Is it possible to prescribe ramp up and ramp down rates for thermal power plants in AnswerTimes? if yes then what is the unit in AnswerTimes as the data available with me is in MW/Minute.

First check if your version of ANSWER-TIMES already supports the parameter ACT_UPS (e.g. look for it under the Parameter Tab).
If it does, you can use that for defining the ramping limits: UP = ramp-up, LO = ramp-down.
Unit is fraction of nominal on-line capacity per hour.
If it doesn't, consider upgrading to the latest version of ANSWER-TIMES.

The unit MW per minute does not seem very useful to me: If the data says 1 MW per minute, the same rate can hardly be valid for a 100 MW plant and a 1000 MW plant. I guess you would then need to have ramp-rate data table for all possible plant sizes?
In TIMES, you need to assume a certain plant size fore each technology in order to define e.g. the appropriate investment costs. And so, you can look up that size in your ramp-rate data table (where the ramp-rate is given in MW / minute, for all plant sizes).

I would like to have some more details on prescribing ramp-up rates to a process. Although I tried to find details on ACT_UPS in TIMES documentation but could not find something concrete.

As per AnswerTIMES, ACT_UPS is the “max change in load level in proportion to the capacity, per hour”. You shared that its unit is fraction of nominal on-line capacity per hour.

For instance, if there is a plant having capacity 100 MW and in hour 01 it is operating at 60 MW with a ramp up and ramp down rate of 10%. So now if the model requires to ramp up the coal generation than what is the maximum capacity it can increase in Hour 02 ?

So, if 10% ramp up rate is prescribed on the online capacity 60 Mw than the capacity that can be achieved will be 66 MW in Hour 02?

Please clarify whether my understanding of the concept is right or not.
One more thing, is it necessary to prescribe unit size while defining ramp up rate for a process?

04-08-2016, 11:18 PM (This post was last modified: 04-08-2016, 11:21 PM by Antti-L.)

Yes, ACT_UPS(r,y,p,s,bd) is defined as "Ramping limit for the load level of process p, vintage y in region r and timeslice s; Unit: fraction of nominal on-line capacity per hour".

The AnswerTIMES description, “max change in load level in proportion to the capacity, per hour” is thus also correct, with the refinement that the "capacity" refers to the on-line capacity.

From this definition, it should obvious that if there is a plant with ramp-up and ramp-down rate defined as 10%, and has 100 MW of capacity on-line but operating only at a 60 MW load level in hour 01, the maximum ramp-up and ramp-down rates are 10 MW per hour in both directions (0.1 × 100 = 10).

It should be equally obvious that if the on-line capacity of this plant is only 60 MW and it is also operating at full load (60 MW) in hour 01, the maximum ramp-rate would be zero in the upward direction and 6 MW per hour in the downward direction (0.1 × 60 = 6).

By default, the on-line capacity of a process is its full capacity, but if you enable start-ups/shut-downs, it will be endogenous.

Greetings of the day.
Thank you for sharing such great insights every time.
I tried the ACT_UPS the way mentioned for a coal based power plant in hourly model.
I prescribed the following to the plant:
a) ACT_EFF as 0.30
b) ACT_UPS (LO) as 0.10 and ACT_UPS (UP) as 0.10
c) NCAP_AF (LO) as 0.55
d) NCAP_AF (UP) as 0.85
e) NCAP_COST, NCAP_FOM, NCAP_TLIFE, etc

Although the plants follow the limits of 55% and 85% for capacity operation however the ramping limits are not followed by the plants during some hours of a year. The ramping rate has been in the order of 20 to 30% for some hours in a year. Please suggest what could be the reason.

Further, I read the document shared by you and I really find that document interesting. I am particularly interested in using the partial load efficiencies for my coal process. However, I am confused about the parameters to be used for the same as in my AnswerTIMES I am not able to see these parameters (I am using Answer Version 6.9.7). Please help me with what parameters I need to use and from where to activate those parameters in my AnswerTIMES.

Sorry, it is not possible to suggest what could be the reason with so little information.

Could you post the listing file (*.lst) from the model run, to see some details about your TIMES version?
Could you also post the result data (activity & capacity) that demonstrate the 20 to 30% ramping rates?

I just tested with a processs like you described, in an hourly test model. Just like you, I specified:
ACT_UPS (LO) = 0.10
ACT_UPS (UP) = 0.10
NCAP_AF (LO) = 0.55
NCAP_AF (UP) = 0.85

I fixed the capacity to 100 MW. In the results, the load levels of the process were the following in a sample day:

As you can see, all the ramp rates were exactly the maximum prescribed, 10% of the capacity per hour.
I also tested by trying to force the ramp rate a bit higher in a few timeslices, and got an infeasible solution, as expected.

Consequently, I cannot reproduce your findings on the basis of your description.
So, please provide more information, or a test model reproducing the unexpected behaviour.

A heartfelt thank you for testing the parameter on your model. I have also done a re-run as per your suggestion and observed some peculiar nature of output that I would like to share with you.

- The ramp rate of 10% is followed by the model in most of the time slices but except for the first hour time slice of each month compared with the previous month last hour time slice.
- All the time slices within the parent month follows the 10% ramp up and down rate accurately (even the first hour and last hour of the same month follow the ramping rates)

Therefore Time slice April 01Hr to April24 Hr follows the ramping rate of 10%. But the time slice of April 24 Hr and May 01 Hr does not obey the ramping constraint of 10% however the time slice May 01 Hr to May 24 Hr follows the ramping constraint.

Model description: My model is an hourly model that’s solves demand and supply for each hours. For each year, I have 12 months and 288 sub time slices under these 12 months. Each time slice representing one hour of a day for each month i.e. April 01Hr time-slice represents first hour (12 a.m. to 1 a.m.) of each day in April and thus every month will have 24 time-slices. Therefore the 24 time slices of April Month will have a parent time slice as April Month.

Please share your views on this.

Further, I read the document shared by you in the previous messages. I am particularly interested in using the partial load efficiencies for my coal process. However, I am confused about the parameters to be used for the same as in my AnswerTIMES I am not able to see these parameters (I am using Answer Version 6.9.7). Please help me with what parameters I need to use and from where to activate those parameters in my AnswerTIMES.

Ok, you are comparing the first hourly time slice of each month compared with the last hourly time slice in the previous month, even though you have 12 seasons (representing months), and 24 DAYNITE timeslices under each.

This implies that you have misunderstood the TIMES conventions concerning such representative days in each season.
As there are actually about 30 days in each month, you cannot assume that after each day in January, the next day would be in February, and then the next day in March, and so on. It would not make much sense; it would not correspond to reality.

Instead, in TIMES, each day in January is assumed to be followed by another day in January! Consequently, the DAYNITE timeslices under each parent represent a daily timeslice cycle for a representative day in that season, such that the last timeslice of the cycle is followed by the first timeslice of that same cycle. This correctly reflects the reality in 29 cases out of the (average) 30 days in each month.

If you want that in your model the last hour of April is followed by the first hour of May, you need to have all hours of these months represented. This means that you should have 8760 timeslices in your model. But I hope you can see that the TIMES timeslice hierarchy does offer a reasonable way of modeling the whole year in an adequate way, with much less timeslices.

Concerning upgrading your ANSWER-TIMES to a more recent version that supports the new parameters, please contact Ken Noble.