NOTE: (it appears to me that N before cubic-meters indicates some kind of metric equivalent to STP, standard-temperature-and-pressure Š but IÕm not sure!)

De-ionized H2O
0.47 liters / hour (while producing 1.14 kg / 24 hours)
=>>> (roughly) 1 liter H20 consumed per 1 liter H2 produced
=>>> 11.28 liters H20 / 1.14 kg H2

H2 Consumption per Electric Energy Produced
1.8 Nm3/h produces 2.5 kw
--- 1.8 Nm3 H2 produces 2.5 kwh electricity

289 kwh toward H2 generation yields 60 kwh electricity generation
Efficiency = 20%

1 kw = 1.35 hp
DonÕt forget to factor motor efficiency when calculating real-world consumption! I think 80% efficiency is typical for an electric motor.
>> RULE OF THUMB >> 1 kw = 1 hp of actual drive power

Fuel cell electricity generators seem to want H2 at about 1.5 atmospheres of pressure, or about 20 psi (I think!). I found some 940 Liter metal-hydride H2 storage cylinders that appear to like 250 psi to fill. Also, their data sheet mentions that they must be cooled while filling and kept warm while discharging. The warm part is typically handled easily by the fuel cell, which generates heat normally, anyway. I am considering cooling during filling by using an even higher-pressure H2 main storage reservoir, with a 250 psi buffer tank between it and the metal-hydride cylinder tanks. Decompressing the high-pressure reservoir into the buffer tank provides evaporative cooling as the liquid H2 changes phases into gas, consuming available heat energy from the hydride cylinders. The buffer tank then pressurizes the cooled hydride tanks, which apparently somehow absorb the hydrogen in a chemical process that allows the hydrogen to be stored as a solid, but at relatively low pressure and high (room) temperature.

Gases like to go through liquid toward solid as temperature decreases, or as pressure increases, so a chemical arrangement that allows H2 to be solid (and much more dense/compact than in liquid or gas form) at room temperature and modest, 250 psi pressure, is pretty neat. I havenÕt a clue how it works beyond what IÕve said already.

Storage Volumes and Weights I found an on-the-market metal hydride storage cylinder with the following attributes:
Capacity: 940 Liters
>>> 1 cu meter = 999 or basically 1000 Liters
>>> Capacity = 0.940 cu meters

I wanted 4 cu meter capacity for a small vehicle application, so I did the following calculations:
(4) canisters ~= 4 cu meters
= 30 kg H2
= 5kwh electric generating capacity
(with an on-the-market fuel cell)
Weight: 7 kg (filled? Unfilled?)
Size: 40 cm tall with 9 (?) cm diameter

The cylinders may be ŌstackedÕ in a magazine arrangement to provide whatever exact capacity is needed. There are also 250 Liter versions.