Luis A. Vega, Ph.D.
Hawaii Natural Energy Institute (HNEI)
       luisvega@hawaii.edu
            October 1, 2009
Mission

Facilitate development and
commercialization of wave
power (WP) devices and
ocean thermal energy
conversion (OTEC...
OTEC Primer
• Energy Consumption & Petroleum
  Resources
• OTEC Generalities
• US OTEC Program 70s, 80s & 90s
• Lessons we...
Economic & Energy Indicators   4
Petroleum Resources

Resources per IEA; API; USGS:                R (barrels)

Present Consumption:               C (barre...
OTEC Primer
• Energy Consumption & Petroleum
  Resources
• OTEC Generalities
• US OTEC Program 70s, 80s & 90s
• Lessons we...
OTEC Visionary Perspective

• Solar energy absorbed by oceans
  is 4000 x humanity annual
  consumption;

• Less than 1 % ...
Typical Temperature vs. Depth   8
       Tropical Oceans
OTEC Engineering Perspective

• Two ocean layers with T: 20 °C to
  25 °C in equatorial waters…
  heat source and heat sin...
Energy Carriers

OTEC energy could be
transported via electrical,
chemical, thermal and
electrochemical carriers:
Presentl...
Vega OTEC   11
Open Cycle OTEC
*Surface (Warm) seawater is flash-
evaporated in a vacuum chamber
resulting low-pressure steam drives
turb...
Open Cycle OTEC   13
Closed Cycle OTEC

Warm (surface) seawater and Cold
(deep) seawater used to vaporize

and condense a working fluid,
such a...
Closed Cycle OTEC   15
Hawaii’s Ocean Thermal Resource:
            Truisms
• OTEC could supply all the electricity
  and potable water consumed ...
OTEC Primer
• Energy Consumption & Petroleum
  Resources
• OTEC Generalities
• US OTEC Program 70s, 80s & 90s
• Lessons we...
US Federal Government
     (Rephrasing late 70’s to early 80’s OTEC Mandate)


    By Year 2000     104 MW Installed
     ...
US Federal Government OTEC
      Program (70’s –80’s)

Hindsight

 should have used funds ($0.25 x 109)
 to build at least...
OTEC Assessment (‘90s)

Continuous (24/7) production of
electricity and water demonstrated:

- MiniOTEC (Hawai’i)
- Nauru ...
210 kW OC-OTEC Experimental Plant




                    (Vega et al:1993-1998)
Desalinated
  Water
Production
(Vega et al:
  ‘94-’98)



       22
OTEC Power Output as Function of
      Control Parameters
• Open Cycle Control Parameters:
  Seawater Mass Flow Rates; Sea...
Vega OTEC   24
OC-OTEC Power Output vs. Cold Water
             Temperature

1-minute Averages of 1-sec samples show:


 Cold Seawater Te...
Vega OTEC   26
OC-OTEC Power Output vs. Warm Water
           Temperature

1-minute Averages of 1-sec samples show:

Surface Seawater Tem...
Development Barriers             (Hawai’i)

 Tech. Issues: Need to Build &
 Operate Pre-Commercial Size Plant
 Cost Issues...
Vega OTEC   29
OTEC-Vega   30
Lessons Learned

• Life-Cycle Design
• Constructability
• System Integration
• Capital Cost
                 Vega OTEC   31
OTEC Primer
• Energy Consumption & Petroleum
  Resources
• OTEC Generalities
• US OTEC Program 70s, 80s & 90s
• Lessons we...
Environmental Impact Assessment
              (EIA)
• OTEC can be an environmentally
  benign alternative for the producti...
Temp. Anomalies & Upwelling
Sustained flow of cold, nutrient-rich,
bacteria-free deep ocean water could
cause:
   - sea su...
Euphotic Zone: Tropical Oceans
• The euphotic zone: layer in which
  there is sufficient light for
  photosynthesis;
• Con...
Typical Temperature vs. Depth   36
       Tropical Oceans
EIA


Can OTEC have an impact on the
environment below the oceanic mixed
layer (sea surface to 100 m) and,
therefore, long...
OTEC Return Water
• Mixed seawater returned at 60 m
  depth   dilution coefficient of 4 (i.e.,
 1 part OTEC effluent is mi...
CO2 Outgassing

• CO2 out-gassing (per kWh) from the
  seawater used for the operation of an
  OC-OTEC plant is < 0.5% the...
Present Situation




      Vega OTEC     40
41
Vega OTEC   42
Cost of Electricity Production
COE ($/kWh) = CC + OMR&R
             + Fuel (for OTEC zero)
              {+ Profit – Env....
Vega OTEC   44
Vega OTEC   45
Vega OTEC   46
Case Studies:
    Hawai’i
Kwajalein (RMI)
American Samoa
Hawai’i Assessment (4Q/07)
Presently, Avoided Energy Cost in SOH
       0.15 to 0.20 $/kWh          [was < 0.06 $/kWh in 9...
Hawai’i: 100 MW OTEC Plant

• Floating platform stationed     10 km
  offshore, delivering:
 800 million kWh/year to the e...
Hawai’i: 100 MW OTEC Plant (’07)

• A PPA from the utility at 17 c/kWh
  includes ample return-on-investment

• In additio...
Hawaii: Updated Assessment
• Securing financing , without operational
  records, remains a daunting challenge;
• Reactivat...
Kwajalein Atoll (Marshall Islands)

According to USN:
COE (May’05-June’06)
  10 MW Capacity (diesel gensets)

 COE ($/kWh)...
Kwajalein Atoll (Marshall Islands)

• USN willing to issue Power-Purchase-
  Agreement if COE reduced by at
  least 10% ( ...
American Samoa

• ASPA records indicate: Annual
  Consumption 148.8 million kWh,
  equivalent to 17,000 kW (17 MW)
  firm ...
American Samoa

• ASPA interested in         35 MW “future”
  additional capacity

• Can OTEC produce electricity at a
  c...
35 MW OTEC COE ($/kWh)
Capital Cost   Loan Term       COE
  [$/kW]                     [$/kWh]
12,000 ± 20%       8%      ...
Samoa: 35 MW OTEC Plant

• Floating platform stationed 3 km
  offshore Fatuasina Pt. , delivering:
 280 million kWh/year t...
50 MW OC-OTEC Plantship


• 414,400 MWh/year

• 118,400 m^3/day (desalinated water)




                Vega OTEC         ...
Vega OTEC   59
OTEC Primer
• Energy Consumption & Petroleum
  Resources
• OTEC Generalities
• US OTEC Program 70s, 80s & 90s
• Lessons we...
Energy Carriers
Two to three decades from now, would
 it make sense to produce H2 or NH3
 in floating OTEC plantships depl...
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Ocean Thermal Energy Conversion

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Luis Vega from the National Marine Renewable Energy Center describes the technical and economic aspects of Ocean Thermal Energy Conversion (OTEC). Slides from the REIS seminar series at the University of Hawaii at Manoa on 2009-10-01.

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Ocean Thermal Energy Conversion

  1. 1. Luis A. Vega, Ph.D. Hawaii Natural Energy Institute (HNEI) luisvega@hawaii.edu October 1, 2009
  2. 2. Mission Facilitate development and commercialization of wave power (WP) devices and ocean thermal energy conversion (OTEC) systems
  3. 3. OTEC Primer • Energy Consumption & Petroleum Resources • OTEC Generalities • US OTEC Program 70s, 80s & 90s • Lessons we should have learned • Environmental Impact Assessment • Present Situation • Next Generation Vega OTEC 3
  4. 4. Economic & Energy Indicators 4
  5. 5. Petroleum Resources Resources per IEA; API; USGS: R (barrels) Present Consumption: C (barrels/year) R/C = 50 years If China & India maintain Growth 30 years diminishing resources price increases
  6. 6. OTEC Primer • Energy Consumption & Petroleum Resources • OTEC Generalities • US OTEC Program 70s, 80s & 90s • Lessons we should have learned • Environmental Impact Assessment • Present Situation • Next Generation Vega OTEC 6
  7. 7. OTEC Visionary Perspective • Solar energy absorbed by oceans is 4000 x humanity annual consumption; • Less than 1 % of this energy would satisfy all needs. [@ thermal electric conversion 3 %] Vega OTEC 7
  8. 8. Typical Temperature vs. Depth 8 Tropical Oceans
  9. 9. OTEC Engineering Perspective • Two ocean layers with T: 20 °C to 25 °C in equatorial waters… heat source and heat sink required to operate heat engine • How to convert to useful form and deliver to user? Vega OTEC 9
  10. 10. Energy Carriers OTEC energy could be transported via electrical, chemical, thermal and electrochemical carriers: Presently, all yield costs higher than those estimated for the submarine power cable (< 400 km offshore). Vega OTEC 10
  11. 11. Vega OTEC 11
  12. 12. Open Cycle OTEC *Surface (Warm) seawater is flash- evaporated in a vacuum chamber resulting low-pressure steam drives turbine-generator; *Cold seawater condenses steam after it has passed through the turbine produces fresh water Vega OTEC 12
  13. 13. Open Cycle OTEC 13
  14. 14. Closed Cycle OTEC Warm (surface) seawater and Cold (deep) seawater used to vaporize and condense a working fluid, such as anhydrous ammonia, which drives a turbine-generator in a closed loop producing kWh Vega OTEC 14
  15. 15. Closed Cycle OTEC 15
  16. 16. Hawaii’s Ocean Thermal Resource: Truisms • OTEC could supply all the electricity and potable water consumed in Hawaii, {but at what cost?}; • Indigenous renewable energy resource that can provide a high degree of energy security and reduce GHG emissions. Vega OTEC 16
  17. 17. OTEC Primer • Energy Consumption & Petroleum Resources • OTEC Generalities • US OTEC Program 70s, 80s & 90s • Lessons we should have learned • Environmental Impact Assessment • Present Situation • Next Generation Vega OTEC 17
  18. 18. US Federal Government (Rephrasing late 70’s to early 80’s OTEC Mandate) By Year 2000 104 MW Installed equivalent to 100 x 100 MW Plants (Capital > $40 x 10 9) Therefore, Must implement optimized designs and industrial facilities for plantships producing OTEC electricity or other energy carriers to be delivered to shore… Vega OTEC 18
  19. 19. US Federal Government OTEC Program (70’s –80’s) Hindsight should have used funds ($0.25 x 109) to build at least one “large” plant with off-the-shelve hardware… Vega OTEC 19
  20. 20. OTEC Assessment (‘90s) Continuous (24/7) production of electricity and water demonstrated: - MiniOTEC (Hawai’i) - Nauru (by Japanese Companies under Tokyo Electric) - OC-OTEC Experimental Apparatus (Hawai’i) Vega OTEC 20
  21. 21. 210 kW OC-OTEC Experimental Plant (Vega et al:1993-1998)
  22. 22. Desalinated Water Production (Vega et al: ‘94-’98) 22
  23. 23. OTEC Power Output as Function of Control Parameters • Open Cycle Control Parameters: Seawater Mass Flow Rates; Seawater Temperatures & Vacuum Compressor Inlet Pressure • Closed Cycle Control Parameters: Seawater Mass Flow Rates; Seawater Temperatures ; NH3 Mass Flow Rate & Recirculation/Feed Flow Ratio Vega OTEC 23
  24. 24. Vega OTEC 24
  25. 25. OC-OTEC Power Output vs. Cold Water Temperature 1-minute Averages of 1-sec samples show: Cold Seawater Temperature Oscillation as Signature of Internal Waves ( 3,500m; P 60 minutes; H 50 m) Vega OTEC 25
  26. 26. Vega OTEC 26
  27. 27. OC-OTEC Power Output vs. Warm Water Temperature 1-minute Averages of 1-sec samples show: Surface Seawater Temperature Variation as Signature of Warmer Water Intrusion driven by Ocean Gyre shed from Alenuihaha Channel between Maui and Hawaii (Big Island) Vega OTEC 27
  28. 28. Development Barriers (Hawai’i) Tech. Issues: Need to Build & Operate Pre-Commercial Size Plant Cost Issues: Cost Effective for Size 100 MW Enviro. Issues: Relatively Minimal Political Issues: Need Federal Help… only Hawai’i “benefits” (1/300 citizens) ? Vega OTEC 28
  29. 29. Vega OTEC 29
  30. 30. OTEC-Vega 30
  31. 31. Lessons Learned • Life-Cycle Design • Constructability • System Integration • Capital Cost Vega OTEC 31
  32. 32. OTEC Primer • Energy Consumption & Petroleum Resources • OTEC Generalities • US OTEC Program 70s, 80s & 90s • Lessons we should have learned • Environmental Impact Assessment • Present Situation • Next Generation Vega OTEC 32
  33. 33. Environmental Impact Assessment (EIA) • OTEC can be an environmentally benign alternative for the production of electricity and desalinated water in tropical islands • Potentially detrimental effects can be mitigated by proper design Vega OTEC 33
  34. 34. Temp. Anomalies & Upwelling Sustained flow of cold, nutrient-rich, bacteria-free deep ocean water could cause: - sea surface temp. anomalies; - biostimulation If and only if resident times in the mixed layer; and, the euphotic zone are long enough Vega OTEC 34
  35. 35. Euphotic Zone: Tropical Oceans • The euphotic zone: layer in which there is sufficient light for photosynthesis; • Conservative Definition: 1 % light- penetration depth (e.g., 120 m in Hawaii); • Practical Definition: biological activity requires radiation levels of at least 10 % of the sea surface value (e.g., 60 m in Hawaii). Vega OTEC 35
  36. 36. Typical Temperature vs. Depth 36 Tropical Oceans
  37. 37. EIA Can OTEC have an impact on the environment below the oceanic mixed layer (sea surface to 100 m) and, therefore, long-term significance in the marine environment? Vega OTEC 37
  38. 38. OTEC Return Water • Mixed seawater returned at 60 m depth dilution coefficient of 4 (i.e., 1 part OTEC effluent is mixed with 3 parts of the ambient seawater) equilibrium (neutral buoyancy) depths below the mixed layer; • Marine food web should be minimally affected and sea surface temperature anomalies should not be induced. Vega OTEC 38
  39. 39. CO2 Outgassing • CO2 out-gassing (per kWh) from the seawater used for the operation of an OC-OTEC plant is < 0.5% the amount released by fuel oil plants; • The value is even lower in the case of a CC-OTEC plant. Vega OTEC 39
  40. 40. Present Situation Vega OTEC 40
  41. 41. 41
  42. 42. Vega OTEC 42
  43. 43. Cost of Electricity Production COE ($/kWh) = CC + OMR&R + Fuel (for OTEC zero) {+ Profit – Env. Credit} CC = Capital Cost Amortization (Note.- much higher for OTEC) OMR&R = Operations + Maintenance + Repair + Replacement Vega OTEC 43
  44. 44. Vega OTEC 44
  45. 45. Vega OTEC 45
  46. 46. Vega OTEC 46
  47. 47. Case Studies: Hawai’i Kwajalein (RMI) American Samoa
  48. 48. Hawai’i Assessment (4Q/07) Presently, Avoided Energy Cost in SOH 0.15 to 0.20 $/kWh [was < 0.06 $/kWh in 90’s] HECO 0.147 (composite values) MECO 0.198 HELCO 0.193 Therefore, OTEC > 50 MW is cost competitive in Hawaii Vega OTEC 48
  49. 49. Hawai’i: 100 MW OTEC Plant • Floating platform stationed 10 km offshore, delivering: 800 million kWh/year to the electrical grid 32 million-gallons-per-day (MGD) of water • Up-to-date cost estimates yield electricity produced at a levelized cost below current avoided cost in Hawaii Vega OTEC 49
  50. 50. Hawai’i: 100 MW OTEC Plant (’07) • A PPA from the utility at 17 c/kWh includes ample return-on-investment • In addition, at $2 per-thousand- gallons sale price to the Board of Water Supply, revenue is equivalent to a reduction of 3 c/kWh in the cost of electricity production. Vega OTEC 50
  51. 51. Hawaii: Updated Assessment • Securing financing , without operational records, remains a daunting challenge; • Reactivate the OTEC Federal program with specific goal of designing and operating a scaled version of a commercial size plant of $25M) ( 5 MW over a 5 year period with annual budgets • Federal Program would show equipment suppliers potential market for the technology, and should lead to design refinement. 51
  52. 52. Kwajalein Atoll (Marshall Islands) According to USN: COE (May’05-June’06) 10 MW Capacity (diesel gensets) COE ($/kWh) : [0.16 + 0.05] = 0.21 [fuel + OMR&R] Vega OTEC 52
  53. 53. Kwajalein Atoll (Marshall Islands) • USN willing to issue Power-Purchase- Agreement if COE reduced by at least 10% ( 0.9 x 0.21 = 0.19 $/kWh) Not feasible with 10 MW OTEC Vega OTEC 53
  54. 54. American Samoa • ASPA records indicate: Annual Consumption 148.8 million kWh, equivalent to 17,000 kW (17 MW) firm capacity • Fuel Cost of electricity 0.1847 $/kWh Vega OTEC 54
  55. 55. American Samoa • ASPA interested in 35 MW “future” additional capacity • Can OTEC produce electricity at a cost comparable to the present Fuel Surcharge of 0.1847 $/kWh ? Vega OTEC 55
  56. 56. 35 MW OTEC COE ($/kWh) Capital Cost Loan Term COE [$/kW] [$/kWh] 12,000 ± 20% 8% 0.21 15 years {0.18 to 0.25} Note: 80% CC “ 4.2% 0.15 20 years {0.13 to 0.18} Note: 70% CC 56
  57. 57. Samoa: 35 MW OTEC Plant • Floating platform stationed 3 km offshore Fatuasina Pt. , delivering: 280 million kWh/year to the electrical grid 11 million-gallons-per-day (MGD) of water • Cost estimates yield electricity produced at a levelized cost comparable to ASPA’s current Fuel Surcharge Vega OTEC 57
  58. 58. 50 MW OC-OTEC Plantship • 414,400 MWh/year • 118,400 m^3/day (desalinated water) Vega OTEC 58
  59. 59. Vega OTEC 59
  60. 60. OTEC Primer • Energy Consumption & Petroleum Resources • OTEC Generalities • US OTEC Program 70s, 80s & 90s • Lessons we should have learned • Environmental Impact Assessment • Present Situation • Next Generation Vega OTEC 60
  61. 61. Energy Carriers Two to three decades from now, would it make sense to produce H2 or NH3 in floating OTEC plantships deployed along Equator? Presently, would need barrel of petroleum fuel at least 7x higher ($400) to be “cost effective” Vega OTEC 61
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