Allow BESS to Export

CHANGELOG.md

@@ -25,6 +25,10 @@ Classify the change according to the following categories:
     ### Deprecated
     ### Removed
 
+## bess-export
+### Added 
+- Added input option **can_export_to_grid** (defaults to _false_) to `ElectricStorage` and decision variable **dvStorageToGrid**
+- 
 
 ## Develop
 ### Added

src/constraints/electric_utility_constraints.jl

@@ -129,8 +129,14 @@ function add_export_constraints(m, p; _n="")
         if typeof(binNEM) <: Real  # no need for wholesale binary
             binWHL = 1
             WHL_benefit = @expression(m, p.pwf_e * p.hours_per_time_step *
-                sum( sum(p.s.electric_tariff.export_rates[:WHL][ts] * m[Symbol("dvProductionToGrid"*_n)][t, :WHL, ts] 
-                        for t in p.techs_by_exportbin[:WHL]) for ts in p.time_steps)
+                # sum( sum(p.s.electric_tariff.export_rates[:WHL][ts] * m[Symbol("dvProductionToGrid"*_n)][t, :WHL, ts] 
+                #         for t in p.techs_by_exportbin[:WHL]) for ts in p.time_steps)
+                sum(p.s.electric_tariff.export_rates[:WHL][ts] *
+                (
+                    sum(m[Symbol("dvStorageToGrid"*_n)][b, ts] for b in p.s.storage.types.elec) + ## TODO: index on metering type?
+                    sum(m[Symbol("dvProductionToGrid"*_n)][t, :WHL, ts] for t in p.techs_by_exportbin[:WHL])
+                ) for ts in p.time_steps
+            )
             )
         else
             binWHL = @variable(m, binary = true)

src/constraints/storage_constraints.jl

@@ -68,7 +68,7 @@ function add_elec_storage_dispatch_constraints(m, p, b; _n="")
         m[Symbol("dvStoredEnergy"*_n)][b, ts] == m[Symbol("dvStoredEnergy"*_n)][b, ts-1] + p.hours_per_time_step * (  
             sum(p.s.storage.attr[b].charge_efficiency * m[Symbol("dvProductionToStorage"*_n)][b, t, ts] for t in p.techs.elec) 
             + p.s.storage.attr[b].grid_charge_efficiency * m[Symbol("dvGridToStorage"*_n)][b, ts] 
-            - m[Symbol("dvDischargeFromStorage"*_n)][b,ts] / p.s.storage.attr[b].discharge_efficiency
+            - ((m[Symbol("dvDischargeFromStorage"*_n)][b,ts] + m[Symbol("dvStorageToGrid"*_n)][b, ts])/ p.s.storage.attr[b].discharge_efficiency)
         )
 	)
 	# Constraint (4g)-2: state-of-charge for electrical storage - no grid
@@ -104,21 +104,33 @@ function add_elec_storage_dispatch_constraints(m, p, b; _n="")
 	@constraint(m, [ts in p.time_steps_with_grid],
         m[Symbol("dvStoragePower"*_n)][b] >= m[Symbol("dvDischargeFromStorage"*_n)][b, ts] + 
             sum(m[Symbol("dvProductionToStorage"*_n)][b, t, ts] for t in p.techs.elec) + m[Symbol("dvGridToStorage"*_n)][b, ts]
+            + m[Symbol("dvStorageToGrid"*_n)][b, ts]
     )
 
+    #Dispatch from electrical storage is no greater than power capacity 
+    @constraint(m, [ts in p.time_steps_without_grid],
+        m[Symbol("dvStoragePower"*_n)][b] >= m[Symbol("dvDischargeFromStorage"*_n)][b,ts] + m[Symbol("dvStorageToGrid"*_n)][b, ts])
+
 	#Constraint (4l)-alt: Dispatch from electrical storage is no greater than power capacity (no grid connection)
 	@constraint(m, [ts in p.time_steps_without_grid],
         m[Symbol("dvStoragePower"*_n)][b] >= m[Symbol("dvDischargeFromStorage"*_n)][b,ts] + 
             sum(m[Symbol("dvProductionToStorage"*_n)][b, t, ts] for t in p.techs.elec)
     )
 
-    # Remove grid-to-storage as an option if option to grid charge is turned off
+    #Constraint (4m)-1: Remove grid-to-storage as an option if option to grid charge is turned off
     if !(p.s.storage.attr[b].can_grid_charge)
         for ts in p.time_steps_with_grid
             fix(m[Symbol("dvGridToStorage"*_n)][b, ts], 0.0, force=true)
         end
 	end
 
+    #Constraint (4m)-2: Force storage export to grid to zero if option to grid export is turned off
+    if !p.s.storage.attr[b].can_export_to_grid
+        for ts in p.time_steps
+            fix(m[Symbol("dvStorageToGrid"*_n)][b, ts], 0.0, force=true)
+        end
+    end
+
     if p.s.storage.attr[b].minimum_avg_soc_fraction > 0
         avg_soc = sum(m[Symbol("dvStoredEnergy"*_n)][b, ts] for ts in p.time_steps) /
                    (8760. / p.hours_per_time_step)

src/core/electric_tariff.jl

@@ -395,7 +395,7 @@ Check length of e and upsample if length(e) != N
 """
 function create_export_rate(e::AbstractArray{<:Real, 1}, N::Int, ts_per_hour::Int=1)
     Ne = length(e)
-    if Ne != Int(N/ts_per_hour) || Ne != N
+    if Ne != Int(N/ts_per_hour) && Ne != N
         throw(@error("Export rates do not have correct number of entries. Must be $(N) or $(Int(N/ts_per_hour))."))
     end
     if Ne != N  # upsample

src/core/energy_storage/electric_storage.jl

@@ -167,6 +167,7 @@ end
     soc_min_applies_during_outages::Bool = false
     soc_init_fraction::Float64 = off_grid_flag ? 1.0 : 0.5
     can_grid_charge::Bool = off_grid_flag ? false : true
+    can_export_to_grid::Bool = false
     installed_cost_per_kw::Real = 910.0
     installed_cost_per_kwh::Real = 455.0
     replace_cost_per_kw::Real = 715.0
@@ -202,6 +203,7 @@ Base.@kwdef struct ElectricStorageDefaults
     soc_min_applies_during_outages::Bool = false
     soc_init_fraction::Float64 = off_grid_flag ? 1.0 : 0.5
     can_grid_charge::Bool = off_grid_flag ? false : true
+    can_export_to_grid::Bool = false
     installed_cost_per_kw::Real = 910.0
     installed_cost_per_kwh::Real = 455.0
     replace_cost_per_kw::Real = 715.0
@@ -243,6 +245,7 @@ struct ElectricStorage <: AbstractElectricStorage
     soc_min_applies_during_outages::Bool
     soc_init_fraction::Float64
     can_grid_charge::Bool
+    can_export_to_grid::Bool
     installed_cost_per_kw::Real
     installed_cost_per_kwh::Real
     replace_cost_per_kw::Real
@@ -336,6 +339,7 @@ struct ElectricStorage <: AbstractElectricStorage
             s.soc_min_applies_during_outages,
             s.soc_init_fraction,
             s.can_grid_charge,
+            s.can_export_to_grid,
             s.installed_cost_per_kw,
             s.installed_cost_per_kwh,
             replace_cost_per_kw,

src/core/reopt.jl

@@ -213,6 +213,7 @@ function build_reopt!(m::JuMP.AbstractModel, p::REoptInputs)
 				@constraint(m, [ts in p.time_steps], m[:dvGridToStorage][b, ts] == 0)
 				@constraint(m, [t in p.techs.elec, ts in p.time_steps_with_grid],
 						m[:dvProductionToStorage][b, t, ts] == 0)
+				@constraint(m, [ts in p.time_steps], m[Symbol("dvStorageToGrid"*_n)][b, ts] == 0)  # if there isn't a battery, then the battery can't export power to the grid
 			elseif b in p.s.storage.types.hot
 				@constraint(m, [q in q in setdiff(p.heating_loads, p.heating_loads_served_by_tes[b]), ts in p.time_steps], m[:dvHeatFromStorage][b,q,ts] == 0)
 				if "DomesticHotWater" in p.heating_loads_served_by_tes[b]
@@ -616,6 +617,7 @@ function add_variables!(m::JuMP.AbstractModel, p::REoptInputs)
 		dvProductionToStorage[p.s.storage.types.all, union(p.techs.ghp,p.techs.all), p.time_steps] >= 0  # Power from technology t used to charge storage system b [kW]
 		dvDischargeFromStorage[p.s.storage.types.all, p.time_steps] >= 0 # Power discharged from storage system b [kW]
 		dvGridToStorage[p.s.storage.types.elec, p.time_steps] >= 0 # Electrical power delivered to storage by the grid [kW]
+		dvStorageToGrid[p.s.storage.types.elec, p.time_steps] >= 0 # TODO, add: "p.StorageSalesTiers" as well? export of energy from storage to the grid
 		dvStoredEnergy[p.s.storage.types.all, 0:p.time_steps[end]] >= 0  # State of charge of storage system b
 		dvStoragePower[p.s.storage.types.all] >= 0   # Power capacity of storage system b [kW]
 		dvStorageEnergy[p.s.storage.types.all] >= 0   # Energy capacity of storage system b [kWh]

src/core/reopt_multinode.jl

@@ -16,7 +16,8 @@ function add_variables!(m::JuMP.AbstractModel, ps::AbstractVector{REoptInputs{T}
 		"dvStorageEnergy",
 	]
 	dvs_idx_on_storagetypes_time_steps = String[
-		"dvDischargeFromStorage"
+		"dvDischargeFromStorage",
+		"dvStorageToGrid"
 	]
 	for p in ps
 		_n = string("_", p.s.site.node)

src/mpc/model.jl

@@ -99,6 +99,7 @@ function build_mpc!(m::JuMP.AbstractModel, p::MPCInputs)
 			@constraint(m, [ts in p.time_steps], m[:dvDischargeFromStorage][b, ts] == 0)
 			if b in p.s.storage.types.elec
 				@constraint(m, [ts in p.time_steps], m[:dvGridToStorage][b, ts] == 0)
+				@constraint(m, [ts in p.time_steps], m[:dvStorageToGrid][b, ts] == 0)
 			end
 		else
 			add_general_storage_dispatch_constraints(m, p, b)
@@ -230,6 +231,7 @@ function add_variables!(m::JuMP.AbstractModel, p::MPCInputs)
 		dvCurtail[p.techs.all, p.time_steps] >= 0  # [kW]
 		dvProductionToStorage[p.s.storage.types.all, p.techs.all, p.time_steps] >= 0  # Power from technology t used to charge storage system b [kW]
 		dvDischargeFromStorage[p.s.storage.types.all, p.time_steps] >= 0 # Power discharged from storage system b [kW]
+		dvStorageToGrid[p.s.storage.types.elec, p.time_steps] >= 0 # TODO, add: "p.StorageSalesTiers" as well? export of energy from storage to the grid
 		dvGridToStorage[p.s.storage.types.elec, p.time_steps] >= 0 # Electrical power delivered to storage by the grid [kW]
 		dvStoredEnergy[p.s.storage.types.all, 0:p.time_steps[end]] >= 0  # State of charge of storage system b
 		dvStoragePower[p.s.storage.types.all] >= 0   # Power capacity of storage system b [kW]

src/mpc/model_multinode.jl

@@ -152,7 +152,8 @@ function add_variables!(m::JuMP.AbstractModel, ps::AbstractVector{MPCInputs})
 		"dvRatedProduction",
 	]
 	dvs_idx_on_storagetypes_time_steps = String[
-		"dvDischargeFromStorage"
+		"dvDischargeFromStorage",
+		"dvStorageToGrid"
 	]
 	for p in ps
 		_n = string("_", p.s.node)

src/mpc/structs.jl

@@ -226,6 +226,7 @@ Base.@kwdef struct MPCElectricStorage < AbstractElectricStorage
     soc_min_fraction::Float64 = 0.2
     soc_init_fraction::Float64 = 0.5
     can_grid_charge::Bool = true
+    can_export_to_grid::Bool = false
     grid_charge_efficiency::Float64 = 0.96 * 0.975^2
 end
 ```
@@ -238,6 +239,7 @@ Base.@kwdef struct MPCElectricStorage <: AbstractElectricStorage
     soc_min_fraction::Float64 = 0.2
     soc_init_fraction::Float64 = 0.5
     can_grid_charge::Bool = true
+    can_export_to_grid::Bool = false
     grid_charge_efficiency::Float64 = 0.96 * 0.975^2
     max_kw::Float64 = size_kw
     max_kwh::Float64 = size_kwh

src/results/electric_storage.jl

@@ -3,8 +3,9 @@
 `ElectricStorage` results keys:
 - `size_kw` Optimal inverter capacity
 - `size_kwh` Optimal storage capacity
-- `soc_series_fraction` Vector of normalized (0-1) state of charge values over the first year
-- `storage_to_load_series_kw` Vector of power used to meet load over the first year
+- `soc_series_fraction` Vector of normalized (0-1) state of charge values over an average year
+- `storage_to_load_series_kw` Vector of power used to meet load over an average year
+- `storage_to_grid_series_kw` Vector of power exported to the grid over an average year
 - `initial_capital_cost` Upfront capital cost for storage and inverter
 # The following results are reported if storage degradation is modeled:
 - `state_of_health`
@@ -44,9 +45,13 @@ function add_electric_storage_results(m::JuMP.AbstractModel, p::REoptInputs, d::
             end
             r["residual_value"] = value(m[:residual_value])
          end
+
+         # report the exported electricity from the battery:
+         r["storage_to_grid_series_kw"] = round.(value.(m[Symbol("dvStorageToGrid"*_n)][b, ts] for ts in p.time_steps), digits = 3)
     else
         r["soc_series_fraction"] = []
         r["storage_to_load_series_kw"] = []
+        r["storage_to_grid_series_kw"] = []
     end
 
     d[b] = r

src/results/pv.jl

@@ -6,10 +6,10 @@
 - `year_one_energy_produced_kwh` Energy produced over the first year
 - `annual_energy_produced_kwh` Average annual energy produced when accounting for degradation
 - `lcoe_per_kwh` Levelized Cost of Energy produced by the PV system
-- `electric_to_load_series_kw` Vector of power used to meet load over the first year
-- `electric_to_storage_series_kw` Vector of power used to charge the battery over the first year
-- `electric_to_grid_series_kw` Vector of power exported to the grid over the first year
-- `electric_curtailed_series_kw` Vector of power curtailed over the first year
+- `electric_to_load_series_kw` Vector of power used to meet load over an average year
+- `electric_to_storage_series_kw` Vector of power used to charge the battery over an average year
+- `electric_to_grid_series_kw` Vector of power exported to the grid over an average year
+- `electric_curtailed_series_kw` Vector of power curtailed over an average year
 - `annual_energy_exported_kwh` Average annual energy exported to the grid
 - `production_factor_series` PV production factor in each time step, either provided by user or obtained from PVWatts
 

src/results/thermal_storage.jl

@@ -2,8 +2,8 @@
 """
 `HotThermalStorage` results keys:
 - `size_gal` Optimal TES capacity, by volume [gal]
-- `soc_series_fraction` Vector of normalized (0-1) state of charge values over the first year [-]
-- `storage_to_load_series_mmbtu_per_hour` Vector of power used to meet load over the first year [MMBTU/hr]
+- `soc_series_fraction` Vector of normalized (0-1) state of charge values over an average year [-]
+- `storage_to_load_series_mmbtu_per_hour` Vector of power used to meet load over an average year [MMBTU/hr]
 
 !!! note "'Series' and 'Annual' energy outputs are average annual"
 	REopt performs load balances using average annual production values for technologies that include degradation. 
@@ -84,8 +84,8 @@ end
 """
 `ColdThermalStorage` results:
 - `size_gal` Optimal TES capacity, by volume [gal]
-- `soc_series_fraction` Vector of normalized (0-1) state of charge values over the first year [-]
-- `storage_to_load_series_ton` Vector of power used to meet load over the first year [ton]
+- `soc_series_fraction` Vector of normalized (0-1) state of charge values over an average year [-]
+- `storage_to_load_series_ton` Vector of power used to meet load over an average year [ton]
 """
 function add_cold_storage_results(m::JuMP.AbstractModel, p::REoptInputs, d::Dict, b::String; _n="")
     #=