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WORLD-GENERATION NOVEMBER/DECEMBER 2016
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PORTLAND, OR - With the growth
trajectory that solar is experiencing, more
solar is being installed due to dramatically
lower installation costs, and considering
that net metering certainly appears to be
going away, batteries are becoming an
asset and in some locations a requirement
for further solar integration. One of the
big emerging use cases for integrating
batteries with solar, is long-duration
storage – and the beneficial impacts that
4+ hours of storage will have on the
market in terms of how the value of solar
and other renewable installations are
measured. For example, having the
flexibility to engage both power and
energy applications utilizing stored solar
power is an incredible use case for this
resource. With long-duration storage you
have the ability to store excess solar
production and time shift that energy to
when it has higher economic value. The
storage allows you to smooth out solar
intermittencies throughout the day,
address expensive demand charges for
C&I customers, and shift that solar power
out into the later afternoon and early
evening where it is far more valuable to
the asset owner and to the grid operator.
Certainly the integration of longer
duration storage will allow us to deploy
even more solar and other renewables.
A 10-kilowatt, 60-kilowatt hour all-iron
flow battery from ESS Inc. installed at the
Stone Edge Farms Advanced Micro Grid
in Sonoma County, CA is primarily for PV
smoothing as well as shifting stored solar
energy to the evening to power irrigation
pumps and a hydrogen electrolizer. The
ESS battery system is coupled with a D.C.
System micro grid controller that controls
the battery using Sun Spec protocols over
a Modbus interface. DC Systems
optimizes the use of the battery system,
locally, on a daily basis. ESS is also able to
monitor and control the system back at its
headquarters.
The ESS system is an environmentally
safe chemistry. It’s iron, salt, and water.
These abundant and low cost materials are
also non-corrosive, so low cost plastic-type
materials can be used in the battery
modules, which keep capital costs
extremely low. The benign ingredients are
also non-flammable which completely
eliminates a costly fire suppression
system.
The system is very easy to install.
The IFB ships in a dry state, is hydrated
on site and because it is a complete
integrated and turnkey system, once the
system is grid connected our team can
have it fully operational in about a day and
a half. Field certified through Intertek.
The IFB has a durable and a long
operating life in excess of 20,000 cycles, or
> 25 years.
The company has done extensive
testing of the IFB, cycling it in two
different depth of discharge modes.
The first one is operating at very high
states of charge, doing very shallow depth
of discharge cycles, so between 80 and 90
percent of state of charge (SOC). The
second one is deep discharge cycles, going
from 95 percent down to 20 percent state
of charge. This simulates doing one full
cycle a day on the battery. This rigorous
testing has validated no capacity loss and
very little efficiency loss over its operating
life.
When you’re doing large-scale PPA’s
that last 20-25 years, the life of the solar
system, you want to couple that with a
battery that’s going to last just as long, so
you don’t have to replace the battery
multiple times, impacting your levelized
cost of storage (LCOS). That’s very
counterintuitive to a lithium ion battery or
a lead acid type battery, which are actually
going to fade over time and have to be
replaced.
Some of the reasons why ESS is able
to achieve these no capacity fade cycles
and long-duration capacities are primarily
due to the type of battery chemistry used.
It’s a flow battery. And in a flow battery
basically all of the reactions occur in the
liquid form. Basically you’re stripping the
electrons on and off of Iron ions. In our
case, on the positive side of the battery,
you are changing the oxidation state of
iron – Fe
2+
to Fe
3+
, as you charge. And
when you discharge the battery, the
positive side goes from Fe
3+
to Fe
2+
. So
you’re basically going from ferrous to
ferric states. On the negative side of the
battery, we go from ferrous chloride,
which is Fe
2+
, to plate iron on the electrode
surface. And on discharge, the reverse
happens.
One of the other reasons, besides
operating in the liquid form, is that we
have very high capacity, operating with
the same electrolyte on both sides of the
battery. So, there’s no ability to cross-
contaminate the battery. In some types of
flow batteries, you have different elements
on both sides of the battery – iron chrome,
zinc iron, vanadium iron. Over time, no
membrane is perfect and will result in
diffusion. Eventually, the elements from
either side of the battery are going to
cross over, which is going to contaminate
the electrolyte and degrade the
performance of a flow battery. Then you
have two choices. One, you can either
replace the electrolyte entirely, which can
be costly and a lot of O&M. Or you can
live with that efficiency and capacity loss.
The ESS IFB does not have this limitation.
In terms of how we keep our efficiency
high over all these cycles – that lends itself
to the positive electrode where typically
you would see a lot of carbon corrosion.
PERSPECTIVE
THE FUTURE OF
ENERGY STORAGE
BY CRAIG EVANS,CEO,ESS, INC.