Added page on Investments in docs

docs/make.jl

@@ -45,6 +45,7 @@ makedocs(
             "Constraint functions" => "manual/constraint-functions.md",
             "TransmissionMode structure" => "manual/transmission-mode.md",
             "Example" => "manual/simple-example.md",
+            "Investment options"=>"manual/investments.md",
             "Release notes" => "manual/NEWS.md",
         ],
         "How to" => Any[

docs/src/index.md

@@ -17,6 +17,7 @@ Pages = [
     "manual/optimization-variables.md",
     "manual/constraint-functions.md",
     "manual/transmission-mode.md",
+    "manual/investments.md",
     "manual/simple-example.md"
 ]
 Depth = 1

docs/src/manual/investments.md

@@ -0,0 +1,27 @@
+# [Adding investments](@id man-emi)
+
+Investment options are added through loading the package [`EnergyModelsInvestments`](https://energymodelsx.github.io/EnergyModelsInvestments.jl/).
+`EnergyModelsInvestments` was previously seen as extension package to `EnergyModelsBase`, that it was dependent on `EnergyModelsBase` and only allowed investment options in `EnergyModelsBase`.
+This approach was reversed from version 0.7 onwards and `EnergyModelsInvestments` is now a standalone package and provides an extension to `EnergyModelsBase`.
+
+As a consequence, it was not also necessary to move the `EnergyModelsGeography` extension of `EnergyModelsInvestments` to an `EnergyModelsInvestments` extension of `EnergyModelsGeography`.
+
+## [General concept](@id man-emi-gen)
+
+Investment options are added separately to each individual transmission mode through the field `data`.
+This is similar to the approach used in
+Hence, it is possible to use different prices for the same technology in different regions or allow investments only in a limited subset of technologies.
+
+Transmission mode investments utilize the same data type [`SingleInvData`] as the majority of the node investments.
+This type inludes as fields [`AbstractInvData`](@extref EnergyModelsInvestments.AbstractInvData) which can be either in the form of [`StartInvData`](@extref EnergyModelsInvestments.StartInvData) or [`NoStartInvData`](@extref EnergyModelsInvestments.NoStartInvData).
+The exact description of the individual investment data and their fields can be found in the *[public library]* of `EnergyModelsInvestments`.
+
+Investments require the application of an [`InvestmentModel`](@ref) instead of an [`OperationalModel`](@ref).
+This allows us to provide two core functions with new methods, `constraints_capacity_installed` (as described on *[Constraint functions]*), `variables_trans_capex`, a function previously not declaring any variables, and the update to the objective functoin `update_objective`.
+
+## [Added variables](@id man-emi-var)
+
+Investment options increase the number of variables.
+The individual variables are described in the *[documentation of `EnergyModelsInvestments`]*.
+
+All transmission modes with investments use the prefix `:trans`.