By
Ben Swerdlow, Policy Extern
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| Source: Energy.gov |
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.
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| Source: Energy.gov |
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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