Geothermal Energy

1. Geothermal Energy

2. Geothermal Power Principle: Heat in earth’s core can be tapped for human use. Near-surface access to this heat is a potential energy source. Only large scale “renewable” that does not depend on sun US current: 2500 megawatts of electricity • equivalent to three large nuclear power plants… Potential: • 12,000 megawatts by the year 2010 • 49,000 megawatts by 2030

3. Geothermal Resources • Natural Hydrothermal reservoir • Spontaneously produces hydrothermal fluid • Hot water or water/steam mixture: “Liquid dominated” • High quality steam (saturated?): “vapor dominated” • Geopressurized • Reservoir of pressurized hot water that does not generate hydrothermal fluid at surface • “Hot Dry Rock” • Rocks at ca. 200oC+ but have no fluid • Drill and inject water to generate fluid at surface • Magma • Molten rocks (650oC+) at accessible depths • Harvesting heat is a real problem (i.e., we don’t know how to)

4. Issues Hydrothermal fluid can have entrained particles and/or salts and gases dissolved • Vapor dominated: direct use • Liquid dominated: • Flash into steam (salts/entrained solids?) • Can diminish deposition of solids by chemical treatment • Run through heat exchanger • What to do to spent hydrothermal fluid (brine like) • Reinject (increases BWR?) • Surface waste (environmental impact?)

5. Approaches to Geothermal

6. Hydrothermal system and temperature gradient Example temperature gradient Usually listed as T in oC/km

7. Gradient has strong impact on facility costs

8. Estimates of electricity cost

10. Geothermal Installations

11. Geothermal heat pumps Also known as “shallow” geothermal Principle: use ground as heat source/heat sink, increase efficiency of heat pump *not* a direct source of energy, but efficiency booster -about 8 PJ/y -reduce need for new generating capacity

12. Ocean Energy

13. Ocean Energy Ocean Thermal Energy Conversion (OTEC) • Use warm surface water (25oC +) and cold deep (1km) water (5oC) Tidal Energy • Use water level differential between enclosed tidal basin and ocean, use water for low head hydro Wave Energy • Capture surge/heave motion of water to power generator

14. OTEC • Need to pump cold deep water to surface • Hard to support weight of pipes, so needs to be built close to land (Hawaii and Taiwan (were) big on this) • Can use cold water for other uses: HVAC, irrigation by condensation, aquaculture • Operate on Rankine cycle • Low pressure water Rankine (higher BWR because need to lower pressure) • “Organic Rankine” cycle (butane, isobutane, methylamine, ammonia) • Many big challenges • Corrosion/biofouling of seawater systems is main one…

15. OTEC Ocean Thermal Energy Conversion • Use warm surface water (25oC +) and cold deep (1km) water (5oC)

17. Tidal Power Use water level differential between enclosed tidal basin and ocean, use water for low head hydro • Tides very predictable • Principle dates back to roman era… (I grew up not far from one)

18. Key parameter(s) Tidal period T (T ≈ 12.5h ≈ 4.5x104 s) Tide height h Tidal basin area A There’s a better model in the Hodges book, but we don’t have the time to discuss in detail…

19. La Rance The largest tidal power plant in the world is the 240 MW (max) La Rance in France, built in the 1960’s. • Average power generation is 68 MW • 330m dam contains a 22 square km basin • Average tides of 8m.

20. Sites with tidal opportunities

21. Tidal Power: hydrokinetic energy Under research (NNMREC!): Tidal stream systems working like wind turbines • No dam required, just natural flows through currently established channels • Admiralty Inlet, WA has 3.5 kts • Sechelt Rapids, BC has 15 kts currents (!) 35 kW max capacity turbine

22. Impact of Tidal Systems • Fish killed in turbines, stopped from natural spawning migrations (e.g., eel, salmon, plaice) • Noise from turbines also must be considered • Intertidal wet/dry habitat modified • Water quality may be affected due to dampened transport • Even tidal stream systems will affect this (big part of NNMERC work) • Blockage to navigation

23. Wave Power Estimated as a very large resource (up to 2 TW worldwide technically accessible resource) Attempt to harness energy not new – first descriptions date to 1799… Many concepts: • Overtopping devices • Oscillating water column (OWC) • Floating devices (point absorbers, etc) • “hose pumps” • Hinged flap devices • Etc “The early bird gets the worm but the second mouse gets the cheese…”

24. How much power in a wave? Where Pmcl is the power per “meter of crest length” l is the wavelength of the wave Wave power potential per meter varies with the square of the wave height and linearly with the period. A 3 meter wave with an 8 second period produces about 36 kW/mcl A 15 meter wave with a 15 second period produces about 1.7 MW/mcl (there aren’t many 15 meter waves near shore, thank God)

25. Wave energy is strongest on the west coasts and increases toward the poles. • At approx. 30 kW/mcl in the Northwest (yearly avg.), a single meter (3.3 feet) of wave has the raw energy to power about 23 homes. Power From Ocean Waves [George Hagerman]

26. Most devices capture heave energy only Therefore only ½ of possible power harvested What does that mean for max efficiency? (don’t have an answer…) Heave (up and down) Surge (back and forward) Water particle orbital motion

27. Oscillating Water Column (OWC) Heave motion of water in enclosed chamber moves air in/out of chamber (think Spouting Horn blowhole at Cape Perpetua) Air turbine in vent harnesses energy Can be onshore or offshore buoy For a great illustration see http://daedalus.gr/OWCsimulation2.html

28. Salter’s Duck Shape carefully chosen to follow particle trajectory 90% efficient with monochromatic waves • (i.e., wave had exactly the right wavelength to fit the chosen shape…) Efficiency decreased rapidly if detuned…

29. Overtopping Devices Wave flows up a channel to create low head hydro Can use devices to focus waves into channel Example shown: tapered channel (TAPCHAN) Wave Dragon

30. Linear Generator Point Absorber (OSU!) Relative motion between two devices at surface History: 1998 AvJ started writing NSF proposals for wave energy (no one else working on this at the time) 2001 finally some funding ($500k cut to $280k due to NSF budget) 2004 concept picks up steam 2008 Northwest National Marine Renewable Energy Center (NNMERC)

31. OSU Strategic Facilities to Advance Wave Energy O.H. Hinsdale Wave Research Lab (HWRL) Wallace Energy Systems & Renewables Facility (WESRF)

32. Linear Test Bed with SeaBeav & Wave Energy Team

33. OSU’s work

34. National Marine Renewable Energy Center • Demonstrate and compare existing technologies • Research and develop advanced systems • Investigate efficient and reliable utility integration/intermittency issues • Advance wave forecasting technologies • Conduct experimental and numerical modeling for device and wave park array optimization • Evaluate potential environmental and ecosystem impacts • Establish protocols for outreach/engagement and how the ocean community best interacts with wave energy devices and parks • Refine wave energy power measurement standards • Improve wave energy device identification/navigation standards • Offer wave energy educational workshops • Enable enhanced testing of instruments, etc.

35. Lysekil project Buoy floating at surface pulls on cable driving generator OPT – generator is at surface (on buoy) instead of on bottom • This is what is going into Reedsport

36. Submerged buoyancy device “Archimedes wave swing” Pressure from wave at surface decreases volume of trapped air Buoyancy decreases, “float” sinks harvesting energy

37. Initial industrial development • World’s first large experimental wave park in Portugal (early bird or second mouse?) • Three Pelamis devices: • 142m long, 3.5 m diameter (700 tons of steel) • Hydraulic ram between each segment harvests power • 2.25 MW capacity