In the scenarios discussed earlier only cryogenic and compressed hydrogen energy storage were used, principally due to very low capital costs ($0.30/ kWh for cryogenic liquid hydrogen and $4.50/kWh compressed hydrogen), in spite of roundtrip efficiencies of only 30-40%. Figure 6.5 shows the significant energy losses (~20%>) attributable to hydrogen storage and reconversion to electricity. Higher efficiency electricity storage alternatives (e.g. flywheels) could dramatically reduce these losses.
Additional scenarios (Table 6.1) exploring the potential of higher efficiency storage indicate that even 100% efficient electricity storage, an optimistic approximation of flywheels or batteries, would only become cost effective at less than $100/kWh as long as some dispatchable (e.g. natural gas) capacity remains in the electricity mix. Flywheels become more cost effective if fossil electric generation is eliminated entirely, and especially in cases with large solar electricity peaks and hydrogen transportation sectors. Flywheels, or any high efficiency electric storage, approach a value of about $200/kWh of storage in this most favorable case. These cost levels may be ultimately achievable through higher performance, lower cost fiber-based composite materials. However, such advances in materials may also reduce the costs of composite pressure vessels used to store compressed hydrogen.
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