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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


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


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


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


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


to Fe


, as you charge. And

when you discharge the battery, the

positive side goes from Fe


to Fe


. 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


, to plate iron on the electrode

surface. And on discharge, the reverse


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.