In April, I wrote about a spring day on the grid to highlight the energy mix from each region of the US during the best time for renewables. In the spring, the days are getting longer, temperatures are moderate, and demand is lower. In areas of the US with the most hydropower, rain is plentiful during spring. The summer is a different story. As days get shorter and temperatures peak, the grid is tested. Let’s revisit the energy mix from a day in the dog days of August and see how each region of the US handled the sweltering heat of the fourth hottest summer on record. I used August 2 as the day to deep dive because August 1-5 saw 1451 highest minimum temperature records tied or broken indicating nighttime temperatures were the most unbearable. The remainder of August had only 2367 records tied or broken, many of which were in Puerto Rico or Alaska where I will not analyze data. All charts are taken from the gridstatus.io dataset.
ERCOT (Texas)
Texas has been on a run of installing batteries and solar in 2024 and is building more energy storage than any other region. Solar and storage have been attributed to save Texas from heat-related blackouts multiple times this summer. The data says there’s still plenty of room to build.
Coal usage still peaks around 15% of the grid capacity during the midday demand spike and even a hefty gas presence needs to be supplemented with coal in the warm Texas evenings. Texas can and should continue building solar and storage at a quick pace to replace coal usage as quickly and cheaply as possible. Texas has been a great renewable energy deployment story for the past couple of years, but there is plenty more to do to handle the summer heat without relying on the collapsing coal industry.
CAISO (California)
The darling of renewable energy deployment still isn’t meeting peak summer demand with carbon-free sources and relies heavily on imports, especially from Nevada, to supplement its grid.
It’s encouraging that storage is starting to depress import and gas reliance in the evenings, but even midday peak solar is far from meeting demand. Wind power is barely making a dent. No coal dependence and a small presence of geothermal starting to show up is good news from a long-term perspective. However, repeated attempts to shut down existing nuclear are short-sighted from an environmental perspective. The summer grid stress is a far cry from the spring optimism. This level of seasonal variation means solar developers are going to have to find buyers for their power during the spring if they are going to capture the summer market away from gas. There’s an opportunity for green hydrogen electrolyzers to operate in the spring and soak up the excess power to store and use later by burning hydrogen instead of gas. The question is if this can become an economical solution when the electrolyzers can’t effectively run during the summer and possibly the winter.
SPP and MISO (the midwest)
In the spring, the Midwestern RTOs were dominated by coal and gas. In the summer, the dominance is even more pronounced. Interestingly, the prevalence of wind power in North and South Dakota turns prices negative routinely throughout the year but a lack of transmission capabilities means that power is stuck where it cannot serve demand in the rest of the Midwest. That leaves more than 35% of this region stuck on more expensive coal. There’s plenty of room to end up with lower electricity prices across the Midwest by enabling the power that’s already coming from wind to serve a larger area.
The western and southern areas of the Midwest have some of the highest solar potential in the US, so there’s plenty of room to build out more solar to drive down prices and protect this region from exposure as the coal industry spirals. This is perhaps the area of the country that would benefit the most from “build baby build” because there are few wrong answers as to where to install wind, solar, storage, or better transmission because all of it will largely displace coal or meet new demand for power.
The Northeast (PJM, NYISO, ISONE)
As we go from Pennslyvania to New York to Maine, there is an evolution of the electricity mix that is at once promising and frustrating. ISONE, which serves all states east of New York, is not known to be particularly sunny but has displaced almost all of its summertime coal usage with solar power. Cooler weather means less air conditioning driving electricity usage, but landfill gas is largely serving the evening peak after solar drops off. The majority of power is still produced with fossil gas but there’s some growing diversity of supply while the region awaits offshore wind.
New York heavily relies on gas as its “Dual Fuel” plants may burn either gas or oil, but with the cheap price of gas, we can assume today that gas is the source. Hydropower helps service the additional load compared to ISONE but there are almost no other renewables in the mix.
The trend continues in PJM where almost five times more electricity is generated and coal makes up about 20% of the total generation. That amount of coal generation would power all of ISONE. To displace that much coal, PJM will have to build an enormous amount of solar and wind while also being home to two prolific coal-producing states in the US.
The contrast between spring and summer for these regions is not particularly pronounced in terms of the mix. The potential impact of offshore wind is huge, and the economics make sense given the skyrocketing operations costs of coal plants. The question is if these mostly politically pro-environment states will get more aggressive, or continue to plod along. Burning coal at this rate, PJM will feel the economic impact first as coal prices are up around 20% since 2022 according to the EIA.
Shoulder season economics
Spring and autumn in the US bring about lower electricity demand due to milder temperatures. Springtime solar and hydro booms typically work to make excess renewable energy on the grid so that peak demand is easily served. In the autumn, the wind typically picks up, so areas with high wind potential do well as we head into the darkest days of the year at the start of winter. The question for passively generated renewables is how to remain economically operational in the spring and autumn when electricity prices plummet. Hydrogen electrolyzers are difficult to start back up once stopped, so running them on solar power alone seems unrealistic. Pumped hydro is geographically dependent and usually not great for surrounding ecosystems that end up flooded. One thing is clear, places like California and soon Texas will have excess power capacity in the spring and autumn that will be later needed to serve the summer and winter peaks. Today, that means taking down fossil fuel plants for maintenance. The next step is to figure out how to cut into fossil fuel market share by becoming a year-round replacement. Cheap battery storage has answered the question of how to generate power when the sun isn’t shining and the wind isn’t blowing. The next big question will be how to build enough renewable power generation to meet summer demand without going bankrupt in the spring and autumn.