Security of supply is often raised as a concern in energy systems dominated by weather-dependent renewable energy sources, particularly solar energy. In this context, most scenarios have highlighted the value of PV-battery hybrid configurations. Researchers from LUT University propose a novel PV-geothermal hybrid solution, as geothermal power could benefits countries with excellent solar resources. This study moves beyond a niche technology perspective that has historically undervalued geothermal energy. This perspective is reinforced by recent research in geologically favorable regions such as Iceland, where abundant geothermal resource and in-situ mineralization potential position the country as a promising carbon dioxide removal hub.
Against this backdrop, detailed research from LUT University estimates the global geothermal potential, which lifts geothermal energy as the third largest renewable energy resource as concluded by energy resource experts. As a firm renewable energy resource, geothermal energy could play a key role in accelerating the shares of renewables in the overall energy mix. In particular, enhanced geothermal systems (EGS) are estimated to offer around 4600 GWe globally at costs between €10-50 ($11.50-58.00)/MWh. The global potential of EGS amounts to a substantial contribution to meeting growing renewable energy demand and could be used beneficially in a fully renewable energy system. Another recent study highlights that several countries around the world can reduce their system costs of 100% renewable energy systems with the inclusion of EGS. The role of geothermal energy in the global energy transition is regarded as underexplored.
Solarization without showstopper: PV-geothermal hybrid solutions for the sunbelt
Solar energy is the most widely available energy resource on Earth and is projected to dominate future energy system architectures due to its rapidly improving economic attractiveness. Since solar energy is weather-dependent, hybrid solutions, such as PV-geothermal hybrid systems, could reduce the levelized cost of electricity (LCOE) and improve overall system flexibility. Sunbelt regions or countries, where favorable solar conditions coincide with hot geothermal zones, could particularly benefit from PV-geothermal hybrid systems, as observed in Guatemala, Honduras and Costa Rica. Accordingly, Guatemala, Costa Rica, and Honduras achieve LCOEs of €18.8, €21.9, and €24.5 /MWh, respectively, with geothermal and solar PV contributing 68%/19%, 51%/24%, and 34%/34% of the LCOE, highlighting solar PV’s cost-reducing role alongside geothermal’s dominant contribution. The cost-containing function of renewable energy like geothermal is essential during low sunshine periods or if storage costs do not decline as expected.
Image: LUT University
Space and water requirements will not constrain PV-geothermal multi-generation systems in Guatemala, Honduras, and Costa Rica. Land needed for solar PV and geothermal is minimal, 0.2% and 0.7% in Guatemala, 0.1% and 0.2% in Honduras, and 0.4% and 0.2% in Costa Rica, based on 75 MW/km2 for PV and 7.5 km2/TWh for geothermal, with PV estimates being conservative. Water use by geothermal plants (binary and EGS) ranges from 0.01–0.2 km3 in Guatemala, Honduras, and Costa Rica. These numbers represent minimal shares of the region’s annual precipitation.
System-wide defossilization driven by PV-geothermal hybrid configurations
Regional cooperation fosters renewable energy integration, maximizing the benefits of defossilization and enabling the effective use of collective assets required to develop a cost-efficient system and safeguard supply security, challenges that could be greater under individual national planning. Across Central America, electricity supply is dominated by solar and geothermal power, contributing 4-90% and 7-38% of generation, respectively, throughout the transition. System LCOE across the region is €20-21 /MWh with grid interconnection, rising slightly to €23 /MWh without it. Solar PV-geothermal hybrid configurations reduce storage requirements by 51-60% and curtailment by about 76% with grid interconnection.
Source-system-service flexibility is achieved through firm and flexible geothermal power, power-to-X (PtX) processes, and sector coupling. Geothermal enhances energy supply diversity, while hybrid PV-geothermal solutions enhance system flexibility in highly renewable energy systems. Service flexibility is delivered via sector coupling and PtX technologies such as heat pumps, electric vehicles, and electrolyzers, enabling the production of e-hydrogen, e-methane, and e-fuels for applications where direct fuel substitution is challenging. The energy system achieves high efficiency and cost competitiveness thanks to access to low-cost renewable energy from solar PV-geothermal configurations and the highly efficient utilization of electricity across the entire system via PtX processes.
Seeking El Dorado: Iceland’s geology favors carbon dioxide removal opportunities
Iceland has an exceptional abundance of geothermal energy, with a maximum potential of 325 GWe, which decreases to 1.1 GWe when sustainability criteria are applied. The potential for geothermal heat extraction exceeds 720 PWh/a, while the sustainable potential declines to 2.4 PWh/a. Building on this resource base, recent research from LUT University explored 28 scenarios with varying geothermal availability to assess impacts on Iceland’s electricity and heat generation systems, as well as on carbon dioxide removal (CDR) deployment under different climate targets.
Geothermal heat is the dominate enabler for direct air capture, enabling cost-competitive CDR service at approximately €50 /tCO2, while geothermal combined with heat and power plants provide dispatchable baseload heat and electricity, ensuring cost-optimal and reliable energy supply.
However, geothermal energy alone cannot sustain very large-scale CDR deployment. Scenarios with a higher geothermal electricity share slightly increase electricity prices, leading to marginally higher levelized CDR costs, particularly in the 2050 transition cases. To ensure a stable supply of the large baseload electricity demand, solar PV plays a vital role in counter-balancing the seasonality of wind power in Iceland.
Although geothermal resource availability is not a limiting factor, the analysis identifies workforce constraints, rather than energy supply, as the primary bottleneck, restricting feasible CDR deployment to around 1 GtCO2/a. Large-scale CDR expansion requires complementary renewables, including onshore wind, solar PV, and wave power, positioning geothermal as a critical but non-exclusive pillar of Iceland’s long-term CDR strategy.
Solar PV-geothermal-led multi-generation systems analysis should be explored for further countries and regions where high-quality solar and geothermal resources coincide, to optimize both heat and electricity supply.
Authors: Ayobami Solomon Oyewo, Dominik Keiner, and Christian Breyer
This article is part of a monthly column by LUT University.
Research at LUT University encompasses various analyses related to power, heat, transport, industry, desalination, and carbon dioxide removal options. Power-to-X research is a core topic at the university, integrated into the focus areas of Planetary Resources, Business and Society, Digital Revolution, and Energy Transition. Solar energy plays a key role in all research aspects.
The views and opinions expressed in this article are the author’s own, and do not necessarily reflect those held by pv magazine.
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