Reserve Generators Response Ratio

Units:	-
Mode:	Input Only
Multi-band:	False
Default Value:	1
Validation Rule:	≥0
Key Property:	No
Description:	Ratio that converts energy ramping to units comparable to reserve ramping units

Response Ratio defines the ratio at which the generator can provide reserve in proportion to its ramping capabilities. It has to be defined along with Reserve.Time Frame and generator's ramp limits (ie. Max Ramp Up and Max Ramp Down). Response Ratio has a direct impact on both generator's ramping limits and reserve response. They are mutually exclusive, which means that if the generator is ramping up/down in consecutive periods, it should limit the response reserve in proportion to the Response Ratio value. In general:

Reserve Response = min { Max Response, Max Ramp / Response Ratio }

A value Response Ratio < 1 means that the unit is capable (if the available capacity permits it) of providing more MWs of reserve as the operating ramp limit. A response ratio of 0.5 (for example) means that energy ramping is half the rate of reserve ramping and vice versa. A response ratio of 0 will not cause PLEXOS to return an error, but will prevent the generator from providing MWs to the reserve (consider setting Max Response or Max Replacement equal to 0 if this is the desired effect). A full numerical example follows.

The following illustrates how Response Ratio is used and, when defined, shows how active ramping limits can affect the reserve provision (and vice versa):

A 150MW generator can provide regulation raise reserve with Effectiveness of one and no Max Response other than available spare capacity,
A Max Ramp Up of 0.5 MW/min: meaning that the generator is capable of changing its dispatch level in consecutive hours at a maximum rate of 30MW,
A response ratio of 0.5 is defined,

Ignoring ramping constraints and assuming the generator operates at 70MW, it could provide the following reserve response:

= Dispatchable Capacity - Generation = 150 - 70 = 80MW

Assume a Timeframe of 1 hr (eg. regulation reserve) and the above Response Ratio, the theoretical reserve response of the unit would then be:

= min{ Dispatchable Capacity - Generation , Max Ramp Up / Response Ratio } = min{ (150 - 70) , (30 / 0.5) } = 60MW

Case 1: Suppose that at the optimal solution:

The generator starts the hour at 40MW and ramps to 70MW (assuming it is limited by a Max Ramp Up of 0.5 MW/min.) Since the unit is ramping Up at its max capability, it can't provide response for reserve Up services.

= (60 - 30 / 0.5) = 0MW reserve.

Case 2: Suppose that at the optimal solution:

The generator changes its dispatch (ramping Up) in 15MW in consecutive hours. In that case the available reserve response of the unit will be limited by:

= Reserve Response - (Ramp / Response Ratio) = (60 - 15 / 0.5) = 30MW reserve.