- 4 Atmospheres in a propane tank -
- 6 cu m or 200 scf in a high pressure welding cylinder - . If hydrogen has about 250 BTU per cu ft, then a 200 scf tank has about 3 kW hr of electrical energy when burned in a small gas engine to produce electricity. This is about the same energy as a 250 gallon propane tank.
- Production rate -  - each Spicer electrolyzer cell produces 1/2 cu ft per hr with 40A x 24V. Under 1 kW of input power. 12 cell system of Walt Pyle had 20A x 24v. The rated production rate of a 12 cell system appears to be 6 cubic feet per hour (170 liter/hour).
- Compare to 600 liter/hr at $1740 on Ebay for a common-duct electrolyzer - 
- p. 66 of The Solar Hydrgen Chronicles indicate $4k cost without PV or storage tanks, which would already be present on a solar homestead. If propane costs are $22 per bottle or $240 per year per house - this has a 17 year payback time. Cost optimization half the cost, and further optimization could probably drop the cost to 25%. It's worthwhile to get real data from a build to see what optimizations can be made.