Form Energy reveals the chemistry of its long-duration battery

You are also right about synthetic hydrocarbons. The extra hydrocarbon synthesis step lowers the total efficiency, compared with using hydrogen.

Nevertheless, the lower efficiency is more than compensated by the simpler methods used for storage and handling, which require much less expensive materials and a much lower volume and total mass.

The benefits of using hydrocarbons for long-term energy storage have been amply demonstrated by the living beings that have been using this method for billions of years, many of which can easily achieve an autonomy of months without eating, while doing activities that would make a present-time robot using batteries inoperational after a few hours at most.

Basically, if you're cycling regularly (e.g. smoothing solar and wind over a day) then Lithium is already pretty good and you can expect it to get bettwr as it scales out to the entire automotive industry and indeed those car batteries will be fed by the grid and can also act as short term storage and demand management.

If you cycle less regularly though, storing power for weeks or more then you need something much cheaper than lithium can ever be but if you're cheap enough you can sacrifice some conversion efficiency and still be useful in a 100% renewable grid.

This is where flow batteries are targetting, you can have a small/cheap "converter" but store the energy in tanks longer term.

But as you say, thats also basically what you can do with hydrogen/ammmonia. And as an added bonus you can buy sell hydrogen/ammonia on the open market as it's used for other purposes, which lets you insure against under/over production and take advantage of economies of scale on the converter and storage parts.

As a final bonus, during the transition you can add a percentage of hydrogen to existing gas turbines to reduce their carbon intensity and GE and other sell turbines that are built to run on gas, hydrogen/gas mixes and also pure hydrogen. This gives an easy ramp up as a carbon price and/or minimum targets can kickstart the green hydrogen industry without any particular customer needing to bear 100% of the cost.

Methane from waste can also be used as a source of hydrogen, making it carbon negative, with a promising tech looking to generate solid carbon in the form of graphite. But even if you released the carbon I to the air it's better than releasing the methane.

> but you need the energy to renew it in the first place.

So am I hearing you could create the iron-fuel someplace with excess energy and then ship this stored energy someplace that wants to burn it?

And while Iron loses out to energy density per kilogram, it wins on kilogram per cubic centimeter :D (your math is much appreciated btw)

if i am using an inverter to convert DC to AC viz 220volt where my AC appliances run, does it matter on the battery side?

if i have a load, say a pc running 1 KWH, will these two battery systems run for 2 hours both (assuming discharge rate is same, i know i know, just calculating)

i am doing this because solar batteries are being sold at 48Volt x small AH to come up with KWH but at the same time lead acid are only sold at 12Volt but high AH. what if i buy 7AH 12Volt x 25 batteries to get same KWH?

does battery voltage or amperage matter when converting to AC? how does that work?

oh, BTW, i have a 5.2KWH solar array that is grid tied

Unless there is a regulatory blip, then there is always a cost to energy. Stuff has to be maintained, connections repaired, monitored and upgraded.

The other thing to note is that its only "free" if you own both the infrastructure and the producer. If you are doing "arbitrage" then the efficiency is your profit margin.