High Renewable Electricity Generation is Correlated with Increased Grid Stability

There is currently a great deal of plain misinformation about whether wind and solar electricity generation cause grid instability. Renewable energy skeptics and fossil fuel boosters frequently argue that an increasing reliance on variable wind and solar generation necessarily results in grid instability. These claims are of the inexact, pernicious, type that are easy to make but take significant work to refute. Large scale grid outages are often blamed in initial headlines on renewable energy generation. When investigation determines the cause was elsewhere, including poor performance by fossil fueled generation, inadequate efforts are made to correct fictions in the public record. Analysis is further complicated by a paucity of relevant historical time series data. But where data is available, the correlation is clear.

In reality, data from California and Germany, two of the world’s largest economies, demonstrate empirically that as renewable electricity generation rates increase are correlated with fewer frequency and voltage disruptions. In other words, high renewable energy generation rates are correlated with increased grid stability. These historical trends were evident long before grid-scale batteries became a significant source of electricity on either grid. As batteries provide more capacity to grids around the world, they will enable even larger deployment of renewable generation that will outcompete fossil fueled generation on price and performance.

Germany

In a research note published in 2024 (PDF), we showed that the rise in renewable generation is contemporaneous with 1) an increase in stability of the German grid, 2) an increase in GDP, and 3) a reduction in CO2 equivalent emissions. Below is an updated figure from that publication showing the correlation of grid stability and load supplied by renewables.

Germany reports grid stability data as the number of minutes per year that the grid voltage deviates from the specified operating range. Despite recent major disruptions to both electricity supply and demand, in the form of the pandemic and the war in Ukraine, the German grid has gradually experienced fewer minutes of disruption over the last two decades as the supply of electricity generated by renewables has climbed to reach nearly 60% of demand. The Fraunhofer Institute asserts that this relationship is causative and is attributable to 1) the vast majority of photovoltaic (PV) solar installations in Germany being at the community scale or smaller, and 2) those distributed installations accounting for more than half the total PV-generating capacity in the country. Distributed rooftop and community solar by definition supplies energy in a distributed manner and reduces demand on the larger grid, thereby stabilizing the larger grid. There is no reason to expect this result to be localized to Germany, and, indeed, it is clearly apparent in another large economy.

Figure 1. German national grid interruptions since 2006, share of renewable electricity capacity, and share of renewable electricity generated. (Sources: German Federal Network Agency and Fraunhofer ISE)

California

In California, now the world’s fourth largest economy, the trend is similar; as the renewable electricity supply has grown, the grid has become ever more stable.

The California grid operator, CAISO, reports grid stability as the number Reliability Based Control (RBC) events per month, which occur when the frequency of the grid deviates above or below the standard of 60 Hz. The RBC count has clearly fallen to multi-decadal lows even as renewable electricity generation has approached, and even surpassed, 100% of load.

Figure 2. The CAISO grid has become increasingly stable as wind and solar electricity production has approached 100% of load. (Sources: CAISO and Planetary Technologies)

Spain

The April, 2025, Iberian blackout was quickly blamed on Spain’s increasing dependence on renewable energy, in particular on solar PV. For example, The Financial Times led its initial reporting with the assertion that “The inability of Spain’s electricity grid to manage an unusually high supply of solar power was a key factor in Monday’s catastrophic blackout,” a claim attributed to “some experts”. The article contains further assertions by another supposed expert that “non-controllable resources [such as photovoltaics] . . . don’t contribute to the stability of the internal electrical system”. However, so far as I am aware, there is no data to support such a claim. (And, alas, there is no obvious source of time series data from Spain to examine the correlation of renewable generation with grid stability, as was possible for Germany and California above.)

Two months later, The Financial Times reported that Spanish authorities, after investigating the blackout, had determined that the event was caused by 1) either a fossil-fueled or a nuclear power plant shutting down and 2) the grid operator failing to manage the resulting fluctuations in voltage. The “high supply of solar” was, in fact, not a “key factor” in the blackout. The FT made no particular effort, in the later article or at any time since, to clean up its original misleading reporting.

Spain had temporarily reached 100% renewable (wind, solar, and hydro) generation in the weeks before the blackout, but has minimal grid scale battery storage to either capture excess renewable energy or serve as a buffer for the grid. Large scale energy storage has been dominated by pumped hydro in the country due to policy, but that policy was changed in July to accelerate battery installation. As Spain continues to install solar generation resources, the addition of battery storage will make the grid even more flexible and resilient to failures at unstable fossil-fueled and nuclear power facilities, as batteries have already done elsewhere.

Batteries

The future of electricity grids around the world can be seen emerging in California. Over the course of a day, renewables now provide the majority of the electricity to the grid. Importantly, it isn’t just that renewables provide the majority of electricity during the day, when demand is highest, they also charge batteries during those hours that then displace gas generation during the evening as the sun is setting. As more batteries are installed, more gas will be displaced.

Below are two charts from CAISO’s “Today’s Outlook” page that show the dynamics of the system. On 17 August, at about noon, renewables provided 3.3X as much electricity to the grid as did the combination of gas, hydro, and nuclear, while also charging batteries at a higher rate than the sum of that non-renewable power production. That renewable generation capacity is dominated by flexible and cheap solar PV. For a longer term view, Gridstatus had a nice writeup in June about how batteries and solar are changing all aspects of CAISOs electricity generation and distribution, including dramatically reducing imports.

Figure 3. Supply of electricity, by source, on the CAISO system for the 24 hours of 17, August, 2025. Power generation, and integrated energy supply, was dominated by renewables. (Source: CAISO.)

Figure 4. Power generation in the renewables mix on the CAISO system on 17 August, 2025, was dominated by solar PV. As it now is every day of the year. (Source: CAISO.)

To be sure, 17 August was a nice sunny day across California, but you can use the tool to pick any day you like, and the trend holds. Sure, there is seasonal variation. And yet, every successive year renewables supply a higher percentage of demand. The chart below, from The Sun Has Won: Historical and Planned U.S. Electricity Generation (PDF), from December 2024, shows that solar, in particular, is providing an increasing share of both the maximum and monthly average load. California is gradually weaning itself from both fossil fuels and imports, without needing new nuclear power.

Figure 5. Over the last 10 years, the maximum electricity generation from renewables has climbed to supply more than 100% of load in some months (Sources: CAISO, Planetary Technologies). Note that California excludes conventional large hydroelectric generation from its reporting on “renewables”. Monthly Average Renewables Serving Load was compiled from CAISO Renewables Performance Reports, which comprise a shorter data set than the Maximum Percent of Load. (Sources: CAISO and Planetary Technologies.)

In Germany, battery storage is presently dominated by small scale, home systems, which as of August, 2025 have a net installed capacity approximately 6 times that of large scale systems. This prevalence of distributed storage may contribute to the conclusion that distributed solar is causal for improved grid stability. Total storage capacity growth in Germany hit 50% annually in 2024. However, this is likely to accelerate significantly as large scale battery storage capacity in particular is expected to grow as much as ten-fold over the next two years. Consequently, Germany will serve as another interesting test case for how a country with different renewable resources will store energy and use that storage to meet daily and seasonal variations in demand.

Back in the U.S., as we have written previously (PDF), it is important to keep an eye on what is happening in Texas. The state is installing ever more wind, solar, and battery capacity, and renewables are keeping the grid stable when coal plants are offline. On July 11, 2025, 37% of ERCOT’s coal generating capacity went down for unplanned maintenance, with wind and solar supplying just shy of 50% of demand while keeping the grid up and running. Last year batteries saved the ERCOT grid from crashing twice in two weeks due to unreliable fossil-fueled power plants.

The data, and the anecdotes, are all consistent: more renewable energy generation and storage means more stable grids.