power and everything below the green line would mostly come from thermal generation. It can be seen that regardless of wind power being generated, there is a surplus of electricity available between approximately 10 pm and 8 am. If there were a period of no wind then there would be an electricity shortfall between 8 am and 10 pm. The required storage level would be calculated by evaluating these surpluses and shortfalls for different percentage levels of wind penetration and a range of no-wind scenarios. The areas between the lines were calculated using basic integration techniques and the differences between the required storage and the available storage were calculated for no-wind periods of up to 10 days. It was also considered that a certain amount of 'flex' was available from thermal generation and this was taken as 4%. The amount of power available from thermal 'flex' would obviously decrease as the contribution from thermal generation decreased. The data was analysed using Excel.

A Matlab program was then written which would give a more comprehensive analysis of the data and would also provide a direct comparison for the results obtained using Excel.

The following flowchart was the basis of the algorithm that was used to write the Matlab program.

The results obtained can be seen in the following 2D and 3D plots.

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It can be seen from the Matlab plots that no storage is required until the wind penetration level exceeds 15%. There is another significant point at 21% penetration where the storage levels begin to diversify depending on the number of consecutive 'no wind days' expected. The Matlab program which was written to produce these graphs proved to be a simple yet valuable analysis tool.