I just did a quick search and it looks like the consumer price of li-ion is more like $250 to $400 per kWh by 1000 * dollars/(volts * amphours), so the bulk pri

I just did a quick search and it looks like the consumer price of li-ion is more like $250 to $400 per kWh by 1000 * dollars/(volts * amphours), so the bulk price of $176 from the article is believable: https://www.ebay.com/sch/i.html?_nkw=lithium+ion+battery+48V+50AH https://www.ebay.com/sch/i.html?_nkw=lithium+ion+battery+48V... I challenge the idea that Li-ion is the lowest price though, because it's one of the densest storage options. The actual cheapest (lowest density) energy storage known is gravity, at a potential energy of E = mgh, so we get roughly 9.8 J per kilogram-meter of height. 1 kWh = 3.6e6 J, so with something like a 95% efficiency winch generator, that's E/(g * efficiency) = 3.6e6/(9.8 * .95) = 387,000 kg or right at 175 metric tons (cubic meters of water). A 90% efficient one-way trip with pumped hydro storage would be 408,000 kg or 185 metric tons. Note that round-trip effiency is the square of one-way, so remember to take the square root of any reported round-trip efficiencies when calculating displacements. An olympic swimming pool holds 2500 cubic meters of water, so that's 2500/185 = 13.5 kWh per meter raised. The average US home uses just over 10 kWh per day. So a good rule of thumb to remember is 1 olympic swimming pool raised 1 meter powers 1 home for 1 day. After writing all of this out, I think that the cheapest energy storage will be to pump air down tubes to big bags under the ocean (or lakes) to displace water. Since volume grows by the cube but surface area only grows by the square, this is the only scalable energy storage system that doesn't require access to a reservoir or oil well. Also since it only requires 1 atmosphere of pressure per 9.8 meters of depth, the low compression might be close to an adiabatic process by not raising the air temperature much, and could get close to an 85% one-way (72% round-trip) efficiency. I feel like by PV = T, for each doubling of pressure but halving of volume, the temperature should stay the same. Maybe someone more experienced with entropy can provide an equation for what percentage is lost per atmosphere of compression, say at 50 F (10 C) ground/water temperature: https://en.wikipedia.org/wiki/Compressed_air_energy_storage#Adiabatic https://en.wikipedia.org/wiki/Compressed_air_energy_storage#... Hey it looks like they're already doing this in Toronto: https://www.youtube.com/watch?v=GicQwXbNnv0 https://www.youtube.com/watch?v=GicQwXbNnv0 But I think it's always good to derive an idea from first principles instead of taking someone's word for it. So I'd put money on this as an alternative to batteries. And just so we have it, about 4 of the $600, 2400 WH Chevy Volt batteries at a total cost of $2400 would also power a home for a day (not counting inverters).