Non-optimal results when 'fixed result to x period'

[Antti-L]

Well, if you fix results up to 2030, then you have a smaller model, which is thus easier to solve than when you fix up to 2020.  So, to me it does make sense that you then reach proven optimal results.  

Anyway, the condition "solution available but not proven optimal due to numerical difficulties" means that the solver is running into some numerical difficulties while trying to complete the solution of the problem. When a model has such problems, the numerical difficulties typically may occur in a rather random manner: some model runs may complete well while others don't.

See this thread on the ETSAP Forum for several options that can be used for troubleshooting "Solution available but not proven optimal due to numerical difficulties":
https://iea-etsap.org/forum/showthread.php?tid=162

Nonetheless, getting rid of all dummy imports has in many cases proven to be the easiest and effective way of improving the numerical stability of large VEDA-TIMES models. Therefore, as the first thing to try I would suggest disabling the dummy imports (if you have enabled them):

* Disable dummy imports to improve numerical stability
  NCAP_START(R,'IMPNRGZ')=2200;
  NCAP_START(R,'IMPMATZ')=2200;
  NCAP_START(R,'IMPDEMZ')=2200;

Under VEDA, you can define these in any scenario file. Of course, disabling the dummy imports requires that your model is in fact feasible.