I am having difficulty calculating the size of electrolyser needed for an off-grid solar system with hydrogen tank storage. I have calculated the number of solar panel needed and the amount of usable hydrogen storage per day, but I don't have any information on how to calculate the amount of electrolyser needed.
You already know the amount of hydrogen needed. 1 kg of hydrogen is equivalent to 500 mole. 1 mole of H2 is equivalent to ~ 22.4 liter under STP condition. The electrolyzer will require 2 * 96485 Ampere. second or 192970 coulombs of charge (assuming 100% efficiency), and approximately 2.2 volt (assuming an over potential of ~1 V for splitting water) to release 1 mole or 2 grams of hydrogen. Here, 96485 is the Faraday's constant and 2 is the number of electrons required for H2 reduction. Using these basic information, you can calculate other parameters. You may want to read the specifications of a commercial electrolyzer and know the capacity of the electrolyzer to calculate number of electrolyzers required.
Manufacturers like Hydrogenics have electrolyzers that produce hydrogen with capacities from 20 kg to over 1,000 kg per day.
Here is the solution for your problem: Let's say you selected a commercially available electrolyzer that consumes 'x' KWh of electricity to produce 'y' kg H2 per day.
If 'W' is the total amount of H2 (in kg) that you like to produce per day, then the number of required electrolyzers would be 'W' divided by 'y'.
In summary, use the specifications of commercially available electrolyzers to calculate how many you would need to produce a required kg of H2 per day.
Hope this helps answer your question and good luck!
I would add at least 20% "catch up" capacity to the value to allow you sell more than you produce (from storage) to work through operating problems without significantly reducing production and eventually expand - after the inevitable reliability issues associated with starting up a first unit are sorted out.
you might find the answer in
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