Basic Research Needs for Solar Energy Utilization - Office of ...

maintenance costs of the small production unit could be minimized with a do-it-yourself owner.
For the larger-sized units, electrical costs dominate the costing. Water is the other feedstock
material and it appears not be a limiting factor. To run the current U.S. light-duty fleet with
hydrogen would require 100 billion gallons/year, which is far smaller than the yearly domestic
personal use of 4,800 billion gallons/year (Turner 2004).
This is how the market stands today. Electrolytic production of hydrogen represents a minute
fraction of the market output of hydrogen and the economies of scale of production of the
electrolyzer units have not yet come into play. The NAE, for example, works with projections of
an eight- to ten-fold decrease in cost of the electrolyzer units for both alkaline and PEM
technologies (NRC and NAE 2004). Of concern, however, is the purity of the water required for
the electrolyzers. Water purification is a mature technology and there should be little economies
of scale of this element of the electrolyzer system.
Part of this perceived reduction in cost involves advances in the design and efficiency of the
membranes and catalysts in the two different technologies. The alkaline electrolyzers will utilize
the well-known Raney nickel catalyst, about which much is known, both in terms of costing and
performance. It is compatible with a low-cost system. The PEM technology, however, relies
upon platinum catalysts for gas evolution, which is a scarce material. Given a practical
0.20–1.0 mg/cm 2 loading level of Pt in a PEM, a typical generation current of 0.4 A/cm 2 , and the
hydrogen production efficiency in Table 1, a yearly production rate of 1 TW would require 170–
850 metric tons of Pt. Even though recovery of Pt from these membranes can approach 98%, this
required base of 170+ tons exceeds the 2005 annual global production of Pt of 165 tons. For
comparison, the automotive industry utilizes about 62 tons of Pt annually. In this situation, the
PEM power business would determine the market for platinum.
Costs of Hydrogen Production with Solar Electricity
It is useful to estimate the costs of hydrogen production using photovoltaic solar cells as a source
of electrical power. In this case, the overall system of solar facility and electrolyzer must be
optimized as a unit. Given the diurnal nature of solar insolation, the electrolyzer cannot be
powered twenty-four hours per day, and the hydrogen output is decreased in a corresponding
manner. The lowest price for hydrogen is obtained through an optimized balance of solar
vis-à-vis electrolyzer costs. The Norsk Hydro 5040 electrolyzer unit from the 1,000 kg/day
electrolyzer example above will run on 240–2,330 kW of power for operation (Ivy 2004). If this
unit is powered with 2,330 kW of peak watt solar power, the daily variation in insolation will
limit the overall production to 250 kg/day of hydrogen. This combination is near optimum for the
lowest hydrogen cost. Over a forty-year period, at the present cost for photovoltaic solar cells of
$6 per peak watt with balance of system costs, and including amortization, the price of hydrogen
can be calculated and is shown in Figure 72 to be $17.78/kg. The capital cost of the electrolyzer
is taken from Figure 71 with an adjustment for the decrease in daily hydrogen production and
assuming constant system efficiency over the entire range of input electrical power. With
improvements in solar technology by 2020 and a drop in solar cell costs to $1.5/Wp, the overall
cost for hydrogen would drop to $8.68/kg.
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