With the increasing feed of renewable energies in times of the energy turnaround (Energiewende) players of the energy market fears supply shortages and grid instabilities due to performance degradation of renewable power plants. The partial solar eclipse on 20 March 2015 tested the flexibility of the energy market with perspective on the period after shutting down the nuclear power plants.

On 20 March 2015 the partial solar eclipse on average covered up to 73 per cent of Germany within 9:30 and 12a.m.

Energy Brainpool forecasted potential additional costs in order to balance the solar dip in case of a possible shutdown of photovoltaic systems on a sunny day. Results showed additional economic costs up to three million euro and up to ten million additional costs for compensation for shutting down pv systems.

Those additional economic costs results from a higher energy trade price during the solar eclipse: flexible power plants generate the majority of energy to balance the dip in the solar feed. Furthermore TSO have to implement strategies to secure grid stability, e. g. additional control power.

Trend of German PV feed

Trend of German PV feed (source: Energy Brainpool)

Figure 1 shows the forecasted trend of German photovoltaic feed in case of a sunny day during the solar eclipse. Standard means of trading products for hourly (day-ahead market) and quarter-hourly (intraday market) trading are given. Calculations were conducted with the fundamental energy market model Power2Sim. The capacity price for this service also account for the cost calculation. Results show that TSO could be challenged during a solar eclipse on a sunny day, because they have to tender additional tertiary reserve, among other things.

Actual price trend on the day of the solar eclipse

Solar energy generation on 20 March 2015 reached a daily peak of almost 20GWh with an installed capacity of 39 GWh in Germany. During the solar eclipse, solar feed decreased down to 5.5GWh resulting in a “solar dip”.

prices at day-ahead market

prices at day-ahead market (source: Energy Brainpool)

Energy prices at the day-ahead market of the EPEX Spot SE in Paris (fig. 2) clearly show a price effect during the solar eclipse: until midday prices fell, in hour 11 (maximum coverage of the eclipse) energy prices were high. Daily price peak at hour 20 was approximately 5Euro/MWh – 5 Euro more than at hour 11. No extreme prices were necessary to balance supply and demand. The average price level of the day (base) was 35 Euro/MWh – an average level compared to the day before the solar eclipse.

The quarter-hourly energy price at the short-term markets of EPEX Spot and EXAA (Austria) were uttermost volatile: Between 9:45-10:00 and 10:00-10:15 a.m. the maximum price hub was 1.925 EUR/MWh (fig. 3). This can be seen as incentive for market flexibility: flexible market players profit from such price fluctuations while balancing supply and demand and simultaneously prevent or reduce the application of control power.

For securing system stability TSO additionally tendered control power. Between 8 and 12a.m. on 20 March 8 GW control power was tendered in total – this accounts for almost double the usual amount. Also negative control power was tendered in a similar amount.

Implication for the Energy Turnaround / Energiewende

Prior to the solar eclipse, market players stated that steep load gradients will become more common on sunny days with additional photovoltaic systems to be built. Price forecasts show that this induces flexibility of the energy market.

Distinct ramps increase the demand for flexibility for the coordination of resources at the spot market. Volatile price trends (e. g. as in the intraday market) set commercial incentives with high price peaks signalising an energy shortage.

Strategies and processes of the “Weißbuch” for the Energy Turnaround, as set by the German economic ministry (BMWi), could strengthen the flexibility. At the same time increased flexibility influences a reduction of energy prices and thereby serves as a regulator for a demand of flexibility itself.