Custom Components with multiple instances

I have two eTRVs that I can control via MQTT. I am likely to purchase more.

Each eTRV as an Id, Reports the current temperature, battery voltage (and more…) and the target temperature and operating mode can be set.

I would like to write a custom component to control them, but the example custom components only show creating a single instance of an item. How do I create an array of custom components?