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bubba-yo t1_j5rne8a wrote

Reply to comment by gerkletoss in Solar powered hydrogen facility being built in California by ForHidingSquirrels

With the most efficient fuel cells and electrolysis processes, about 75%.

But that misses the point. California is currently working to address some of the problems associated with large scale solar production. Because demand for power doesn't move in alignment with production, each additional megawatt of generation you add reduces its efficiency because you are also adding production at times when there's no demand. There's a few ways of mitigating this, such as batteries, but also by adding demand. As such, in a configuration like this, the hydrogen is a battery, and how efficient of a battery depends on how this plant is being operated. Without mechanisms to either add demand during peak power times, or mechanisms to bank it, the efficiency of the solar infrastructure will continue to decline as it builds out.

CA is currently curtailing about 2TWh of renewable power annually. That's solar/wind that has an efficiency rating of 0%. Using it for literally anything is an improvement.

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gerkletoss t1_j5rtodz wrote

>But that misses the point.

Does it? 75% is already much better than iron-air batteries, so that's pretty good before even considering this other stuff.

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bubba-yo t1_j5s6wsg wrote

The problem with batteries is that their capacity and throughput are basically the same thing. Capacity is VERY expensive with batteries.

With hydrogen it's different - throughput is the cost of the fuel cell, but capacity is just the tank you store the hydrogen in. You can grow capacity for a LOT less money than throughput. So for short term storage, battery is great. For longer term storage, it falls off.

Iron air is designed to fill that gap a bit - really cheap, but pretty shit efficiency. But you can package them up, slap one under every solar panel, and get a huge gain. Hydrogen still needs distribution, and all that, or getting a reversible fuel cell down in cost enough to compete so you can slap them down as frequently. That's probably not going to happen.

But in both cases, these things are trying to convert a 0% efficiency due to oversupply into something positive. Almost anything is a gain.

FWIW, some breakthroughs in iron air has gotten their efficiencies up over 65%, so given their costs, they're pretty viable. Not useful for transportation applications though, where hydrogen is. Solid state hydrogen energy density is upwards of double that of lithium ion.

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