Hydrogen as an export commodity – Capital expenditure and energy evaluation of hydrogen carriers

Abstract

In this paper, we describe a case-study exploring the use of 600 MW of power from New Zealand's Manapouri Power Station to produce hydrogen for export via water electrolysis. Three H2 carriers were considered: liquid H2, ammonia, and toluene hydrogenation/methylcyclohexane dehydrogenation. Processes were simulated in Aspen's HYSYS for each of the carriers to determine their associated energy and annualised capital expenditure costs. We found that the total capital investment for all carriers was surprisingly consistent, but with quite different splits between the electrolysis and carrier formation plants. Based on our analysis the energy availability for liquid H2 ranged from 53.9 to 60.7% depending on the energy cost associated with cryogenic H2 liquefaction. The energy availability for liquid ammonia was 37.5% after conversion back to H2, or 53.6% if the ammonia can be used directly as a fuel. For toluene/methylcyclohexane the energy availability was 41.2%. The total of the electricity and annualised capital costs per kg of H2 ranged from NZ$5.63 to NZ$6.43 for liquid H2, NZ$6.24 to NZ$8.91 for ammonia and was NZ$7.86 for toluene/methylcyclohexane, using a net electricity cost of NZ$70/MWh. The cost of hydrogen (or energy in the case of direct use ammonia) was more strongly influenced by the efficiency of energy retention than on capital investment, as the electricity costs contributed approximately two thirds of total costs. In the long-term, liquid hydrogen looks to be the most versatile H2 carrier, but significant infrastructure investment is required.