400 watts is $700 or less.
Solar power is improving as a way to provide low cost robustness in the event of emergencies.
Batteries are too expensive and don’t last long enough. Pumped hydro is cheap but not feasible for most locations. Thermal storage is promising but still too expensive or hard to scale. Compressed air is cheap and scalable but not yet efficient enough.
Flywheels may be getting a second life, however. Silicon Valley inventor Bill Gray has a new flywheel design that would deliver distributed and highly scalable storage for around $1,333 a kilowatt [?hour? if it is $1333 per kilowatt, does that mean $50-75 per kwh ? That is pumped hydro prices.], making it price competitive with pumped hydro and compressed air. With an efficiency of more than 80 percent, it would rival the best storage alternatives, and come with a 10-year guarantee.
A new flywheel design offers some hope of affordable energy storage for home systems, such as rooftop photovoltaic panels.
Gray calls his invention the Velkess (for VEry Large Kinetic Energy Storage System).
Gray uses a flexible rotor made of “E-glass,” a common fiberglass used in everything from sporting goods to shower doors. Rather than use advanced carbon-fiber composites manufactured to exact tolerances, Gray’s soft rotor flexes in response to destabilizing forces. It is thereby able to adjust to speed transitions that confound other designs.
While carbon fiber reinforced polymer is 6 to 8 times stronger than E-glass, he notes that E-glass is 10 to 20 times stronger per dollar. Similarly, E-glass will store 10 to 20 times more energy per dollar. The current prototype floats on a magnetic bearing assembly that can handle 2kW of power, and store 0.5 kWh of energy. Their final device will need storage closer to 15kWh to meet the first projected 48-volt off-grid power backup.
This scale up means replacing the 25lb flywheel rotor used for the video footage with a 750lb rotor.
Assuming that the Velkess flywheel and other new energy storage were to pan out then you could get about 2000 watts of solar power combined with 15 kwh of storage for about $3500 or less as prices drop. You could have about 200-300 watts of power all through the night. Refrigerator, basic lighting and other devices could be powered even during long power outages.
There are smaller super efficient fridges that only use 0.5 kwh per day or less. There are medium size (for american homes) fridges that use about 1.0 kwh per day.