Merge pull request #82 from staadecker/multi-fuel

Small optimizations

Author: PatyHidalgo

switch_model/energy_sources/fuel_costs/markets.py

@@ -209,6 +209,10 @@ def define_components(mod):
     become non-linear.
 
     """
+    # When this variable is True we only allow positive fuel costs
+    # This simplifies the model since we can set some of our constraints
+    # as greater than instead of equals.
+    ONLY_POSITIVE_RFM_COSTS = False
 
     mod.REGIONAL_FUEL_MARKETS = Set(dimen=1)
     mod.rfm_fuel = Param(mod.REGIONAL_FUEL_MARKETS, within=mod.FUELS)
@@ -244,7 +248,9 @@ def zone_rfm_init(m, load_zone, fuel):
         dimen=3,
         validate=lambda m, r, p, st: (r in m.REGIONAL_FUEL_MARKETS and p in m.PERIODS),
     )
-    mod.rfm_supply_tier_cost = Param(mod.RFM_SUPPLY_TIERS, within=Reals)
+    mod.rfm_supply_tier_cost = Param(
+        mod.RFM_SUPPLY_TIERS, within=PositiveReals if ONLY_POSITIVE_RFM_COSTS else Reals
+    )
     mod.rfm_supply_tier_limit = Param(
         mod.RFM_SUPPLY_TIERS, within=NonNegativeReals, default=float("inf")
     )
@@ -365,13 +371,20 @@ def GENS_FOR_RFM_PERIOD_rule(m, rfm, p):
     enforce_fuel_consumption_scaling_factor = 1e-2
 
     def Enforce_Fuel_Consumption_rule(m, rfm, p):
-        return m.FuelConsumptionInMarket[
-            rfm, p
-        ] * enforce_fuel_consumption_scaling_factor == enforce_fuel_consumption_scaling_factor * sum(
+        lhs = (
+            m.FuelConsumptionInMarket[rfm, p] * enforce_fuel_consumption_scaling_factor
+        )
+        rhs = enforce_fuel_consumption_scaling_factor * sum(
             m.GenFuelUseRate[g, t, m.rfm_fuel[rfm]] * m.tp_weight_in_year[t]
             for g in m.GENS_FOR_RFM_PERIOD[rfm, p]
             for t in m.TPS_IN_PERIOD[p]
         )
+        # If we have only positive costs, FuelConsumptionInMarket will automatically
+        # try to be minimized in which case we can use a one-sided constraint
+        if ONLY_POSITIVE_RFM_COSTS:
+            return lhs >= rhs
+        else:
+            return lhs == rhs
 
     mod.Enforce_Fuel_Consumption = Constraint(
         mod.REGIONAL_FUEL_MARKETS, mod.PERIODS, rule=Enforce_Fuel_Consumption_rule

switch_model/generators/core/dispatch.py

@@ -246,15 +246,57 @@ def init(m, gen, period):
         mod.GEN_TPS, rule=lambda m, g, t: m.GenCapacity[g, m.tp_period[t]]
     )
     mod.DispatchGen = Var(mod.GEN_TPS, within=NonNegativeReals)
-    mod.DispatchGenByFuel = Var(mod.GEN_TP_FUELS, within=NonNegativeReals)
+
+    ##########################################
+    # Define DispatchGenByFuel
+    #
+    # Previously DispatchGenByFuel was simply a Variable for all the projects and a constraint ensured
+    # that the sum of DispatchGenByFuel across all fuels was equal the total dispatch for that project.
+    # However this approach creates extra variables in our model for projects that have only one fuel.
+    # Although these extra variables likely get removed during Gurobi pre-solve, we've nonetheless
+    # simplified the model here to reduce time in presolve and ensure the model is always
+    # simplified regardless of the solving method.
+    #
+    # To do this we redefine DispatchGenByFuel to be an
+    # expression that is equal to DispatchGenByFuelVar when we have multiple fuels but
+    # equal to DispatchGen when we have only one fuel.
+
+    # Define a set that is used to define DispatchGenByFuelVar
+    mod.GEN_TP_FUELS_FOR_MULTIFUELS = Set(
+        dimen=3,
+        initialize=mod.GEN_TP_FUELS,
+        filter=lambda m, g, t, f: g in m.MULTIFUEL_GENS,
+        doc="Same as GEN_TP_FUELS but only includes multi-fuel projects",
+    )
+    # DispatchGenByFuelVar is a variable that exists only for multi-fuel projects.
+    mod.DispatchGenByFuelVar = Var(
+        mod.GEN_TP_FUELS_FOR_MULTIFUELS, within=NonNegativeReals
+    )
+    # DispatchGenByFuel_Constraint ensures that the sum of all the fuels is DispatchGen
     mod.DispatchGenByFuel_Constraint = Constraint(
         mod.FUEL_BASED_GEN_TPS,
-        rule=lambda m, g, t: sum(
-            m.DispatchGenByFuel[g, t, f] for f in m.FUELS_FOR_GEN[g]
-        )
-        == m.DispatchGen[g, t],
+        rule=lambda m, g, t: (
+            Constraint.Skip
+            if g not in m.MULTIFUEL_GENS
+            else sum(
+                m.DispatchGenByFuelVar[g, t, f] for f in m.FUELS_FOR_MULTIFUEL_GEN[g]
+            )
+            == m.DispatchGen[g, t]
+        ),
     )
 
+    # Define DispatchGenByFuel to equal the matching variable if we have many fuels but to equal
+    # the total dispatch if we have only one fuel.
+    mod.DispatchGenByFuel = Expression(
+        mod.GEN_TP_FUELS,
+        rule=lambda m, g, t, f: m.DispatchGenByFuelVar[g, t, f]
+        if g in m.MULTIFUEL_GENS
+        else m.DispatchGen[g, t],
+    )
+
+    # End Defining DispatchGenByFuel
+    ##########################################
+
     # Only used to improve the performance of calculating ZoneTotalCentralDispatch and ZoneTotalDistributedDispatch
     mod.GENS_FOR_ZONE_TPS = Set(
         mod.LOAD_ZONES,