I wonder, how hard would it be to make a vacuum insulated oven like a big thermos flask?
I know this is “low-tech” but still think it might be possible to fabricate something even if it means spending some of your power budget maintaining the vacuum with a pump.
I have in fact cooked eggs at night by running water over them that was heated in such vacuum-insulated-tube collectors, then held in an insulated tank. This used to be an economical way to get hot water when PV was more expensive.
I know this is “low-tech” but still think it might be possible to fabricate something even if it means spending some of your power budget maintaining the vacuum with a pump.