Allow create PVPool instances in locations without PV (#1215)

Closes #1130

Author: shsms

RELEASE_NOTES.md

@@ -53,3 +53,5 @@
   | Battery            | 0.0                                       |
   | PV                 | Minimum power (aka max production power)  |
   | EV Chargers        | Maximum power (aka max consumption power) |
+
+- PV Pool instances can now be created in sites without any PV.  This allows for writing generic code that works for all locations, that depends on the PV power formula, for example.

src/frequenz/sdk/timeseries/pv_pool/_pv_pool_reference_store.py

@@ -97,15 +97,20 @@ def __init__(  # pylint: disable=too-many-arguments
             name=f"System Bounds for PV inverters: {component_ids}",
             resend_latest=True,
         )
-        self.bounds_tracker: PVSystemBoundsTracker = PVSystemBoundsTracker(
-            self.component_ids,
-            self.status_receiver,
-            self.bounds_channel.new_sender(),
-        )
-        self.bounds_tracker.start()
+
+        self.bounds_tracker: PVSystemBoundsTracker | None = None
+        # In locations without PV inverters, the bounds tracker will not be started.
+        if self.component_ids:
+            self.bounds_tracker = PVSystemBoundsTracker(
+                self.component_ids,
+                self.status_receiver,
+                self.bounds_channel.new_sender(),
+            )
+            self.bounds_tracker.start()
 
     async def stop(self) -> None:
         """Stop all tasks and channels owned by the PVInverterPool."""
         await self.formula_pool.stop()
-        await self.bounds_tracker.stop()
+        if self.bounds_tracker is not None:
+            await self.bounds_tracker.stop()
         self.status_receiver.close()