How to Power the Grid with Renewables When the Sun is Gone

For decades, a major point of concern for renewable energy has been its intermittency and lack of energy production when the wind and sun are gone.

Last Monday's solar eclipse, however, provided grid operators valuable insight into how to run the electric grid in times of low solar production, as well as proof of concept for how to go over that hurdle.

Caption: Chart of solar generation in the ISO-NE region on the day of the eclipse. Source:

As solar generation dipped, Vermont’s Green Mountain Power (GMP) made the most of their distributed network of battery storage systems. By deploying energy stored in batteries, GMP was able to offset the lost production and prevent the need to fire up peaker plants, which are both expensive to run and responsible for disproportionate amounts of pollution.

This smooth shift to stored energy can serve as proof-of-concept that we do not have to depend on fossil fuel production to have a reliable, flexible electricity supply. An appropriate mix of storage resources can continue to support our demand for electricity even in times of low renewable energy production.

However, storage capacity is not yet where it needs to be. Despite GMP’s energy storage deployment, the greater New England region did not go through the eclipse fossil-fuel free. A substantial portion of the loss of solar energy was replaced by natural gas as the moon obstructed the sun’s rays for about an hour on April 8.

Caption: Chart of the fuel mix on April 8 in the ISO-NE region. A sudden spike in natural gas use can be seen around 3:30pm. Source:

So how can we prevent the need to fire up the most polluting power plants the next time solar generation dips temporarily, whether due to an eclipse, wildfire smoke, or a uniquely cloudy day?

One necessary action for the New England region to take will be to continue developing our energy storage systems, to ensure that we can capture excess energy production and disseminate it when it is needed.

Of course, the benefits of energy storage can be felt in many other scenarios, not just during an eclipse. They can continue delivering energy at night or on cloudy, windless days. They can also react to sudden spikes of energy demand caused by air conditioning or electric heat use during extreme weather events.

Whether the difference between supply and demand is caused by external factors or human behavior, energy storage can help even out that difference by absorbing excess production and releasing energy in times of insufficient supply.

Here’s what we’re watching across the states to advance the development of energy storage:

  • In Massachusetts, we’re supporting bill H.4503 (previously H.3216), which holds a section for increasing opportunities for clean peak energy storage.
  • In Rhode Island, we’re working to pass a state-wide storage deployment goal through legislation.
  • In Connecticut, we’re supporting S.B.298, which would study combining the deployment of energy storage batteries with new residential solar installations, as well as H.B.5442 which would expand storage deployment programs.
  • In New Hampshire, we’re tracking the progress of two bills, SB540 and SB386, which would require multiple studies of storage systems as a solution to creating a better, more modernized grid.

It’s a big year for storage, and we will continue to support efforts across the region that integrate storage into the broader effort to create a decarbonized, affordable electric grid system for all.

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