HomeMy WebLinkAboutThayer Lake Hydropower Project Interconnection Study - Oct 2015 - REF Grants 7040038, 7050825
Thayer Creek Hydroelectric
Interconnection Study
Kootznoowoo Incorporated
To Serve Angoon, Alaska
Technical and Financial Review
Review Prepared for: Review Funded By: Review Prepared By:
Stephen F. Anderson
503.297.8263
October 2015
Table of Contents
........................................................................ 1 Introduction, Purpose and Scope of Interconnection Study
............................................................................................................................... 2 The Angoon Community
................................................................................................... 2 Inside Passage Electric Cooperative (IPEC)
................................................................................................................. 4 Thayer Creek Project Description
..................................................................................................................... 6 Transmission Line Alternatives
................................................................................................................... 7 Interconnection Cost Estimates.
.......................................................................................................................... 10 Interconnection with IPEC
.............................................................................................................. 10 Conclusions & Recommendations
................................................................ 11 Appendix 1: IPEC Electric Power Distribution Drawing, Angoon
.......................... 16 Appendix 2: Harbor Offshore, Inc. Estimate of Submersible Cable Installation, Angoon
...................................... 17 Appendix 3: Elevation Contour Maps of Thayer Creek Hydroelectric Plant Sites
................. 20 Appendix 4: Depth Chart off Angoon, Indicating Location of Existing Communication Cables
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Introduction, Purpose and Scope of Interconnection Study
The small community of Angoon, Alaska is located on Admiralty Island about 60 miles south of Juneau. The
-
profit independent electric utility owned by the members it serves. IPEC serves the communities of Angoon
(234 electric services in 2014), Hoonah (478 services), Kake (302 services), Chilkat Valley (245 services) and
Klukwan (64 services). These are all separate service areas with no electrical interconnections between them
nor to any other utility. The Angoon community has about 600 people and just over 200 households. The peak
power requirement has been in the range of 320 kilowatts for the entire community.
Power is generated by reciprocating diesel engines in these communities. While this is the most reliable and
least expensive method to date, it is very costly. The approved rate for power sales is in the range of 58 cents
to 64 cents per kilowatt-hour, depending on customer type. This reflects the high cost of operating small power
systems in locations that require fuel deliveries by plane or barge. The Alaska Energy Authority provides
financial subsidies to the communities in order to make power more affordable.
The community of Angoon has considered arranging for a hydroelectric power plant that possibly could result
in lower cost and more reliable supply. The nearest potential site for hydroelectric power is on Thayer Creek,
about six and a half miles to the north, across a channel to the Kootznahoo Inlet. This is a remote location, and
the cost of construction is high. But equally challenging is the cost and method of delivering the power to the
community through densely wooded areas of difficult terrain and across the inlet.
It is the purpose of this feasibility review to develop one or two options for the route of the power transmission
line from a proposed hydroelectric power plant which may be located at one of two possible sites.
Funding for this feasibility review has been provided by the Alaska Energy Authority as a part of a larger grant
to complete a feasibility study for the hydroelectric facility. The work is being completed for the benefit and in
consideration of the people of Admiralty Island, home of the Kootznoowoo Tingit group and the community of
Angoon. As a matter of interest,
Figure 1. Location map of Angoon, Alaska
Angoon, Alaska
Located on SW
Admiralty Island
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Figure 2. Angoon, Alaska is located on the west side of Admiralty Island, south of Juneau
The Angoon Community
on both the east and west sides of the isthmus, the village is tied to the sea. IPEC serves 221 housing units in
Angoon, a water plant, a sewer lift station, two schools, a post office, a ferry terminal, a lodge and an inn. They
serve a total of 234 electric services and delivered 1,586,879 kilowatt-hours to customers in 2014. That is an
average of only 565 kilowatt-hours per month for each customer, not a large use per customer.
The key commercial activities in the community include fishing and fish processing. The community uses very
little electric power.
Inside Passage Electric Cooperative (IPEC)
IPEC is a non-profit, independent electric utility owned by the members we serve. Electric cooperatives are
democratically governed businesses, intended to be closely regulated by their consumers. IPEC is
headquartered in Juneau, and serves 234 customers in Angoon. The utility operates three Caterpillar diesel
generators with a total capacity of 1,200 kilowatts. They have heat recovery systems on the diesel generators
which capture discharge heat which is then sold to the Angoon High School for space and water heating. They
have recently received a $544,000 grant to install additional equipment for this purpose.
Diagrams showing the layout and circuit diagrams are included in Appendix 1. These drawings indicate the key
electrical loads and distribution system. The ideal point to interconnect a new generation resource would be on
the west side near the existing power plant, as indicated on the first drawing.
The distribution voltage is 7,200 / 12,470 volts wye connected.
A summary of monthly power generated and delivered is presented in Table 1.
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Month Peak Demand,
kilowatts
Kilowatt-hours
Sold
Average
kilowatts
Fuel Cost Recovered Heat
to School, Mbtu
Recovered
Heat Revenue
January 2014 307 136,781 183.8 $46,148 2,264 $4,200
February 2014 274 141,948 211.2 $45,528 2,436 $4,519
March 2014 267 131,280 176.4 $47,554 2,247 $4,169
April 2014 264 127,396 176.9 $38,284 2,209 $4,018
May 2014 233 122,313 164.4 $41,047 1,395 $2,538
June 2014 221 111,883 155.4 $34,261 920 $1,674
July 2014 271 126,778 170.4 $36,460 911 $1,651
August 2014 257 136,767 189.9 $39,036 784 $1,420
September 2014 271 135,259 187.9 $39,293 884 $1,602
October 2014 276 125,609 168.1 $34,530 1,181 $2,130
November 2014 321 141,739 196.8 $49,558 1,761 $3,176
December 2014 283 149,126 200.4 $46,493 2,363 $4,262
Table 1. Monthly power generation and sales in Angoon in 2014. The total fuel cost for the year was $499,200.
Figure 3. Aerial view of Angoon, Alaska showing key landmarks
Favorite Bay
Chatham Straits
Kootznahoo
Inlet
Ferry Terminal &
Cold Storage
Power Plant
High School
Sea Plane Dock
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Figure 4. IPEC System map of Angoon.
Thayer Creek Project Description
Numerous studies have been carried out to determine the feasibility of constructing a hydroelectric plant on
Thayer Creek, which is located about six and a half miles north of Angoon and across the isthmus to the east.
One of these was published by Harza Engineering Company of Chicago in 1979. It reported that the streamflow
in the creek varies from 150 and 715 cubic feet per second seasonally. Depending on the location of a power
plant and the amount of head the plant has, several hundred kilowatts of power could be generated.
Work completed recently by another electric utility was focused on construction of a multi-megawatt power
plant much larger than the community requires or could fully use in the expected future. That work has
stopped, and the focus of this work is on a plant in the range of 600 kilowatts of capacity.
Two sites have been identified for the potential hydro plant. One would involve the construction of a dam and
power plant about 1,400 feet above the outflow of the creek. The second site would be upstream 5,400 feet
and would involve a diversion structure and the installation of a penstock that would direct water to a
powerhouse at the lower elevation. These two powerhouse locations are the two possible sites from which the
transmission line may originate.
an overhead
powerline.
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Figure 5. Aerial view of the area north of Angoon, Alaska showing the proximate location of the Thayer Creek Hydroelectric Project
Site A. Barrier Falls location. The Barrier Falls site is located about 1,400 feet upstream from the ocean. The
facility would include the construction of a 45 foot high dam and impoundment above the falls. A power plant
would be constructed at the dam, and a transmission line would follow the road built for the construction
activities south to the marine terminal or directly to the waterfront. The proposed plant would be rated in the
range of 600 to 800 kilowatts. The preferred approach is directly to the waterfront.
Site B. Thayer Creek Penstock location. An alternative to the Barrier falls Site is upstream about 5,400 feet
upstream from the Thayer Creek outfalls. This facility would involve construction of a diversion structure
upstream and a 3,600 foot penstock to convey the water downstream to this power plant location. Again, the
Thayer Creek
Penstock Site
Proposed Point of
Power Delivery
Long Island
Mitchell Bay
Kootznahoo Inlet
Favorite Bay
Proposed
Submersible
Interconnection
Line
Thayer Creek
Three Crosses Island
Location of Proposed
Marine Terminal
Barrier Falls
Site
Admiralty Island
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power plant would be rated at about 600 to 800 kilowatts. A transmission line would either run down alongside
a roadway directly to the waterfront or south along the roadway built for the power plant construction. This
site would require less concrete than for the dam construction, but more physical area would be disrupted for
the penstock installation. Each site has challenges and benefits, and each has costs that will be considered.
Transmission Line Alternatives
Three key alternatives are to be considered for the construction of the interconnection line from the proposed
power plant and the community of Angoon, depending on how far the line is constructed on land. These
alternatives are displayed in figure 6.
Option A would involve installing a submersible cable from the waterfront near the outfall of Thayer Creek;
Option B would involve construction of an overhead power line from the hydro plant south along the roadway
to Three Crosses, then connecting to a submersible cable to Angoon;
Option C would involve constructing the overhead line all the way south to Turn Point directly opposite
Angoon, and connect to a 0.4 mile cable crossing. The drawbacks to this approach involve the expense of
extensive tree clearing and a crossing in a more turbulent channel.
No matter where the line crosses the water, the cable must be installed in such a way that it remains in place
when the tidal flows run as much as 12 knots in the narrow portion of the channel. And it must be secured and
protected from anchorages in the area that range in depth ranging from 50 to 400 feet.
Figure 6. Initial submersible cable installation options considered for interconnection routes.
Option A
From the Waterfront
Below the Power Plant
To Angoon ~ 6.5 miles
Option B
From Three Crosses Island
(Potential Marine Terminal)
To Angoon ~ 4.5 miles
Option C
From Turn Point
To Angoon ~ 0.4 miles
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The power distribution system in Angoon is operated at 7,200 / 12,470 volts wye connected. The step-up
transformer for the proposed power plant will be rated at this voltage, as will the transmission line to Angoon.
After careful review, it became clear that the best approach would be to interconnect the submersible cable
from a point nearest the power plant sites. The preferred options are those associated with a direct connection
at the waterfront below the power plant sites. These route options are presented in figure 7.
Interconnection Cost Estimates.
Construction cost estimates have been prepared for the completion of an electrical interconnection between
the proposed hydroelectric plant and the village of Angoon. Estimates were prepared for both of the two
proposed plant sites. There are four key components necessary to consider in the estimate of cost. These
include (A) the interconnection, switchgear and step-up transformer necessary at the power plant; (B) a line to
the waterfront; (C) a submersible cable from the waterfront area below the power plant to the shore in
Angoon below the main substation; and (D) an interconnection at the IPEC substation in Angoon.
The largest portion of these costs is associated with the installation of the submersible cable. But the majority
of the cost is related to the preparation of the cable installation. The cost per mile of the actual installation is
modest. A summary of the cost estimates is included in Table 2.
Line Section
Option 1.
Overhead, Barrier Falls
to Waterfront
Option 2.
Underground, Barrier
Falls to Waterfront
Option 3.
Overhead, Penstock
Site to Waterfront
Power Plant
Interconnection,
Transformer and
switchgear:
$235,500
$217,500
$235,500
Line to Waterfront: $208,170 $207,480 $595,455
Submersible Cable: $2,209,000 $2,209,000 $2,209,000
IPEC Interconnection: $561,420 $561,420 $561,420
Total: $3,214,090 $3,195,400 $3,601,375
Table 2. Estimated construction costs to interconnect proposed Thayer Creek Hydroelectric Plant
The estimate for the installation of the submersible cable has been based on a number of conversations and
estimates provided by contractors familiar with similar installations of power, communications and video cable
in the region. One of the most experienced contractors, Harbor Offshore Inc. has provided a detailed estimate
of the component costs associated with the installation of an underwater line at this location. This cost
estimate is included in Appendix 2.
Cost Saving Potential. A portion of the cost of this installation may be reduced if the line may be installed
coincident with another submersible line (power or communications) in the vicinity. This savings may be as
much as $500,000 if another cable installation may be scheduled at the same time. Mobilization and loading of
the other cable system in Seattle must occur at the same time.
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Figure 7. Topographical view of the area around Thayer Creek indicating the location
of the proposed hydroelectric plant and preferred interconnection options.
Barrier
Falls Line
Penstock
Line
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Additional Cost Considerations. One of the concerns about the submersible cable installation involves the
crossing of the existing communication cables that connect on the west side of Angoon. This crossing could be
costly depending of the requirements of the communications company, GCI Cable Company. An allowance has
been included in the cost estimate for these fiber crossings in the amount of $195,000. This would normally be
adequate for protection of existing cables crossed by new power cables, but the actual expense could be more.
The depth of the waters in the region varies dramatically, up to several hundred feet. It will be critical that the
cable be located where it is least likely to be harmed by a boat anchoring or a fishing activity. Yet it also must
not be buried deeper than necessary in order that any repairs or maintenance be unnecessarily costly.
Figure 8. Aerial map indicating the location of existing fiber communication lines
Figure 9. Depth chart in the area of Angoon, Alaska. Soundings in fathoms (6 feet/fathom). Existing fiber cable lines indicated.
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Interconnection with IPEC
Estimates have been prepared to evaluate the cost to interconnect with the existing utility system in Angoon. These
estimates are based on comparable interconnections in other locations, but not as a result of designs and engineering
based upon specific requirements of the utility or on-site conditions. For this reason, the estimated $561,000 cost may
vary.
Figure 10. IPEC s diesel power plant and fuel storage facilities in Angoon
Conclusions & Recommendations
The potential interconnection of the Thayer Creek Project appears to be both technically feasible and reasonably
affordable. There appear to be no roadblocks that would prevent completion of an interconnection system for the
hydroelectric system.
There are a number of unknowns yet to be determined associated with this project. Additional studies and engineering
could reduce the cost of the proposed line. A survey of the proposed route could enable a more precise cost estimate.
In addition, it would be valuable to communicate with other companies that are involved with submersible cable
installations. If one or more projects could be scheduled coincident with the Thayer Creek Project, significant cost savings
could be achieved. If an agreement could be reached that would reduce the overall cost of the undersea cable, this
project could become even more viable.
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Appendix 2: Harbor Offshore, Inc. Estimate of Submersible Cable Installation, Angoon
Description pl
u
D
A QuantityUnit Cost Labor Material Equipment Subs Misc Contingency Rounded
Mobilization Subtotals Subtotals
Site visits 2 ea 11,429$ 22,857
Submittal 80 hrs 114$ 9,143
Management bet. award and mobilization 600 hrs 114$ 68,571
HOI labor, prep and load out equip 20 days 5,280$ 105,600
Lay barge during mob 1 mo 42,857$ 42,857
Spuds and spud wells 3 months 28,571$ 85,714
Crane on barge 3 mo 12,857$ 38,571
Crane services dockside 80 hrs 464$ 37,143
Ousite mob labor, loading and welding 200 hrs 129$ 25,714
Trucking 6 ea 1,143$ 6,857
HOI cable equipment new fab 1 ls 214,286$ 214,286
HOI equipment, rental during mob 1 ls 28,571$ 28,571
ROV mob 1 ls 14,286$ 14,286
Survey mob 1 ls 5,714$ 5,714
Land equipment for pull ins 3 mo 14,286$ 42,857
Shipping shore pull equip to Angoon 1 ea 2,857$ 2,857 ROUND up
total cost 183,314 0 242,857 302,571 22,857 0 751,600 752,000
Site survey
Surveyor 1 ls 35,714$ 35,714
survey equipment 1 ls 71,429$ 71,429
Report 1 ls 4,286$ 4,286
HOI 1 ls 28,571$ 28,571
Travel 1 ls 2,571$ 2,571
local boat 1 week 14,286$ 14,286
perdiems 28 mndy 357$ 10,000
total cost 28,571 0 0 128,286 10,000 0 166,857 167,000
Fiber crossings
matts 8 ea 4,286$ 34,286
Lay barge 2 days 14,286$ 28,571
Tug 2 days 14,286$ 28,571
HOI crew 2 days 22,997$ 45,994
HOI equipment 2 days 28,571$ 57,143
total cost 45,994 34,286 57,143 57,143 0 0 194,566 195,000
Cable transfer ship to barge
Laybarge 2 days 14,286$ 28,571
Tug 2 days 14,286$ 28,571
HOI labor 2 days 22,997$ 45,994
Testing 1 ls 8,571$ 8,571
Crane barge 1 days 22,857$ 22,857
total cost 45,994 0 0 88,571 0 0 134,566 135,000
In transit, round trip
Crew travel airfares 20 rt 1,000$ 20,000
Crew labor in transit 32 ea 714$ 22,857
Laybarge 7 days 14,286$ 100,000
Tug 7 days 14,286$ 100,000
perdiems 40 mndys 357$ 14,286
Surveyors labor 1 rt 4,286$ 4,286
Rov operators labor 1 rt 4,286$ 4,286
total cost 22,857 0 0 208,571 34,286 0 265,714 266,000
On site
HOI labor 5 days 22,997$ 114,986
Laybarge 5 days 14,286$ 71,429
HOI equipment 5 days 14,286$ 71,429
Tug 5 days 14,286$ 71,429
Surveyors (2) 5 days 8,571$ 42,857
ROV with crew 5 days 14,286$ 71,429
perdiem 100 mndy 357$ 35,714
total cost 114,986 0 71,429 257,143 35,714 0 479,271 480,000
Demob
HOI labor, demob equip 20 days 5,280$ 105,600
Lay barge during demob 1 mo 42,857$ 42,857
Crane services dockside 20 hrs 464$ 9,286
Outside mob labor, off loading & welding 200 hrs 129$ 25,714
Trucking 6 ea 1,143$ 6,857
HOI equipment, rental during mob 1 mo 14,286$ 14,286
ROV demob 1 ls 5,714$ 5,714
Survey demob 1 ls 2,857$ 2,857
total cost 105,600 0 14,286 93,286 0 0 213,171 214,000
Labor Material Equip. subs misc Totals
Total cost per category 547,317 34,286 385,714 1,135,571 102,857 0 2,205,746 2,209,000
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Appendix 3: Elevation Contour Maps of Thayer Creek Hydroelectric Plant Sites
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Appendix 4: Depth Chart off Angoon, Indicating Location of Existing Communication Cables
http://www.charts.noaa.gov/OnLineViewer/17339.shtml Depth Chart Map