svenonderbeke@hotmail.com:
Thanks wvmarle and GoForSmoke,wvmarle indeed heat distribution might be a problem that i didn't consider. I will make a setup anyway so then I can analyse how severe this problem is. Keeping it liquid all the time would require a lot more energy since it may take a month to have a full tank and then someone will come and empty the tank...
So it could be melted just one day beforehand which reduces elektricity use of the heater with a factor 30.GoForSmoke, I was also considering this at first. Afterwards a was concerned about overshoot but now I might reconsider and try this in my setup, thanks! The MCU is used because this is only a part of a bigger project (sigfox, LCD, level tank) but I only explained what is relevant to my worries/problem.
The set points must be inside of your acceptable range and perhaps as temperature approaches the top limit the heater could be pulsed smaller. If possible... maybe the heater ON state could be finessed to stay between the set points if the rise is not too fast.
Could you heat the grease with microwaves? Microwaves do heat lipids and it wouldn't be just an area on the outside.