Documentation for $SET OBLONG, and its effect on lump-sum investment cost re

[KristofferEML]

Returning to your question again, because I found it confusing:

> Is exact reconciliation between reported lump-sum investment cost and INVCOST only guaranteed under OBLONG=NO, or is there a different switch/reporting option that lets me keep the recommended OBLONG=YES formulation while still getting a lump-sum figure that ties out cleanly to INVCOST?

As far as I can tell, agreement between the reported LUMPINV lump-sum investment cost and NCAP_COST is guaranteed if you are neither using NCAP_ILED nor NCAP_DISC for the technology. If you use NCAP_ILED, then the IDC will be included both in the objective function and in the reported LUMPINV value. And if you use NCAP_DISC, also the risk premium is included both in the objective function and in the reported LUMPINV value(s) (optionally split in two values, the second being the risk premium). But if you use neither, you should be seeing that LUMPINV = NCAP_COST × INSTCAP, regardless of any OBLONG setting.

Hello Antti,
Thanks for the detailed replies — and fair correction on the code reading. Thank you also for the the pointer to the ObjVariants.pdf — that's exactly the kind of documentation reference I was missing.

I've attached a small demo model (zip) that isolates the effect. It has a single investment decision, no NCAP_ILED, no NCAP_DRATE, integer NCAP_TLIFE, and fully contiguous periods — so per your reply, LUMPINV should equal NCAP_COST × INSTCAP regardless of OBLONG.

The CAP_NEW/INSTCAP is identical in both runs (100, 20, 20, 20, 20, 20 GW for 2025–2030 under both oblong_false and oblong_true). However, the LUMPINV differs by a constant ~1.976% uplift in every period, independent of the amount of capacity added (NCAP_COST = 100/unit here, so LUMPINV reconciles exactly under OBLONG=NO but not under OBLONG=YES).

Here's the part I think narrows this down: I also pulled Cost_Inv (annualized/levelized investment cost) for the same runs, and it is essentially unchanged between the two settings, with the small residual differences (~0.004%). So the actual annualized cost stream that enters the objective function, and presumably drives the optimal investment decision, is virtually unaffected by OBLONG. It's specifically the back-calculated LUMPINV figure that picks up the ~2% gap. Is there somewhere I can see what exactly is driving this gap? 




If I want a lump-sum figure that ties out to INVCOST for external cash-flow work, would you recommend just computing NCAP_COST × INSTCAP directly from the input assumptions rather than relying on LUMPINV when OBLONG=YES?
 
Thanks for your patience with this, Kristoffer