Geothermal energy presents a promising pathway for low-carbon hydrogen production, either through powering electrolysis or enabling direct thermal water splitting. Unlike wind or solar, geothermal provides consistent baseload energy, reducing intermittency challenges in hydrogen generation. However, the full lifecycle emissions of geothermal hydrogen must account for drilling, plant construction, reservoir management, and operational energy inputs. When compared to other renewable hydrogen methods, geothermal-assisted production exhibits distinct advantages and trade-offs in environmental impact.

Drilling geothermal wells contributes significantly to initial emissions due to energy-intensive processes and material use. Constructing a geothermal plant requires steel, cement, and other materials with embedded carbon footprints. Enhanced geothermal systems (EGS), which stimulate reservoirs in dry rock, demand additional energy for hydraulic fracturing and circulation. These upfront emissions vary based on site geology, drilling depth, and technology. On average, drilling and plant construction for geothermal projects emit between 10 to 50 grams of CO2 equivalent per kilowatt-hour of capacity over the project lifetime.

Once operational, emissions from geothermal hydrogen depend on the production method. For electrolysis, emissions stem mostly from the electricity source. Geothermal power typically has a lifecycle emission intensity of 15 to 50 g CO2/kWh, significantly lower than grid electricity in fossil-fuel-dependent regions. Direct thermal water splitting, though less mature, avoids electrolysis losses but requires high-temperature heat (above 800°C), which only certain geothermal reservoirs can provide. Reservoir maintenance, including reinjection of fluids and managing subsurface pressure, adds minor but non-negligible energy costs.

In comparison, wind-powered electrolysis has lower upfront emissions since turbine construction emits around 5 to 20 g CO2/kWh over its lifetime. However, wind’s intermittency necessitates energy storage or grid backup, which can increase indirect emissions if fossil fuels are involved. Solar PV electrolysis follows a similar pattern, with lifecycle emissions of 20 to 40 g CO2/kWh, but also faces intermittency. Biomass gasification can achieve negative emissions if coupled with carbon capture, but land use and feedstock logistics complicate scalability.

Water usage is another critical factor. Geothermal plants consume water for cooling and reservoir maintenance, though less than coal or nuclear facilities. Electrolysis, regardless of the energy source, requires high-purity water, with approximately 9 liters needed per kilogram of hydrogen. Direct thermal splitting reduces water needs but remains constrained by high-temperature requirements.

Long-term reservoir sustainability affects emissions. Depleted geothermal sites may require additional drilling or energy inputs to maintain output, whereas wind and solar farms can be repowered with minimal new emissions. However, geothermal’s high capacity factor—often exceeding 70%—means it can produce hydrogen more consistently than wind or solar, reducing the need for energy storage or redundant capacity.

A comparative table of emissions for renewable hydrogen methods illustrates key differences:

Method | Upfront Emissions (g CO2/kWh) | Operational Emissions (g CO2/kg H2)
Geothermal Electrolysis | 10-50 | 100-500
Wind Electrolysis | 5-20 | 200-600
Solar PV Electrolysis | 20-40 | 300-800
Biomass Gasification | 30-70 | -50 to 200 (with CCS)

Geothermal hydrogen’s advantage lies in its steady output and lower operational emissions compared to variable renewables. However, site-specific constraints, such as reservoir depth and temperature, limit widespread deployment. Advances in drilling technology and materials could reduce upfront emissions, while hybrid systems—combining geothermal with wind or solar—could optimize efficiency and lower costs.

In summary, geothermal-assisted hydrogen production offers a balanced emissions profile, particularly in regions with high-quality geothermal resources. While not as low-impact as wind or solar in upfront emissions, its reliability and consistent output present a compelling case for integration into a diversified renewable hydrogen economy. Future improvements in EGS and high-temperature electrolysis could further enhance its sustainability.