Three energy storage technologies can help the move
toward 100% renewable electricity.
by Kerry Rippy , The
A typical flow battery consists of two
tanks of liquids that are pumped past a membrane held between two
electrodes. Credit: Qi
and Koenig, 2017, CC
In recent decades the cost of wind and solar power
generation has dropped dramatically. This is one reason that the U.S.
Department of Energy projects that renewable energy will be the fastest-growing
U.S. energy source through 2050.
However, it's still relatively expensive to store energy.
And since renewable
energy generation isn't
available all the time—it happens when the wind blows or the sun
shines—storage is essential.
As a researcher
at the National Renewable Energy Laboratory, I work with the
federal government and private industry to develop renewable energy
storage technologies. In a recent report,
researchers at NREL estimated that the potential exists to increase
U.S. renewable energy storage capacity by as
much as 3,000% percent by 2050.
Here are three emerging technologies that could help make this happen.
From alkaline batteries for small electronics to lithium-ion
batteries for cars and laptops, most people already use batteries
in many aspects of their daily lives. But there is still lots of room
For example, high-capacity batteries with long discharge times—up to
10 hours—could be valuable for storing solar
power at night or increasing the range of electric vehicles. Right
now there are very few such batteries in use. However, according to recent
projections, upwards of 100 gigawatts' worth of these batteries
will likely be installed by 2050. For comparison, that's 50
times the generating capacity of Hoover Dam. This could have a
major impact on the viability of renewable energy.
One of the biggest obstacles is limited supplies of lithium and
cobalt, which currently are essential for making lightweight, powerful
batteries. According to some
estimates, around 10% of the world's lithium and nearly all of the
world's cobalt reserves will be depleted by 2050.
Furthermore, nearly 70% of the world's cobalt is mined in the Congo,
under conditions that have long been documented as inhumane.
Scientists are working to develop techniques for recycling
lithium and cobalt batteries, and to design batteries based on
other materials. Tesla plans to produce cobalt-free batteries
within the next few years. Others aim to replace
lithium with sodium, which has properties very similar to
lithium's but is much more abundant.
Another priority is to make batteries safer. One area for improvement
is electrolytes—the medium, often liquid, that allows
an electric charge to flow from the battery's anode, or negative
terminal, to the cathode, or positive terminal.
When a battery is in use, charged particles in the electrolyte move
around to balance out the charge of the electricity flowing out of the
battery. Electrolytes often contain flammable materials. If they leak,
the battery can overheat and catch fire or melt.
Scientists are developing solid
electrolytes, which would make batteries more robust. It is much
harder for particles to move around through solids than through
liquids, but encouraging
lab-scale results suggest that these batteries could be ready for
use in electric vehicles in the coming years, with target dates for commercialization as
early as 2026.
While solid-state batteries would be well suited for consumer
electronics and electric vehicles, for large-scale energy storage,
scientists are pursuing all-liquid designs called flow
In these devices both the electrolyte and the electrodes are liquids.
This allows for super-fast charging and makes it easy to make really
big batteries. Currently these systems are very expensive, but
research continues to bring
down the price.
Storing sunlight as heat
Other renewable energy storage solutions cost less than batteries in
some cases. For example, concentrated
solar power plants use mirrors to concentrate
sunlight, which heats up hundreds or thousands of tons of salt
until it melts. This molten salt then is used to drive an electric
generator, much as coal or nuclear power is used to heat steam and
drive a generator in traditional plants.
These heated materials can also be stored to produce electricity when
it is cloudy, or even at night. This approach allows concentrated
solar power to work around the clock.
This idea could be adapted for use with nonsolar power generation
technologies. For example, electricity made with wind power could be
used to heat salt for use later when it isn't windy.
Checking a molten salt valve for
corrosion at Sandia’s Molten Salt Test Loop. Credit: Randy
Montoya, Sandia Labs/Flickr, CC
Concentrating solar power is still relatively expensive. To compete
with other forms of energy generation and storage, it needs to become
more efficient. One way to achieve this is to increase the temperature
the salt is heated to, enabling more efficient electricity production.
Unfortunately, the salts currently in use aren't stable at high
temperatures. Researchers are working to develop new salts or other
materials that can withstand temperatures as high as 1,300 degrees
Fahrenheit (705 C).
One leading idea for how to reach higher temperature involves heating
up sand instead of salt, which can withstand the higher temperature.
The sand would then be moved with conveyor belts from the heating
point to storage. The Department of Energy recently announced funding
for a pilot
concentrated solar power plant based on this concept.
Advanced renewable fuels
Batteries are useful for short-term energy storage, and concentrated
solar power plants could help stabilize the electric grid. However,
utilities also need to store a lot of energy for indefinite amounts of
time. This is a role for renewable
fuels like hydrogen and ammonia.
Utilities would store energy in these fuels by producing them with
when wind turbines and solar panels are generating more electricity
than the utilities' customers need.
Hydrogen and ammonia contain more energy per pound than batteries, so
they work where batteries don't. For example, they could be used for
shipping heavy loads and running heavy equipment, and for rocket
Today these fuels are mostly made from natural gas or other
fuels via extremely inefficient reactions. While we think of it as
a green fuel, most hydrogen gas today is made from natural gas.
Scientists are looking for ways to produce hydrogen and other fuels
using renewable electricity. For example, it is possible to make
hydrogen fuel by splitting
water molecules using electricity. The key challenge is optimizing
the process to make it efficient and economical. The potential payoff
is enormous: inexhaustible, completely renewable energy.
Green Play Ammonia™, Yielder® NFuel Energy.
Spokane, Washington. 99212
509 995 1879 cell, Pacific.