Solar Mythbusters #3: Too much solar power?

John D. Wilson | February 21, 2014 | Energy Policy, Solar

Myth: High levels of solar penetration are too disruptive for utility and grid operations.

This is the third in our Solar Mythbusters series: check out the cloud and intermittency myths we already busted.

Cost and complexity are often cited as barriers to integrating large amounts of solar power on a utility grid system. More specifically, utilities flag solar as being intermittent and non-dispatchable, and therefore incapable of being a reliable and investment-worthy source of generation. So when I testified before the South Carolina Public Service Commission regarding our proposal to add a 375 megawatt solar power plant to Duke Energy’s proposed Lee natural gas plant, I guess I shouldn’t have been surprised with Duke’s response that the size of the project was too large.

This got me wondering, how much is too much solar power?

Under current demand conditions, TVA system operators must respond to changes in demand of more than 1,000 MW only 15% of the time. Solar power would have no effect on this up to at least 3,000 or 4,000 megawatts. Which is a lot more than we have today!

It’s really hard to answer that question (maybe there’s never too much?), but one way to look at it is to consider whether solar power is making it more difficult to operate the power grid. It’s a problem called intermittency. Demand for power fluctuates from minute-to-minute, and hour-to-hour. Some power plants operate without much adjustment, but others are “ramped up” or down in response to changes in power needs. One common critique of solar power is that it increases these fluctuations, making it harder for the utility to operate its system of power plants.

We tested this theory using 15 years of solar power data and load data for the Tennessee Valley Authority, which was discussed in our February 19th blog. We assumed that TVA’s system operators would prefer it if the demand for power didn’t fluctuate by more than 1,000 megawatts from hour to hour. It turns out that on average, this is true about 85% of the time.

In the graph above, you can see that with even as much as 3,000 megawatts of solar, there’s effectively no change in how often the system is “easy” to operate. We are a long way from having 3,000 megawatts of solar deployed in TVA – about 3% of the way, actually, and with the continuing skepticism about solar by utility executives and interest groups, the myth that solar power disrupts system operations will probably continue to resurface.

John D. Wilson
For more than a decade, John has directed SACE’s research activities and led SACE’s utility reform campaigns. He often represents SACE in formal or informal stakeholder engagement with utilities, and…
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