Tour pg 3 of 7


Basically, hydrogen stores energy. The term "hydrogen economy" really means using hydrogen to store and transport energy. In our system, it's an alternative to batteries. It also replaces the diesel which ran a back-up generator. However, converting the solar panels' DC into hydrogen and back into DC again involves some extra gear and some stunning inefficiencies.

On sunny days, the PV array powers our electrolyzers. We have two desk-top units from Proton Energy. These are basically PEM (proton exchange membrane) fuel cells operated in reverse: Instead of feeding in hydrogen and oxygen and getting out electricity and water, they feed in water and electricity and return hydrogen and oxygen. (A single unit acting as both electrolyzer and fuel cell would have been elegant; but like many elegant ideas, it doesn't work.) Our electrolyzers are roughly 18% efficient- 5.5 kWatt-hours of electricity from the PV array gives us 1 kWh of hydrogen.

The electrolyzers send H2 at 200 psi (the same pressure propane uses) to a propane-type storage tank. Our 500 gallon tank, at 200 psi, holds about 90 kWh of hydrogen.

Above: The electrolyzers. On the left is a water deionizer.

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