Study of environmental impact of underground electric transmission systems. Final report

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 capital cost to the generation-transmission system of ∼5%. We report the results of several studies of the technical and economic feasibility of large-scale renewables — hydrogen systems. Windplants are the lowest-cost new renewable energy sources; we focus on wind, although concentrating solar power (CSP) is probably synergistic and will become attractive in cost. The largest and richest renewable resources in North America, with high average annual windspeed and sunlight, are stranded in the Great Plains: extant electric transmission capacity is insignificant relative to the resource potential. Large, new, electric transmission systems will be costly, difficult to site and permit, and may be difficult to finance, because of public opposition, uncertainties about transmission cost recovery, and inherently low CF in renewables service. The industrial gas companies’ decades of success and safety in operating thousands of km of GH2 pipelines worldwide is encouraging, but these are relatively short, small-diameter pipelines, and operating at low and constant pressure: not subject to the technical demands of renewables-hydrogen service (RHS), nor to the economic challenge of delivering low-volumetric-energy-density GH2 over hundreds or thousands of km to compete with other hydrogen sources at the destination. The salt cavern storage industry is also mature; several GH2 storage caverns have been in service for over twenty years; construction and operating and maintenance (O&M) costs are well understood; O&M costs are low.

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