Performance Indicator Hydropower Maximize Power Production March 28, 2011

Transcription

1 Performance Indicator Hydropower Maximize Power Production March 28, 2011 Performance Indicator (PI): Maximize Hydropower production. The operations of the hydropower plants in the Great Lakes St. Lawrence River system are affected by water levels and flows of the system. The International Upper Great Lakes Study (IUGLS) is examining possible improvements to the current Lake Superior outflow regulation plan and other potential new structural measures as part of the integrated system-wide water management. Hydropower production has been selected one of the performance indicators (PI) to evaluate the impacts on hydropower operations of the regulation plans under a range water supply conditions and climate regimes. Maximizing power production is one of the criteria in the development of new outflow regulation plans. Three other hydropower performance indicators are: maximize value of power production; flow stability and ice cover formation, and their discussion appear in separate papers. Technical Work Group: Hydropower Technical Work Group Prepared by: Peter Yee, Bill Werick Governance: The operations of most of the major hydropower plants examined in the International Upper Great Lakes Study (IUGLS) are governed by Treaties between Canada and the United States, and Orders of Approval issued by the International Joint Commission. A discussion of these institutional arrangements is presented in the hydropower coping zone report prepared by the Hydropower Technical Work Group. Link to Water Levels and Flows: The amount of electricity a power plant produces for a given duration (production measured in kilowatt-hours), and the maximum possible power it can produce (capacity in megawatt or MW) is a measure of the performance of the plant given the water level and flow conditions on the lake and in the river. The turbine connecting to the generator is driven by the falling water passing through the plant, and the theoretically power available from the falling water can be expressed as: P = ρ q g h, where P is the power theoretically available, in kilowatts (kw), ρ is the density of water, about 1000 kilograms per cubic metre, q is rate of water flow, in cubic metres per second (m 3 /s), g is acceleration of gravity being 9.81 m/s 2, and h is the height of the fall of water in metres (m), also termed operating head. Due to energy loss resulting from unit efficiency and turbulence, the actual power generation is less than the theoretical power. Modern hydropower plants have combined turbine-generator efficiency as high as 95 percent. For a plant located in the river, the headwater is hydraulically 1

2 affected by the conveyance of the river and power canal between the lake and the plant. Hence, the more efficient the conveyance is for these channels, the lesser the headloss and thus higher the water level immediately upstream of the plant. High tailrace level below the power dam decreases the operating head. It follows, then, that increase in flow and/or operating head increase power production, and reduction in either or both reduce power production. An example of the relationships between flow, head and power is shown in the following graph: Source: The Engineering ToolBox Ratings for the Great Lakes St. Lawrence River Hydropower Plants Mathematical formula correlating flow, head and power production for the major hydropower plants in the Great Lakes St. Lawrence River system are developed by plant operators in coordination with the IJC Boards and government agencies. In the report Estimation of Power Production at Hydropower Plants on the St. Marys River, October 2009, Yin Fan and David Fay presented relationships at each of the three hydropower plants on the St. Marys River. Current Operating Practices and Measures to Increase Production Maximizing power production is one of the objectives in the development and evaluation of potential Lake Superior outflow regulation plans. In actual operations, a range of measures can be taken to increase power production, as follows: 2

3 increase diversion and discharge capability This is taken into account in the design and construction of the project. The conveyance of power canal and river are improved through river/canal deepening/widening and reduction of channel roughness, construction of new diversion channel (e.g., current Niagara tunnel project). structural measures to enhance reliability of infrastructure of dams and dykes. upgrade turbines and generators to attain better operating efficiency. schedule unit outage/repairs to capture as much as possible available (or allocated) water. design /operate runner blade opening and wicket gate opening at peak efficiency. manage the cycle of ice process from formation to dissipation, through timely management of the flow, use of ice booms, sluice gates, ice breakers, etc. Other measures to maximize power production include legislations and tax incentives for hydropower development; and some operators employ techniques through mathematical modelling aimed at maximizing production. While increase in turbine flow increases power, as shown in the following diagram, the efficiency curves represent a parabolic function which, after reaching peak value, declines showing a decrease in efficiency in terms of additional power per unit volume of water. Straying from the optimum is what plant operators prefer to avoid so there is a segment in the curve they consider ideal. These curves show that after attaining peak efficiency, there are small gains in power resulting in drastic reductions in efficiency. High flows increase risk of cavitation damage to the turbine and accelerate bearing wear. Source and credit: 3

4 Score Practices.pdf; Patrick A March, Charles W. Almquist and Paul J. Wolff, Best Practice Guidelines for Hydro Performance Processess. Given that water allocated to the three hydropower plants in the St. Marys River is determined on a monthly basis, plant operators thrive to schedule their generation and water flow, including maintenance scheduling, to utilize all available water without spilling and at the best possible sector in the efficient curve. At the Brookfield s Clergue plant at Sault Ste. Marie, Ontario, the ideal peak flow is about 1140 m 3 /s although the plant can pass flows as high as 1200 m 3 /s. When the amount of water allocated to the plant is more than 1200 m 3 /s, the unused portion is typically released at the Compensating Works meaning opportunity foregone in the use of the surplus water. Given the design of its three turbines, plant operators prefer to operate all three units as long as possible as water availability varies to avoid frequent unit shutdown and startup. Another plant in the St. Marys River the Cloverland plant (formerly called Edison Sault) requires a flow of 90 m 3 /s (see graph below) to meet energy market while a minimum flow of about 311 m 3 /s is needed in winter to heat the powerhouse and equipment and to facilitate proper ice management in the power canal to reduce ice-related problem during the winter Edison Sault Electric Hydro Plant St Marys Outflow (cms) The third plant US Government Plant is vulnerable to cold and stormy weathers which can cause equipment freezing and clogging of its power canal, and has minimum flow requirements to reduce the risk. 4

5 For the plants in the Niagara River and those by the Welland Canal, available water for power purposes is determined by the Niagara River Treaty. After the requirements for the scenic purposes of the Falls (minimum values for tourist and non-tourist hours and seasons), domestic and sanitary and navigation, are met, the Lake Erie outflow water including the Welland Canal flow can be diverted for hydropower purposes. Actual diversion is determined by a number of factors including plant capacity and hydraulic (including ice) conditions in the river and power canals, and energy market demand. To make the most efficient of available water, storage reservoirs have been built at the Beck complex in Canada and at the Moses plant in the United States to store water during the night time when water availability increases but not fully used, and the stored water is released for production the following day when electricity demand increases. Well-above average Lake Erie outflows increase the incidence of water spilled over Niagara Falls. In the international reach of the St. Lawrence River, the Saunders and Moses plant operators plan and schedule their hourly operations weekly to maximize power generation given that available water for hydropower purposes is determined weekly in accordance with the Lake Ontario regulation plan. River flows above the plant s capacity necessitates release of the unused portion at the Long Sault Dam; however, whenever capacity exists at the other plant, its unused portion may be released at that plant to avoid spills. At the Beauharnois-Cedars complex near Montreal, some water spills typically take place during the Ottawa River spring freshet and larger spill may occur when the freshet coincides with high Lake Ontario levels and outflows. Accurate advance knowledge of the flow in the Ottawa River and outflow of Lake Ontario is crucial for Hydro Quebec operators to properly schedule their unit shut down for maintenance so as to minimize spillage. Temporary and Spatial Validity: The power generation vs. flow and operating head relationships for a plant is valid for all seasons. Correction factors are applied when needed to adjust for the effects of flow retardation in river and canal due to ice and aquatic growth in these channels. These relationships are site-specific for individual plants. They are periodically updated and verified via flow measurements using a variety of measurement techniques and equipments, and data analysis. These relationships are used to evaluate and compare the amount of power produced at the plants for different Lake Superior outflow regulation plans. In evaluating future possible climate regimes, assumptions are made for possible changes in the ice cover regimes on the Great Lakes and their connecting channels. Algorithm The attributes related to a hydropower plant s diversion and generating capacities, unit performance, the institutional arrangements and hydrometeorological and hydraulic conditions under which it operates, are taken into consideration in the development and evaluation of Lake Superior outflow regulation plans. Information is also extracted from the hydropower coping zone report which lists capabilities and limitations. From these, performance indicators are 5

6 incorporated into the Shared Vision Model to evaluate the merits of a range of possible Lake Superior outflow regulation plans. As an example, energy and capacity are computed for a plant given water level and flow hydrographs for a candidate Lake Superior outflow regulation plan. The hydrographs being generated in the IUGLS are historical sequence and simulated and stochastic series for a range of climate scenarios. Assumptions are made on the current and foreseeable future installed hydropower infrastructure. Risk and Uncertainty Assessment: The development of the relationships between hydropower production and water levels and flows is fairly straightforward. There are however, variations between actual production and that theoretically calculated due to a number of physical factors at the plant and in the river/canal. The month-by-month differences in lake level and outflow among the various Lake Superior outflow regulation options are expected to be small; however the use of these relationships provide a consistent method of assessing the relative merits of different management options. Confidence, Significance and Sensitivity Modern water level and flow measuring equipments and techniques provide accurate picture of the hydraulic conditions at a plant and in the river. There are uncertainties associated with future climate change forecasts and electricity price forecasts. Assumptions of different monetary values for energy and capacity can be made to assess how significant and sensitive the various water management options would be in terms of project economic feasibility. References Yin Fan and David Fay, Oct. 19, 2009, Great Lakes St. Lawrence Regulation Office, Environment Canada. Estimation of Power Production at Hydropower Plants on the St Marys River. Missy Kropfreiter and Rob Caldwell, June 18, Physical & Operational Limits/Capacities of Sault Ste. Marie Control Works Structures, International Upper Great Lakes Study. Hydropower Technical Work Group, January 2011, International Upper Great Lakes Study working paper. Coping Zones of Hydropower Operations In the Great Lakes St. Lawrence River System. 6