Power for a Mars colony

[Vultur]

Yeahhhh.

Hydrogen as energy storage/transport mechanism maybe made some kind of sense in the 90s when lithium-ion batteries weren't practical. I don't think there has been any reason to think about it for general/ground use (as opposed to upper stage rocket fuel or similarly specialized uses!) for at least 20 years.

[Twark_Main]

Batteries for daily storage and ground transport. Hydrogen for annualized storage, chemical production, rockets, and dust storms.

"Make hay hydrogen while the sun shines."

https://www.moderndescartes.com/essays/factobattery/

[DanClemmensen]

Batteries for daily storage and ground transport. Hydrogen for annualized storage, chemical production, rockets, and dust storms.

"Make hay hydrogen while the sun shines."

https://www.moderndescartes.com/essays/factobattery/

But on Mars, you probably need to produce and store methane as a rocket propellant, using hydrogen as an intermediate. Therefore, it is likely to be more cost-effective to use methane as your annualized storage. Yes, E-->H-->E is more theoretically efficient than E-->CH₄-->E, but it's cheaper and easier to store methane, especially if you are doing it anyway for propellant.

[Twark_Main]

Batteries for daily storage and ground transport. Hydrogen for annualized storage, chemical production, rockets, and dust storms.

"Make hay hydrogen while the sun shines."

https://www.moderndescartes.com/essays/factobattery/

But on Mars, you probably need to produce and store methane as a rocket propellant, using hydrogen as an intermediate. Therefore, it is likely to be more cost-effective to use methane as your annualized storage.

You won't find any disagreement from me!  I said make hydrogen, not necessarily store it long-term.

The same electrolysis gives you big tanks of liquid oxygen, of course, which is nice if you like breathing. That's effectively "stored energy" if you'd otherwise have to power an oxygen generator.

Yes, E-->H-->E is more theoretically efficient than E-->CH₄-->E, but it's cheaper and easier to store methane, especially if you are doing it anyway for propellant.

Check out the FactoBattery essay I linked. The whole idea is that you don't convert (most of) the chemical energy back to thermal/electrical energy, with the exceptions here being dust storms and power equipment failures.

You basically just manufacture the same hydrogen you would need per year anyway (and methane, ethylene, etc), but you ramp the production up during the times of year when you have excess solar power. It's annualized demand response, not bidirectional energy storage.

This isn't "free", because you're paying for more capacity in your electrolysis equipment (and Sabatier etc) versus running the equipment at the same flow rate year-round (but that would require constant power). So you balance those two costs, using back-of-the-envelope math to find the cheapest mix of wasted PV vs wasted electrolysis equipment.  No Free Lunch still applies, as always!


Figure source: https://www.powerandresources.com/blog/solar-power-is-challenging-on-mars

[Robotbeat]

Batteries for daily storage and ground transport. Hydrogen for annualized storage, chemical production, rockets, and dust storms.

"Make hay hydrogen while the sun shines."

https://www.moderndescartes.com/essays/factobattery/

bingo

[Vultur]

Ramping methane production during high solar power times of year seems almost inevitable.

I actually don't think burning methane during dust storms will be needed; life support power needs will probably be a pretty small proportion of the total, so if you can do the high power demand stuff (like methane production) at other times of year, the limited solar power that does get through the dust storms should be enough for what's left.

[Twark_Main]

Ramping methane production during high solar power times of year seems almost inevitable.

I actually don't think burning methane during dust storms will be needed; life support power needs will probably be a pretty small proportion of the total, so if you can do the high power demand stuff (like methane production) at other times of year, the limited solar power that does get through the dust storms should be enough for what's left.

I would be delighted if this is true. Mostly this is just to "head off at the pass" people who make bad engineering assumptions and then complain that dust storms kill everyone. 

The only time you turn chemicals back into energy to power the base will be during dust storms, and maybe not even that. But you definitely won't do it at other times of year as part of regular operation, which was my main point.

[Vultur]

Ramping methane production during high solar power times of year seems almost inevitable.

I actually don't think burning methane during dust storms will be needed; life support power needs will probably be a pretty small proportion of the total, so if you can do the high power demand stuff (like methane production) at other times of year, the limited solar power that does get through the dust storms should be enough for what's left.

I would be delighted if this is true. Mostly this is just to "head off at the pass" people who make bad engineering assumptions and then complain that dust storms kill everyone. 

The only time you turn chemicals back into energy to power the base will be during dust storms, and maybe not even that. But you definitely won't do it at other times of year as part of regular operation, which was my main point.

Ahhh ok yeah then agreed.