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Unfortunately what’s shipping today seems it would offer maybe half that.
For the batteries that were announced this past week, a larger-than-refrigerator-sized cabinet held a capacity of around 15kWh.
Around half the energy density by mass of Lithium batteries, and in the order of a sixth of the density by volume.
Now if only we could come up with a system where your car could be charged while stopped at traffic lights, we might be onto a winner (:
Considering however that the price of sodium is around 1-2% that of lithium, I expect we will see significant R&D and those numbers quickly start to improve.
It is a good question.
Where I live, electricity costs around $0.28/kWh, but generation is typically >85% renewable (predominantly hydroelectric).
My heat pump (4.7 COP when heating) would cost $0.06 to run for every 1kWh of heat it produces, with only 0.03kWh of that electricity coming from fossil fuel sources.
Gas - which I don’t have at my house - would have pricing in the neighbourhood of $0.15/kWh. Even at 95% efficiency getting 1kWh of heat from gas would cost $0.16, using 1.05kWh of gas.
35x the fossil fuel usage and 2.5x the price, for the same quantity of heat. Some luck of living in a moderate climate where an air-source heat pump almost never loses efficiency, to be fair.