be able to give you an update on our GCEP project on Solid Oxide Flow Batteries for

Grid-Energy Storage.

A couple years back, we, we gave a talk as well on the cell material

advancements we've been working on.

In today's talk we're going to focus more on the system concepts,

that will hopefully enable the technology to move it forward.

Before moving into that I just want to acknowledge our team members

PhD student Chris Wendel, Professor Bob Kee at the School of Mines.

Professor Scott Barnett and, and Doctors Gareth Hughes and, and

Zhan Gao at Northwestern are really working at advancing the Cell Technology.

So, in today's talk I'm going to briefly give you an overview of what, exactly,

is this technology.

And followed by, with I guess, I would say our view of some of the motivation and

the technology requirements that are needed for energy storage to move forward.

I'll then move in to some descriptions of reversible solid

oxide cells as flow batteries.

Here we'll look at, little bit at the theory of operation and

performance considerations.

As well as some performance estimates of really these large scale, megawatt size,

gigawatt hours, capacity systems that we would envision for, for bulk storage.

Brief, I'll give a brief update of some of the exciting developments in the South

development area where we're, we're really trying to push towards the 600 in sea

operation salutes and all this GM technology.

And we have some very interesting and encouraging results related to,

to cycling to show of these cells.

And that's very important how we're going to operate forward and

backward modes with this technology.

We don't want degradation there.

Lastly we'll, we'll touch on some of the economic projections for

these kind of large scale bulk energy storage systems.

I'll then briefly touch a little bit on what we've learned, in,

in featured reactions.

So in principle, a solid oxide flow battery really leverages

similarities to fuel cells where we're going to operate reversibly.

Here reversibly is not in the thermodynamic sense.

It's in the sense of reversing the current for the system to operate in a power

producing mode, and in an electrolysis or charging mode.

And we're, we're going to tank the reactants and, and

capture those in, in gaseous storage, and that's particular useful for

us because it gives us really the flow battery advantage.

We get the decouple power capacity from storage.

And so the power will scale with the size of the cell stack and

the energies will scale with the size of the storage tanks.

We also get the high efficiency advantage of solid oxide cell technology.

Which enables us to have really high round-trip

efficiencies as we move between modes.

We don't experience high polarization in electrolysis mode.

And the novel, relatively novel HCO chemistry that is experienced directly

within the cell, allows us to, to produce high energy dense fuels.

So shown here is a, is a, a real simple schematic of,

of a solid oxide cell and oxygen conducting one with some fuel storage.

Here we are showing methane and syngas and we are going to feed it with air, and

we're going to take the oxygen from there, reduce it, get those anions.

Moving and electrochemically oxidized those gaseous reactants into H2O and CO2.

We will capture that gas in a tank and essentially produce our power.

Now, in reverse mode, we can then accept ply voltage,

driver currents, and essentially put our power into the, the device.

And then move into the opposite mode, where we'll remove those previous

products of reaction out of storage back to our cell.

We'll strip out the oxygen.

Liberate some of that oxygen.

And in the meantime, directly within the cell, we will produce methane and, and

syngas.

In general, that'll give us favorable scaling this device, but

also something additionally unique is that it gives us really low-cost working

fluids compared to advanced, and other types of flow batteries.

In terms of motivation, certainly, the variability of renewable energy resources

is is well-known and motivates developing grid-energy solutions.

I like to at least see some picture of what that means?

Here are some minute by minute data shown from Hawaiian Electro Power

on a wind farm.

We can see really a ten exchanged within 30 minutes of, of power requirements.

And it's not just wind variability if we look at developing activities and

concentrating solar power and of course, PV penetration,

they've got power fall-off in, in the evening hours as well that would,

will need to be addressed to get high-capacity factors.

So currently there is no battery technology that really serves

most of our energy storage.

Worldwide is predominantly pumped hydro.

In, that's, but this problem still exists, and those who are facing this,

primarily, often island nations for example, are,

are already trying to develop solutions, and I'll call them poor solutions.

Taking high grade electrical energy, and storing it in low-grade hot water for

example, so called thermal battery.

That's being done by Hawaiian Electro Power to, to manage this,

this variability.

It's also being done in an Electricity Arbitrage Models in Minnesota,

for example.

I've called them the, the dubious honor of having the largest thermal battery in

perhaps in the country at one-gigawatt hours.

High-grade electrical energy,

low-grade hot water is essentially thermodynamic syn.

But in, on the other hand you know,

good economics doesn't necessarily always mean good thermodynamics.

In general,

though, in order to enable that technology we've got to reach some certain targets.

We've been keeping our eye on these as we look at this technology.

Certainly capital cost and round-trip efficiency but perhaps most importantly

some levelized cost of electricity storage around a dime per kilowatt hour cycle.

We need cycle capability, and depending on the application,

you'll need various modes various duration of storage.

If we now turn to looking at the technology itself.

Just operationally, we can take a look at a voltage current

plot which is a representation of the cells performance characteristic.

And shown here, we can see that in power producing mode or fuel cell mode

the voltage will decrease as you increase the current density or, or produce more

power in response to, to overpotentials and irreversibilities within the cell.

The slope of this curve represent the overall resistance.

In fuel cell mode, the higher the voltage the higher the efficiency.

And in electrolysis mode we can see a rel, a relatively smooth transition shown here

in this cartoon, but that's actually what we see experimentally as well.

There isn't a large over potential that gives us good electrolysis efficiencies

low-applied voltage needed there.

But here you want low voltage equals high electricity in electrolysis mode.

So, if we look at the round-trip stack efficiency, which is not shown here, okay.

It's basically the voltage of the fuel cell divided by the voltage

of the electrolysis device.

That's the ratio.

So you want high fuel cell voltage, low electrolysis voltage,

that will give you a high round-trip efficiency.

At the system level we not only need to be mindful of the stack but.

We're moving these reactants back and forth between the tank and the stack and

so there's an auxiliary power component that enters into this ratio.

So, in the end, how we can improve system efficiency.

We can improve the cell by reducing over potential and at the system level,

we got to mindful of the balance of plant and thermal management.

And when we look at thermal management,

one of the unique attributes here is by doing methanation locally,

within the cell and electrolysis mode, we are able to obtain low

electrolysis voltages, get towards a thermal neutral operation, as well.

So, when we look at a fuel cell, it requires heat rejection.

We're air cooled we're operating it at relatively high temperatures.

But in electrolysis this is of course and endothermic process.

It requires a heat source.

As, and we can see that when we reduce H2O that's certainly the case.

We're going to leverage HCO chemistry here and because of the nickel in, in,

in the fuel electrode we can also do heterogeneous chemical reactions and

reduce CO2 as well through H2 and

provide us with some CO which can then be combined with hydrogen to methanate.

Which is highly exothermic, okay?

And that's very nice for us.

Because we have a exothermic local source where we have an endothermic process.

We've got good matching of sources and sinks there.

And ultimately, low temperature is what we would want in relatively high pressure

to achieve that methanation.

One of the considerations we're faced with as well is.

If we're going to design one of these systems, what do we charge the tanks with?

What is the composition we want?

And what are the considerations therein?

So in these systems, we have to be concerned about carbon deposition.

This is a deleterious effect on, on, on, solid oxide cells.

And it degrades their performance rapidly should that happen.

So shown here is in the right is essentially

a compositional space used in a so called Gibs diagram or ternary diagram.

Where the shaded area above the rad indicates the thermodynamically

favorable region for carbon deposition to occur.

And the, the open, the white zone really is is unfavorable for

that, and that's where we want to operate.

So in doing so, you can see the red dot up here is where we might start on

a hydrogen carbon ratio oxygen ratio for, for fuel cell mode.

As we oxidize the fuel, we'll move towards this fully oxidized region shown in

the light blue, and we don't really want to be fully oxidized.

In this system, we want to be not fully oxidized and not fully reduced.

This is our operating window, if you will, to move back and forth.

If we look at the bottom graph, we can see basically on the left hand side

equilibrium gas constitution on a molar basis.

It's, it's a wet basis shown here versus oxygen content.

And we can basically move back and forth between, shown here between 4 and

40% oxygen conversion, which will allow us to have fairly high storage capacity.

We can produce methane in a 60-40 ratio with hydrogen here, on a dry basis.

And at this end of the cell, so basically as you produce a fuel cell mode,

you'll see us reducing the CH4, producing H2O.

These, of course, will be tanked for electrolysis mode.

So one of the proposed applications we've been looking at is really bulk storage.

To, in order to get there, we need very large tanks.

And very large tanks can be realized with pressurized underground

gaseous storage of our reactants.

Using salt caverns, for example, natural gas reservoirs, saline aquifers.

And so we're, this concept is actually being very seriously considered.

Particularly in Europe in, in, in Germany.

And we're looking, in collaboration with the Danish Technical University, at,

at designing this so-called surface system which will, will convert and

store our reactants.

Using, survey data on natural gas, reservoirs in Denmark, for example.

We can estimate 500 gigawatt hours of storage would be available for

one plant that has a 250 megawatt capacity.

And the punch line here is, we'll get to this later.

But in the end, these storage costs can reach $0.03 to

$0.04 per kilowatt hour with storage durations of months.

Which is particularly important.

Germany in particular, very interested in month long duration storage.

Because of the low PV insulation during the winter in particular.

Because we produce methane we find it really interesting if the technology is

also suitable to support the so called power to gas platforms.

They're very of, of increasing interest and particularly by Europe and

getting off of Russian natural gas and using renewable green electricity,

if you will, to make SNG.

This technology is perfectly applicable to that.

In the end, though, we need this top surface system.

And that involves systems integration and thermal management strategies

in moving essentially, between the caverns and the stack.

And so, just very briefly.

We have to pressurize and preheat the reactants that get over to the stack.

We can recover some of that energy from fuel cell exothermic operation

to reduce our balance of plant parasitics.

From the cavern and we'll take our CH4, preheat it, and

expand it because it's operating at say 160 bar and the stack is at 20 bar.

We'll recuperate some power, and we'll introduce steam and