Surplus Baseload Generation (SBG)
Background
Renewable energy will soon represent a significant portion of Ontario’s generation fleet. By 2018 at the
latest, an estimated 10,700 MW of new renewable generation is expected to be in service, with substantial
amounts by early 2013. With demand expected to remain at current levels, increases in output from
variable generation and the return to service of refurbished nuclear units, periods of surplus baseload
generation (SBG) will increase significantly.
The purpose of this document is to establish which generation sources are considered in the definition of
SBG. It is not the aim of this document to propose the specific mechanism for achieving an appropriate
dispatch order or mitigating SBG.
Definition and Description
Surplus baseload generation (SBG) conditions can occur on both a global and local level. Global SBG is a
condition that occurs when Ontario’s electricity production from baseload facilities, if not managed,
would otherwise be greater than demand. Local SBG is a condition that occurs when a region’s
electricity production from baseload facilities, if not managed, would otherwise be greater than the local
demand and the transmission system’s ability to move the excess generation out of the area (the energy
is locked‐in to the area).
In order for the IESO to maintain a continuous balance of supply and demand, potential SBG conditions
must be anticipated ahead of time and mitigated to manage real-time operations. Mitigation can be
achieved by reducing the surplus energy and/or increasing the load. Managing SBG is a complex task
due to certain risks and limitations in manoeuvring baseload generation (as described further below).
The concept of SBG can be viewed from three perspectives, (1) up to day-ahead, (2) hour-ahead, and
(3) real time. In each of these timeframes we consider a different set of generation sources that constitute
‘baseload generation,’ recognizing that generator flexibility can decrease as we get closer to real time. In
other words, although a generation source may not fit the traditional definition of a baseload facility it
may, at times, be treated as such when it is operating. It should also be noted that each timeframe uses a
different assessment of demand. Leading up to day ahead, SBG is determined using Ontario demand
and an assumption of exports. Together, these figures represent an assumed market demand. In the
interval from day-ahead to hour-ahead and then into real time, SBG is calculated using market demand
consistent with scheduled and flow exports respectively.
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1. SBG Forecast – Up to Day-Ahead Baseload Generation
In a forecast scenario from months ahead up to a day ahead, the IESO will include the following
generation facilities in their assessment of SBG:
Generation Source
Combined Heat and Power
Facility
Rationale for being considered
Baseload Generation
Inability to curtail as they are
already running to provide steam
to an associated load facility.
Embedded Generation
Limited ability by the IESO to
control embedded generation.
Non-Utility Generators (NUGs)
NUG contracts allow them to be
self-scheduling, resulting in a
limited ability to curtail production.
Nuclear
(Note that as these contracts come up
for renewal, responsiveness to market
forces is an expectation of the IESO.)
In general, nuclear is not intended
to be manoeuvrable.
There is however, limited capability
for manoeuvring at the Bruce
Power facility as detailed at the end
of this document*.
Implications of Curtailment
Generation curtailment would result in a
curtailment of the associated load facility,
potentially exacerbating the surplus
condition.
IESO currently has minimal visibility of
installed facilities and their output.
IESO has authority, but limited ability, to
curtail but only for reliability reasons.
Some curtailment can be accommodated
within the contracts but it is typically
arranged days ahead.
Regulatory: If curtailment leads to an
operating state outside the bounds of the
operating licence, the unit would be
taken offline. Also there is a need to
respect limits to the temperature of water
being discharged into the lake.
Equipment: Reactor power reductions
require long lead times. Multiple units at
the same plant cannot be manoeuvred
simultaneously using this method. Once
manoeuvred, a unit requires 8 to 12
hours elapsed time in order to further
reduce the unit.
An alternative to reactor power
reductions is to reduce output using
condenser steam discharge valves (CSDV).
This can lead to increased costs
associated with inspections and repairs.
The primary function of the CSDV is to
bypass steam to the condenser under
turbine load rejection conditions and not
unit manoeuvring. Using the CSDV for
something other than its intended
purpose may result in increased risk of
equipment failure.
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Generation Source
Rationale for being considered
Baseload Generation
Implications of Curtailment
If a unit is removed from service and
poisons out, it will not be able to provide
energy for short-term future needs, due
to lengthy minimum downtimes.
Run of River Hydro
Limited ability to ‘spill water’
results in continuous production.
Solar
Economic considerations, contract
terms.
Economic considerations, contract
terms.
Wind
Safety: Need to conduct visual inspection
prior to spilling water to verify that
spillways are clear.
Regulatory: Spilling water can affect
wildlife, cause flooding and shoreline
erosion. Need to maintain prescribed
water levels for navigation.
None
None
2. SBG Forecast – Hour-Ahead and Real-time Baseload Generation
In a forecast scenario looking from day-ahead to hour-ahead right up to real-time operation, the IESO
will have a much different definition of which generation to include in its SBG assessment. The IESO
will consider ‘traditional’ baseload generation in addition to the operating characteristics of generation
that is online and not manoeuvrable in the short term. The assessment of SBG in this timeframe will
include the generation facilities listed in the table above plus the following:
Generation Source
Coal
Commissioning Units
Gas Unit
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Rationale for being Baseload
Generation
Inability to curtail once started and
committed due to equipment
minimum run times. Inability to
curtail when providing regulation
service.
Inability to curtail as they are
already scheduled to commission.
Commissioning units are treated as
self-scheduling.
Inability to curtail once started and
committed due to equipment
minimum run times.
Public
Implications of Curtailment
Due to equipment limitations, minimum
run time must be respected. Regulation
is an essential service that cannot be
interrupted.
A delay in commissioning may result in
contractual in-service dates not being
met.
Due to equipment limitations, minimum
run time must be respected.
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Generation Source
Peaking Hydro
Rationale for being Baseload
Generation
During periods of excess water
levels, limited ability to ‘pond’ or
‘spill’ water results in their forced
production proportional to flow.
Implications of Curtailment
Safety: Need to conduct visual
inspection prior to spilling water to
verify that spillways are clear.
Regulatory: Limitations on spilling water
which can affect wildlife, cause flooding
and shoreline erosion, and need to
maintain prescribed water levels for
navigation.
* Bruce Power Manoeuvrability
Bruce Power will have the capability to reduce their facility’s output by nearly 2,400 MW when all Bruce
A and B units are in operation (~300 MW each). This increased flexibility is obtained using condenser
steam discharge valves (CSDVs), effectively bypassing steam from the turbine to the condenser. The
magnitude of the reduction and its duration are contingent on the time of year and corresponding lake
water temperature limits. Reducing output using this method results in discrete blocks of MW reduction
over a period of time (i.e., their full capability cannot be obtained instantaneously).
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