Add documentation for Mercury NZ Limited (opower) (#33978)

source/_integrations/mercury_nz.markdown

@@ -0,0 +1,20 @@
+---
+title: Mercury NZ Limited
+description: Get energy usage from Mercury NZ Limited using the Opower integration
+ha_category:
+  - Energy
+  - Sensor
+ha_release: 2024.8
+ha_domain: mercury_nz
+ha_integration_type: virtual
+ha_supporting_domain: opower
+ha_supporting_integration: Opower
+ha_codeowners:
+  - '@tronikos'
+ha_config_flow: true
+ha_platforms:
+  - sensor
+ha_iot_class: Cloud Polling
+---
+
+{% include integrations/supported_brand.md %}

source/_integrations/opower.markdown

@@ -40,6 +40,7 @@ More than 175 utilities use Opower. Currently only the following utilities are s
   - Delmarva Power
   - PECO Energy Company (PECO)
   - Potomac Electric Power Company (Pepco)
+- Mercury NZ Limited
 - Pacific Gas & Electric (PG&E)
 - Portland General Electric (PGE)
 - Puget Sound Energy (PSE)