The world's richest renewable energy resources - of large geographic extent and high intensity - are stranded: far from end-users with inadequate or nonexistent gathering and transmission systems to deliver the energy. The energy output of most renewables varies greatly, at time scales of seconds to seasons: the energy capture assets thus operate at inherently low capacity factor (CF); energy delivery to end-users is not "firm". New electric transmission systems, or fractions thereof, dedicated to renewables, will suffer the same low CF, and represent substantial stranded capital assets, which increases the cost of delivered renewable-source energy. Electric energy storage cannot affordably firm large renewables at annual scale. At gigawatt (GW = 1,000 MW) scale, renewable-source electricity from diverse sources, worldwide, can be converted to hydrogen and oxygen, via high-pressure-output electrolyzers, with the hydrogen pipelined to load centers (cities, refineries, chemical plants) for use as vehicle fuel, combined-heat-and-power generation on the retail side of the customers' meters, ammonia production, and petroleum refinery feedstock. The oxygen byproduct may be sold to adjacent dry biomass and / or coal gasification plants. Figures 1 - 3. New, large, solution-mined salt caverns in the southern Great Plains, and probably elsewhere in the world, may economically store enough energy as compressed gaseous hydrogen (GH2) to "firm" renewables at annual scale, adding great market and strategic value to diverse, stranded, rich, renewable resources. Figures 2 and 3. For example, Great Plains, USA, wind energy, if fully harvested and "firmed" and transmitted to markets, could supply the entire energy consumption of USA. If gathered, transmitted, and delivered as hydrogen, about 15,000 new solution-mined salt caverns, of ～8 million cubic feet (225,000 cubic meters) each, would be required, at an incremental.
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