Image of electric grid for a solar farm
From left, Jackson Siff ’19, Jeff Sward, and Jiajun Gu examined ramping on the electric grid and land parcels for solar farms.

By adding utility-scale solar farms throughout New York state, summer electricity demand from conventional sources could be reduced by up to 9.6% in some places. But Cornell engineers caution that upstate winters will be a problem to deal with.

With low energy demand around midday in the winter, combined with solar-electricity production, New York’s power system could face volatile swings of “ramping” — which is how power system operators describe quick increases or decreases in demand.

“It’s a very surprising finding,” said senior author Max Zhang, associate professor at Cornell’s Sibley School of Mechanical and Aerospace Engineering. “When are you going to have maximum ramping take place in New York? It’s not going to be in the summer when the solar power is the highest and the needs are more balanced. It turns out to be in the winter.” Said Zhang, “When you have several days of sunshine in a row during winter, that causes the largest ramping on the power system in New York state”.

The energy industry’s ramping dilemma — due to spikes in net load, which is the total electric demand minus renewable electricity generation — creates a so-called “duck curve.” When people wake up and prepare for the day, it takes energy to run the house — and that becomes the morning peak. Since solar reaches peak production in the middle of the day, the net load lags. When people get home from work in the evening, energy demands create a second peak. Thus, with a peak, a large lag and a second peak that slowly diminishes in the evening, the graphic curve of net load resembles a duck.

Ramping makes the grid less efficient, because system operators then must employ natural gas or other carbon methods to keep up with demand. “This paper can inform regional development trends and could lead to the improvement of electricity transmission from upstate to downstate,” said co-author Jeff Sward.

“The increasing ramping requirement will be a challenge in pursuing our renewable energy target,” said Zhang, “but it can be met with flexible resources, both in the supply and demand sides, as well as energy storage.”

As part of the paper, Jackson Siff, another co-author, worked with David Kay, senior extension associate in development sociology, at Cornell’s Community and Regional Development Institute to conduct spatial analysis of New York state land parcels in order to identify places where utility-scale solar farms could work best.

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