Allow assets to have continuous (non-tranched) capacities

docs/model/investment.md

@@ -123,13 +123,14 @@ The annualised fixed cost (AFC) per unit of capacity differs between the two cat
 
 ## Asset Capacities
 
-Every asset consists of one or more equal-capacity tranches. A single-tranche asset is retained or
-mothballed as a whole, while the tranches of a multi-tranche asset can be retained or mothballed
-independently (see [Mothballing and Decommissioning](#mothballing-and-decommissioning)).
+Every asset consists of either a continuous capacity or one or more equal-capacity tranches. A
+continuous-capacity asset, like a single-tranche asset, is retained or mothballed as a whole, while
+the tranches of a multi-tranche asset can be retained or mothballed independently (see
+[Mothballing and Decommissioning](#mothballing-and-decommissioning)).
 
 - For assets defined in `assets.csv`, an explicitly supplied `num_tranches` determines the tranche size.
   Otherwise, a process `tranche_size` determines the tranche size. If neither is supplied, the asset
-  consists of one tranche with its full capacity.
+  has continuous capacity.
 - Assets invested in _by MUSE_ are commissioned one tranche at a time, using the process
   `tranche_size` if defined, or a tranche size inferred from demand at the time of investment (see
   "trial capacity" below).

schemas/input/assets.yaml

@@ -23,8 +23,8 @@ fields:
       `capacity / num_tranches` (taking precedence over the process's `tranche_size`). If omitted and the
       process has a `tranche_size`, the asset is divided into `ceil(capacity / tranche_size)` tranches
       (note that rounding up the number of tranches can result in a total capacity greater than the
-      specified capacity). If both values are omitted, the asset is represented as one tranche with
-      the full asset capacity. Must be >0 if provided.
+      specified capacity). If both values are omitted, the asset has continuous capacity (it is not
+      divided into tranches). Must be >0 if provided.
   - name: commission_year
     type: integer
     description: The year in which to commission this asset

schemas/input/processes.yaml

@@ -39,4 +39,4 @@ fields:
       Optional (defaults to None). If present, must be >0. If no tranche size is specified, the tranche
       size for a MUSE2 investment is inferred from demand at the time of investment and
       `capacity_tranche_fraction`. For a user-provided asset, `num_tranches` in `assets.csv` can instead
-      determine the tranche size.
+      determine the tranche size; if neither is given, the asset has continuous capacity.

schemas/output/asset_capacities.yaml

@@ -13,10 +13,14 @@ fields:
     description: The total capacity of the asset in this year
   - name: num_tranches
     type: integer
-    description: The total number of tranches making up the asset in this year
+    description: |
+      The total number of tranches making up the asset in this year. Empty for assets with
+      continuous capacities
   - name: mothballed_capacity
     type: number
     description: The capacity of the asset that is mothballed in this year
   - name: mothballed_tranches
     type: integer
-    description: The number of tranches that are mothballed in this year
+    description: |
+      The number of tranches that are mothballed in this year. Empty for assets with continuous
+      capacities