diff --git a/src/instance/read.jl b/src/instance/read.jl
index 635be8d..b095b0a 100644
--- a/src/instance/read.jl
+++ b/src/instance/read.jl
@@ -129,7 +129,7 @@ end
 
 function _from_json(json; repair = true)::UnitCommitmentScenario
     _migrate(json)
-    units = Unit[]
+    thermal_units = ThermalUnit[]
     buses = Bus[]
     contingencies = Contingency[]
     lines = TransmissionLine[]
@@ -160,7 +160,7 @@ function _from_json(json; repair = true)::UnitCommitmentScenario
 
     name_to_bus = Dict{String,Bus}()
     name_to_line = Dict{String,TransmissionLine}()
-    name_to_unit = Dict{String,Unit}()
+    name_to_unit = Dict{String,ThermalUnit}()
     name_to_reserve = Dict{String,Reserve}()
 
     function timeseries(x; default = nothing)
@@ -181,7 +181,7 @@ function _from_json(json; repair = true)::UnitCommitmentScenario
             bus_name,
             length(buses),
             timeseries(dict["Load (MW)"]),
-            Unit[],
+            ThermalUnit[],
             PriceSensitiveLoad[],
             ProfiledUnit[],
         )
@@ -196,7 +196,7 @@ function _from_json(json; repair = true)::UnitCommitmentScenario
                 name = reserve_name,
                 type = lowercase(dict["Type"]),
                 amount = timeseries(dict["Amount (MW)"]),
-                units = [],
+                thermal_units = [],
                 shortfall_penalty = scalar(
                     dict["Shortfall penalty (\$/MW)"],
                     default = -1,
@@ -282,7 +282,7 @@ function _from_json(json; repair = true)::UnitCommitmentScenario
                 initial_status *= time_multiplier
             end
 
-            unit = Unit(
+            unit = ThermalUnit(
                 unit_name,
                 bus,
                 max_power,
@@ -303,12 +303,12 @@ function _from_json(json; repair = true)::UnitCommitmentScenario
                 startup_categories,
                 unit_reserves,
             )
-            push!(bus.units, unit)
+            push!(bus.thermal_units, unit)
             for r in unit_reserves
-                push!(r.units, unit)
+                push!(r.thermal_units, unit)
             end
             name_to_unit[unit_name] = unit
-            push!(units, unit)
+            push!(thermal_units, unit)
         elseif lowercase(unit_type) === "profiled"
             bus = name_to_bus[dict["Bus"]]
             pu = ProfiledUnit(
@@ -355,7 +355,7 @@ function _from_json(json; repair = true)::UnitCommitmentScenario
     # Read contingencies
     if "Contingencies" in keys(json)
         for (cont_name, dict) in json["Contingencies"]
-            affected_units = Unit[]
+            affected_units = ThermalUnit[]
             affected_lines = TransmissionLine[]
             if "Affected lines" in keys(dict)
                 affected_lines =
@@ -400,8 +400,8 @@ function _from_json(json; repair = true)::UnitCommitmentScenario
         reserves = reserves,
         reserves_by_name = name_to_reserve,
         time = T,
-        units_by_name = Dict(g.name => g for g in units),
-        units = units,
+        thermal_units_by_name = Dict(g.name => g for g in thermal_units),
+        thermal_units = thermal_units,
         profiled_units_by_name = Dict(pu.name => pu for pu in profiled_units),
         profiled_units = profiled_units,
         isf = spzeros(Float64, length(lines), length(buses) - 1),
diff --git a/src/instance/structs.jl b/src/instance/structs.jl
index 88a64fd..9d6cc5c 100644
--- a/src/instance/structs.jl
+++ b/src/instance/structs.jl
@@ -6,7 +6,7 @@ mutable struct Bus
     name::String
     offset::Int
     load::Vector{Float64}
-    units::Vector
+    thermal_units::Vector
     price_sensitive_loads::Vector
     profiled_units::Vector
 end
@@ -25,11 +25,11 @@ Base.@kwdef mutable struct Reserve
     name::String
     type::String
     amount::Vector{Float64}
-    units::Vector
+    thermal_units::Vector
     shortfall_penalty::Float64
 end
 
-mutable struct Unit
+mutable struct ThermalUnit
     name::String
     bus::Bus
     max_power::Vector{Float64}
@@ -64,7 +64,7 @@ end
 mutable struct Contingency
     name::String
     lines::Vector{TransmissionLine}
-    units::Vector{Unit}
+    thermal_units::Vector{ThermalUnit}
 end
 
 mutable struct PriceSensitiveLoad
@@ -95,13 +95,13 @@ Base.@kwdef mutable struct UnitCommitmentScenario
     price_sensitive_loads_by_name::Dict{AbstractString,PriceSensitiveLoad}
     price_sensitive_loads::Vector{PriceSensitiveLoad}
     probability::Float64
+    profiled_units_by_name::Dict{AbstractString,ProfiledUnit}
+    profiled_units::Vector{ProfiledUnit}
     reserves_by_name::Dict{AbstractString,Reserve}
     reserves::Vector{Reserve}
+    thermal_units_by_name::Dict{AbstractString,ThermalUnit}
+    thermal_units::Vector{ThermalUnit}
     time::Int
-    units_by_name::Dict{AbstractString,Unit}
-    units::Vector{Unit}
-    profiled_units_by_name::Dict{AbstractString,ProfiledUnit}
-    profiled_units::Vector{ProfiledUnit}
 end
 
 Base.@kwdef mutable struct UnitCommitmentInstance
@@ -113,12 +113,12 @@ function Base.show(io::IO, instance::UnitCommitmentInstance)
     sc = instance.scenarios[1]
     print(io, "UnitCommitmentInstance(")
     print(io, "$(length(instance.scenarios)) scenarios, ")
-    print(io, "$(length(sc.units)) units, ")
+    print(io, "$(length(sc.thermal_units)) thermal units, ")
+    print(io, "$(length(sc.profiled_units)) profiled units, ")
     print(io, "$(length(sc.buses)) buses, ")
     print(io, "$(length(sc.lines)) lines, ")
     print(io, "$(length(sc.contingencies)) contingencies, ")
     print(io, "$(length(sc.price_sensitive_loads)) price sensitive loads, ")
-    print(io, "$(length(sc.profiled_units)) profiled units, ")
     print(io, "$(instance.time) time steps")
     print(io, ")")
     return
diff --git a/src/lmp/aelmp.jl b/src/lmp/aelmp.jl
index 71278f1..7afd350 100644
--- a/src/lmp/aelmp.jl
+++ b/src/lmp/aelmp.jl
@@ -131,7 +131,7 @@ function _aelmp_check_parameters(
             )
         end
     end
-    all_units = sc.units
+    all_units = sc.thermal_units
     # CHECK: model cannot handle non-fast-starts (MISO Phase I: can ONLY solve fast-starts)
     if any(u -> u.min_uptime > 1 || u.min_downtime > 1, all_units)
         error(
@@ -159,25 +159,25 @@ function _modify_scenario!(
     if !method.allow_offline_participation
         # 1. remove (if NOT allowing) the offline generators
         units_to_remove = []
-        for unit in sc.units
+        for unit in sc.thermal_units
             # remove based on the solved UC model result
             # remove the unit if it is never on
             if all(t -> value(model[:is_on][unit.name, t]) == 0, sc.time)
                 # unregister from the bus 
-                filter!(x -> x.name != unit.name, unit.bus.units)
+                filter!(x -> x.name != unit.name, unit.bus.thermal_units)
                 # unregister from the reserve
                 for r in unit.reserves
-                    filter!(x -> x.name != unit.name, r.units)
+                    filter!(x -> x.name != unit.name, r.thermal_units)
                 end
                 # append the name to the remove list
                 push!(units_to_remove, unit.name)
             end
         end
         # unregister the units from the remove list
-        filter!(x -> !(x.name in units_to_remove), sc.units)
+        filter!(x -> !(x.name in units_to_remove), sc.thermal_units)
     end
 
-    for unit in sc.units
+    for unit in sc.thermal_units
         # 2. set min generation requirement to 0 by adding 0 to production curve and cost 
         # min_power & min_costs are vectors with dimension T
         if unit.min_power[1] != 0
@@ -207,5 +207,6 @@ function _modify_scenario!(
         unit.startup_categories =
             StartupCategory[StartupCategory(0, first_startup_cost)]
     end
-    return sc.units_by_name = Dict(g.name => g for g in sc.units)
+    return sc.thermal_units_by_name =
+        Dict(g.name => g for g in sc.thermal_units)
 end
diff --git a/src/model/build.jl b/src/model/build.jl
index 1bd1987..a812011 100644
--- a/src/model/build.jl
+++ b/src/model/build.jl
@@ -77,7 +77,7 @@ function build_model(;
         end
         model[:obj] = AffExpr()
         model[:instance] = instance
-        for g in instance.scenarios[1].units
+        for g in instance.scenarios[1].thermal_units
             _add_unit_commitment!(model, g, formulation)
         end
         for sc in instance.scenarios
@@ -93,7 +93,7 @@ function build_model(;
             for ps in sc.price_sensitive_loads
                 _add_price_sensitive_load!(model, ps, sc)
             end
-            for g in sc.units
+            for g in sc.thermal_units
                 _add_unit_dispatch!(model, g, formulation, sc)
             end
             for pu in sc.profiled_units
diff --git a/src/model/formulations/ArrCon2000/ramp.jl b/src/model/formulations/ArrCon2000/ramp.jl
index a043311..3bd48b5 100644
--- a/src/model/formulations/ArrCon2000/ramp.jl
+++ b/src/model/formulations/ArrCon2000/ramp.jl
@@ -4,7 +4,7 @@
 
 function _add_ramp_eqs!(
     model::JuMP.Model,
-    g::Unit,
+    g::ThermalUnit,
     formulation_prod_vars::Gar1962.ProdVars,
     formulation_ramping::ArrCon2000.Ramping,
     formulation_status_vars::Gar1962.StatusVars,
diff --git a/src/model/formulations/CarArr2006/pwlcosts.jl b/src/model/formulations/CarArr2006/pwlcosts.jl
index 9b236f7..2e133f3 100644
--- a/src/model/formulations/CarArr2006/pwlcosts.jl
+++ b/src/model/formulations/CarArr2006/pwlcosts.jl
@@ -4,7 +4,7 @@
 
 function _add_production_piecewise_linear_eqs!(
     model::JuMP.Model,
-    g::Unit,
+    g::ThermalUnit,
     formulation_prod_vars::Gar1962.ProdVars,
     formulation_pwl_costs::CarArr2006.PwlCosts,
     formulation_status_vars::StatusVarsFormulation,
diff --git a/src/model/formulations/DamKucRajAta2016/ramp.jl b/src/model/formulations/DamKucRajAta2016/ramp.jl
index fa380c3..304430c 100644
--- a/src/model/formulations/DamKucRajAta2016/ramp.jl
+++ b/src/model/formulations/DamKucRajAta2016/ramp.jl
@@ -4,7 +4,7 @@
 
 function _add_ramp_eqs!(
     model::JuMP.Model,
-    g::Unit,
+    g::ThermalUnit,
     formulation_prod_vars::Gar1962.ProdVars,
     formulation_ramping::DamKucRajAta2016.Ramping,
     formulation_status_vars::Gar1962.StatusVars,
diff --git a/src/model/formulations/Gar1962/prod.jl b/src/model/formulations/Gar1962/prod.jl
index 3e70a04..c7b8308 100644
--- a/src/model/formulations/Gar1962/prod.jl
+++ b/src/model/formulations/Gar1962/prod.jl
@@ -4,7 +4,7 @@
 
 function _add_production_vars!(
     model::JuMP.Model,
-    g::Unit,
+    g::ThermalUnit,
     formulation_prod_vars::Gar1962.ProdVars,
     sc::UnitCommitmentScenario,
 )::Nothing
@@ -21,7 +21,7 @@ end
 
 function _add_production_limit_eqs!(
     model::JuMP.Model,
-    g::Unit,
+    g::ThermalUnit,
     formulation_prod_vars::Gar1962.ProdVars,
     sc::UnitCommitmentScenario,
 )::Nothing
diff --git a/src/model/formulations/Gar1962/pwlcosts.jl b/src/model/formulations/Gar1962/pwlcosts.jl
index 62d0b5c..94ac942 100644
--- a/src/model/formulations/Gar1962/pwlcosts.jl
+++ b/src/model/formulations/Gar1962/pwlcosts.jl
@@ -4,7 +4,7 @@
 
 function _add_production_piecewise_linear_eqs!(
     model::JuMP.Model,
-    g::Unit,
+    g::ThermalUnit,
     formulation_prod_vars::Gar1962.ProdVars,
     formulation_pwl_costs::Gar1962.PwlCosts,
     formulation_status_vars::Gar1962.StatusVars,
diff --git a/src/model/formulations/Gar1962/status.jl b/src/model/formulations/Gar1962/status.jl
index 2a4a911..ea57258 100644
--- a/src/model/formulations/Gar1962/status.jl
+++ b/src/model/formulations/Gar1962/status.jl
@@ -4,7 +4,7 @@
 
 function _add_status_vars!(
     model::JuMP.Model,
-    g::Unit,
+    g::ThermalUnit,
     formulation_status_vars::Gar1962.StatusVars,
 )::Nothing
     is_on = _init(model, :is_on)
@@ -27,7 +27,7 @@ end
 
 function _add_status_eqs!(
     model::JuMP.Model,
-    g::Unit,
+    g::ThermalUnit,
     formulation_status_vars::Gar1962.StatusVars,
 )::Nothing
     eq_binary_link = _init(model, :eq_binary_link)
diff --git a/src/model/formulations/KnuOstWat2018/pwlcosts.jl b/src/model/formulations/KnuOstWat2018/pwlcosts.jl
index 0da8217..d3d4bdb 100644
--- a/src/model/formulations/KnuOstWat2018/pwlcosts.jl
+++ b/src/model/formulations/KnuOstWat2018/pwlcosts.jl
@@ -4,7 +4,7 @@
 
 function _add_production_piecewise_linear_eqs!(
     model::JuMP.Model,
-    g::Unit,
+    g::ThermalUnit,
     formulation_prod_vars::Gar1962.ProdVars,
     formulation_pwl_costs::KnuOstWat2018.PwlCosts,
     formulation_status_vars::Gar1962.StatusVars,
diff --git a/src/model/formulations/MorLatRam2013/ramp.jl b/src/model/formulations/MorLatRam2013/ramp.jl
index 90afd71..29d56e3 100644
--- a/src/model/formulations/MorLatRam2013/ramp.jl
+++ b/src/model/formulations/MorLatRam2013/ramp.jl
@@ -4,7 +4,7 @@
 
 function _add_ramp_eqs!(
     model::JuMP.Model,
-    g::Unit,
+    g::ThermalUnit,
     formulation_prod_vars::Gar1962.ProdVars,
     formulation_ramping::MorLatRam2013.Ramping,
     formulation_status_vars::Gar1962.StatusVars,
diff --git a/src/model/formulations/MorLatRam2013/scosts.jl b/src/model/formulations/MorLatRam2013/scosts.jl
index 2d68747..ce565c7 100644
--- a/src/model/formulations/MorLatRam2013/scosts.jl
+++ b/src/model/formulations/MorLatRam2013/scosts.jl
@@ -4,7 +4,7 @@
 
 function _add_startup_cost_eqs!(
     model::JuMP.Model,
-    g::Unit,
+    g::ThermalUnit,
     formulation::MorLatRam2013.StartupCosts,
 )::Nothing
     eq_startup_choose = _init(model, :eq_startup_choose)
diff --git a/src/model/formulations/PanGua2016/ramp.jl b/src/model/formulations/PanGua2016/ramp.jl
index 62a83ba..511f91f 100644
--- a/src/model/formulations/PanGua2016/ramp.jl
+++ b/src/model/formulations/PanGua2016/ramp.jl
@@ -4,7 +4,7 @@
 
 function _add_ramp_eqs!(
     model::JuMP.Model,
-    g::Unit,
+    g::ThermalUnit,
     formulation_prod_vars::Gar1962.ProdVars,
     formulation_ramping::PanGua2016.Ramping,
     formulation_status_vars::Gar1962.StatusVars,
diff --git a/src/model/formulations/WanHob2016/ramp.jl b/src/model/formulations/WanHob2016/ramp.jl
index 417d2a3..e634fc2 100644
--- a/src/model/formulations/WanHob2016/ramp.jl
+++ b/src/model/formulations/WanHob2016/ramp.jl
@@ -4,7 +4,7 @@
 
 function _add_ramp_eqs!(
     model::JuMP.Model,
-    g::Unit,
+    g::ThermalUnit,
     ::Gar1962.ProdVars,
     ::WanHob2016.Ramping,
     ::Gar1962.StatusVars,
diff --git a/src/model/formulations/base/system.jl b/src/model/formulations/base/system.jl
index 1591db4..7291648 100644
--- a/src/model/formulations/base/system.jl
+++ b/src/model/formulations/base/system.jl
@@ -53,7 +53,7 @@ function _add_spinning_reserve_eqs!(
                 model,
                 sum(
                     model[:reserve][sc.name, r.name, g.name, t] for
-                    g in r.units
+                    g in r.thermal_units
                 ) + model[:reserve_shortfall][sc.name, r.name, t] >=
                 r.amount[t]
             )
@@ -91,7 +91,7 @@ function _add_flexiramp_reserve_eqs!(
                 model,
                 sum(
                     model[:upflexiramp][sc.name, r.name, g.name, t] for
-                    g in r.units
+                    g in r.thermal_units
                 ) + model[:upflexiramp_shortfall][sc.name, r.name, t] >=
                 r.amount[t]
             )
@@ -100,7 +100,7 @@ function _add_flexiramp_reserve_eqs!(
                 model,
                 sum(
                     model[:dwflexiramp][sc.name, r.name, g.name, t] for
-                    g in r.units
+                    g in r.thermal_units
                 ) + model[:dwflexiramp_shortfall][sc.name, r.name, t] >=
                 r.amount[t]
             )
diff --git a/src/model/formulations/base/unit.jl b/src/model/formulations/base/unit.jl
index 27cbba6..06b18a2 100644
--- a/src/model/formulations/base/unit.jl
+++ b/src/model/formulations/base/unit.jl
@@ -6,7 +6,7 @@
 # related to the binary commitment, startup and shutdown decisions of units
 function _add_unit_commitment!(
     model::JuMP.Model,
-    g::Unit,
+    g::ThermalUnit,
     formulation::Formulation,
 )
     if !all(g.must_run) && any(g.must_run)
@@ -31,7 +31,7 @@ end
 # related to the continuous dispatch decisions of units
 function _add_unit_dispatch!(
     model::JuMP.Model,
-    g::Unit,
+    g::ThermalUnit,
     formulation::Formulation,
     sc::UnitCommitmentScenario,
 )
@@ -64,11 +64,11 @@ function _add_unit_dispatch!(
     return
 end
 
-_is_initially_on(g::Unit)::Float64 = (g.initial_status > 0 ? 1.0 : 0.0)
+_is_initially_on(g::ThermalUnit)::Float64 = (g.initial_status > 0 ? 1.0 : 0.0)
 
 function _add_spinning_reserve_vars!(
     model::JuMP.Model,
-    g::Unit,
+    g::ThermalUnit,
     sc::UnitCommitmentScenario,
 )::Nothing
     reserve = _init(model, :reserve)
@@ -92,7 +92,7 @@ end
 
 function _add_flexiramp_reserve_vars!(
     model::JuMP.Model,
-    g::Unit,
+    g::ThermalUnit,
     sc::UnitCommitmentScenario,
 )::Nothing
     upflexiramp = _init(model, :upflexiramp)
@@ -128,7 +128,7 @@ function _add_flexiramp_reserve_vars!(
     return
 end
 
-function _add_startup_shutdown_vars!(model::JuMP.Model, g::Unit)::Nothing
+function _add_startup_shutdown_vars!(model::JuMP.Model, g::ThermalUnit)::Nothing
     startup = _init(model, :startup)
     for t in 1:model[:instance].time
         for s in 1:length(g.startup_categories)
@@ -140,7 +140,7 @@ end
 
 function _add_startup_shutdown_limit_eqs!(
     model::JuMP.Model,
-    g::Unit,
+    g::ThermalUnit,
     sc::UnitCommitmentScenario,
 )::Nothing
     eq_shutdown_limit = _init(model, :eq_shutdown_limit)
@@ -179,7 +179,7 @@ end
 
 function _add_ramp_eqs!(
     model::JuMP.Model,
-    g::Unit,
+    g::ThermalUnit,
     formulation::RampingFormulation,
     sc::UnitCommitmentScenario,
 )::Nothing
@@ -224,7 +224,10 @@ function _add_ramp_eqs!(
     end
 end
 
-function _add_min_uptime_downtime_eqs!(model::JuMP.Model, g::Unit)::Nothing
+function _add_min_uptime_downtime_eqs!(
+    model::JuMP.Model,
+    g::ThermalUnit,
+)::Nothing
     is_on = model[:is_on]
     switch_off = model[:switch_off]
     switch_on = model[:switch_on]
@@ -269,7 +272,7 @@ end
 
 function _add_net_injection_eqs!(
     model::JuMP.Model,
-    g::Unit,
+    g::ThermalUnit,
     sc::UnitCommitmentScenario,
 )::Nothing
     expr_net_injection = model[:expr_net_injection]
diff --git a/src/solution/fix.jl b/src/solution/fix.jl
index ca7703d..3ce6170 100644
--- a/src/solution/fix.jl
+++ b/src/solution/fix.jl
@@ -16,7 +16,7 @@ function fix!(model::JuMP.Model, solution::AbstractDict)::Nothing
     prod_above = model[:prod_above]
     reserve = model[:reserve]
     for sc in instance.scenarios
-        for g in sc.units
+        for g in sc.thermal_units
             for t in 1:T
                 is_on_value = round(solution[sc.name]["Is on"][g.name][t])
                 prod_value = round(
@@ -33,7 +33,7 @@ function fix!(model::JuMP.Model, solution::AbstractDict)::Nothing
         end
         for r in sc.reserves
             r.type == "spinning" || continue
-            for g in r.units
+            for g in r.thermal_units
                 for t in 1:T
                     reserve_value = round(
                         solution[sc.name]["Spinning reserve (MW)"][r.name][g.name][t],
diff --git a/src/solution/solution.jl b/src/solution/solution.jl
index 25666a2..3ee9dbc 100644
--- a/src/solution/solution.jl
+++ b/src/solution/solution.jl
@@ -65,17 +65,21 @@ function solution(model::JuMP.Model)::OrderedDict
     sol = OrderedDict()
     for sc in instance.scenarios
         sol[sc.name] = OrderedDict()
-        if !isempty(sc.units)
-            sol[sc.name]["Production (MW)"] =
-                OrderedDict(g.name => production(g, sc) for g in sc.units)
-            sol[sc.name]["Production cost (\$)"] =
-                OrderedDict(g.name => production_cost(g, sc) for g in sc.units)
-            sol[sc.name]["Startup cost (\$)"] =
-                OrderedDict(g.name => startup_cost(g, sc) for g in sc.units)
-            sol[sc.name]["Is on"] = timeseries(model[:is_on], sc.units)
-            sol[sc.name]["Switch on"] = timeseries(model[:switch_on], sc.units)
+        if !isempty(sc.thermal_units)
+            sol[sc.name]["Production (MW)"] = OrderedDict(
+                g.name => production(g, sc) for g in sc.thermal_units
+            )
+            sol[sc.name]["Production cost (\$)"] = OrderedDict(
+                g.name => production_cost(g, sc) for g in sc.thermal_units
+            )
+            sol[sc.name]["Startup cost (\$)"] = OrderedDict(
+                g.name => startup_cost(g, sc) for g in sc.thermal_units
+            )
+            sol[sc.name]["Is on"] = timeseries(model[:is_on], sc.thermal_units)
+            sol[sc.name]["Switch on"] =
+                timeseries(model[:switch_on], sc.thermal_units)
             sol[sc.name]["Switch off"] =
-                timeseries(model[:switch_off], sc.units)
+                timeseries(model[:switch_off], sc.thermal_units)
             sol[sc.name]["Net injection (MW)"] =
                 timeseries(model[:net_injection], sc.buses, sc = sc)
             sol[sc.name]["Load curtail (MW)"] =
@@ -103,7 +107,7 @@ function solution(model::JuMP.Model)::OrderedDict
             r.name => OrderedDict(
                 g.name => [
                     value(model[:reserve][sc.name, r.name, g.name, t]) for t in 1:instance.time
-                ] for g in r.units
+                ] for g in r.thermal_units
             ) for r in sc.reserves if r.type == "spinning"
         )
         sol[sc.name]["Spinning reserve shortfall (MW)"] = OrderedDict(
@@ -116,7 +120,7 @@ function solution(model::JuMP.Model)::OrderedDict
             r.name => OrderedDict(
                 g.name => [
                     value(model[:upflexiramp][sc.name, r.name, g.name, t]) for t in 1:instance.time
-                ] for g in r.units
+                ] for g in r.thermal_units
             ) for r in sc.reserves if r.type == "flexiramp"
         )
         sol[sc.name]["Up-flexiramp shortfall (MW)"] = OrderedDict(
@@ -128,7 +132,7 @@ function solution(model::JuMP.Model)::OrderedDict
             r.name => OrderedDict(
                 g.name => [
                     value(model[:dwflexiramp][sc.name, r.name, g.name, t]) for t in 1:instance.time
-                ] for g in r.units
+                ] for g in r.thermal_units
             ) for r in sc.reserves if r.type == "flexiramp"
         )
         sol[sc.name]["Down-flexiramp shortfall (MW)"] = OrderedDict(
diff --git a/src/solution/warmstart.jl b/src/solution/warmstart.jl
index 678f250..c9fba50 100644
--- a/src/solution/warmstart.jl
+++ b/src/solution/warmstart.jl
@@ -5,7 +5,7 @@
 function set_warm_start!(model::JuMP.Model, solution::AbstractDict)::Nothing
     instance, T = model[:instance], model[:instance].time
     is_on = model[:is_on]
-    for g in instance.units
+    for g in instance.thermal_units
         for t in 1:T
             JuMP.set_start_value(is_on[g.name, t], solution["Is on"][g.name][t])
             JuMP.set_start_value(
diff --git a/src/transform/initcond.jl b/src/transform/initcond.jl
index cfbce02..697d4fd 100644
--- a/src/transform/initcond.jl
+++ b/src/transform/initcond.jl
@@ -15,7 +15,7 @@ function generate_initial_conditions!(
     sc::UnitCommitmentScenario,
     optimizer,
 )::Nothing
-    G = sc.units
+    G = sc.thermal_units
     B = sc.buses
     t = 1
     mip = JuMP.Model(optimizer)
diff --git a/src/transform/randomize/XavQiuAhm2021.jl b/src/transform/randomize/XavQiuAhm2021.jl
index b60cafd..630c7f0 100644
--- a/src/transform/randomize/XavQiuAhm2021.jl
+++ b/src/transform/randomize/XavQiuAhm2021.jl
@@ -123,7 +123,7 @@ function _randomize_costs(
     sc::UnitCommitmentScenario,
     distribution,
 )::Nothing
-    for unit in sc.units
+    for unit in sc.thermal_units
         α = rand(rng, distribution)
         unit.min_power_cost *= α
         for k in unit.cost_segments
@@ -168,7 +168,7 @@ function _randomize_load_profile(
         )
         push!(system_load, system_load[t-1] * gamma)
     end
-    capacity = sum(maximum(u.max_power) for u in sc.units)
+    capacity = sum(maximum(u.max_power) for u in sc.thermal_units)
     peak_load = rand(rng, params.peak_load) * capacity
     system_load = system_load ./ maximum(system_load) .* peak_load
 
diff --git a/src/transform/slice.jl b/src/transform/slice.jl
index e1c6799..051e105 100644
--- a/src/transform/slice.jl
+++ b/src/transform/slice.jl
@@ -29,7 +29,7 @@ function slice(
         for r in sc.reserves
             r.amount = r.amount[range]
         end
-        for u in sc.units
+        for u in sc.thermal_units
             u.max_power = u.max_power[range]
             u.min_power = u.min_power[range]
             u.must_run = u.must_run[range]
diff --git a/src/validation/repair.jl b/src/validation/repair.jl
index 50ee614..440854e 100644
--- a/src/validation/repair.jl
+++ b/src/validation/repair.jl
@@ -15,7 +15,7 @@ Returns the number of validation errors found.
 function repair!(sc::UnitCommitmentScenario)::Int
     n_errors = 0
 
-    for g in sc.units
+    for g in sc.thermal_units
 
         # Startup costs and delays must be increasing
         for s in 2:length(g.startup_categories)
diff --git a/src/validation/validate.jl b/src/validation/validate.jl
index be8234d..88ee36f 100644
--- a/src/validation/validate.jl
+++ b/src/validation/validate.jl
@@ -45,7 +45,7 @@ end
 function _validate_units(instance::UnitCommitmentInstance, solution; tol = 0.01)
     err_count = 0
     for sc in instance.scenarios
-        for unit in sc.units
+        for unit in sc.thermal_units
             production = solution[sc.name]["Production (MW)"][unit.name]
             reserve = [0.0 for _ in 1:instance.time]
             spinning_reserves =
@@ -114,7 +114,7 @@ function _validate_units(instance::UnitCommitmentInstance, solution; tol = 0.01)
                 # Verify reserve eligibility
                 for r in sc.reserves
                     if r.type == "spinning"
-                        if unit ∉ r.units && (
+                        if unit ∉ r.thermal_units && (
                             unit in keys(
                                 solution[sc.name]["Spinning reserve (MW)"][r.name],
                             )
@@ -324,7 +324,7 @@ function _validate_reserve_and_demand(instance, solution, tol = 0.01)
             end
             production = sum(
                 solution[sc.name]["Production (MW)"][g.name][t] for
-                g in sc.units
+                g in sc.thermal_units
             )
             if "Load curtail (MW)" in keys(solution)
                 load_curtail = sum(
@@ -352,7 +352,7 @@ function _validate_reserve_and_demand(instance, solution, tol = 0.01)
                 if r.type == "spinning"
                     provided = sum(
                         solution[sc.name]["Spinning reserve (MW)"][r.name][g.name][t]
-                        for g in r.units
+                        for g in r.thermal_units
                     )
                     shortfall =
                         solution[sc.name]["Spinning reserve shortfall (MW)"][r.name][t]
@@ -371,7 +371,7 @@ function _validate_reserve_and_demand(instance, solution, tol = 0.01)
                 elseif r.type == "flexiramp"
                     upflexiramp = sum(
                         solution[sc.name]["Up-flexiramp (MW)"][r.name][g.name][t]
-                        for g in r.units
+                        for g in r.thermal_units
                     )
                     upflexiramp_shortfall =
                         solution[sc.name]["Up-flexiramp shortfall (MW)"][r.name][t]
@@ -389,7 +389,7 @@ function _validate_reserve_and_demand(instance, solution, tol = 0.01)
 
                     dwflexiramp = sum(
                         solution[sc.name]["Down-flexiramp (MW)"][r.name][g.name][t]
-                        for g in r.units
+                        for g in r.thermal_units
                     )
                     dwflexiramp_shortfall =
                         solution[sc.name]["Down-flexiramp shortfall (MW)"][r.name][t]
diff --git a/test/instance/migrate_test.jl b/test/instance/migrate_test.jl
index 3fe1e09..1176a01 100644
--- a/test/instance/migrate_test.jl
+++ b/test/instance/migrate_test.jl
@@ -9,14 +9,14 @@ using UnitCommitment, LinearAlgebra, Cbc, JuMP, JSON, GZip
     @test length(instance.scenarios) == 1
     sc = instance.scenarios[1]
     @test length(sc.reserves_by_name["r1"].amount) == 4
-    @test sc.units_by_name["g2"].reserves[1].name == "r1"
+    @test sc.thermal_units_by_name["g2"].reserves[1].name == "r1"
 end
 
 @testset "read v0.3" begin
     instance = UnitCommitment.read("$FIXTURES/ucjl-0.3.json.gz")
     @test length(instance.scenarios) == 1
     sc = instance.scenarios[1]
-    @test length(sc.units) == 6
+    @test length(sc.thermal_units) == 6
     @test length(sc.buses) == 14
     @test length(sc.lines) == 20
 end
diff --git a/test/instance/read_test.jl b/test/instance/read_test.jl
index 81e16d1..b7e27f0 100644
--- a/test/instance/read_test.jl
+++ b/test/instance/read_test.jl
@@ -8,15 +8,15 @@ using UnitCommitment, LinearAlgebra, Cbc, JuMP, JSON, GZip
     instance = UnitCommitment.read("$FIXTURES/case14.json.gz")
 
     @test repr(instance) == (
-        "UnitCommitmentInstance(1 scenarios, 6 units, 14 buses, " *
-        "20 lines, 19 contingencies, 1 price sensitive loads, 0 profiled units, 4 time steps)"
+        "UnitCommitmentInstance(1 scenarios, 6 thermal units, 0 profiled units, 14 buses, " *
+        "20 lines, 19 contingencies, 1 price sensitive loads, 4 time steps)"
     )
 
     @test length(instance.scenarios) == 1
     sc = instance.scenarios[1]
     @test length(sc.lines) == 20
     @test length(sc.buses) == 14
-    @test length(sc.units) == 6
+    @test length(sc.thermal_units) == 6
     @test length(sc.contingencies) == 19
     @test length(sc.price_sensitive_loads) == 1
     @test instance.time == 4
@@ -49,7 +49,7 @@ using UnitCommitment, LinearAlgebra, Cbc, JuMP, JSON, GZip
     @test sc.reserves[1].amount == [100.0, 100.0, 100.0, 100.0]
     @test sc.reserves_by_name["r1"].name == "r1"
 
-    unit = sc.units[1]
+    unit = sc.thermal_units[1]
     @test unit.name == "g1"
     @test unit.bus.name == "b1"
     @test unit.ramp_up_limit == 1e6
@@ -76,14 +76,14 @@ using UnitCommitment, LinearAlgebra, Cbc, JuMP, JSON, GZip
     @test unit.startup_categories[2].cost == 1500.0
     @test unit.startup_categories[3].cost == 2000.0
     @test length(unit.reserves) == 0
-    @test sc.units_by_name["g1"].name == "g1"
+    @test sc.thermal_units_by_name["g1"].name == "g1"
 
-    unit = sc.units[2]
+    unit = sc.thermal_units[2]
     @test unit.name == "g2"
     @test unit.must_run == [false for t in 1:4]
     @test length(unit.reserves) == 1
 
-    unit = sc.units[3]
+    unit = sc.thermal_units[3]
     @test unit.name == "g3"
     @test unit.bus.name == "b3"
     @test unit.ramp_up_limit == 70.0
@@ -106,7 +106,7 @@ using UnitCommitment, LinearAlgebra, Cbc, JuMP, JSON, GZip
     @test unit.reserves[1].name == "r1"
 
     @test sc.contingencies[1].lines == [sc.lines[1]]
-    @test sc.contingencies[1].units == []
+    @test sc.contingencies[1].thermal_units == []
     @test sc.contingencies[1].name == "c1"
     @test sc.contingencies_by_name["c1"].name == "c1"
 
@@ -121,7 +121,7 @@ end
 @testset "read_benchmark sub-hourly" begin
     instance = UnitCommitment.read("$FIXTURES/case14-sub-hourly.json.gz")
     @test instance.time == 4
-    unit = instance.scenarios[1].units[1]
+    unit = instance.scenarios[1].thermal_units[1]
     @test unit.name == "g1"
     @test unit.min_uptime == 2
     @test unit.min_downtime == 2
diff --git a/test/transform/initcond_test.jl b/test/transform/initcond_test.jl
index 11304bb..744eaf7 100644
--- a/test/transform/initcond_test.jl
+++ b/test/transform/initcond_test.jl
@@ -10,7 +10,7 @@ using UnitCommitment, Cbc, JuMP
     optimizer = optimizer_with_attributes(Cbc.Optimizer, "logLevel" => 0)
     sc = instance.scenarios[1]
     # All units should have unknown initial conditions
-    for g in sc.units
+    for g in sc.thermal_units
         @test g.initial_power === nothing
         @test g.initial_status === nothing
     end
@@ -19,7 +19,7 @@ using UnitCommitment, Cbc, JuMP
     UnitCommitment.generate_initial_conditions!(sc, optimizer)
 
     # All units should now have known initial conditions
-    for g in sc.units
+    for g in sc.thermal_units
         @test g.initial_power !== nothing
         @test g.initial_status !== nothing
     end
diff --git a/test/transform/randomize/XavQiuAhm2021_test.jl b/test/transform/randomize/XavQiuAhm2021_test.jl
index 226db47..2c1f473 100644
--- a/test/transform/randomize/XavQiuAhm2021_test.jl
+++ b/test/transform/randomize/XavQiuAhm2021_test.jl
@@ -21,7 +21,7 @@ test_approx(x, y) = @test isapprox(x, y, atol = 1e-3)
     @testset "cost and load share" begin
         sc = get_scenario()
         # Check original costs
-        unit = sc.units[10]
+        unit = sc.thermal_units[10]
         test_approx(unit.min_power_cost[1], 825.023)
         test_approx(unit.cost_segments[1].cost[1], 36.659)
         test_approx(unit.startup_categories[1].cost[1], 7570.42)
diff --git a/test/transform/slice_test.jl b/test/transform/slice_test.jl
index 173ebbb..f4bd8f5 100644
--- a/test/transform/slice_test.jl
+++ b/test/transform/slice_test.jl
@@ -13,7 +13,7 @@ using UnitCommitment, LinearAlgebra, Cbc, JuMP, JSON, GZip
     @test modified.time == 2
     @test length(sc.power_balance_penalty) == 2
     @test length(sc.reserves_by_name["r1"].amount) == 2
-    for u in sc.units
+    for u in sc.thermal_units
         @test length(u.max_power) == 2
         @test length(u.min_power) == 2
         @test length(u.must_run) == 2