Solar Mythbusters #3: Too much solar power?

This blog was written by John D. Wilson, former Deputy Director for Regulatory Policy at the Southern Alliance for Clean Energy.

Guest Blog | 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?

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.

In fact, solar power actually makes the system easier to operate for 3,000 megawatts or less.  The number of hours with the more difficult system demand changes actually goes down with the first two gigawatts (1,000 megawatts) of solar. Let’s get some gigawatts underway!!!

The more challenging conditions are represented in the graph by increases or drops of about 3,000 megawatts in system demand (see red and purple parts of bars).  Solar doesn’t increase these conditions until the system reaches 7,000 megawatts! For perspective, the entire U.S. had about 10,000 megawatts of solar in mid-2013.

Fortunately, the fuel savings generated by increases in solar would compensate for operational challenges or expenses incurred by such huge amounts of solar penetration. And in reality, one would hope that in the duration of time it would take a utility like TVA to reach 7,000 megwatts of solar, the currently aging grid will be updated and better equipped to deal with more diverse energy sources – whether generated by the utility or its customers.

So, are utilities warranted in claiming large amounts of solar are operationally too challenging? NO! Utilities would actually benefit from adding more solar now, and would be wise to make parallel investments in their grid infrastructure and operations to accommodate even greater levels of solar in the future.

Another myth debunked!

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