Its a feature not a Bug

So I have decided to embrace the fact that Fe-Cr batteries operate at a fundamentally higher temperature. But now you'll say it makes no sense to heat the battery, the costs alone would bankrupt me. 

Let's take a sample system of 1 MW / 10 MWh, 

If we assume a conservative energy density of 10 Wh/L,

Volume of electrolyte (L) = Total energy required  / Energy density 

Volume = 10,000,000Wh /10 Wh/L 

=1,000,000 L 

We would need 1 million liters of electrolyte and calculate the mass of water as by keeping density as 1 kg/L.

 mass (kg) = volume  x density of water 

m = 1,000,000 L x 1 kg/L = 1,000,000 kg 

If I take the conservative specific heat of water as 4,187 J/kg·K, start with an ambient temperature of 20°C and keep my ΔT as 20°C, 

Q (heat energy) = m x c x ΔT  

m = mass of water = 1,000,000 kg , c = specific heat capacity of water = 4,187 J/(kg·K) 

ΔT = temperature change = 40°C - 20°C = 20 K 

 Q = 1,000,000 x 4,187 x 20 

Q = 8.374 x 10^10 J 

To convert Joules into kWh,

E(kWh) = Q / 3,600,000 

E(kWh) = 8.374 x 10^10 / 3,600,000 

E(kWh) = 23,261 kWh

Thermal losses in a heated tank 

Source

In order for my battery to operate at 40°C, I need 23,261 kWh of energy. That's more energy than my battery can store in a day !!! 

Here's the kicker. The cost of this energy according to $0.08/kWh (which is on the higher side btw) would be $1,861. That is nothing compared to the cost of the battery which is more than $1,000,000.

​Now if I achieve 80% efficiency at the cell level, I would waste 20% of the battery's energy. That means 2,000 kWh would be wasted, 

Heat generated = 2,000 kWh x 3,600,000 

Heat generated = 7.2 x 10^9 J 

ΔT per cycle = 7.2 x 10^9 / (1,000,000 x 4,187) 

ΔT per cycle = 1.72 K per cycle

So a temperature rise of 1.72 Kelvin per charge cycle. My battery is self-heating.​It heats itself while charging, and the good thing is since there is no precipitation of salts like VFBs, the temperature range can be set from 40°C to 55°C.

Number of Cycles to reach ΔT of 15 K = 15/1.72 = 8 cycles

Whenever the battery reaches 55°C, you would need to switch on a 5 kW or 10 kW water pump and cool the battery back to its operating range of 40°C, which would happen once every 8 cycles. That's not bad, considering LFP batteries need a continuous HVAC system running during every charge cycle.

Yes, like all other batteries, my battery also needs cooling but not regularly, only from time to time. Yes, I have the cost of a heat exchanger, but it is minuscule compared to the efficiency gain I get from accepting the operating temperature range of the battery, instead of spending years in the lab trying to become another VFB.

And here's the thing — since the tanks of the battery are made of PP (polypropylene), their thermal conductivity is very less, and if you insulate these tanks with appropriate thickness, say 1 mm or 2 mm, the battery would reach thermal equilibrium with its the surroundings . So the whole problem shifts from being a chemical headache to a thermal headache..... and a thermal headache is a much more manageable one, because humanity has had solutions for thermal management since well.... we discovered fire. 

This thermal management is used in aquaponics, vertical farming, the food industry and widely in the chemical sector to attain different temperatures of different fluids.

So it turns out the heat requirement for the battery was a feature, not a bug. I just didn't know it yet.

None of this is AI generated, so feel free to fact check me and looking forward to your views and help. 

Mayank Jately

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