Update optimization.py

[michaelpiron]

Implemented changes:

• Inverted the objective formulas in the case of "grid cost" cost function
• Changed the cost calculation to be consistent with the objective formula, in case of "grid cost" cost function (the cost calculation didn't distinguish between set_total_pv_sell = TRUE vs FALSE, whereas the objective function did).

To resolve following issue:

While looking at the code in order to understand the functioning of EMHASS, I noticed an inconsistency in the objective formulas. The profit cost function shows this: https://github.com/davidusb-geek/emhass/blob/bec6f76f1d7795a1ab8730fb0a61f883e75caf0c/src/emhass/optimization.py#L196-L204 which looks correct, and is consistent with the EMHASS documentation:

• In the case of an energy contract where the totality of the PV produced energy is injected into the grid, the grid offtake volume equals = P_load + P_deferrable_sum
• Else (only the excess of PV produced energy is injected), the grid offtake equals = P_grid_pos

However, the "grid cost" cost function seems to have the formulas inverted, which is unexpected: https://github.com/davidusb-geek/emhass/blob/bec6f76f1d7795a1ab8730fb0a61f883e75caf0c/src/emhass/optimization.py#L205-L211

Therefore, I wonder if the objective formulas in "Grid cost" cost function shouldn't be inverted.

[michaelpiron]

For the sake of clarity: I didn't test these changes, as I don't have my dev space/container set up yet. I hope someone else can test this. On the other hand, the proposed changes are limited.

[codecov[bot]]

Codecov Report

Attention: 2 lines in your changes are missing coverage. Please review.

Comparison is base (bec6f76) 88.16% compared to head (d77c4f6) 88.11%.

Files	Patch %	Lines
src/emhass/optimization.py	60.00%	2 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #135 +/- ## ========================================== - Coverage 88.16% 88.11% -0.06% ========================================== Files 6 6 Lines 1420 1422 +2 ========================================== + Hits 1252 1253 +1 - Misses 168 169 +1 ```

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