99.9% purity, 500ml/min, 4 atmosphere. [1].
At 4 atmospheres, can fill a 1000 gallon propane tank - in 4 days. At 1 atmosphere - one day!
$3500 of generators (same as above but at $700/unit) gets us 1.5 kWhr of usable storage with a generator. That is the same cost as a 20kW new battery bank - which can last 10 years in off-grid apps. We are a factor of 13x higher capital cost than batteries at this stage - which can be solved only by reducing cost of hydrogen generation equipment.
Ideal conditions - 40kWhr to generate 1 kg of hydrogen - [2]
Look at basic capital cost from last link:

For sensemaking - $1-5k capital costs per kW electrolyzer. A 1 kW electrolyzer - for reference, the 500 ml/hr generator in link above requires 180W. If we take the electrolyzer above at $1k for 500 ml/hr - we need about 24 of those to equal the 10kg/day level in the paper. So that is only $24k in capital costs, or about $17k if we use cheaper electrolyzers at $700 a pop (see Solar Hydrogen Production).

Hydrogen Gas Generator

Links