Solver not stable for an objective with binary requirement in the formula

[rplnmrsh]

I am trying to make a power saving model to lower the total power bill, with a primary goal to find the trigger price at which the power saving starts.

Logic elements:

• When the power in the hour exceeds the price trigger, then power saving starts, BUT
• The constraint is over the period, there's a certain must run volume, therefore the power saving volume must be less than the must run volume.

Based on my setup in Pic 1, with GRG Non Linear, I got a result that makes sense ($240/MWh). However, when I then overwrote the trigger price manually to say $800, then run the solver again, solver said it found a solution but did not change the $800 at all. At other times the solver won't find a solution or just won't return anything. Is there something wrong with my setup that makes Solver unstable?

I expect the solver to be able to produce an accurate and stable response when I play around with the "Must run Volume", or just simply when I overwrite the price trigger.

Picture 1 shows how the workbook was setup, the SUMPRODUCT formula and the solver settings.
Picture 2 sshows when I overwrote the price tigger to 800, ran solver again. Solver said it found a solution but did not change the 800.
Picture 3 shows when I overwrote the number to 100 and Solver couldn't find a solution.

 

[Kaper]

Welcome to the forum,

You set as a variable E7. I assume, it influences the goal (E18) indirectly - via simple IF formulas in D11:D15.

Note the comment in dialog box on screenshots about GRG method you selected.
It is dedicated to smooth problems.
An your problem is not smooth one. With every "triggered" hour you have a step (not smooth) change of total power saving value.

First proposition:

- Use Evolutionary engine as suggested by the comments in this dialog. Be prepared that solving with this engine requires more time.

Second (especially if first does not work):
- Use xl2bb add in (see XL2BB - Excel Range to BBCode ) to post a useable part of your worksheet and we could test other solutions - may be by reformulating problem setup in Solver