I’ve looked into this. Even sent an email to Amber Kinetics (the flywheel company in the OP) some months back asking for some basic economic parameters, but did

I’ve looked into this. Even sent an email to Amber Kinetics (the flywheel company in the OP) some months back asking for some basic economic parameters, but didn’t get a reply. My conclusion was that simple electricity arbitrage using refurbished lithium ion batteries would be reasonably profitable right now but that business case depends on volatility staying high. The CAPEX is approximately 500 EUR per kWh storage capacity, and you can maybe make 0.25 EUR per kWh and day doing arbitrage. It’s hard to know what the electricity market will look like in the relevant timeframe.