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The Challenge of Intermittent Energy


Some are blaming wind energy for the ERCOT failure to meet winter peak demand. Some are defending wind energy and blaming fossil and nuclear generation. Both are wrong and both are right. There is a real need for a more nuanced assessment, which unfortunately may be hard to achieve.


The chart below is from the ERCOT Wind Integration Report for February 14th, showing Actual Wind Output and ERCOT Load for the period from February 7th through the 14th with Wind Output in green (right scale) and ERCOT Load in black (left scale).



On February 7th, wind energy output peaked at 22,000 MW before it began a precipitous fall on the 8th, dropping to a low of under 1,000 MW before rebounding to 7,000 MW. The change in wind output paralleled the change in weather in west Texas where highs on the 7th were in the 70 degree range and dropped to a high in the low 30s by the 9th. The falling output in wind energy created demand for "backup" power to be brought online. Rapidly falling temperatures reportedly caused those systems to begin experiencing their own weather related challenges.


With wind output falling by 95% in less than 36 hours it would be wrong to say that wind was not the principle problem. However, intermittency is a known problem with wind generation. The second problem was the inability of the "backup" power systems to reliably pick up the load created by the loss of wind generation.


The problem became particularly egregious because at the time wind energy output was falling, demand for energy (reflected as Integrated Load) was increasing due to falling temperatures. The wind energy low coincided with an increase in load between 6,000 and 10,000 MW. Demand for "backup" power was hit by both the fall in wind output and the increase in load. As temperatures fell across the state demand continued to increase escalating the call for additional power. Since the time temperatures began falling on the 9th of February wind output has only briefly delivered 9,000 MW, of its near 32,000 MW capacity and has twice fallen to near 1,000 MW.


In the last ten days increased demand for energy and lack of output from wind has been met by a combination of backup power generation, increased delivery from baseload power systems and unfortunately, rolling blackouts to limit load. It is doubtful that any battery system could have met the ten day demand for an increase of over 20,000 MW of variable load without recharge. One of the challenges to be addressed for the future of energy will be the duration and capacity of reliable backup to meet future weather events (hot or cold).


The full assessment of what happened and what the response should be will occur over the months to come. Hopefully a balanced approach will help create the investments necessary to provide a highly reliable "backup" to meet future energy demand as more intermittent energy is incorporated into baseload power.

Roy Hartstein

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