Wednesday, February 24, 2016

The Future of Energy Storage Might Just Be a Bunch of Hot Air

By Ben Swerdlow, Policy Extern
            As renewables become more prevalent in our energy system, it is important to discuss how we plan to deal with the associated intermittency of variable renewables like wind and solar power. One option for addressing the intermittency challenge is through energy storage. Energy storage provides additional benefits beyond integrating variable renewables. For example, energy storage can provide stability for the grid and limit the need for peak production facilities. The significant factor that will spur installation of energy storage is cost, and storage costs are on par or cheaper than adding new generation we will see a change to how power is produced and transmitted in the United States.

            In order to understand where we are going it is important to discuss the current state of energy storage in the United States. For a long time the energy storage of choice was pumped hydro, which relies on creating an upper reservoir where water is pumped during times of low energy demand— with low energy prices— and then released down into a lower reservoir to spin turbines and generate electricity when demand is high. In the United States there are 36 pumped hydro facilities with a total storage potential of 20.36 GW. Although pumped hydro provides a significant portion of the energy storage in the United States, the upfront capital costs of $353 kW to $2,216 kW mean that this is not the technology that will pave the way toward more energy storage in the near-term.

            Many advocates argue that lithium-ion batteries are the future of energy storage, and in some ways they are right. However, there may be better options. Currently, these batteries are just too expense to be a viable option for grid-scale energy storage, with costs at around $400 per kW stored. This stands as one of the main reasons why energy storage has not become a more significant part of our grid.

            Fortunately, there are several energy storage technologies which promise to be much more affordable, less resource intensive and more readily expandable than pumped hydro or lithium ion batteries. One is known as the “flow battery,” which operates by storing charged liquids in containers. The benefit of this technology is that expansion is extremely easy, as the size of the container is the main limiting factor. Although there have been significant breakthroughs in this technology, flow batteries remain very expensive, but as the science improves it is possible that these batteries could one day be part of our electricity grid.

            Another significant technology that promises to be important to our energy future is compressed air storage, or as LightSail has dubbed it,regenerative air energy storage.” The goal of LightSail is produce a low-cost, scalable energy storage solution that focuses on the use of compressed air energy storage. While the technology of compressed air energy storage has been around for a while, LightSail believes they have improved upon the technology so as to make it the most viable energy storage option. During the course of compression, air becomes very hot, which has been one of the limiting factors to storage. However, this problem may be solved through the well-timed introduction of water droplets. By employing this concept, LightSail has achieved very high thermodynamic efficiencies which leads to higher revolution per minute (RPMs), and therefore a lower cost per kilowatt-hour. Just as with the flow battery, the size of the container is the main limitation in the amount of energy that can be stored through compressed air energy storage, which leads to the possibility of significant expansion potential. Additionally, as air is the “fuel,” there are limited costs associated with running a LightSail product.

            While the future remains uncertain for energy storage, significant investments have been made in these technologies to achieve additional storage capacity in the future, with every year resulting in more and more energy storage construction. This indicates that we are moving toward a future with less wasted energy, and as more companies experiment with these technologies we get closer to achieving the goal of a green energy grid.

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