So for a 200-sq m house you might have about 1.7 kwH of storage (including walls) . Might just be enough to run "smart house" sensors and control systems during an outage. Or you could stow a power bank in the corner.

Paul314: Yeah but for a home with a basement with 10 inch thick side walls and 6 inch slabs you could have perhaps 3 times that much of about 5 kWH. that's enough to run things for a night without power.

And don't forget the footings as well. Most basement footings around the country are required to be 24 inches thick by 24" width and that would add another 2 kW so you could on a 3000 sf home have easily a 7 kW of storage--equivalent to a Tesla powerwall.

And don't forget the post supported homes with up to 10 feet deep 18" circular concreted poured posts to support basement walls in Bentonnite soils. That could add another 1 kW.

Hopefully it's good for more than 1000 recharge cycles so you don't have to rebuild every few years.

I will say it again; HEMPCRETE is FAR BETTER than any concrete! Lighter, strong, breathes, acts as a filter for pollutants; FAR BETTER!

What a cool idea, building an Edison battery inside a concrete wall. I like it

Does the concrete need to be isolated from the earth? In the photo it looks like the concrete is wet and that the concrete slabs may be sitting on damp paper towels in a tray with water? If water is part of the design won't the iron particles corrode?

Nice pun toward the end Nick: 'problems to still iron out'.
Most concrete is water porous - especially footings and basement walls. One of the destructive forces causing early weakening of concrete structures is water incursion. Placing battery plates inside? Would that continuous back and forth ionic exchange reduce the structural lifespan of the concrete? Would the concrete need to be sealed against water infiltration? Will this construction technique allow for rebar placement or will another strengthening component be required? Possibly the "plates" can be made strong enough - or enough layers included - to replace the rebar. But I'm not holding my breath.

Novel yes, practical no. Compressed air in concrete structures like a basement have hundreds of times better energy density at a fraction of the area while providing heating and air conditioning as well as power. I am interested to see what electromagnetic field propagates from building sized batteries, that could be a serious issue.