Pumped Storage Speaker 9655 Session 664 1

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    HYDROVISION 2011Evaluation of Pumped Storage Operations for Coordination with

    Wind Resources and for Supplying Ancillary Services.

    Authors

    Diana Hurdowar-Castro, Ph.D., P.Eng, Director, Power and Water Optimization, Hatch,

    Ontario, Canada

    Dieter Matzner, MScE, Principal Power Consultant, Hatch Woodmead, South Africa

    Francois Welt, Ph.D., P. Eng., Senior Optimization Specialist and Mechanical Engineer, Hatch,

    Ontario, Canada

    Abstract

    Pumped storage has the capability to support renewable power projects by providing the

    necessary generation required to firm such supplies. Pumped storage capacity can also be

    used to trade between off and on-peak energy and to provide ancillary services especiallyfor systems where conventional hydro is small or nonexistent. Spinning and non-spinning

    reserves can be produced in both the generating and pumping modes of operation,depending on the selected design of the pumping/generating units and control system.

    This paper discusses pump/generation facilities and their interaction in the market by

    describing specific experiences gained with pumped storage plants. Of particular interestis the growing role of wind power in the overall energy mix and the increased variability

    that results from its large scale implementation. To demonstrate the economic and

    operational viability of pumped storage in re-regulating wind energy, an optimizationmodel has been setup for a potential pumped storage plant and wind farm in Lesotho,

    Africa. Results were generated over a full year of operation for various wind scenariosand an associated pumped storage plant.

    With a growing demand for energy storage and rapid expansion of renewable energy, the

    analysis discussed herein is applicable to the evaluation of any future large scale

    renewable project.

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    Introduction

    Pumped storage stations are used worldwide as a means to increase on-peak powerdelivery capability by storing energy during low demand periods. This is particularly

    useful in areas that do not have a high percentage of conventional storage hydro power in

    their generation resource mix and which are heavily base loaded with nuclear or coal

    fired plants (e.g. parts of North America, Asia and Europe). With the increasedpenetration of non firm renewable energy such as wind, the issue of energy storage is

    becoming even more significant as wind generation is highly variable and can take placeat any time of the day or night.

    In addition, the use of renewable energy requires a higher amount of regulation andspinning reserves. Pumped storage stations can significantly contribute to the ever

    increasing reserve requirements. In some particular cases, pump storage stations serve a

    dual purpose, i.e. not only do they firm up the on-peak capacity, but they also provide

    water for irrigation purposes.

    Design ConsiderationsPumped storage stations use an upper and one lower reservoir to re-circulate water in a

    close loop cycle. A pumped storage station can have two artificial reservoirs; however,

    many facilities have the lowerreservoir located on an existing

    waterway. There are also

    concepts and preliminary

    designs where the lowerreservoir is an (abandoned)

    underground mine or an

    underground excavation madespecifically for the pumped

    storage project. It is preferable

    that the two storage areas arequite close to each other to minimize losses in the tunnels and conduits, and the cost of

    long penstocks. A typical pump storage station configuration is shown in Figure 1.

    Pumped storage stations operate on a daily, weekly or even seasonal basis, the differencebeing the size of the upper reservoir and inflows. When the upper reservoir is part of the

    watershed and receives natural inflow from upstream, it is considered to be an in-stream

    pump storage station and the operation may be affected by the changes in precipitation.

    Typically, the elevation differential between the upper and lower reservoir is quite large

    to minimize the amount of water that is required to store. Plant heads are usually greaterthan 100 m, and there are many instances where plant heads are in excess of 300 m (e.g.

    Bleinheim Bilboa, NY, USA). Pumped storage stations with 700 or 800 m heads are

    also increasingly common worldwide (e.g., Kazunogawa, Japan, LaCoche, France).

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    For a given amount of energy storage, the volume of water in the system is inversely

    proportional to the head. Therefore the physical size and cost of reservoirs, pump-turbineequipment and water conduits is reduced as head increases. For this reason higher head

    pumped storage developments are generally more economic.

    Large pumped storage stations are more cost effective and plant capacities tend to bequite large. Most plants have a capacity that is at least a few hundred MW, and a

    significant number of pump storage stations have a capacity in excess of a 1000 MW(e.g., Ludington with 1800 MW, Michigan, USA) especially for the newer plants constructed

    in the 1960s and beyond.

    The (cycle) efficiency of a pumped storage station is the ratio of energy output to energy

    input. Efficiency for plants constructed from the 1960s to mid 1980s is usually 68% to

    74%. More modern plants have an overall cycle efficiency in the 72% to 78% range,

    with some designs approaching 80%. Traditionally, very large motors and generators inthe power industry (and other industry) have been single speed synchronous types. This

    means pump-turbines will operate at a single point of operation in the pump mode, e.g.,the flow and MW range reduces to a single point at any given head. However, over thepast 20 years, variable speed technology has advanced to large hydro units. This is an

    increasingly popular design for pumped storage station as the variable speed permits a

    wide range of operation in both pumping and generating modes. This allows foradditional reserve capability, especially in the pumping mode of operation, as well as

    modest increases in efficiencies. However, the cost of such units can be as much as 30%

    higher than the fixed speed type. Such units have been installed in Europe (e.g.,

    Goldisthal, Germany) and Asia (e.g., Kazunogawa, Japan).

    Plant Operation

    In most cases, units are used in pumping mode during off-peak periods, typically at night,and in generating mode during the day. For the vast majority of units, there is a minimum

    amount of time required to switch from the pumping to generating mode, or vice versa.

    For newer units the minimum time for the changeover is fairly short (e.g., of the order of10 minutes), but it can be of the order of 1 hour and can be even two hours for certain

    operations.

    In older plants, it may also be required that no more than one pump cycle per day beused, and some restriction may also exist on the generating side. These rules of operation

    are imposed to prevent excessive wear and tear on the units, but also to facilitate

    scheduling of the operation in a smooth and predictable fashion. Newer plants have beendesigned for a much more flexible operation and may not exhibit such restrictions (e.g.,

    Dinorwig, UK, with up to 35 mode changes per day).

    Operation in a Coordinated Hydro-Thermal Environment

    In this regulated environment, the use of available resources is well coordinated and

    planned ahead of time according to the best available load forecast. The utilization of apump storage station is then heavily dictated by the difference between on-peak and off-

    peak load demand.

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    The cost savings comes from the ability to displace more expensive non hydro peaking

    units required to meet load,such as diesel or natural gas

    fired units, during on-peak

    hours. The savings in

    production costs has to begreater than the sum of lost

    revenue from the 20%-30%loss in cycle efficiency,

    amortized debt payment and

    expected equity cost for theplant operation to be

    profitable. As a result, pump

    storage stations have usually

    a fairly low utilization factor(0.08 to 0.18). A typical

    schedule of operation isshown in Figure 2, where theplant is operated in pumping mode for a few hours at night, and similarly for a few hours

    in generation mode during the day.

    Operation in an Open Energy Market Environment

    In this environment, the utilization of a pump storage station is heavily dictated by the

    difference between on-peak and off-peak market prices. Similar to the hydro-thermal

    environment, the price differential has to be greater than the sum of losses in pumpgenerating efficiency (e.g., 20-30%), amortized debt payment and expected equity cost

    for the plant operation to be profitable. As a result, there is a strong incentive to pump at

    low price hours and generate during high price hours. Because of price variability, theeconomic operation of a pump storage station may lead to a more dynamic schedule with

    an increased number of starts and stops or mode changes, as compared to the operation

    within a regulated environment such as described previously.

    Operation to Provide Ancillary Services

    Conventional hydro power plants are very effective at providing regulation and spinning

    reserves, as compared to other non hydro