Bengt J. Olsson
Twitter: @bengtxyz
LinkedIn: beos
With the increasing amount of renewable and weather-dependent power, firming or balancing power becomes more important. The question is: which are the major contributing balancing power sources in the pan-European power system?
One way to measure the contribution from balancing powers in the power mix is to look at how they vary with the variation of residual load. The residual load is the remaining load after wind and solar power have been accounted for. Essentially, it’s the load that must be served by all the other power sources.
In this scenario, we analyze the aggregated power production and load for all of Europe during 2023 up to September 2024—almost two years. Data is sourced from EnergyCharts. EnergyCharts calculates Residual Load as (Total Load – Onshore Wind – Offshore Wind – Solar Power). However, we define Residual Load here as the sum of the complementary power sources. These two methods should yield the same result, but in practice, slight differences may occur due to data imperfections.
We group power sources that contribute to serving the Residual Load to make them easier to overview. Data is sampled on different time scales to see how much balancing sources contribute at each scale. Some sources contribute little to balance on an hourly scale, but more on a seasonal basis, and vice versa.
Relative Importance of Balancing Power Sources
More than half the contribution comes from fossil fuels. Pumped hydro contributes significantly to hourly balancing but less to longer time scales, as expected since it’s used for daily balancing. Nuclear, on the other hand, shows less (but not zero) balancing contribution on the hourly scale but more on the seasonal scale. Essentially, nuclear “follows residual load” seasonally by being more available in the winter than in the summer.
For longer sampling periods (weeks and months), the “All Others” power source actually anti-correlates with the residual load. The main contributor here is Hydro run-of-river, which varies out of phase with the Residual Load over longer periods.
Absolute Contributions from Balancing Power Sources
This graph shows that the residual load varies more on a shorter time scale than on a longer one, which is to be expected with less averaging at shorter timescales. With an hourly sampling period, the standard deviation of residual load is 46 GW. Averaging or sampling over months reduces the standard deviation to 23 GW.
Note that balancing must be performed at the hourly, or shorter, time scale. The longer time-scales just contribute to the general perspective.
Key Takeaways
- Fossil Dependency: More than half of Europe’s balancing power comes from fossil fuels on all time scales. Eliminating this dependency requires either lowering the residual load variation or having non-fossil dispatchable power sources handle much larger variations. With a higher share of variable renewable power sources, it’s unlikely that residual load variance will decrease, despite potential increases in load flexibility. Therefore, dispatchable power sources other than fossil fuels will need to step up, not only to replace fossil balancing power but also to increase the total balancing power.
- National vs. Pan-European Scale: On a national scale, increased import/export could provide additional balancing resources. However, on a pan-European scale, there’s no import or export. Multiple countries may want to import or export simultaneously, limiting this source of flexibility.
- The Growing Gap: Europe faces a dilemma where residual load variation increases due to a higher share of variable renewable energy, but more than 50% of the balancing power, which is fossil, must be phased out. This creates a growing gap that needs to be addressed.