Cool! Thanks for the link. A 10 kWh flywheel that can charge/discharge at 20 kW (lasts for 20~30 min at this power) costs ~11500 USD + installation and control

Cool! Thanks for the link. A 10 kWh flywheel that can charge/discharge at 20 kW (lasts for 20~30 min at this power) costs ~11500 USD + installation and control system. A Tesla Powerwall has 13.5 kWh capacity, delivers power at ~6 kW and costs ~11500 USD. That doesn't seem a large difference to me.