This document discusses ocean thermal energy conversion (OTEC) and its potential applications. It provides an overview of OTEC, describes lessons learned from past US OTEC programs in the 1970s-1990s, assesses the present situation and barriers to development, and envisions future generations of OTEC that could produce hydrogen or ammonia as energy carriers. The document contains technical details on open-cycle and closed-cycle OTEC systems as well as case studies for Hawaii, Kwajalein Atoll, and American Samoa.

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

2. Mission
Facilitate development and
commercialization of wave
power (WP) devices and
ocean thermal energy
conversion (OTEC) systems

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. Economic & Energy Indicators 4

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. 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. 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. Typical Temperature vs. Depth 8
Tropical Oceans

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. 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. Vega OTEC 11

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. Open Cycle OTEC 13

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. Closed Cycle OTEC 15

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. 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. 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. 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. 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. 210 kW OC-OTEC Experimental Plant
(Vega et al:1993-1998)

22. Desalinated
Water
Production
(Vega et al:
‘94-’98)
22

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. Vega OTEC 24

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. Vega OTEC 26

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. 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. Vega OTEC 29

30. OTEC-Vega 30

31. Lessons Learned
• Life-Cycle Design
• Constructability
• System Integration
• Capital Cost
Vega OTEC 31

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. 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. 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. 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. Typical Temperature vs. Depth 36
Tropical Oceans

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. 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. 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. Present Situation
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41. 41

42. Vega OTEC 42

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. Vega OTEC 44

45. Vega OTEC 45

46. Vega OTEC 46

47. Case Studies:
Hawai’i
Kwajalein (RMI)
American Samoa

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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 50 MW OC-OTEC Plantship
• 414,400 MWh/year
• 118,400 m^3/day (desalinated water)
Vega OTEC 58

59. Vega OTEC 59

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. 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