A life cycle assessment of chemical energy carriers for the seasonal storage of renewable power under a net-zero CO2 emissions constraint.

Abstract

The purpose of this research is to assess the environmental impact of three chemical energy carriers for seasonal energy storage, so called Power-to-Fuel-to-Power (P-X-P) systems. Hydrogen, methane and ammonia are picked as storage media and the systems are designed to have net-zero CO2 emissions. In order to find the degree of storage needed in the systems, first a demand-supply model is created. The electricity is assumed to be produced by a mixture of wind and PV. The result of the model is that between 8.1% and 8.8% of demand will come from the storage medium.

A life cycle assessment is then performed on the systems and these results are compared to the CCS system where electricity is produced by a natural gas combined cycle (NGCC) with both post combustion capture, Direct Air Capture (DAC) and underground CO2 storage in order have a net-zero CO2 emission system. The results show that hydrogen scores best on all seven impact categories if compared with the other storage media. If compared with the CCS system however there is no clear winner. The hydrogen system has a global warming potential of 0.073 kg CO2 eq./kWh compared to 0.134 kg CO2 eq./kWh of the CCS system. But on marine eutrophication and mineral resource scarcity the P-X-P systems score four times higher than the CCS system.

As the EU has pronounced that it is its goal to become a climate neutral society, this research also looked into systems where there is zero global warming potential in the entire lifetime. First the origin of the residual background emissions of the net-zero CO2 systems is analysed. As the emissions are spread over a large amount of processes and a lot are outside of the EU, completely abating these emissions will be difficult for the EU. Secondly the impact is determined with the residual global warming potential being abated by the implementation of Direct Air Capture and Storage (DACS). Completely abating the global warming potential of the systems would lead to an 11% increase in other impact categories for the P-X-P systems and a 21% increase in the CCS system.