Tangentially... Most California solar farms under construction today are sited, rather stupidly, in deserts. Why stupidly? Because deserts are hot and dusty, co

Tangentially... Most California solar farms under construction today are sited, rather stupidly, in deserts. Why stupidly? Because deserts are hot and dusty, conditions that curtail output and shorten panel life. Why build there anyway? Ignorant investors still think it's a great idea. Siting over water, though, really is a great idea. Healdsburg, near Santa Rosa, floated a big array very successfully. Construction on a canal near Modesto has begun; official estimate is that solar built out on California canals would yield 12 GW, save millions of gallons lost to evaporation, cut biofouling, and provide protected habitat for wildlife underneath. Singapore is well ahead on this. Sacramento delta "islands" could be easily converted to floating solar farms, eliminating the major ecological threat of failing dikes, and resuming sequestration of carbon in peat bogs underneath. Storage, the actual topic, seems to generate confusion on the level of the investors favoring desert solar farms. Most of California's "batteries" are not batteries, but reservoirs high up in the Sierra Nevada mountains, built starting in the 1920s, connected to water wheels at the bottom of penstocks thousands of feet below. They are turned into storage simply by attaching an electric pump to the penstock. Of course you can float solar on those reservoirs, too. Chemical batteries are the expensive storage alternative. There won't be very much of that, except in cars, because they are expensive; or anyway will be until new and much cheaper chemistry matures. Promising chemistries include zinc/bromine, antimony/calcium, and iron/air, all of which are at the stage where manufacturing capacity is being built out. There are plenty of other storage alternatives, of varying maturity. Compressed air storage is deployed at industrial scale successfully, and is extremely mature technology. Liquified air is similar; efficient air liquidation had a long industrial pedigree before its adoption for storage. Synthesizing hydrogen to keep underground is somewhat less mature, but that mainly means conversion efficiency (E => H2) is soaring, and lately exceeded 90%. Ammonia synthesis is attractive because tankage is cheap and very transportable, and it may be burned in already paid-for combined-cycle turbines. Expect solar and wind farms in favorable spots to produce industrially huge stocks of ammonia for export, eliminating need for any seasonal storage. Underground and underwater gravitic storage is still in prototyping phase, but the tech involved is centuries old, involving winches and water pumps. One especially promising relies on buoyancy, winching floats down to seabed-mounted pulleys.