Allow BESS to Export by adfarth · Pull Request #471 · NatLabRockies/REopt.jl

adfarth · 2025-01-07T16:00:28Z

Added

Add decision variable dvStorageToGrid and ElectricStorage input options for grid export: can_net_meter, can_wholesale, can_export_beyond_nem_limit (all default to False)

TODO:

Add BESS inputs for can_net_meter, can_wholesale, can_export_beyond_nem_limit
index dvStorageToGrid on metering type, following the logic of tech export bins
Determine whether to use dvs for total BESS discharge & BESStoGrid vs. BESStoLoad & BESStoGrid --> Choosing to mirror tech production by using dvDischargeFromStorage as total discharge with dvStorageToGrid
Incorporate dvStorageToGrid into load balancing constraints
Test outputs against expected values
Review and update emissions calculations to account for BESS export
Address TODOs throughout code
Check and remove all references to "can_export_to_grid" (currently commented out)

Things to test:

BESS has NEM and PV does not --> currently errors. should allow this (and test)
BESS has wholesale and PV does not --> should allow this (and test)
All 3 new inputs for BESS
Different solvers (with vs without indicator constraint compatibility)
PV has NEM or WHL and BESS does not
Make sure BESS serves load first
Test with thermal storage

Known issues:

If you have a net_metering_limit_kw > 0, PV.can_net_meter = false, and ElectricStorage.can_net_meter = true, will error --> Could maybe add a check that not only BESS can net meter without a generating tech? Or just allow this?
ElectricStorage can end up being sized, and export, much more than the peak load (this is currently true in develop, too, but now the issue is more extreme)

Nice to haves / future work:

Test solve time impacts compared to master branch (impacting solve times even without allowing BESS to export?)
Check export in MPC -- not currently high priority so could remove if this adds a lot of work
Consider adding other frameworks outside of net metering or net billing. E.g. BESS can export, potentially not receive any NEM or NB compensation, and receive a per kWh compensation during defined periods (similar, but different from, CPs). Or: BESS can export but doesn't receive any compensation at all.
If compensated through net metering, assess whether the BESS capacity should be included in the net_metering_limit_kw. --> Xiang and I think BESS should not contribute towards NEM limit

hdunham · 2025-06-04T17:11:01Z

    WHL_benefit = 0
    NEM_techs = String[t for t in p.techs.elec if :NEM in p.export_bins_by_tech[t]]
    WHL_techs = String[t for t in p.techs.elec if :WHL in p.export_bins_by_tech[t]]
+    NEM_storage = String[b for b in p.s.storage.types.elec if :NEM in p.export_bins_by_storage[b]]


This isn't really about what you added, but isn't NEM_techs just equal to techs_by_exportbins[:NEM]? Same with WHL_techs, NEM_storage, WHL_storage. Do you agree? If so idk why we are recreating it.

Yes I just double checked and I agree. We could probably replace all instances of NEM_techs and WHL_techs with their techs_by_export bin equivalent

@hdunham it looks like you made this change and then reverted it. I'm assuming it broke some things and if so can I resolve this convo?

hdunham · 2025-06-10T17:04:28Z

+        @constraint(m, [b in p.s.storage.attr[b], ts in p.time_steps_with_grid],
+            sum(m[Symbol("dvStorageToGrid"*_n)][b, u, ts] for u in p.export_bins_by_storage[b])
+            <= 
+            m[Symbol("dvDischargeFromStorage"*_n)][b, ts] # TODO: should this be divided by p.s.storage.attr[b].discharge_efficiency ?


no discharge_efficiency here, that is applied in the SOC constraints (4g)

To be sure I understand, is dvProductionToStorage on the AC side of the converter (so, before efficiency losses) and dvDischargeFromStorage is on the AC side of the inverter (so, after efficiency losses)? So everything is AC

rm resolved TODOs

adfarth · 2025-07-03T16:53:12Z

+    for t in techs.elec
+        export_bins_by_tech[t] = s.electric_tariff.export_bins
+    end
+    # TODO implement export bins by tech (rather than assuming that all techs share the export_bins)


@hdunham how does this suggestion differ from export_bins_by_tech?

zolanaj

Approval of big-M implementation

this is all now in cost-to-utility branch

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+    m = Model(optimizer_with_attributes(HiGHS.Optimizer, "output_flag" => false, "log_to_console" => false))
+    results = run_reopt(m, p)
+    open("debug_results.json","w") do f
+        JSON.print(f, results, 4)
+    end


+    d["ElectricUtility"]["allow_simultaneous_export_import"] = false
+    m = Model(optimizer_with_attributes(HiGHS.Optimizer, "output_flag" => false, "log_to_console" => false))
+    results = run_reopt(m, d)
+    open("debug_results2.json","w") do f
+        JSON.print(f, results, 4)
+    end


+    # d["ElectricStorage"]["can_wholesale"] = true
+    d["ElectricStorage"]["can_export_beyond_nem_limit"] = true
+    p = REoptInputs(d)
+    println(p.export_bins_by_storage["ElectricStorage"])


        @testset "January Export Rates" begin
            model = Model(optimizer_with_attributes(HiGHS.Optimizer, "output_flag" => false, "log_to_console" => false))
            data = JSON.parsefile("./scenarios/monthly_rate.json")

-            # create wholesale_rate with compensation in January > retail rate
+            # 1) create wholesale_rate with compensation in January > retail rate
+            # and check that PV exports instead of serving load
            jan_rate = data["ElectricTariff"]["monthly_energy_rates"][1]
            data["ElectricTariff"]["wholesale_rate"] =
                append!(repeat([jan_rate + 0.1], 31 * 24), repeat([0.0], 8760 - 31*24))
            data["ElectricTariff"]["monthly_demand_rates"] = repeat([0], 12)

+            model = Model(optimizer_with_attributes(HiGHS.Optimizer, "output_flag" => false, "log_to_console" => false))
            s = Scenario(data)


 	m[:AnnualOnsiteREEleckWh] = @expression(m, p.hours_per_time_step * (
+			#total RE elec generation, excl steam turbine
 			sum(p.production_factor[t,ts] * p.levelization_factor[t] * m[:dvRatedProduction][t,ts] * 
 				p.tech_renewable_energy_fraction[t] for t in setdiff(p.techs.elec, p.techs.steam_turbine), ts in p.time_steps
-			) - #total RE elec generation, excl steam turbine
-			sum(m[:dvProductionToStorage][b,t,ts]*p.tech_renewable_energy_fraction[t]*(
+			)
+			#minus battery efficiency losses
+			- sum(m[:dvProductionToStorage][b,t,ts]*p.tech_renewable_energy_fraction[t]*(
 				1-p.s.storage.attr[b].charge_efficiency*p.s.storage.attr[b].discharge_efficiency) 
 				for t in setdiff(p.techs.elec, p.techs.steam_turbine), b in p.s.storage.types.elec, ts in p.time_steps
-			) - #minus battery efficiency losses
-			sum(m[:dvCurtail][t,ts] * p.tech_renewable_energy_fraction[t] 
+			)
+			# minus curtailment
+			- sum(m[:dvCurtail][t,ts] * p.tech_renewable_energy_fraction[t] 
 				for t in setdiff(p.techs.elec, p.techs.steam_turbine), ts in p.time_steps
-			) - # minus curtailment
-			(1 - p.s.site.include_exported_renewable_electricity_in_total) *
+			)
+			# minus exported RE, if RE accounting method = 0.
+			- (1 - p.s.site.include_exported_renewable_electricity_in_total) *
 			sum(m[:dvProductionToGrid][t,u,ts]*p.tech_renewable_energy_fraction[t] 
 				for t in setdiff(p.techs.elec, p.techs.steam_turbine), u in p.export_bins_by_tech[t], ts in p.time_steps
-			) # minus exported RE, if RE accounting method = 0.
+			)
+			# TODO: battery can now discharge to the grid, but this export is not yet accounted for in the RE calculation. 
+			# 	This is only relevant if include_exported_renewable_electricity_in_total = false. If false, the 
+			# 	battery could become a "back door" for export of RE to the grid since it's not subtracted here. Will require tracking of RE in BESS. 
 		)


+    if !isempty(vcat(NEM_techs, NEM_storage))
        # Constraint (9c): Net metering only -- can't sell more than you purchase
        # hours_per_time_step is cancelled on both sides, but used for unit consistency (convert power to energy)
        @constraint(m,
-            p.hours_per_time_step * sum( m[Symbol("dvProductionToGrid"*_n)][t, :NEM, ts] 
-            for t in NEM_techs, ts in p.time_steps)
+            p.hours_per_time_step * (
+                sum( m[Symbol("dvProductionToGrid"*_n)][t, :NEM, ts] for t in NEM_techs, ts in p.time_steps) + 
+                sum( m[Symbol("dvStorageToGrid"*_n)][b, :NEM, ts] for b in NEM_storage, ts in p.time_steps)
+            )
            <= p.hours_per_time_step * sum( m[Symbol("dvGridPurchase"*_n)][ts, tier]
                for ts in p.time_steps, tier in 1:p.s.electric_tariff.n_energy_tiers)
        )


        binGHP[p.ghp_options], Bin  # Can be <= 1 if require_ghp_purchase=0, and is ==1 if require_ghp_purchase=1
+		dvNetLoad[p.time_steps]  # Net load after on-site generation and storage [kW]
 	end


adfarth and others added 15 commits January 7, 2025 08:52

initial commit

a6c74d0

Merge branch 'develop' into bess-export

bb9cbfb

start adding inputs

3cebd7e

Merge branch 'develop' into bess-export

1575a9b

rm can_grid_charge

b211b44

set up framework

e065d2f

Merge branch 'develop' into bess-export

a8b2dca

update electric_utility_constraints

52f036b

make discharge from storage total discharge

47bfc79

update results

8d9be52

fix reopt_inputs

b897e47

Merge branch 'develop' into bess-export

946f8a0

fix indexing

5ac4c84

Update inputs.jl

a302d7f

add todo

ae2f872

hdunham reviewed Jun 4, 2025

View reviewed changes

hdunham added 2 commits June 10, 2025 10:36

Update CHANGELOG.md

f823ae4

condense 4 constraints into 1

9322adf