I was looking at electric cars, then at home batteries, solar panels, air-source heat pumps, etc.. Websites talk about typical savings and hence typical paybacks. I thought I’d consider “what if I invest that money instead” to see what different levels of investment return would do to the payback. The result is certainly food for thought. Solar panels are currently a non-starter. Home batteries (Tesla, Solax, etc.) to enable use of Economy 7 tariff is a far longer payback than I had thought. The cost of solar panels is reducing, and similarly home batteries are becoming more cost-effective, so in a few years I can look again. I suspect that if enough people have electric cars and home batteries, both charging overnight, energy companies won’t be offering such good deals for Economy 7. I’ve done a page to show my spreadsheet model.