New analysis outlines US national opportunities to remove carbon dioxide at the gigaton scale
ITOCHU, Hive to collaborate on green ammonia project in South Africa

PNNL study finds compound energy droughts in wind and solar can last nearly a week

Researchers at Pacific Northwest National Laboratory (PNNL) have found that in some parts of the country, compound energy droughts—i.e., when the sun doesn’t shine and the wind doesn’t blow, both at the sametime—can last nearly a week. The team published the findings in an open-access paper in the journal Renewable Energy and will be presenting at this week’s annual meeting of the American Geophysical Union.

When we have a completely decarbonized grid and depend heavily on solar and wind, energy droughts could have huge amounts of impact on the grid.

—Cameron Bracken, an Earth scientist at PNNL and lead author

Grid operators need to know when energy droughts will occur so they can prepare to pull energy from different sources. On top of that, understanding where, when, and for how long energy droughts occur will help experts manage grid-level battery systems that can store enough electricity to deploy during times when energy is needed most.

In the past, researchers studied compound energy droughts on a state or regional scale. But not much has been studied on a nationwide scale. To find out more about the risk of energy droughts over the entire continental US, the researchers dug into weather data and then used historical energy demand data to understand how often an energy drought occurs when that energy is needed the most.

The team examined 4 decades of hourly weather data for the continental US and homed in on geographical areas where actual solar and wind energy plants operate today. Weather data included wind speeds at the height of wind turbines as well as the intensity of solar energy falling on solar panels. Times when the weather data showed stagnant air and cloudy skies translated into lower energy generation from the wind and solar plants—a compound energy drought.

The researchers found that energy droughts can occur in any season across the continental US, though they vary widely in frequency and duration. In California, for instance, cloudy and windless conditions might last several days, whereas the same conditions might last for only a few hours in Texas. Utah, Colorado, and Kansas experience frequent energy droughts both over several-hour timescales as well as several-day timescales. The Pacific Northwest and Northeast, meanwhile, seem to experience energy droughts that last several hours more frequently than several days. The different timescales (hourly versus daily) will help inform the energy drought’s impact on the grid.

Overall, researchers found that the longest potential compound energy drought on an hourly timescale was 37 hours (in Texas), while the longest energy drought on a daily timescale was six days (in California).

Energy drought at peak demand. Simply knowing the where and how of energy droughts is just one piece of the puzzle, Bracken said. He also stressed that a drought of solar and wind power won’t necessarily cause an energy shortage. Grid operators can turn to other sources of energy such as hydropower, fossil fuels, or energy transmitted from other regions in the US.

However, as the nation aims to move away from fossil fuels and rely more on solar and wind power, grid operators must understand whether energy droughts will occur during times when the demand for electricity might exceed supply.

To understand the possible connection between energy droughts and energy demand, the team mapped their historical, hypothetical generation data onto 40 years of historical energy demand data that also covered real power plants across the continent.


Magnitude, duration and frequency of energy droughts for all Balancing Authorities (BAs) (and aggregation periods. Wind and Solar (WS) droughts are shown in the left panel and Load, Wind, and Solar (LWS) droughts in the right panel. The points indicate the mean drought duration for a BA at a given time scale, the vertical lines indicate the range of drought durations from the min to the max observed duration in the 40 year period. The curved line is an exponential curve meant to illustrate a rough upper bounding region for the data. Bracken et al.

The data showed that wind and solar droughts happen during peak demand events more than you would expect due to chance, Bracken said—meaning that more often than not, windless and cloudless periods occurred during times when demand for power was high. For now, Bracken isn’t certain that the correlation means causation.

Energy storage for energy droughts. Studying patterns in the frequency and duration of energy droughts will also help inform the deployment of long-duration energy storage projects, said Nathalie Voisin, an Earth scientist at PNNL and coauthor on the paper. The paper is the first to provide a uniform standard of what a compound energy drought is and how long it can last in different parts of the country.

Next, Bracken and the team will extrapolate weather and demand data into the future to see how climate change will affect the frequency and duration of energy droughts. The team plans to model energy droughts all the way to the end of the century combined with evolving infrastructure.

This research was funded by PNNL through its internal GODEEEP initiative.


  • Bracken C.W., N. Voisin, C.D. Burleyson, A.M. Campbell, Z. Hou, and D.P. Broman. (2024) “Standardized Benchmark of Historical Compound Wind and Solar Energy Droughts Across the Continental United States.” Renewable Energy 220. PNNL-SA-186419. doi: 10.1016/j.renene.2023.119550



We had a week in Ireland, around Xmas 2010 when it was very cold and no wind (and not much sun either), so it was all gas and coal for that week.
Similarly, we had a 10-12 day period one July when the wind did not get above 10% capacity. + the sun did not shine at all during the night.
So you need full backup for these days: a few hours of battery or hydro storage won't cut it. Even 24 hours of battery storage (~80 GWh for Ireland) won't do it.
Backup can be gas, (coal (yuck)) or transmission, but IMO, you really need full gas coverage on your own soil, because the transmission could fail some day (like if a submarine cut the cable, (or a trawler).
Or go / add nuclear.


What this means is that renewables can be used to reduce the use of, but not eliminate, dispatchable power, which means nuclear or fossil or big hydro, if you have it.
As you increase the percentage of renewables on the grid it gets more and more expensive to fill the last 20%, 10%, 5% etc.
To what end ? Once you have it down to say 20% fossil, you should stop wasting money on a number, because the rest of the world certainly won't want to commit economic suicide by increasing the cost of energy to ridiculous prices.


Once you store power plant carbon dioxide in empty natural gas wells you can do compressed air energy storage easily.


This is why Hydro Quebec is considered to be the "battery" for the East Coast. I read this year that HQ imports electricity when spot prices are low (times with high solar and wind production) in order to replenish their water reserves, and then sells electricity when spot prices are high.
The same system can be implemented for the West Coast grid, although arguably not for the Texas grid: use solar and wind when supply is plentiful, switch to hydro power when the sun isn't shining and the wind isn't blowing.


Hydro is a perfect compliment to renewables, if you have it, and have a lot of it.
I was not aware of compressed air storage being used in practice + what is the round trip efficiency & typical capacity?


You can search it to find the latest news last time I read there is a plant in Alabama that's been running for decades successfully profitably at about 70% efficiency round trip.


Hi mahonj,

Hydrostor have signed a deal to provide a compressed air storage facility in Broken Hill, in far western NSW. They will use an old silver mine for their system. Broken Hill, the home of miner BHP, is at the end of the grid although they have both wind and solar farms that can supply the storage. Not sure of the round trip efficiency. It's as hot as buggery out there, 38 degrees C today, so it should be a good test for the technology.


Hi Jim

Check out compressed CO2 storage:

Way more efficient round trip and less complex than compressing air.
A demo unit is up and running and a full scale 20MW 200 MWH unit is under construction in Sardinia due for completion 3rd quarter 2024

In its simplest form it is good for around 10 hours storage rather than weeks.

My own view is that the occasional week long outage is less of a show stopper than it appears at first, as the overall percentage of energy is quite low, and so efficiency is not paramount.
Chemical storage, hydrogen, ammonia, whatever can cover that.

Do tell me what you think of Energy Dome, as it seems pretty darn good to me!
However, it has to be able to withstand criticism, so fire away!


I think that the most reasonable solution is to have about 30% total wind and solar and then have the other 70% nuclear, hydro (if available), and geothermal (if available). Otherwise, to have a stable grid, you will need to have a prohibitive amount of storage and/or transmission lines to distant sources or fossil fuel backup. While the difference is not huge, nuclear is safer the wind or solar (although the numbers for solar may be influenced by home installation falls) and requires less steel and concrete, etc. than wind or solar. Hopefully, we are going to have a prototype high temp sodium cooled fast reactor in Kemmerer, Wyoming that will have molten salt storage that will allow the base power of 325 MW (electric) to load follow from 100 MW to 500 MW.


Roger Pham

Use Green Hydrogen to replace natural gas in the natural gas piping system, then use the H2 for power generation for backing the Renewable-Energy grid. When there'll be a surplus of RE, use that to make green H2 and store that H2 in underground reservoirs. It is a no-brainer!


Using Green Hydrogen to replace natural gas in the natural gas piping system is a no-brainer OK. Hydrogen has a higher energy content in terms of mass but not in terms of volume which means that you can not flow the same amount of energy down the pipe line with hydrogen as you can with natural gas. And if you thought that the problems with methane leakage are bad with old natural gas pipe lines, they will nothing like the amount of leakage you will get with hydrogen. Also, the hydrogen will cause further damage to the old old natural gas pipe lines by causing embrittlement.

Futhermore, even if this was a practical solution, the energy efficiency of electricity to H2 to electricity is about 40% at best. If you have water and elevation, pumped storage is a better solution with 80% efficiency.

Personally, I like Terrapower's high temp sodium cooled fast reactor solution which promises reliable base load with load following a lot better. If really want to play with hydrogen, which we do need for ammonia based fertilizer, using a high temp reactor is better solution as the electric power required goes down as the temperature goes up and if you get the temperature high enough, you do not even need electric power.


The Terrapower fast reactor is a great idea it reduces the amount of long-term radioactive waste immensely. Fast reactors were developed in the late 50s we should have kept going instead Russia China India are all ahead of us.


Hi sd.

The perspective I am most informed about is the UK, where there are indeed substangtial lulls of a week or more.

Off shore in the North sea is the most substantial potential source for hydrogen from electrolysis,.

Over distance, it is often preferable to turn the electricity into hydrogen either on site, or on the coast using often existing pipelines for NG,

There are indeed of course losses in turning the electricity into hydrogen, but after that pumping it etc is very efficient.

Using fuel cells on site it is then possible to utilise it at extraordinarily high efficiencies for electricity plus thermal, which is a totally different proposition to the present situation where natural gas is burnt , with the heat simply chucked out through a cooling stack, then transmitted as electricity with further losses, and other natural gas sent to homes and offices etc for heating with no electricity generated .

So the present natural gas network upgraded to handle hydrogen would appear to be of the right order of magnitude to pump hydrogen for way more efficient use than at present.

Although I have been a nuclear advocate for 60 years and more, I find it difficult to realistically think that with the extraordinary falls in renewables prices it will play any more than a bit part, even with SMNRs,

But to the extent that it does, using waste heat from SMNRs to produce hydrogen for use locally looks like a great way to increase electrical plus thermal efficiency and reduce costs


' Off shore in the North sea is the most substantial potential source for hydrogen from electrolysis,.'

I refer to the UK here.

Most places solar is likely to be way more important.

The comments to this entry are closed.