Analysis of renewable energy points toward more affordable carbon-free electricity

Date:
August 6, 2020
Source:
California Institute of Technology
Summary:
A study identifies long-term storage technologies that would
enhance the affordability and reliability of renewable electricity.



FULL STORY ==========================================================================
As more states in the U.S. push for increased reliance on variable
renewable energy in the form of wind or solar power, long-term energy
storage may play an important role in assuring reliability and reducing electricity costs, according to a new paper published by Caltech
researchers.


========================================================================== Graduate student Jackie Dowling, who works in the lab of Nathan Lewis (BS
'77), the George L. Argyros Professor and professor of chemistry, has collaborated with Ken Caldeira at the Carnegie Institution for Science
and others to examine energy-storage options and multiple decades of
data about wind and solar availability. Dowling and her collaborators determined that currently available battery technology is prohibitively expensive for long-term energy storage services for the power grid and
that alternative technologies that can store a few weeks' to a month's
worth of energy for entire seasons or even multiple years may be the
key to building affordable, reliable renewable electricity systems.

Energy storage is needed with renewable energy because wind and solar
energy are not as reliably available as fossil fuels. For example, wind
power is often at its lowest during the summer in the United States,
which is when the electrical grid is strained the most by the demand
for air conditioning in homes and businesses.

"This research is motivated by the fact that laws in several states have mandated 100 percent carbon-free electricity systems by midcentury," says Dowling, lead author of a paper about the work. "Within these mandates,
a lot of states include requirements for wind and solar power. Both wind
and solar are variable from day to day, or even year to year, yet high reliability is mandatory for a viable electricity system. Energy storage
can fill in for the gaps between supply and demand." Dowling looked
at short-duration storage systems, such as lithium-ion batteries, and long-duration storage methods, such as hydrogen storage, compressed-air storage, and pumped-storage hydroelectricity.

To see how to optimize the use of those storage technologies at the
lowest energy cost, Dowling built a mathematical simulation of each
and incorporated historical electricity-demand data and four decades of
hourly resolved historical weather data across the contiguous U.S. The
Macro Energy Model, as she calls it, reveals that adding long-duration
storage to a wind-solar-battery system lowers energy costs. In contrast,
using batteries alone for storage makes renewable energy more expensive.

Dowling says that the extra expense associated with batteries occurs
because they cannot cost-effectively store enough energy for an entire
season during which electricity is generated in lower amounts. That
means an electrical grid would require many costlier solar panels or
wind turbines to compensate and would result in wasteful idling of electricity-generation equipment for much of the year.

Currently available battery technology is not even close to being cost effective for seasonal storage, Dowling says.

"The huge dip in wind power in the summer in the U.S. is problematic,
and batteries are not suitable for filling that gap. So, if you only
have batteries, you have to overbuild wind or solar capacity," she
says. "Long- duration storage helps avoid the need to overbuild power generation infrastructure and provides electricity when people need it
rather than only when nature provides it. At current technology costs,
storage in underground caverns of green hydrogen generated by water electrolysis would provide a cost- effective approach for long-duration
grid storage." Other researchers have built renewable energy models,
but the team's data- driven approach is the first to incorporate four
decades of historical wind and solar variability data, thus factoring
in variability from year to year and periodic episodes of rare weather
events that affect power generation, such as wind and solar droughts.

"The more years of data we use in our models, the more we find a
compelling need for long-term storage to get the reliability that we
expect from an electricity system," she says.

Dowling suggests her findings may be helpful to policy makers in states
with 100 percent carbon-free electricity laws and high wind/solar mandates
and to other U.S. states considering the adoption of similar laws. In
the future, she plans to extend her research to take an in-depth look
at the roles that specific types of energy storage, such as hydrogen or
redox flow batteries, can play in renewable energy systems. For instance,
some types of batteries might effectively serve as medium-duration energy storage, she says.


========================================================================== Story Source: Materials provided by
California_Institute_of_Technology. Note: Content may be edited for
style and length.


========================================================================== Journal Reference:
1. Jacqueline A. Dowling, Katherine Z. Rinaldi, Tyler H. Ruggles,
Steven J.

Davis, Mengyao Yuan, Fan Tong, Nathan S. Lewis, Ken Caldeira. Role
of Long-Duration Energy Storage in Variable Renewable Electricity
Systems.

Joule, 2020; DOI: 10.1016/j.joule.2020.07.007 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/08/200806133513.htm

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