Eclipse Impact on Shared Solar

The solar eclipse is a learning opportunity for utilities nationwide.

The solar eclipse on Aug. 21, 2017, captivated people across the United States, including many of us at MGE! It wasn't simply because a solar eclipse is a rare event but rather it presented an opportunity for us to learn from other utilities. Many southern and western utilities have community grids that rely heavily on solar energy compared to utilities in the upper Midwest.

According to the U.S. Energy Information Administration (EIA), the eclipse was expected to obscure sunlight in varying degrees to about 1,900 utility-scale solar installations. Some were impacted more than others depending upon whether they were in the path of totality— a line stretching from Oregon to South Carolina where the moon completely covered the sun. A drop in sunshine meant a drop in solar energy generation during the eclipse, forcing other sources of generation (such as natural gas-fired power plants and other sources) to make up the difference to ensure no short-lived outages for customers.

The Madison area wasn't in the path of totality; however, we saw the effects of a partial solar eclipse on our Shared Solar installation in Middleton. Energy 2030 Together went out to our Shared Solar array during the eclipse and tapped the expertise of MGE Senior Engineer Dave Toso to explain the impact locally in a brief video and Q&A.

Q: How did the solar eclipse—a partial solar eclipse for south central Wisconsin—impact MGE's Shared Solar array?
A: During the two-hour and 47-minute eclipse, the array produced 373 kilowatt-hours (kWh). Had the array been exposed to full sun, it would have generated 1,100 kWh. This represents a decrease of 66% solar production during the eclipse.

The speed and magnitude of the decrease in and ramping back up of the array's power production also was more pronounced than is typical during days of intermittent cloud cover. This allows us to observe how successfully the solar project's control systems manage this unusual swing in production.

Q: Why is this type of event a learning experience for utilities nationwide?
A: Solar power production can vary widely from moment to moment due to shading. As solar grows and makes up more of the electricity supplying the grid, utilities will need to anticipate and manage these changes in production to keep the grid stable and reliable. Technology like smart power inverters, other generation sources like natural gas and eventually electricity storage are tools helping utilities do this. Utilities more impacted by the eclipse due to the higher penetration of solar arrays in their areas will be studying the use of these tools and sharing this information with the rest of us.

Q: MGE's Shared Solar array has "smart inverters." What are they and why are they useful during variations in generation such as those caused by a solar eclipse?
A: Inverters convert DC current generated by the solar array to AC current used by electric appliances in our homes and businesses. Inverters also act as the gateway between the solar arrays and the power grid. Smart inverters can make it possible to better and automatically manage the electricity flowing to the grid. They will help assure fluctuations in solar power are smoothly integrated into operating the grid.

Q: Did the solar eclipse have any impact on the reliability of the grid in MGE's service territory?
A: MGE did not anticipate or experience any impacts on the reliability of the grid in our service territory during the eclipse.

Q: What if I miss the solar eclipse, when is the next occurrence in the U.S.?
A: The next total solar eclipse visible in the U.S. will occur on April 18, 2024. It will be visible from a path running from central Texas to upstate New York.

Anyone can follow electric production by MGE's Shared Solar array at

published: 08-22-2017 | updated: 09-18-2017