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XYLENE POWER LTD.

SEASONAL HYDRAULIC ENERGY STORAGE

By Charles Rhodes, P. Eng., Ph.D.

INTRODUCTION:
A major problem with large scale use of renewable energy for electricity generation in Ontario is the seasonal availability of that energy. In Ontario on a monthly average basis both wind and run-of-river hydro are two times more plentiful in mid-winter than in mid-summer. However, in Ontario the peak electricity load occurs in mid-summer. In order to fully utilize renewable energy Ontario needs a practical means of efficiently and reliably storing energy for about six months.

At this time the only technology that is both efficient and economic for large scale seasonal energy storage is hydraulic energy storage between the great lakes or in Quebec based hydroelectric dam river reservoirs.

This web page assesses the amount of hydraulic energy storage that can reasonably be obtained using Lake Erie as the upper reservoir and Lake Ontario as the lower reservoir while maintaining the existing annual average Niagara River flow. This document then addresses practical realization of that energy storage with Niagara River upstream flow control and 7 GW of additional electricity generation at Niagara Falls.

The economics of Ontario using the same concept with hydroelectric dams in Quebec are analogous. In both cases the economic and power system benefits must be shared with another jurisdiction.

The overall concept is to change the Niagara River electricity generation from base load to seasonal peaking generation. The base load generation presently provided by the Niagara River would be replaced by nuclear generation. The fraction of the Niagara River flow required to sustain Niagara Falls as a tourist attraction would be maintained.
 

FRINGE BENEFIT:
A fringe benefit of this project is that it would allow better level control of Lake Erie. At the present water runs out of Lake Erie at an uncontrolled rate set by the level of Lake Erie and the contour of the Niagara River bottom. Under the plan set out herein the Niagara River bottom would be dredged and the outflow from Lake Erie would be set by control gates located close to the point where Lake Erie discharges into the Niagara River.
 

SAFETY:
Lake Erie and Lake Ontario are presently separated by a 30 km wide natural land barrier. There is about a 99 m difference in lake surface elevations. The amount of gravitational potential energy that could be released by uncontrolled water flow from Lake Erie to Lake Ontario is enormous. Hence this project must be designed to tolerate major earthquakes. This project must also be resistant to ice jams.
 

FINANCING:
As with any large electricity project, to minimize the cost of construction financing it is necessary to minimize the time between expenditure of capital funds and ratepayers receiving a tangible benefit. Hence the project must be designed to proceed in stages such that there is a nearly immediate tangible benefit to the ratepayers as each stage is completed. This staging requirement significantly affects the detailed design of the energy storage system.
 

ASSUMPTIONS:
It is assumed herein that Niagara Falls must be kept substantially unchanged as an international tourist attraction. It is assumed that additional electricity generation will be built in the proximity of Niagara Falls and that over a period of years the upper Niagara River valley and the downstream Niagara gorge will be enlarged to allow an increase in the peak Niagara River flow. It is assumed that once this project is operational due to rapid changes in water flow recreational boating on the Niagara River will be prohibited.
 

TECHNOLOGY:
This web page indicates how the contemplated energy storage system could be realized using construction methodology similar to that which was used in British Columbia in the mid 1960s for construction of a major gravity dam on the Peace River. The control gates at the Lake Erie end of the Niagara River would be similar to the flow control gates used at the Thames Barrier in the UK.
 

INTERNATIONAL CONSIDERATIONS:
It is envisaged that the costs and benefits of this energy storage system would be shared with the USA, so that this energy storage system would ultimately provide about 6 GW of seasonal peaking generation for Ontario and about 6 GW of seasonal peaking generation for the USA. The use of dedicated US tunnels and turbogenerators would allow system operation without having to integrate the US electricity flows into the Ontario electricity system or vice versa. Similarly, subject to international treaty constraints, once the Niagara River flow is controlled, Canada or the USA could proceed with its portion of the project with minimal participation by the other party.
 

PROJECT SIZE:
The size of this energy storage project project is less than half the size of the existing hydroelectric development on the Columbia River in British Columbia and Washington State.
 

GEOGRAPHICAL CONSTRAINTS:
The nominal elevation difference between the surface of Lake Ontario and the Surface of Lake Erie is 99 m. However, 5 m of water head is lost in moving water horizonatally between Lake Erie and Lake Ontario. Thus the net discharge generator head Hdd available for electricity generation is:
Hdd = 99 m - 5 m = 94 m.

However, during operation as an energy storage system due to lake level fluctuations the average head would drop by about a further 4 m.

In order to control the flow through the Niagara River it is necessary to build a set of very robust control gates at the inlet to the Niagara River from Lake Erie. These control gates must be earthquake and ice jam resistant. It is envisaged that these control gates would be similar in design to the control gates used at the existing Thames Barrier in the UK. The exact location of these control gates will be dictated by local topographic features and local depth to bedrock. These control gates should be engineered to allow an ultimate depth swing in Lake Erie of up to 4 m.
 

HYDRAULIC ENERGY STORAGE SYSTEM POTENTIAL:
1. A reasonable estimate of the costs of realizing hydraulic energy storage between Lake Erie and Lake Ontario indicates a total project cost of the order of:
$40 billion
It is envisaged that the project would proceed in up to seven stages. The first stage is to install upstream gates to control the water flow into the Niagara River. Subsequent stages involve construction of more generation tunnels, turbogenerators and transmission lines. Completion of each stage would potentially increase the annual level swing in Lake Ontario and Lake Erie. The increase in level swing amplitude would be gradually implemented at about 0.1 m / year.

2. In order to justify the project cost it is essential that the amount of seasonal energy storage be maximized.

3. The gravitational potential energy recoverable from hydraulic storage is:
M X G X Hdd
where:
M = mass of water used for energy storage
G = gravitational acceleration = 9.8 m / s^2
Hdd = height differential

4.The surface area of Lake Ontario = 19,525 km^2

5.The surface area of Lake Erie = 25,700 km^2

6. M = (area of the smaller lake) X (maximum acceptable change in lake level) X (density of water)

7. The (maximum acceptable change in lake level) is ultimately governed by the change in water level that can be accommodated by future marine installations. At major ocean seaports throughout the world this change in water level due to ocean tides is typically 5 m. Hence, given sufficient time to implement changes in lake marine facilities (50 years), an annual 5 m water level swing could be accommodated in Lake Ontario. The corresponding water level swing in Lake Erie would be only 3.8 m due to Lake Erie's larger surface area. However, other issues controlled by the USA and by natural events might further affect the level of Lake Erie.

8. Thus a reasonable estimate of M is:
M = (19,525 km^2) X (10^6 m^2 / km^2) X (1000 kg / m^3) X 5 m
= 97.625 X 10^12 kg

9. Thus the contemplated available gravitational potential energy is:
M X G X Hdd
= 97.625 X 10^12 kg X (9.8 m / s^2) X 90 m
= 86.1 X 10^15 joules

10. Assume that the hydraulic turbine-generator efficiency is 0.80. Then the recoverable energy from storage is:
0.8 X 86.1 X 10^15 J = 68.9 X 10^15 J
= 68.9 X 10^15 watt-s X (1kw / 1000 w) X 1 h / 3600 s
= 19.1 X 10^9 kwh
= 19,100 GWh

11. Thus in changing from the fully charged state to the fully discharged state the pumped storage system could supply 5 GW of electricity for 3820 hours. Canada's share of this storage capacity would displace much of the existing fossil fueled peaking electricity generation in Ontario.

12. The additional water mass flow required to supply this 5 GW is:
97.625 X 10^12 kg / 3820 h
= 25.55 X 10^9 kg / h

13. Converting this mass flow into a volume flow gives:
25.55 X 10^9 kg / h X 1 m^3 / 1000 kg X 1 h / 3600 s
= 7.09 X 10^3 m^3 / s

14. This volume flow compares to the present average Niagara River volume flow of about 5.7 X 10^3 m^3 / s

15. Thus the new peak volume flow would be:
(7.09 + 5.7) / 5.7
= 2.25
times the present average Niagara River volume flow. Attaining this increase in peak river flow upstream of the generation tunnel intakes likely entails extensive dredging of the river bottom.
 

PROJECT REALIZATION:
1. Several new 10 km long tunnels, each comparable to the new Niagara tunnel, would be required to convey water from the tunnel intake upstream of Niagara Falls to the head water pond of the generation station which is downstream of Niagara Falls. These tunnels, if built sequentially, would likely each cost about $1.5 billion to provide a 500 MW generation increment.

2. The volumetric flow through the new Niagara Tunnel is 500 M^3 / s.
The inside diameter of the Niagara Tunnel is 12.7 m.
The cross sectional area of the Niagara Tunnel is given by:
Pi X (12.7 m / 2)^2 = 126.67 m^2
Hence the axial flow velocity is given by:
(500 m^3 / s) / (126.67 m^2) = 3.947 m / s

3. Hence the number of additional tunnels similar in size to the new Niagara Tunnel is: (7.09 X 10^3 m^3 / s) / (500 m^3 / s - tunnel) = 14 new tunnels

4. At an average cost of $1.5 billion / tunnel the projected cost of the tunnels alone would be about $21 billion. The cost of the headwater control gates, river dredging, additional hydraulic turbogeneration and related transmission would likely raise the total project cost to about $40 billion.
 

PROJECT LIMITATION:
From a power system perspective this project does have one important limitation as compared to a conventional hydroelectric dam. The response time of the electricity generation to a change in upstream control gate position is limited by the length of the Niagara River and the velocity of the water flow. Even if the average water flow velocity is increased to 4 m / s the response time will still be:
30 km / (4 m / s) = 7500 s ~ 2 hour

Hence to make efficient use of the control gates for load following the Independent Electrical System Operator (IESO) must anticipate a load change several hours before it actually occurs. If the future load is underestimated the generation will fail to track the load. If the future load is over estimated some of the stored water may be wasted via diversion over Niagara Falls. In view of the IESO expertise at projecting near term future load this limitation is not believed to be a serious problem.
 

SUMMARY:
Physical realization of a hydraulic seasonal energy storage system using Lake Erie, Lake Ontario and the existing Niagara River generation entails the construction new tunnels, new downstream generators and upper river bed dredging. This project also entails construction of upstream control gates on the Niagara River.

This web page outlines a large project that could be built in stages spread over many years. However, even when complete this project is less than half the size of the combined Canadian and US hydroelectric power development on the Columbia River. The Grand Coulee Dam alone has 6.8 GW of electricity generation capacity.

A major benefit of the contemplated Lake Erie-Lake Ontario hydraulic storage project is that it offers a large amount of seasonal energy storage located close to major electricity markets with no land flooding due to formation of new lakes.
 

POLITICAL AND SEAWAY CONSIDERATIONS:
1. During the depression of the 1930s, the Grand Coulee Dam on the Columbia River was a major public works project in the USA. Today this dam provides 6.8 GW of load following electricity generation. The seasonal energy storage system contemplated herein offers comparable public benefits.

2. The seasonal energy storage system would cause the levels of Lake Ontario and Lake Erie to oscillate on an annual basis. It is envisaged that the amplitude of this water level swing would be increased 10 cm per year for Lake Ontario (8 cm / year for Lake Erie) and would be capped at 5 m for Lake Ontario and 3.8 m for Lake Erie after 50 years. That implementation time should be sufficient to allow owners of docks, marinas and seaway facilities to adapt to the lake level changes. During the implementation period the energy storage system would be operated as a blended daily energy and seasonal energy storage system to make best use of the facility subject to the agreed constraints on the change in lake levels.

3. The governments that would have to consent to the changes in lake levels and the related water recycling from Lake Ontario to Lake Erie are:
Canada, USA, Ontario, New YorK, Pennsylvania, Ohio and Michigan. The municipalities adjacent to the upper Niagara River would also be significantly affected.

4. It is anticipated that there might have to be minor changes to the Boundary Waters Treaty.

5. During the late winter the level of Lake Ontario would be relatively low. During the late summer the level of Lake Erie would be relatively low. Some shipping channels, especially in Lake Erie, would likely require dredging to provide adequate keel clearance when the lake level is low.
 

FEASIBILITY STUDIES:
It is contemplated that this project should proceed by way of three feasibility studies.
1. Overview Engineering study;
2. Detailed engineering study;
3. Detailed legal study.

The overview engineering study would be done by a small group of senior engineers each of whom has hands-on relevant experience with similar work. These engineers should list and realistically quantify and cost the major physical implementation elements to determine if the cost of any of these elements is so large as to prevent the project succeeding. It is contemplated that this study team would include at least one expert in each of the following areas:
Control Gate construction (Thames Barrier)
Rock Fill Hydro-Electric Dam construction (BC Hydro, Quebec Hydro)
Great Lakes Dredging
Niagara escarpment geology (Rethink Technology, OPG)
Niagara escarpment power generation (Ontario Power Generation)
Transmission Integration (OPA, Hydro One, New York Edison, Detroit Edison)
St. Lawrence Seaway operations

The detailed engineering study would proceed only if the overview engineering study indicates that there are no insurmountable technical or cost problems. The first phase of the detailed engineering study would identify the real estate impacts with sufficient detail to allow the detailed legal study to proceed.

The detailed legal study would address enabling modifications to the Boundary Water Treaty and all other legislative changes, expropriations and international agreements that are necessary to implement the project.

It is contemplated that all three feasibility studies would require 100% government funding.
 

This web page last updated May 19, 2015.

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