Serpent River – Run-of-River

A major challenge with hydroelectric in Ontario is that there are no consistent definitions.  Many hydroelectric facilities are referred to as Run-of-River when they are in fact cycling or peaking facilities.  Below are some good definitions which should be incorporated by government in their policy and legislation.   Just keep in mind that because they call it run-of-river it doesn’t mean it is – it is most likely a Peaking plant described under “Storage” here.  Peaking facilities using headponds (pondage) allow for power generation and profits to be maximized; however, the environmental and health and safety impacts can be severe:

3.6 Hydroelectric Generation in Ontario

3.6.3.2 Classes of Hydroelectric Generating Stations

Hydroelectric installations can be classified into three basic types.  These are:

• Storage or Pondage plants (sometimes known as “peaking” plants)
• Run-of-the-River plants
• Pumped Storage plants

Some of the characteristics of these types are discussed below.

Storage or Pondage (Peaking) Plants:  At many hydroelectric plants, production economics can be enhanced by storing water in the head pond (forebay) for a limited number of hours.  This is normally done by partially or completely shutting the plant down (i.e., stopping the water flow) overnight or on weekends, when the demand for electricity is light.  The stored water is used during the peak load period of the following day.  This type of operation is called peaking and is carried out routinely on most large power systems.

Peaking power installations are characterized by proportionally large units (in terms of discharge capability) and relatively small forebays (storage capability).  They an only sustain continuous generation for a few hours a day before they start running out of water and need additional inflow from upstream reservoirs.  Forebays of peaking installations must have large operating ranges, which has impacts on the use and environment of the shoreline of the reservoir.  As well, the environment downstream of the plant must be protected against wide fluctuations in discharge flow.

Run-of-the-River Plants:  Some plants are not suited to peaking operations because they do not have adequate forebay storage capacity and/or their discharge capacity must match the streamflow of the river they are on.  Some examples are plants located on a waterway where shipping interests and other considerations impose restrictions on such peaking operation and where the river flow must be passed on downstream in a more uniform manner.

Run-of-the-river installations are usually low-head and their operation, which is often classified as base load, does not follow the economics of supplying the load, but rather the variations of the river flow over time.  Water management at this type of installation is often based on established “rule curves”.

Pumped Storage Plants:  A Pumped storage generating station (PGS) represents a logical complement to load-following operations that are carried out elsewhere on a power system.  A PGS time-shifts energy production by storing energy in the form of water.  At night when demand and the cost for power are low, water is diverted from a lower river or lake and is pumped up into a storage reservoir with electric motors.  The water is let back down from that reservoir through a set of turbo-generators when the energy is ready to be sold (and used) during periods of high value or need.

Electricity used for the pumping operation is obtained from the system during periods of low demand.  This carries an economic penalty in that it takes about 30% more energy to pump the water uphill to the reservoir than can be generated when the time comes to let it back down through the turbines.  In addition, there is uncontrolled consumption of that water while it is in the reservoir, through evaporation.

PGS plants are not new.  These generating stations are used extensively to time-shift energy production on a daily or weekly basis – away from weekends and into high demand weekday peak hours.  One example is the PGS at OPG’s Sir Adam Beck complex at Niagara Falls.  Another is at the Robert Moses installation across the river in Lewiston, NY.  One of the world’s largest PGS installations is located at Ludington, Michigan, relatively close to the Ontario-Michigan border.[1]