https://eandt.theiet.org/content/articles/2019/07/high-performance-flow-batteries-could-enable-grid-level-renewable-energy-storage/
[High efficiency, cost-effective, non-hazardous energy storage coupled
with renewables to provide reliable electric power is the new low-cost
winner for new generation & supply construction. Already cheaper than
operating coal facilities, and new-build / major refurbishment nuclear
fission, and now poised to take on new-build natural gas. The green
approach also lends itself to distributed generation and power
'islanding' in the event of grid outages (weather-related or other
causes), creates on-going local employment and eliminates the need to
import fossil fuels - which is the flip side of exporting wealth and
income. This does not even include the advantages to electric utilities
from having a fast-response energy storage system which can be used to
stabilize voltage and frequency. Why are we even looking at more fossil
fuel and nuclear generation? Better batteries will come, and they will
be 'plug-in' compatible with whatever current technology is being
installed.]
High-performance flow batteries could enable grid-level green energy storage
By E&T editorial staff
Published Friday, July 26, 2019
A low-cost, high-performance battery chemistry developed by University
of Colorado Boulder researchers could one day lead to scalable
grid-level storage for wind and solar energy, which in turn could help
electrical utilities reduce their dependency on fossil fuels.
The innovation, described in the journal Joule, outlines two aqueous
flow batteries, also known as redox flow batteries, which use chromium
and organic binding agents to achieve exceptional voltage and high
efficiencies. The components are abundant in nature, offering future
promise for cost-effective manufacturing.
“We’re excited to report some of highest-performing battery chemistries
ever, beyond previous limits,” said Michael Marshak, senior author of
the study and an assistant professor in CU Boulder’s Department of
Chemistry. “The materials are low-cost, non-toxic and readily available.”
Renewable energy sources provide a growing share of electrical
production in the US, but currently lack a large-scale solution for
storing harvested energy and re-deploying it to meet demand during
periods when the Sun isn’t shining and the wind isn’t blowing.
“There are mismatches between supply and demand on the energy grid
during the day,” said Marshak, who is also a fellow in the Renewable and
Sustainable Energy Institute (RASEI). “The Sun might meet the grid’s
needs in the morning, but demand tends to peak in the late afternoon and
continue into the evening after the Sun has set.
“Right now, utility companies have to fill that gap by quickly revving
up their coal and natural gas production, just like you’d take a car
from zero to sixty.”
Although lithium-ion can provide power for smaller-scale applications,
you would need millions of batteries to back up even a small fossil fuel
power plant for an hour, Marshak said. While the lithium-ion chemistry
is effective, it’s ill-suited to meet the capacity of an entire wind
turbine field or solar panel array.
“The basic problem with lithium-ion batteries is that they don’t scale
very well,” Marshak said. “The more solid material you add, the more
resistance you add and then all of the other components need to increase
in tandem. In essence, if you want twice the energy, you need to build
twice the batteries and that’s just not cost-effective when you’re
talking about this many megawatt hours.”
Flow batteries have been identified as a more promising avenue. Aqueous
batteries keep their active ingredients separated in liquid form in
large tanks, allowing the system to distribute energy in a managed
fashion, similar to the way a petrol tank provides steady fuel
combustion to a car’s engine when the accelerator pedal is pushed.
While there are some examples of flow batteries operating consistently
for decades, such as in Japan, they have struggled to gain a broad
foothold in commercial and municipal operations due in part to their
unwieldy size, high operating costs and comparably low voltage.
“The size is less of an issue for grid-scale systems, because it would
just be attached to an already large structure,” Marshak said. “What
matters is cost and that’s what we wanted to improve on.”
The researchers went back to basics, re-examining flow battery
chemistries that had been studied years ago, but abandoned. The key
turned out to be combining organic binding agents, or chelates, with
chromium ions in order to stabilise a potent electrolyte.
“Some people have taken this approach before, but hadn’t paid enough
attention to the binding agents,” said Brian Robb, lead author of the
new study and a doctoral student in the Department of Chemical and
Biological Engineering (CHBE). “You need to tailor the chelate for the
metal ion and we did a lot of work finding the right one that would bind
them tightly.”
Marshak, Robb and co-author Jason Farrell customised chelate known as
PDTA, creating a ‘shield’ around the chromium electron and preventing
water from hampering the reactant and allowing one of the battery cells
to disperse 2.13 volts – nearly double the operational average for a
flow battery.
PDTA is a spinoff of EDTA, an agent already used in some hand soap, food
preservatives and municipal water treatments due to its
bacteria-stymying properties. EDTA is considered non-toxic. The
chemistry also uses the benign form of chromium, the same type used in
stainless-steel surgical instruments.
“We got this to work at the relatively neutral pH of 9, unlike other
batteries which use highly corrosive acid that’s difficult to work with
and difficult to dispose of responsibly,” Robb said. “This is more akin
to laundry detergent.”
“You could order 15 tonnes of these materials tomorrow if you wanted,
because there are existing factories already producing them,” Marshak added.
Marshak and Robb have filed a patent on the innovation with assistance
from CU Boulder Venture Partners. They plan to continue optimising their
system, including scaling it up in the lab in order to cycle the battery
for even longer periods of time.
“We’ve solved the problem on a fundamental level,” Marshak said. “Now
there are a lot of things we can try in order to keep pushing the
performance limit.”
--
Darryl McMahon
Freelance Project Manager (sustainable systems)
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