Loading...
HomeMy WebLinkAboutAn Investigation of Small Tidal Power Plant Possibilities on Cook Inlet AK 1976AN INVESTIGATION OF SMALL TIDAL PONER PLANT POSSIBILITIES QN COOK INLET, ALASKA ALASKA POWER AUTHORITY LIBRARY COPIES PLEASE DO NOT REMOVE! ! by Dr. Charles E. Behike, P.E., Dean, School of Engineering and Dr. Robert F. Carlson, P.E., Director, Institute of Water Resources UNIVERSITY OF ALASKA FAIRBANKS, ALASKA April, 1976 AN INVESTIGATION OF SMALL TIDAL POMER PLANT POSSIBILITIES ON COOK INLET, ALASKA ALASKA POWER AUTHORITY LIBRARY COPIES PLEASE DO NOT REMOVE! ! by Dr. Charles E. Behike, P.E., Dean, School of Engineering and Dr. Robert F. Carlson, P.E., Director, Institute of Water Resources UNIVERSITY OF ALASKA FAIRBANKS, ALASKA April, 1976 t . ~ » UNIVERSITY OF ALASKA AN INVESTIGATION OF SMALL TIDAL POWER PLANT POSSIBILITIES ON COOK INLET, ALASKA In the year 1778, Captain James Cook, on one of his famous voyages of exploration, made the following comments in his journal:? Saturday, May 30, 1778: ". . . Here? we lay during the Ebb which ran now 5 knots an hour. . ." Sunday, May 31, 1778: "At 9 o'clock we came to Anchor in 16 fathom about two leagues from the west shore, and found the Ebb already made; which when at its greatest strength ran only 3 knots and fell upon a perpendicular, after we had anchored, 21 feet. . ." / Monday, June 1, 1778: ". . . After we had entered the bay the flood set strong into the River Turnagain®, and Ebb came out with still greater force and the Water fell upon a perpendicular, while we lay at anchor 20 feet. . ." Even two centuries ago, the importance of tidal phenomena in the large Alaskan tidal inlet which now bear Cook's name, was well appreciated by ex- Plorers and navigators. More recently, fishermen and resource developers have become aware of the significant tidal amplitudes and currents found in Cook Inlet. Prior to investigating Cook Inlet's unique potential for exploitation by small tidal power plants, a review of the principles of hydraulic power 1Reproduced from "The Journals of Captain James Cook on His Voyages of Discovery." 2North Foreland, upper Cook Inlet, Alaska. 5Turnagain Arm, upper Cook Inlet, Alaska. Ck “ UNIVERSITY OF ALASKA potential available from the tides is briefly presented here. No attempt * will be made to explain the inter-relationship between tidal power and that of a complex electrical network. ELEMENTARY HYDRAULICS OF TIDAL POWER PLANTS Energy of the tides exists in both kinetic and potential forms. Gen- erally, only the potential energy component of tidal energy has been con- sidered for possible development of tidal power stations around the world. It is, however, worthwhile to calculate the power present in the kinetic energy form for a cross-section on Cook Inlet. The kinetic energy of fluid passing through a given cross-section of an estuary is: oe f (o#? a Eq. 1. where d4 is an element of the cross-sectional area, A, of the estuary and V is the fluid velocity at the element of area, dA, being considered. For ease of discussion, it is assumed that: A pv2 -.p _@ | [F] va =—3 “az = 2 2 2 av ave = 2 3 = -3 AV ave Eq. 2. + & . my , UNIVERSITY OF ALASKA where @ is the volumetric discharge rate through the area, A, at the instant being considered. The kinetic energy flux through the section is also equal to and given by Equation 2. Expressing the velocity as a sinusoidal function of time as follows: - in out V= Vinci? sin Eq. 3. where Y ane is the maximum tidal velocity over the tidal cycle being con- sidered and 7 is the tidal period, the kinetic power passing through the area, A, at any instant becomes: pAv3 3 mage [e in 2rt| Eq. 4. 2 Equation 4 expresses the power due to kinetic energy flux during both the ebb and the flood tides. The average power possessed by the current over a half tidal cycle in the kinetic form is: 7/2 Av3_ ot 7/2 _ 1 _ max {1 -. Qnt)3(2n Fwe ~ TE fi Pdt = —Teq)- [rs] f, [ez Fr} (| i 3 (_ein2 (2xt ant) i _ AV maze sin 7 cos 7 ( Ont = --_ -cos |= Tp 3 3 T 0 3 _ 4 AV" maze ~ oT 7! Eq. 5. _UNIVERSITY OF ALASKA As an example of the magnitude of P, for Turnagain Arm, highway crossing studies indicate a maximum velocity of seven knots or 11.84 ft./sec. = 8re- = P we 3.87 x 10°ft-#/see = 700,000 HP However, when kinetic energy is considered in light of its possible practical exploitation for useful power, it is more useful to normalize on the basis of each square foot of estuarial cross-sectional area which could be exploited by possible reversible, propeller type turbines. If such a turbine could extract all of the kinetic energy present---an impossible situation because the fluid would have no exit velocity from the turbine---an upper limit on any scheme of kinetic energy extraction can be established. Equation 5 yields per square foot of estuary cross- ’ section, y3 4 : P= > aT = .21 V3 (Eng. units) Eq. 6. in seawater, and the horsepower equivalency, P : HP = 35g = 00089 V? (Eng. units) £q. 7. For a turbine 100 feet in diameter (certainly a massive machine), BP (pe. a 3 100") ~ 5.06 V" ee Recalling the Turnagain Arm case, Ve = 12'/sec, the average horsepower available from a hypothetical 100' diameter turbine would be, HP = 3.06 (12)3 = 5288 HP. UNIVERSITY OF ALaskKA This exercise certainly proves that kinetic energy of even rather fast tidal currents is quite unattractive as a practical and economically viable energy source. Clearly, any viability of economic tidal power schemes rests with possible exploitation of the potential energy of tidal waters. Single basin tidal power projects extract potential energy from sea water as it enters the basin and, for double action basins, as it leaves the basin with the rising or falling of the tide outside. To illustrate the potential energy available from a tidal basin, consider an appro- priately gated basin which is filled quickly at high tide and emptied quickly through a turbine of sufficient capacity at low tide. The element of energy, dz, generated from a basin of plan area 4, for a differential decrease in water surface elevation of the basin sur- face would be: dE = -yAhdh Eq. 8. where h is the instantaneous difference in head between the basin surface elevation and the simultaneous sea surface elevation. When a basin of con- stant area is filled completely at high water and emptied quickly at low water, Eq. 1 is integrated as follows: E R2 aT YE Eq. 9. For a simple tidal basin, to raise the basin above high tide or be- low low tide elevations, with no pumping, Equation 9 defines the maximum ‘ - . Basin Water Surface Area =A h = instantaneous 4 head — —LW. “Basin Side Sea Side TIDAL BASIN SURFACE. ELEVATION een we ee oe SEA SURFACE ELEVATION f > — TIDAL RANGE R ELEVATION —» TIME ——> FIG. Q, RAPID DISCHARGE FROM A TIDAL POWER BASIN, Ce UNIVERSITY OF ALasKA potential energy available from a single acting basin from a half cycle of the tide. The process can, of course, be reversed so, ideally, twice this energy becomes available from a single, double acting basin during each complete tidal cycle. Realistically, rapid filling (or emptying) near the crest of the tide is difficult because required turbine passages would be unrealistically large, and the quickly generated energy would have to be rapidly stored and later retrieved with attendant losses. A more realizable situation for a double acting basin is afd teated by Figure 3. Bernshtein* has shown that for best operation of non-pumping, single-basin tidal power plants, turbine operation should begin at ap- proximately half tide with the flow through the turbines filling the basin in such a manner that the rate of change of water surface elevation in the basin is approximately the same as that of the outside sea surface. Thus, head and discharge remain reasonably constant over a significant portion of the tide. This operating procedure results ‘from the fact that, in the real world, the time required for filling the basin and the desir- ability of spreading the power generation process over as much of the tidal cycle as is economically feasible both mitigate against rapid filling, as previously discussed, if maximum energy per unit of basin area, E/A, is to be derived. Further examination of Equation 9 reveals that, if a full basin be- “Bernshtein, L.B., Tidal Energy for Electric Power Plants, Israel Programs for Science Translation, 1965, pg. 66-//. 8 ELEVATION BASIN FULL ‘ BASIN EMPTYING TIME ——> ~ DOUBLE-ACTION, TIDAL POWER PRODUCING BASIN SCHEME FIG, 3 BASIN ~~! FILLING/ ,UNIVERSITY OF ALASKA gins emptying at half tide and follows the tide for the remainder of the emptying cycle, the ideal value of Z/A given by Equation 9, is accom- plished by this "with the tide" filling pattern. This requires that water remaining in the basin when low water occurs outside must be released through the turbine at an elevated discharge rate as the water elevation in the basin approaches the outside level. Thus, the lower half of the basin emptying process must occur during the time period near or at low tide outside the basin. This "with the tide" procedure would yield energy approximately as follows: r - rH) ++] =——. = Yili! ty h(-dh) A 242 R/2 R2 nz R/2 “v9 +? 0 : - 1 + ae Eq. 10. 2 He ca 1 Here, the first term in the right side of Equation 10 represents the po- tential energy extracted from the top half of a unit area, basin prism which is discharged with a head of R/2. The second term of Equation 10 represents that energy extracted for the bottom half of the unit area, basin prism as it is discharged with a head varying from half the tidal range to zero, ideally at low water outside the basin. 10 UNIVERSITY OF ALASKA Since the tidal range, R, varies from tide to tide throughout the month and year, the energy developed per unit of basin area, Z/A, varies accordingly. For example, in Cook Inlet, near Anchorage, it varies from approximately 12.3 feet (4.1 m) to 39 feet (12.9 m). The value of the Anchorage range ratio to the second power varies as (12.9/4.1)2 or by a ratio of almost ten to one. . Generalized operational curves which maximize the generation of power from single basin, double acting tidal power plants for a complete diurnal tidal cycle have been presented by L. B. Bernshtein®, and are reproduced in Figure 4. These curves indicate instantaneous values of Power/Area (P/A = KW/Km2) for any stage of a semidiurnal tide. Figure 4 clearly illustrates difficulties to be expected from a single basin tidal power plant. These are: (1) two to three hour periods of no power production, and (2) variations in power produced during the four power producing operations of two tidal cycles. Additional, but not so apparent, difficulties are those of the long period variations of tidal range and the variation in length (and phase) between the solar and lunar days. These are of major importance because of the reduced energy available during neap tides and the frequent phase difference between the daily time of peak power demand and the most favorable time each day for power generation. More complex tidal power plant arrangements, utilizing ingenious SIbid., Page 76. 11 ZL POWER, Kw/Km? 5 lO 15 2 25 TIDAL RANGE, meters HOURS OF THE TIDE UNIVERSAL CHART OF POWER OUTPUT PER UNIT OF BASIN AREA FOR TIDAL POWER PLANTS OF ANY TIDAL RANGE, FIG, 4 - UNIVERSITY OF ALASKA schemes, have been hypothesized which couple either simple or complex power plant-sluice arrangements with two or more adjacent, linked basins. These are generally designed to reduce the undesirable diurnal power fluctuations which are so obvious in Figure 4, but for a given total basin area, such schemes are not capable of producing as much overall energy as the single basin, double-acting arrangements previously dis- cussed. (The reader is referred to References 4, 5, and 6 for compre- hensive discussions and bibl iography of most of these. A Note on the Addition of Pumping: Pumps may be added to the turbines of a tidal power project, and modern machinery allows for turbine-pumps to function as a turbine or pump in either direction. Gibrat® has extensively delved into the coupling of pumping with turbine operations for the Rance project in France, and has found that the use of pumping during certain times, together with double tidal tur- bining, produces economic advantages over simple double tidal operations for the Rance project”. He illustrates that pumping produces advantages at neap tide but not significantly at spring tides. 5Gibrat, R., L'energie des Marees, Bulletin de la Societe Francais des Electricies, 7-e series, VOl. 3, 1953, pg. 283-332. "Ibid. 13 UNIVERSITY OF AL..JcKA LARGE SCALE TIDAL POWER POTENTIAL OF COOK INLET Figure 5 indicates the plan geometry and size of Cook Inlet. It is geometrically shaped such that tidal amplitudes are amplified with distance from the sea. For example, mean tidal range of Seldovia, near the Inlet mouth, is 15.4 feet while at Anchorage it is 26.1 feet and at Sunrise, on Turnagain Arm, it is 30.3 feet. Wilson and Swales® have presented a study of some potential, large tidal power schemes for upper Cook Inlet. These are indicated in Table 1 and Figure 6. They also outline a massive scheme which involves a dam and power plant, extending from East Forelands to West Forelands which could produce seven percent of the power generated in the U.S. High Water Low Water Mean Tide Energy Area Area Range Per Annum Site Reference Square Miles Square Miles Ft. GWh By and Bo 460 230 24.5 18,600 B, and B3 330 175 24.5 12,500 D 120, 47 24.5 6,000 Table 1 Their study details plans for enclosures as follows: By + B3, By + Bo and D. These projects entail enclosure dams constructed in water depths ®Wilson, E.M. and M.C. Swales, "Tidal Power from Cook Inlet, Alaska," Tidal Power, edited by T.V. Gray and 0.K. Gashus, 1972, pg.239. 14 oe Goch atdte dA ode Li : Send anack ee deena We ue erent, De neh ue ete oe De Ee ie etkearec hut .. f uJ oO xt ao oO <= oO 2 qt [acer err cg were we ETE Te a ee FIG. & COOK INLET, ALASKA 15 or NORTH FORELAND ; ‘SUNRISE DSS Foreland: nautical miles FIG, ©. COOK INLET TIDAL POWER BARRAGES OUTLINED BY WILSON & SHALES,” ,UNIVERSITY OF ALASKA ranging from 20 to 150 feet (360 feet for the East Foreland-West Foreland project) and considerable dam lengths. The large scale schemes proposed by Wilson and Swales® have areas of 1200 mi2 (3072 km?) for the massive East Foreland to West Foreland pro- ject, 460/230 mi2 for scheme B, + By, 330/175 mi2 for scheme B, + B3 and 120/47 mi2 for scheme D. (High water basin area/low water basin area). Though these are all very large projects involving large closures, power produced, would be very considerable (see Table 1). The economics and desirability of these schemes do not make them feasible at present, but those schemes should certainly be periodically reviewed. SMALL SCALE TIDAL POWER POTENTIAL OF COOK INLET The purpose of this paper is to suggest an alternative, much smaller, arrangement than those of Wilson and Swales for tidal power plants in Cook Inlet. The scheme is designed to function in the in- terim period until their much larger schemes become economically at- tractive. The stimulus for a conceptual study of small tidal power projects in Cook Inlet is the possibility of coupling of tidal amplification with considerable spatial phase change of the tide as it progresses up the Inlet. The phase of the tide at Anchorage, at the upper end of the In- °Ibid. 17 UNIVERSITY OF ALASKA let, lags the Seldovia tide by approximately five hours. ~. tide of the upper end of Knik and Turnagain Arms lag the Seldovia tide by approx- imately six hours. Thus, the tide, is high at one end of the Inlet and low at the other end. Consequently, the intriguing potential of a 1/4 wave length basin is present in Cook Inlet. The problem of the diurnally spasmodic nature of power production from single basin tidal power plants may, perhaps, be obviated in Cook Inlet by means of a series of "spatially lagged" tidal power projects at the side or sides of the Inlet. It is clear from Figure 4, that if several identical power curves were each appropriately time lagged and superposed, the resultant power produced would vary with several periodic components above and below a mean value (not zero). However, with the sharp, abrupt reduction to zero power production four times every 24.8 hours, could be eliminated. Indeed, a large number of ap- propriately sized tidal power basins lining the sides of the Inlet and arms would produce power with only semi-monthly or longer period fluct- uations which could be eliminated through the use of subsidiary pumped storage. Figure 7 indicates the results over a lunar day of a phased difference of three hours, 15 minutes between two, double acting basins. Comparisons with the single basin concept indicates that minimum tidal power production from two such geographically (and time) lagged basins increases from zero to 47 percent of maximum tidal power production over the diurnal tidal cycle with only brief times when energy loads would have to be picked up by alternate power sources (hydro or gas turbines). 18 ~ 6L POWE ED GENERALIZE o ae pebble falta tat todbnbt dt Sond lonabentdnt Lenton ad 8. a IS. 24 6 > 2 TIME, hrs. ENERALIZED POVER AF tne BY TWO MATCHED TIDAL BASINS ». OUT OF PHASE BY 3- Va HOURS. . cie fF UNIVERSITY OF ALASKA When three double acting, paired basins of appropriate sizes are properly lagged geographically such that one is lagged two hours, four minutes and a second lagged four hours, eight minutes behind the initial basin, the overlap of power production smooths out minimums in the daily tidal power cycle significantly and allows for sharp peaks of additional power which suggest utilization of pumping into either fresh water, power plant reservoirs or for pumping of tide water either into or out of one or both of the two "resting" power basins. (See Figure 8). The quantity of tidal power available per unit of basin area was shown to be proportional to the square of the tidal range, R. Tidal ranges and times of high water at discrete positions along Cook Inlet, in relation to Seldovia, occur as shown in Figure 9. In order to achieve a phase difference of four hours, eight minutes between two basins, it is necessary to choose a site for one basin so close to the sea that the tidal range at its location is diminished from those of production basins located farther up the Inlet. Thus, the tidal power production per unit of area for the sea-most basins of a two or three basin scheme would be approximately a quarter that of a basin in either of the arms. Basin size for the sea-most basin must therefore be almost four times that of basins at the upper end of the Inlet if the basins were to produce identical powers. Perhaps the most economical arrangement of smal] tidal power basins for Cook Inlet would be one location near Gray Cliff or Bershta Bay, phased by approximately two hours, with another at either Goose Bay on 20 GENERALIZED POWER ge | momen 4:0 n enero tot } ! ! O 6 12 is 24 TIME, hrs. POWER PRODUCED BY THREE MATCHED TIDAL POWER BASINS, (BASIN 2 LAGGED 2:04 HOURS, BASIN 3 LAGGED 4:08 HOURS.) FIG, 8. ie Qa on 6 » UNIVERSITY OF ALasKA Knik Arm or near Sunrise Creek on Turnagain Arm, and a third of com- Parable capacity located at Kalgon Island. It is important to recognize that the enclosures necessary to develop smal] tidal basins would be located at points along the shores of the Inlet in shallow water, thus minimizing closure problems. Rockfill (eight inch or smaller) dams or dikes with impermeable sheet piling cut-off walls, driven through the small rocks, have been proposed by F. L. Lawter?® for the Bay of Fundy and appear to have the potential for providing the necessary essentials of stability and imper- meability necessary to function in this environment. Such rock cores would require armor protection from waves and sea ice. This is discussed later. POWER PLANT The bulb type, straight flow turbine utilized on the Rance project in France appears to be well suited for the power plants suggested here. Since the proposed projects are quite small, movable blade turbines ap- pear to offer advantages over fixed blade turbines for best regulation over a spectrum of head and discharge conditions. Additionally, pump turbines would make possible some daily evening-out of power production. The authors have not, however, made an economic analysis of the various Mlawter, F.L., "Tidal Power on the Bay of Fundy," Tidal Power, edited by Gray and Gashus, 1972, pg. 49. 23 ‘ - UNIVERSITY OF ALacKA possible turbine and pump turbine schemes to suggest an alternate solu- tion to this question. Ice considerations mitigating against open sluiceways favor utilizing the turbines in a feathered condition as -high and low water sluiceways, hence, further suggesting adjustable blade turbines (or pump turbines). Professor Ruus'! indicates that tolerances of 1/1000 of an inch or less would be required for successful operation of gear driven generators. The suspended sediments of upper Cook Inlet contain larger particle diameter than this, so this type of turbine-generator apparatus is ruled out. Large diameter turbines would not be feasible for small plants. The possible depths of water, even with moderate dredging, are in the order of 40-75 feet at low tide. Thus, several small turbines would be more desirable than a few large, deeply set turbines. It is doubtful that turbines in excess of 10,000 kw would be favorable for the small tidal plants along the shores of Cook Inlet. Cook Inlet is a very high cost construction area. Thus, any tidal power scheme should envision construction, at a convenient location in the U.S., of turn-key power plants which could be floated in the open ocean as scows and towed to Cook Inlet for installation on prepared found- ations. It is envisioned that sluiceways would be through the turbine for adjustable blade turbines or would be separate if fixed blade tur- ™Ruus, Prof. E., "Power Unit and Sluice Gates Design," Tidal Power, edited by Gray and Gashus, 1972, pg. 383. 24 .- Ly ; ~, ,UNIVERSITY OF ALASKA . bines were determined to be more economical. If, however, separate sluices were constructed, they, too, could be fabricated at a less costly location and towed to Cook Inlet for installation. ICE CONSIDERATIONS Cook Inlet experiences two differing sea ice problems during the winter months. The first of these is that of floating sheet and pan types of ice which move with tides and winds. These sometimes reach a thickness of three to six feet and are subject to rafting and pres- sure ridging, thus increasing local ice thicknesses beyond that of a single sheet. Since the inception of oi] development in the Inlet in the early 1960's, oil platforms have successfully withstood ice forces produced by these types of ice. It is envisioned that this icing would certainly produce significant problems for tidal power projects unless turbines and sluices are set at low elevations, thus keeping water pass- ages and movable equipment well below the water surface and floating ice levels. A second sea ice problem abundant in Cook Inlét's peripheral areas, and especially so in its arms, is that of "chunk-ice" formation. Such ice forms in large blocks on tidal flats during alternating exposure to tide water and cold air as the tide rises and falls. This ice captures bottom sand and silts, has the appearance of large rocks, and grows as winter progresses. Some of these chunks attain the magnitude of medium 25 ~ , , UNIVERSITY OF ALASKA size houses. Much of this ice does not migrate far with the tidal cycle but occupies a large segment of tide flats. This type of icing could significantly affect small tidal power projects of the type here ens visioned. It would be too large to pass through turbines, and it could rob winter-time tidal basin storage. It would certainly have a de- vastating effect on improperly designed sluiceways. To obviate this problem, it would be imperative to utilize basin areas which do not expose the bottom of the basin during low tides. Ice formation on structures in Cook Inlet has long been a serious problem. The alternate wetting and exposure to cold air of structures functioning in the tidal zone has produced build-ups of ice resulting in some structural failure of the Anchorage ship docking wharf. Rip-rap rock has also been "stolen" from the shoreline railroad embankment on Turnagain Arm when considerable ice build-up surrounded rocks and the resultant composite material became positively buoyant and floated away at high tide. These problems also suggest that any sluicing be per- formed through sluices or turbines at depths which allow for continuous wetting of moving or movable equipment. In addition, enclosure dams or dikes should be faced with a smooth, probably asphaltic, material to pre- vent ice theft of rip-rap. Experience of the Alaska Railroad of more recent years along the shores of Turnagain Arm indicates that large rip-rap rock, also solves this problem. 26 a t a » a . 7 UNIVERSITY OF ALasKA ENVIRONMENTAL CONSIDERATIONS Envirenmental questions surrounding small tidal power projects in the Cook Inlet appear to center around commercial fishing, aesthetics, and navigation. The projects here outlined are not environmentally detrimental. They do, however, displace near-shore fish runs farther out into the Inlet. At present, there is little sport fishing in upper Cook Inlet because the water is quite muddy and tidal currents are fierce. However, commercial salmon gillnets line the shores of Kalgon Island and the eastern shore of Cook Inlet from the vicinity of Ninilchik to Moose Point. The question of entrapment of salmon in basins would have to be investigated. Razor clams are taken by subsistence "fishermen" from several of the shallow beaches along the eastern shore. Beluga whales are quite populous in the Inlet during certain times of the year. However, they should not be affected seriously by close- to-shore structures. No rivers or salmon creeks need be blocked by small tidal power schemes in Cook Inlet if streamflows were not to be exploited for power. It is doubtful, however, that schemes utilizing riverflow in addition to tidal water would hinder salmon movements into rivers or streams because fish could pass freely through appropriately set, low head turbines with- out difficulty. Care must be taken to prevent encroachment of clam beaches, as clam digging is quite important to the area. The aesthetics of small tidal power projects certainly present quest- 27 a - UNIvERSITY OF ALASKA ions which the authors cannot answer. Whether engineers can design dams, dikes and power plants aesthetically acceptable to Alaskans is an im- ponderable. Navigation should not be significantly affected by the schemes pro- posed because small tidal power projects would be located away from present navigational patterns and where shallow water makes navigation impossible. COSTS Costs of the proposed projects have been extremely difficult to estimate because contractors do not have experience with large-scale excavation and dredging projects in the area. Also, American firms have not manufactured power plants of the type here discussed. How- ever, recognizing very broad confidence limits, the authors, best esti- mates are that the power to be obtained from small tidal power projects would cost 30 to 40 mills/kwh. Such power is not competitive with hy- dro power which could be produced by a number of streams in the South- central Alaska area. It is really not competitive with gas turbine power at this time. However, with a continuously tightening energy picture, it appears that at some future time, this renewable energy resource will be quite competitive with fossil-fuel plants. 28 4 ~@e - “UNIVERSITY OF ALasKA FUTURE WORKS This paper is a modest addition to che brief studies which have Z thus far been made of Cook Inlet tidal power. This is a large, complex body of water which warrants a great deal of additional study in an at- tempt to maximize its total productivity--energy, food, recreation, in- dustry, and aesthetics. 29