Monash University in Australia completed a lifecycle analysis and net energy analysis (LCA/NEA) of a potential large-scale solar-electrolysis facility for green hydrogen production.
The study’s open-access publication has been published in the RSC journal Energy & Environmental Science.
They computed hydrogen generation by dividing annual solar farm power output (without transmission losses and balance-of-plant loads) by electrolyzer efficiency. The average global horizontal irradiance (GHI) for Learmonth, Western Australia was 2,200 kWh m-2 yr-1, which was used to calculate solar farm energy generation. They assumed an electrolyzer efficiency of 55 kWh kg-1 H2, as well as sensitivity values of 50 and 60 kWh kg-1 H2.
They experimented with two baseline scenarios:
- The solar-battery scenario assumed that on-site battery storage powers standby operation with no grid connection and maintains minimum electrolyzer running during periods of low solar electricity, depending on electrolyzer turndown.
- The solar-grid scenario anticipated that the hydrogen plant is linked to Western Australia’s regional grid, the North West Interconnected System (NWIS). The grid link enables grid imports to help load balancing of variable solar supply, as well as grid exports during periods of surplus solar power (i.e. solar generation exceeding electrolyzer capacity). The NWIS is primarily powered by gas and has a GHG emission factor of 620 g CO2-e kWh-1. This exceeds the global average of 510 g CO2-e kWh-1.
The following were the study’s key findings:
- The GHG emission intensity for both baseline scenarios is roughly one-quarter that of H2 produced by SMR. However, GHG emissions may be equivalent to SMR under reasonably anticipated scenarios with grid buffering.
- The EROI for both baseline scenarios is less than, and in some cases substantially less than, comparable estimates for fossil fuels.
- The solar modules were the most important component that influenced EROI and GHG emissions in the solar-battery scenario.
- The solar modules were crucial for EROI in the solar-grid scenario, while grid emissions were as relevant for GHG emissions.
- The electrolyzer turndown is a critical sensitivity. The baseline turndown was set at 95%, but at 80 to 90% turndown, the EROI and GHG are negatively influenced. Due to impractically huge battery capacity, a lower turndown (higher minimum electrolyzer load) for the solar-battery arrangement may be infeasible.
- The power emissions factor for the solar module supply chain is a critical sensitivity. Production in a lower emission location would dramatically reduce the intensity of GHG emissions.
- Both EROI and GHG intensity are affected by operational lifetime. Both metrics would be harmed if equipment was decommissioned prematurely owing to obsolescence, increased degradation, or premature failure.