Key Takeaways:

  • Storage is required for wind and solar because they are not “dispatchable”
  • $20 per kilowatt hour for storage is the target to reach 100% renewables.
  • Storage isn’t the only way to go: Demand-side programs & enhanced transmission can help

Proponents of clean energy know there are hurdles to reach 100% renewables. One of the biggest is how to store wind and solar energy for use when the sun is not shining, and the wind isn’t blowing. Storage must be economical, too. However, until now no one has identified a target for storage costs, so we can make renewables competitive with other forms of generation to meet 100% of energy demand.

A research team led by Jessika Trancik at a Massachusetts Institute of Technology (MIT) lab studied 20 years of weather data from locations in Arizona, Iowa, Massachusetts and Texas. They created a model of a renewable energy storage system based on a mix of wind and solar power which could meet demand at a rate of 100% over 20 years.  Within this model, the team made a goal to obtain a competitive price in relation to other forms of generation.

The result of the high bar of 100% over 20 was a $20/kWh energy capacity cost target. However, if any of the assumptions are softened even a little, the competitive storage cost rises (and thus far more likely to be reached in a realistic time frame).

For example, if wind and solar need to be available 95% of the time (rather than 100%) to meet demand over 20 years, the cost of storage is $150/kWh. Over 20 years there will be rare times when the weather is not conducive over an extended period for wind and solar generation. Building enough storage to fill that gap is exponentially more expensive.. Many believe this will be where flexible dispatchable power plants could make up for the lack of demand. It’s reasonable to assume that some other form of generation may be used during those rare events when wind and solar cannot fill the demand.

Likewise, the MIT research doesn’t consider 1) demand-side programs that shift energy consumption to other times of the day and 2) the benefits of enhanced long-distance transmission to carry renewable energy from regions where it’s overproduced to regions where it’s needed.

The bottom line:

  • Storage doesn’t have to do all the work.
  • Costs vary depending on the storage technology (think pumped hydro v. lithium-ion batteries), and many new low-cost technologies are promising.
  • Solar and wind generation continues to get cheaper too, which will ease pressure on storage costs.
  • A US grid run on renewable energy at least 95 percent of the time looks to be more achievable.


What We’re Reading: “Getting to 100% renewables requires cheap energy storage. But how cheap?” by David Roberts as published on