Resilient Energy Strategy in Times of Dark Calm

“Dark doldrums,” the German term “Dunkelflaute,” or as U.S. energy management company ACES coined it, “dark calms,” all refer to the same concept – a period of little to no solar or wind generation in an area. The phenomena can occur in the middle of the summer, especially in Midwestern and Southern states, when hot, muggy air takes over and there is not even the slightest hint of a breeze. It can also occur in the winter, in periods of constant cloud cover and short days causing barely any sunlight to reach Earth’s surface. This results in very little solar or wind energy generation at a time when demand for power is typically at its peak, such as powering air conditioning for homes in the middle of a heatwave or keeping a home warm in the depths of winter. That is why it is vital for companies that produce solar and wind energy to understand dark calms and know how to prepare to continue to produce power and avoid an outage, allowing their customers to remain safe, comfortable, and none the wiser.

The NASA Prediction of Worldwide Energy Resources (POWER) project, which makes globally gridded data collected from NASA Earth observation satellites and models accessible through its web offerings, provided ACES, an energy management company, the historical data it needed to help one of its customers do just that.

ACES, headquartered in Indiana, serves 24 electric cooperative members and more than 70 customers across the United States, including independent power producers, investor-owned utilities, and industrial companies. One of its customers, the Platte River Power Authority (PRPA), provides power to 174,000 customers in Northern Colorado and relies largely on its solar and wind farms. The PRPA tasked ACES to conduct market research on dark calms, resulting in the Extreme Weather Event and Dark Calm Analysis report published in 2023.

“PRPA is committed to working toward achieving a 100% noncarbon energy mix by 2030,” said Frank Hull, the director of analytics at ACES and co-author of the report. “With a resource mix ... like solar and wind, it is important to create robust weather simulations to understand the worst-case scenarios.”

ACES said that, in the analysis, it easily accessed solar and wind speed data through the POWER application programming interface (API). ACES’ data scientists gathered data from airports at “70 locations west of the Mississippi River” including 27 locations in the Colorado Region (Achmano, Hull, 2023, p. 5). The team said they were initially conducting the analysis using only airport data but found POWER’s hourly historical solar irradiance data from the Clouds and the Earth’s Radiant Energy System (CERES) and 100-meter wind speed generation data derived from the Modern-Era Retrospective analysis for Research and Applications, Version 2 (MERRA-2) to be more accurate. ACES’ data scientists analyzed 20 years of POWER historical data (2002-2022) at the same airport locations plotted below.

ACES’ analysis of dark calms using POWER data allowed them to pinpoint when and where dark calms occur the most frequently. Ultimately, they found, “overall, regions with high wind penetration experience dark calm events during the summer, and regions with high solar penetration experience dark calm events during the winter,” (Achmano, Hull, 2023, p. 39). The report goes on to chart and compare when different regions faced dark calms, determining how many hours a region should prepare for a low percent of energy from solar or wind resources. For example, regarding the table below, Hull explained, “Northwest ERCOT (Electric Reliability Council of Texas) should plan for four unique 48-hour dark calms each year when they should expect only 10% of total installed renewable resources to generate power. Central MISO (Midcontinent Independent System Operator), which has a lot of wind generation, should plan for two unique 120-hour dark calms each year when only 10% of total installed renewable resources are generating power."

Dr. Masood Ahmad, the senior resource planning manager at PRPA, said ACES’ study on dark calms allowed it to develop, a more reliable future power supply portfolio by planning backup generation to support its wind and solar power during dark calms.

“We needed datasets with long historical records and wide geographical coverage to ensure the analysis appropriately captured this risk. ACES was able to get this data from NASA POWER,” said Dr. Ahmad.

Planning for power generation with the help of POWER data also allowed PRPA to determine pricing during times of high demand. However, Abenezer Achmano, manager of data science at ACES and the co-author of the report, said the impact goes beyond customer pricing.

“It’s not just about the money … it’s also about the safety of people,” Achmano said. “This data is helping companies provide power to people when they really need it.”

“During August and September in Texas or January in Minnesota, this is really what we’re trying to plan for. And we’re trying to determine the risk,” said Hull.

POWER’s accessible solar and wind data allowed Hull and Achmano to accomplish a successful risk analysis on dark calms for the PRPA. This type of assessment allowed the PRPA to determine how to remain energy resilient, making sure, at the end of the day, homes and businesses across the region have energy no matter the elements or lack thereof.

Outside of the study for the PRPA, ACES has also used NASA POWER data when conducting 8760 analyses – a type of report on expected supply, demand, or prices for every hour in a non-leap year, equaling 8,760 hours. ACES said these projects are confidential, however, one example is using POWER historical data to predict the energy generation for a solar or wind farm being built in a specific location for 2030.

“The generation output and subsequent capacity factor of the wind or solar farm can help determine whether the site is ideal for the wind or solar farm and specification of the technology,” said Hull.

The NASA POWER project is committed to serving as a reliable and ongoing resource for ACES and other energy management companies. ACES’ analysis highlights the critical role that accurate and dependable long-term data plays in market research, strategic planning, and the development of a diversified energy portfolio.