Feasibility Study on Supply Chain of Hydrogen Produced from Photovoltaic Power Energy‒Availability Assessment of Utilizing LNG Vaporization Cold Heat

Abstract

The power produced from renewable energy sources should ideally be converted into H2 carrier for the purpose of long-term storage and long-distance transportation. In this study, an energy supply chain was considered by assuming that some large scale photovoltaic (PV) systems of 1.9 MW, 7.5 MW and 1.9 GW classes installed in Yokkaichi City, the electricity generated, was calculated based on meteorological data, the obtained electricity was converted into H2 by a water electrolyzer, then transported and consumed after (1) compression, (2) liquefaction, (3) conversion into compressed CH4 or liquefied CH4, (4) conversion into organic hydride, and (5) conversion into NH3. The energy efficiency, CO2 emission reduction and resilience upon transporting to the composition area were evaluated. In addition, a case of utilizing the cold heat generated by vaporization of liquefied natural gas upon liquefaction of H2 as a supplemental heat source was also evaluated from the viewpoint of energy efficiency. As a result, it was revealed that the energy consumption and CO2 emissions during the transportation process in the case of liquefied CH4 were smaller compared to the other H2 carrier cases. In addition, it became evident that, as the resilience effect for the power generation by H2 transported to a consumer, the annual available power energy which was supplied for two-person household satisfied the energy demand of 227 households in the case of H2 carriers excluding compressed and liquefied CH4, when assuming the photovoltaic system of 1.9 GW class. When providing H2 to the consumer as a fuel for mobility, the best CO2 emission suppression effect was the case of using in gasoline vehicles. The energy loss ratio was the smallest in the case of liquefaction of H2 considering the use of the cold heat generated upon vaporization of liquefied natural gas. This is because the energy assist ratio of the cold heat derived from vaporization of liquefied natural gas, relative to the total energy needed for liquefaction process of H2, was high at 64.3%. Furthermore, the energy recovery ratio decreased accompanying an increase in the transportation distance. The energy recovery ratios were the best when the transportation distance being 0, in the case of liquefaction of H2 utilizing the cold heat generated upon liquefied natural gas vaporization, and when considering transport, in the case of compressed CH4.