The Current State of Energy Storage

As the world begins to derive more and more of its energy from renewable sources, the topic of energy storage will become increasingly important. Though wind and solar are significantly more environmentally friendly than coal, oil, and natural gas, the intermittent nature of these greener sources necessitates the creation of technology to hold the energy they generate for use in the future. Such infrastructure does exist, but much more will be needed before we can make the transition to a world primarily powered by clean energy.

pumped hydro storage
Pumped hydro storage.

At the moment, pumped hydro storage is the most commonly employed technique for storing renewably generated energy for later use. In this simple method, excess energy generated by renewable (or nonrenewable) sources is used to move water from a low point to a higher point. In more technical terms, electrical energy is converted into gravitational potential energy during times of low demand. When more electrical is demanded of the grid, the water is allowed to fall back down to a lower point, and runs through turbines in the process. As it does so, gravitational potential energy is converted back into electricity. 

Pumped hydro plants last for a long time, and have a roundtrip efficiency (https://energymag.net/round-trip-efficiency/) of around 80%, which is considered to be quite good. These attributes, coupled with several others, have led to pumped hydro accounting for over 90% of utility scale energy storage technology in the U.S, and a majority of energy storage in the world. While this dominance will no doubt continue into the future, other options must be pursued for several reasons. The most important of which, is that there are many locations where the topology makes it impossible to employ this storage strategy. In the much of the midwest for example, there is not enough difference in elevation to create a pumped hydro plant. Additionally, pumped hydro plants are very expensive to both construct and maintain. 

The second most popular form of energy storage is thermal storage. In this method, excess energy is used to heat a substance, such as a salt. This heat can later be converted back into electrical energy and transferred into the grid. 

The third most popular energy storage strategy, and in my mind the most promising, is lithium ion batteries. When compared to other similar technologies, lithium ion batteries either perform competitively or are rapidly improving in the following important areas: 

  1. Calendar Life (The number of years the technology generally lasts)
  2. Cycle Life (The number of times the technology can be charged and discharged)
  3. Cost (The cost of storing / releasing a unit of energy)
  4. Gravimetric and Volumetric Energy Density (How much energy the technology can store per unit of weight and volume, respectively)
  5. Round Trip Efficiency (The percentage of energy put into the storage technology that can be discharged back into the grid)
  6. Safety

Out of all these metrics, cost is the most important in regards to the future of lithium ion batteries. Though it is currently cheaper to supply excess grid demand by starting up auxiliary natural gas burning power plants, projections indicate that by 2030, lithium ion batteries will be a more economical technology for filling this role. This prediction is based largely on the fact that lithium batteries price per kilowatt has fallen by an averaged for 85% since 2018, and that this trend seems very likely to continue into the future. 

If you would like to help increase the rate at which the cost of lithium ion energy storage falls and you already have solar panels on your roof, you might want to consider installing a battery storage system such as the Tesla Powerwall (https://www.tesla.com/powerwall). The cost of this installation can be offset in some states with tax incentives. California, for example, offers the Self Generation Incentive Program (https://www.cpuc.ca.gov/sgip/), which encourages homeowners to install clean energy technology. 

If you know of any other energy storage systems that you’d like to recommend, or energy related tax incentive programs that you would like to draw attention to, please do so in the comments. 

Additional energy storage facts and information: 

  • If you would like to get a better idea of the world’s currently installed energy storage infrastructure, this map created by the Department of Energy (https://www.energystorageexchange.org/projects) will be very helpful.
  • If you would like to learn more about how the price of a technology falls as more of it is produced (a process that is rapidly taking place with lithium ion batteries), check out this Forbes article on the topic. https://www.forbes.com/sites/jimhandy/2013/03/25/moores-law-vs-wrights-law/#1d5e45ba77d2
  • It likely that the batteries from electric cars will be repurposed for home and industrial energy storage, once they have derated to the point that they are unsuitable for powering a moving vehicle.
  • It is predicted that electric cars will eventually be able to help regulate the electrical grid by sending current into it when they are connected to charge ports.