Geothermal Electricity

The primary energy source is heat energy from the earth’s core from its molten past, radioactive decomposition, and tidal energy.

This heat is usually turned into electricity, a secondary energy source. It is created using a steam turbine (Rankine cycle) similar to coal but usually at lower temperatures.

Conditions

A traditional geothermal site must have heat to extract, fluid to extract the heat, and porosity to allow the fluid to move. The nearby Geysers have all three of these factors at the site.

In the Geysers, about 20 years ago the fluids were depleting so Lake County and Santa Rosa began sending treated wastewater to inject underground.

Enhanced Geothermal

Enhanced Geothermal uses hydraulic fracturing to create the porosity needed for fluid flow.

This means a site with only heat could be a viable geothermal site since humans can create porosity and inject water.

Source: DOE

Types of Geothermal

Some plants use the underground water directly to spin the turbine, while others heat up a separate “working fluid” that spins the turbine.

Geothermal Plant Types

Technical Advantages

Geothermal electricity can run continuously and can help stabilize a grid with high amounts of variable renewable energy (solar and wind).

Geothermal uses mature drilling technologies from the petroleum industry. However, lots of technical development is needed for the different rock types and higher temperatures of geothermal drilling.

NREL map of Geothermal Resources

Ground Source Heat Pumps

Geothermal energy is also used to refer to the use of the ground to exchange heat with for heating and cooling.

In this case the earth is not being used as a source of high temperature heat, but as a large battery to store and extract low temperature heat.

Question: Quadrilemma Priorities

How do you see geothermal in terms of the priorities?

  • Security and Reliability
  • Cost and Access
  • Environmental Sustainability
  • Social Justice/Energy Justice/Energy Democracy

Techno-economic

US Department of Energy has set a target of $45/MWh for the cost of advanced geothermal electricity by 2035.

  • Cannot currently be imported or exported
  • Could be used to substitute heat for coal plants, unstranding assets

Environmental Issues

  • Construction and drilling
  • Groundwater risk from fracking and pumping
  • Increased seismicity risk

Socio-technical

  • Uses skills and technology from the petroleum industry
  • Currently enjoys bipartisan support
  • Subsidies from the Inflation Reduction Act were retained in OB3 while most other renewable subsidies were canceled

Policies

  • Exploration wells exempt from federal environmental review
    • Legislation to exempt exploration wells from CEQA has been attempted
  • IRA Geothermal tax credits were not changed by OB3

References