After help from people in the Givenergy developer community and some clues from the Terravolt website, I've been able to access the API functions from Node-RED. I've uploaded the flow to the Node-RED contributed flows. It does nothing other than return the API call payload to the debug node, but once you can see the JSON, you can choose how to process the key values.
The key for me is that I was struggling with finding how to enable access to the APIs (Userid/Password or Auth key?) and I was clueless of how to attach a cookie to an HTTP Request (thanks Mickey Wang). The rest was relatively straighforward.
