Clare complained that she didn’t know what to do when. I gave her my favourite user support answer: “It depends!” I knew that the forecast was for another hot and bright day, so we’d get plenty of sun to charge the batteries. We also had a flight of locks to go through, so we were likely to drive electric through them. There was also a risk of thunderstorms in the afternoon, so we might not drive any great distance, and so wouldn’t be charging the batteries. So burning some diesel directly to heat the water seemed like a good idea, and using the batteries to speed it up was a good compromise.