Potentially misssing efficiency for inflows in equity constraints

[davide-f]

Describe the feature you'd like to see

The current function add_EQ_constraints in solve_network calculates the contribution of energy by hydro powerplants as:
inflow - spillage.
However, if discharging efficiency applies it may lead to overestimation of the production in the node. I'm advising in the case this may be of interest.

Possible reformulation may adopt:

• inflow * efficiency_dispatch - spillage, or
• direclty use the p_dispatch variable

See

pypsa-eur/scripts/solve_network.py

Lines 580 to 603 in 12d7107

	n.snapshot_weightings.stores
	@ n.storage_units_t.inflow.groupby(sgrouper, axis=1).sum()
	)
	inflow = inflow.reindex(load.index).fillna(0.0)
	rhs = scaling * (level * load - inflow)
	p = n.model["Generator-p"]
	lhs_gen = (
	(p * (n.snapshot_weightings.generators * scaling))
	.groupby(ggrouper.to_xarray())
	.sum()
	.sum("snapshot")
	)
	# TODO: double check that this is really needed, why do have to subtract the spillage
	if not n.storage_units_t.inflow.empty:
	spillage = n.model["StorageUnit-spill"]
	lhs_spill = (
	(spillage * (-n.snapshot_weightings.stores * scaling))
	.groupby(sgrouper.to_xarray())
	.sum()
	.sum("snapshot")
	)
	lhs = lhs_gen + lhs_spill
	else:
	lhs = lhs_gen

Following from pypsa-meets-earth/pypsa-earth#1245