Curtailment of Variable Renewable Energy Generation


The issue of Variable Renewable Energy (VRE) is explained in the pages: Wind Intermittency and Solar Mismatch with Demand.  Due to weather, wind electricity production has enormous fluctuations which occur on the same days over large regions of Europe. Solar production is only significant a few hours near mid-day which do not match the consumer demand peaks in the morning and evening. 

The example plots below show wind+solar generation during 2019 for Germany, Denmark and United Kingdom as well as a combination of nine countries in NW Europe. For these examples wind+solar generation varies between 5% to 120% of consumption.


Simulation of Increased VRE generation with battery storage and curtailment

To explore solutions to the fluctuations of VRE production, this page presents exercises with a simulation varying overproduction of electricity and varying amounts of available storage.

The simulation uses real electricity generation data with the fossil generation and imports/exports removed. The production from nuclear, hydro and biomass are kept at the real values for 2019 and the amount of wind+solar added with a scaling factor, keeping the real ratio of wind to solar production. Then the real consumption data day by day is matched with the simulated production with the increased amounts of wind+solar data and using varying amounts of available storage. For a given day if the amount of simulated production is greater than the actual 2019 consumption data, the excess is stored in a simulated battery until it reaches its full charge and for more the excess is wasted. If the simulated production is less than the consumption date the simulated battery is discharged to make up the difference.

The simulations scans the space of scaling factor for wind+solar versus minimum battery size to satisfy consumption demand for every day in the year. For each example, the minimum battery size used, is that needed to store the average scaled solar production for one day. All aspects of the simulation are on the daily time scale. For all examples shown, actual electricity production data for 2019 is used from entsoe.

The figure below gives an illustrative example with wind+solar data scaled by a factor 2.5 and with a 5 TWh storage battery.


Germany 2019 Consumption with No Imports/Exports

Germany has the largest wind generation capacity  and also the largest solar generation capacity  in Europe. The figure below shows daily  wind+solar generation as fraction of total consumption.

The figure below shows the resulting points with minimum battery size versus curtailment to satisfy the consumption demand for every day.


Denmark 2019 Consumption with No Imports/Exports

Denmark is the country in Europe with the biggest fraction of wind generation in electricity production. On occasions wind+solar exceeds demand.


United Kingdom 2019 consumption with No Imports/Exports

The United Kingdom had 19% wind and 4% solar in the generation mix averaged over 2019.

In these examples, for an overproduction of generation and curtailment of 30%, the battery requirements are seen to be 3.0 TWh, 1.7 TWh and 0.4 TWh for Germany, United Kingdom and Denmark respectively. The scale of these storage requirement range from 3000 to 23000 times the size of the Hornsdale Tesla "Big Battery". The Germany requirement is 33% of the current world pumped hydro storage capacity. Clearly it is not reasonable to expect such and increase in storage capacity in a long time.


North West Europe, including internal border exchanges.

A further simulation uses all countries in North West Europe: United Kingdom, Ireland, France, Germany, Belgium, Netherlands, Denmark, Norway and Sweden. Imports and Exports over internal borders are taken into account. The external exchanges from this region amount to 4% exports and so have little influence on conclusions, except perhaps in reducing waste by exporting the excess.

Because of the inclusion of France in the NW Europe entity, the  wind and solar fraction of consumption is lower than Germany and Denmark but similar to the United Kingdom. It can be seen that even with the much large region the similar weather conditions still give large VRE fluctuations from 5 to 40% of consumption.

The minimum battery to satisfy daily demand for NW Europe with 30% curtailment, is 3 TWh, similar to a stand-alone Germany. This is 23000 times the storage of the Hornsdale Tesla Big Battery and 33% of current global pumped hydro storage.

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