Geothermal and Hydropower Study Notes

Modeling and Design of Energy Systems

Geothermal and Hydropower Lecture Notes - March 5, 2025

  • ENVE 162– CRN 111515 Spring 2025
  • MW 1:30-2:45pm; Granite Pass Room 135
  • Abbas Ghassemi, Ph.D. Emeritus Professor Teaching Professor; Civil and Environmental Engineering
  • SE2 372; aghassemi2@ucmerced.edu
  • Renewable Energy Sources

Brief Overview

  • Challenge: We do not know how to store electrical energy on a massive scale.

Geothermal Energy

  • Use heat to make steam, which turns a turbine for electrical generation.
  • Deep hot waters are corrosive; inject clean water in a closed system and bring it back to the surface as steam.
  • In the U.S., much of geothermal energy production is done on public land (subsidized).
  • Little geothermal potential exists in the east and mid-west of the U.S.
What is Geothermal Energy?
  • Geothermal energy is heat within the earth.
  • The word geothermal comes from the Greek words "geo" (earth) and "therme" (heat).
  • Geothermal energy is a renewable energy source because heat is continuously produced inside the earth.
  • People use geothermal heat for bathing, heating buildings, and generating electricity.
How it Works
  • Geothermal power plants use the earth’s heat to power steam turbines.
  • Geothermal direct use involves using hot springs (etc.) as a heat source.
  • Geothermal heat pumps are also utilized.
Advantages of Geothermal Energy
  • Clean: Very low greenhouse gas emissions; life cycle emissions are four times lower than solar PV and six to 20 times lower than natural gas.
  • Baseload: Produces electricity consistently and can run essentially 24/7.
  • Small footprint: Uses less land per gigawatt-hour (404 m2m^2) compared to coal (3,642 m2m^2), wind (1,335 m2m^2), and solar photovoltaic (PV) power (3,237 m2m^2).
Disadvantages of Geothermal Energy
  • Not available everywhere.
  • Can cause H2SH_2S pollution.
  • Produces some water pollution (somewhat similar to mining).
Types of Geothermal Power Plants
  • Dry steam power plant:
    • Uses steam directly from the geothermal reservoir to turn a turbine connected to a generator.
  • Flash steam power plant:
    • Uses high-pressure hot water from the geothermal reservoir that is flashed into steam to turn a turbine.
  • Binary cycle power plant:
    • Transfers the heat from geothermal water to a secondary working fluid with a lower boiling point, which then turns a turbine.
Geothermal Heat Pumps
  • Geothermal heat pumps are used for heating and cooling.
  • Air temperatures above ground change throughout the day and with the seasons, but temperatures of the earth 10 feet below ground are consistently between 50°F and 60°F.
  • Soil temperatures are usually warmer than the air in winter and cooler than the air in summer.
Geothermal Resources in the United States
  • Identified hydrothermal sites and favorability of deep enhanced geothermal systems (EGS) vary across the U.S.
  • Map includes relative favorability, identified hydrothermal sites (≥ 90°C), and data disclaimers.
  • "N/A" regions have temperatures less than 150°C at 10 km depth and were not assessed for deep EGS potential.
State Rankings for Geothermal Electricity Generation (2022)
  • Rankings:
    • #1: CA
    • #2: NV
    • #3: UT
    • #4: HI
    • #5: OR
    • #6: ID
    • #7: NM
Extracting Geothermal Energy
  • Drill deep enough to find heat.
  • Rock is a poor conductor of heat; use ways to crack the rock to allow heat to move.
  • Pump down water to make steam.
The Geysers Geothermal Complex
  • The largest geothermal plant in the world is located in California.
  • The Geysers Geothermal Complex, located north of San Francisco, is comprised of 18 power plants.
Geothermal Energy Uses
  • Diagram shows various uses of geothermal energy at different temperature ranges, including:
    • Geothermal heat pumps
    • Mushroom culture
    • Fruit & vegetable drying
    • Soft drink carbonation
    • Binary geothermal power plants
    • Greenhousing & soil sterilization
    • Fabric dyeing
    • Aquaculture
    • Pulp & paper processing
    • Bathing
    • Concrete block curing
    • Lumber drying
    • Snow melting & deicing
    • Soil warming
    • Refrigeration & ice making
    • Food processing
    • Onion & garlic drying
Top 10 Geothermal Countries (2022)
  • Installed capacity in MWe (January 2023):
    • U.S.: 3,794
    • Indonesia: 2,356
    • Philippines: 1,935
    • Türkiye: 1,682
    • New Zealand: 1,037
    • Mexico: 963
    • Kenya: 944
    • Italy: 944
    • Iceland: 754
    • Japan: 621
    • Other: 1,097

Hydropower

  • Hydropower is a semi-renewable resource that has to be carefully managed to ensure it is not used faster than it can be replenished.
  • Two major approaches to generating electricity from hydropower:
    • Storage hydroelectric systems store water for later use and are a versatile resource for the grid.
    • Run-of-river systems are generally smaller and use the river’s natural flow.
  • Hydro can also be used to store electricity in systems called pumped storage hydropower.
    • Pump water to a higher elevation when electricity demand is low to use during high demand periods.
How it Works – Principle of Operation - Hydro Power Potential
  • Hydroelectric Dam Components:
    • Reservoir
    • Intake
    • Penstock
    • Turbine
    • Generator
    • Powerhouse
    • Stator
    • Rotor
    • Wicket gate
    • Generator shaft
    • Turbine blades
Advantages of Hydropower
  • Low operating cost, long life, and high yield (lower energy cost).
  • The lowest-cost source of electricity globally based on LCOE.
  • Plentiful where available.
  • Some countries depend almost entirely on hydropower.
  • Not intermittent with a large reservoir; pumped storage alleviates intermittency.
  • Reservoirs have multiple uses: flood control, drinking water, aquaculture, recreation.
  • Less air pollution than fossil fuel combustion.
Disadvantages of Hydropower
  • Human population displacement.
  • Droughts and climate change can impact the water cycle, changing long-term availability.
  • Expensive initial capital costs to build dams.
  • Reduces the availability of water downstream.
  • Ecosystem impacts: barriers to migrating fish, loss of biodiversity (up and downstream).
  • Siltation problems (also shortens dam life).
  • Decommissioning problems; the size issue/safety.
Hydropower Challenges in the U.S.
  • Location: unused rivers are in extreme north or low population areas.
  • Competition with recreational uses (U.S.) and environmental concerns.
  • Hard to build dams in populated river valleys.
  • Local opposition to dam construction (NIMBY - not in my backyard; BANANA - build absolutely nothing anywhere near anyone).
  • Siltation of dams – limited life.
Hydropower Investments

  • Global power generation by source in 2021:

  • Total hydropower investments (Billion USD) from 2017 to 2022.

Hydropower Capacity by Region in 2022
  • Hydropower capacity and new installed capacity by region:
    • East Asia and Pacific: 548 GW (24,944 MW new)
    • North and Central America: 206 GW (1,142 MW new)
    • Europe: 258 GW (2,712 MW new)
    • South America: 177 GW (1,525 MW new)
    • South and Central Asia: 164 GW (1,940 MW new)
    • Africa: 40 GW (1,860 MW new)
  • Hydropower generation by region in 2022 (TWh):
    • East Asia and Pacific: 1,714 TWh
    • North America: 723 TWh
    • Europe: 569 TWh
    • South America: 712 TWh
    • South and Central Asia: 539 TWh
    • Africa: 150 TWh
Hydropower Installed Capacity (2022)
  • Total hydropower installed capacity in 2022: 1,397 GW
  • Hydropower installed capacity (GW) of top 20 hydropower producers and the rest of the world, including pumped storage (2022):
    • China: 415
    • Brazil: 110
    • United States: 102
    • Canada: 83
    • Russia: 56
    • India: 52
    • Japan: 50
    • Norway: 34
    • Turkey: 32
    • France: 26
    • Italy: 23
    • Spain: 20
    • Switzerland: 18
    • Viet Nam: 17
    • Venezuela: 17
    • Sweden: 16
    • Austria: 15
    • Mexico: 13
    • Colombia: 13
    • Iran: 13
    • Rest of the world: 275
Hydropower Market Size, 2022 to 2032 (USD Billion)
  • Forecasted hydropower market size from 2022 to 2032, with a steady increase expected over the decade.
Largest Hydropower Plants

  • The Itaipu Hydroelectric Plant (Brazil/Paraguay) produces 103 billion kWhs a year.

  • Biggest power plants in the world by annual electricity production:

    • Itaipu Hydroelectric Station (Brazil/Paraguay): 103,000,000,000 kWhs
    • Three Gorges Hydroelectric Plant (China): 93,500,000,000 kWhs
    • Xiluodo Hydroelectric Station (China): 52,200,000,000 kWhs
    • Hanul Nuclear Generating Station (S. Korea): 48,160,000,000 kWhs
    • Bruce Nuclear Generating Station (Canada): 47,630,000,000 kWhs
    • Hanbit Nuclear Generating Station (S. Korea): 47,620,000,000 kWhs
    • Guri Hydroelectric Station (Venezuela): 47,000,000,000 kWhs
    • Surgut-2 Natural Gas Plant (Russia): 39,850,000,000 kWhs
    • Palo Verde Nuclear Station (United States): 32,846,202,000 kWhs
    • Xiangjiaba Hydroelectric Station (China): 30,700,000,000 kWhs

Tidal Power

  • Tidal energy is a renewable energy powered by the natural rise and fall of ocean tides and currents.
  • Some technologies include turbines and paddles.
How Tidal Power Works
  1. The turbine is mounted on a foundation structure and set on the seabed.
  2. Tidal currents cause the blades to rotate, powering a generator that produces electricity.
  3. Underwater cables carry the electricity to an onshore substation.
  4. The substation is connected to the national grid, which distributes the electricity.

  • The output varies with the tides and is predictable.

  • Rotor blades rotate very slowly—between 7-15 RPM.

  • Each turbine can generate enough electricity to power around 1,400 homes.

  • More predictable: Unlike wind and solar energy, tidal energy is predictable as tidal currents can be accurately forecast years in advance.

  • Large untapped resources: Water covers about 70% of the world's surface, and every continent has potential sites for harnessing the power of tidal currents.

Highest Tides in the World = Bay of Fundy
  • The Bay of Fundy has the highest tides in the world (16 meters = 48+ feet).
Challenges of Tidal Power
  1. Corrosion
  2. Navigation
  3. Appearance
  4. Harm to sea lions and other mammals
  5. Amount of energy available is low
  6. Best tides are near poles – away from people.