| Let's look at chemical storage with hydrocarbons in the mix, allowing some as-yet non-commercial (air-metal & combined cycle home generators) to make good food for speculation. A consumer to operate a small gas turbine and store their energy in the form of hydrocarbons. If this is to be sensible, then 43MJ/kg would have to be enough, because that's what they're going to get with kerosene/jet fuel. Now let's consider lithium. The problem with metal-air batteries has mostly been poisoning by unwanted gases. Let's assume for a moment that a membrane material is developed that only allows high purity oxygen through, but suffers low throughput. This is no problem for our off-grid solution because we're talking about large storage relative to power, similar to some flow battery applications. Using some method of specific ion or biological style solution, such a membrane is not implausible. Lithium-air weighs in at 40MJ/kg specific energy. How much does it cost? Given that a metal-air battery uses lithium oxide, the lithium carbonate and lithium hydroxide prices are not quite valid guides, but the price of $7/kg is obtainable for the carbonate of "battery grade." If the pure oxide can be the material used in manufacture, then possibly the $7 value is in the ballpark. Jet-A is $0.45 per kilogram. 1.41 $/gal / 3.78541 l/gal / 0.820 kg/l Higher efficiency must be allowed because even with combined cycle at high latitudes where it's cold, we're looking at 90% round-trip for a battery vs ~75% for our Brayton cycle + home heating. There are external costs to a large tank of kerosene and a pile of lithium carbonate. One requires a gas turbine and the other requires a battery & significant manufacturing. Excepting those two things, we're left with a roughly 7:1 factor of cost for the raw material, so a seven year payoff it is. Lithium might not be the cheapest rechargeable precursor. It might be great for EV's (high power output is a requirement) and maybe something else will show up as the cheapest energy storage without requiring off-grid people to rely on ARES gravity trains. Perovskites (new paper just suggested that hot-carrier phonons can be used to raise theoretical efficiency to 66%) throw yet another wrinkle into solar. Both energy storage and generation could become quite a bit cheaper. All hypothetical, yes, but my napkin does tell me not to rule out off-grid, not that I'm sympathetic to off-grid, anti-social Ayn Rand acolytes =D Whatever matters for off-grid matters for a ton of settings, such as places where there is no grid still. It's tough to say definitively that a straight-renewable energy source won't become cost-competitive even in grid areas of high latitude within the decade. Source on Jet A specific heat:
http://www.exxonmobil.com/AviationGlobal/Files/WorldJetFuelS... Source on Lithum Air theoretical specific energy:
https://en.wikipedia.org/wiki/Lithium%E2%80%93air_battery Jet A price:
http://www.indexmundi.com/commodities/?commodity=jet-fuel Lithium Carbonate Price (ev grade):
http://www.globalstrategicmetalsnl.com/_content/documents/40... |