Comment by namibj
5 months ago
Though they are also poised to get iron ore refining to work. That alone could be worth a bunch (numbers assuming 20y amortization and 30% average duty cycle (using only summer surplus) suggest around 10ct/kg iron metal capex plus 3 kWh/kg iron metal electricity).
How do these numbers compare with traditional methods?
Blast furnace based raw metallic (no longer ore/now-reduced) iron costs currently around 30~40 ct/kg in international trade. Iron ore of nominal 62% purity runs at a surprisingly even 10 ct/kg[ore], thus contributing about 16 ct/kg[metal] to the metal output price.
I have not seen much data on these designs, but conceptually they should be cheap. Require holding tanks and iron. No high pressures or other exotic requirements.
Round trip efficiency is way worse than lithium, but that might not be meaningful for grid batteries. You just want something that cheaply scales.
Seasonal iron as I described wouldn't be for electrical round-tripping, but for moving iron ore reduction to the summer where PV energy is abundant (assuming a PV buildout sufficient to cover winter heating heat pump demand without residual fossil fueled peaker plants) and with tricks like co-localizing these to not require the grid to be sized for the summer surplus production, thus overall enabling internationally-competitive production costs for this green-refined iron, vs. the traditional coal/coke blast furnace production.
"Grid batteries" are also a wide concept, from retired electric car lithium packs to 100-hour-scale batteries like what Form is building. You need 3 types of battery, though the two fast ones may want to be unified: - grid stabilizing/synthetic inertia (1~20 C charge/discharge rate) - day/night PV energy shifting (0.15~0.3 C charge/discharge rate) - multi-day weather pattern smoothing (around the 0.01 C Form Energy is targeting)
Other than that the grid stabilizing kind needing much higher security/criticality due to bugs/errors in it's behavior threatening e.g. the European super grid, they would all benefit from co-locating with large solar farms and being connected on the DC side to share AC-side current capacity of the as-built infrastructure (from the inverter/converter through the lines and nearby transformers).