Mobile Solar Hydrogen Overnight

[slomobile]

I camp off grid in a Promaster van and want to avoid unnecessary idling at night. I'm ready to install 24v 400W nominal solar in Tennessee connected to a 24v power wheelchair with MK Gel AGM batteries. I use the chair during the day for power wherever I go leaving the panels available. I use a CPAP machine every night. The CPAP consumes most of its energy heating up distilled water.

It occurred to me that it might be possible to use solar electrolysis all day, then react the products all night to produce warm pure humid CPAP air(8oz water), excess heat warming the van, excess water for whatever, power to charge the chair (200w), run the CPAP fan (20w), a controller/phone charger (10W).

I need help selecting the most appropriate reactor. Small internal combustion engine and alternator, fuel cell, other? Everywhere I search for small hydrogen I run into crackpots. Hard to know who to trust.
Sizing the reactor, gas generator, storage.
Gas production, purification, compression, storage.
The fact that all gas will be fully reacted each night might relax some of the usual assumptions for 300PSI storage or higher, struct purification, etc. But the fact that it needs to be mobile imposes other requirements. It must fit inside the van with room left for me. Be reliable and safe enough to run unmonitored in a confined space with a sleeping person.

That probably makes it completely impractical and I should just replace all the hydrogen stuff with a battery bank. Frankly that is probably what will happen.
But first I would like to discuss it, identify some hardware and tests to try and see if it might actually be viable.

 

[fechter]

To make power from hydrogen you’d want to use a fuel cell.
It would be much more practical to get another battery you can charge during the day and run the inverter off of at night.
You could also charge it from the van if there’s no sun.

 

[slomobile]

To make power from hydrogen you’d want to use a fuel cell.
It would be much more practical to get another battery you can charge during the day and run the inverter off of at night.
You could also charge it from the van if there’s no sun.

But we aren't just making power. The ability to transform contaminated water into inhalation quality is the killer app for me.
Think of it more like an overengineered off grid CPAP that can also charge stuff. Like how everything we buy has a USB port now making everything also a pretty bad but acceptable charger.

Here is a randomly selected fuel cell candidate.
fuelcellstore.com/fuel-cell-stacks/5w-100w-fuel-cell-stacks/g-hfcs-10w6v-10w-hydrogen-fuel-cell-power-generator
"Hydrogen Purity: >99.99% (CO content being <1 ppm)" I don't think I can make that purity in my van.
Hydrogen pressure at half of atmospheric? How does that work?
What temperature will the water vapor output be from this unit? I need 75-90F from a heat exchanger I can regulate.
Hydrogen Consumption: 120 mL/min (at nominal power), but what is the output gas flow? How does it vary with power? I need 20 cm H2O pressure at about 45SLPM flow. The specs I need aren't reported and I don't yet know how to estimate them.
However the CC of an internal combustion engine and its throttle are pretty easy to understand. I could even run it on propane or natural gas if I were desperate for power more than breathing.

Getting jugs of $0.89 distilled water at Walmart and refilling the little CPAP container every night seems easy. I have difficulty with both in the best of circumstances. We have frequent power outages and road closures making it a bit harder even at home. When something you need to breathe fails a lot, you start looking for alternatives.

Right now there is a Xantrex pure sine inverter on the stock battery and a PowerDrive pure sine on an auxiliary deep cycle. We almost never use either one because even without any load, they will drain their battery if left on overnight. All our loads are DC. I like knowing when I unplug them the battery drain stops. Too many times I've been left stranded because someone turned on the inverter to top off their phone, but forgot to shut it off.

My 75Ah chair batteries take 12 hours on the AC charger, that is a lot of wasted overhead. Trying to charge them directly from another 24v lead pack would literally take forever. I might could use 12S LTO parallel without a charge controller, that would make me happy. Not sure if the charge rate would be limited by LTO impedance or lead acid. Maybe put a 300W incandescent bulb on the chair charge lead to limit inrush current just in case.

 

[offGridDownUnder]

transform contaminated water into inhalation quality is the killer app for me

Your system must have a power input source.

Have you eliminated a solar distiller for water purification? If so, can you share your reasoning?

 

[slomobile]

Your system must have a power input source.

Have you eliminated a solar distiller for water purification? If so, can you share your reasoning?

Its a van. It moves. Doesn't always point at the sun. Large portion of the roof is PV panels. Thermal solar collector acts like a sail and must be aimed. If there is a solar still design that could be easily deployed to cover the front window for shade, but pack compactly, I would love that.

The fact that water, heat, electricity, and a fan are needed at night when solar doesn't work was the kernel of an idea.
A hydrogen weed eater motor spinning a small 24v alternator gives me all of those. I wanted to explore if it would work, even if not the ideal solution. Because boredom is the other problem it solves.