CurrentMode=0 and EnergyTarget > 0 #2
Description
Following the "Fast-Start Inflexibility profile.pdf" document, units with CurrentMode=0 can be committed for dispatch. The process involves two NEMDE runs. From the docs:
"A fast-start commitment solve is performed in the first pass. In this solve all fast-start units are modelled with their dispatch inflexibility profile constraints ignored. Any bid and SCADA-metered energy ramp rate constraints and joint ramping constraints for fast-start units that are in modes 0, 1, or 2 at the start of the current dispatch interval are also ignored."
Also from the docs:
"Units in Mode 0 at the start of the current dispatch interval are candidates for start-up (entering into Mode 1). A unit will be started if its MW result from Step 1 is greater than the fast-start threshold of 0.005 MW. The target mode for the end of current dispatch interval, which is used in Step 3, is calculated according to its start-up profile. For example, units having T1+T2 < 5 minutes will enter into Mode 3. Step 3 may then determine non-zero MW generation targets for the end of the current dispatch period."
In order to correctly implement fast-start inflexibility profile constraints a multi-solve framework must be adopted. However, there is a trade-off between model accurracy and solve time. To implement this approach would require 3 solves instead of the current 2 (at present one is used to determine dispatch targets, and another used to determine prices).
This deficiency can be listed as a caveat for users. In the future a multi-solve framework incorporating inflexibility profile solves could be adopted, with the user able to choose which model to use. For now I'm not going to incorporate this feature as the cost of the additional complexity seems to outweigh the benefit - numerical experiments suggest this issue has a material impact only in a small percentage of dispatch intervals.