Update flow_cap_min description (#672)

Co-authored-by: Stefan Pfenninger <[email protected]>

CHANGELOG.md

@@ -2,6 +2,8 @@
 
 ### User-facing changes
 
+|fixed| clarity of `flow_cap_min` description in documentation (#653).
+
 |changed| API/schema documentation is de-ranked in documentation search bar results (#670).
 
 |new| Math component cross-references in both directions ("uses" and "used in") in Markdown math documentation (#643).

src/calliope/config/model_def_schema.yaml

@@ -407,9 +407,16 @@ properties:
             x-type: float
             title: Minimum rated flow capacity.
             description: >-
-              Limits `flow_cap` to a minimum.
-              NOTE: this will _force_ `flow_cap` to a minimum value unless `cap_method` is set to `integer`.
-              If `cap_method=integer`, this will be scaled by the number of integer units of a technology purchased.
+              This acts as lower limit (lower bound) for flow_cap.
+              If `cap_method` = integer, this will be scaled by the number of integer units of a technology purchased.
+
+              !!! note
+                  If `cap_method` = continuous (which is set by default), then setting `flow_cap_min` to any value greater than 0 forces the model to always respect that limit, which in turn forces investment into the technology.
+                  Use this to enforce given investment plans, or to account for existing technologies that cannot be decommissioned.
+
+                  An example: If `cap_method` = continuous and `flow_cap_min` = 100, then flow_cap has to be at least 100.
+                  This means that going to 0 is not possible, unless you switch to `cap_method` = integer (see [cap_method][]).
+
             x-unit: power or $\frac{\text{power}}{\text{unit}}$.
 
           flow_cap_min_systemwide: