I would think just use the solar panel to charge top off the batteries would be more then enough for 85 of the situations you run into.
Diesel block heater solar panel.
Video shows how to set up a small off grid 12v desktop air heater.
Radiator stays ice cold though won t even melt snow in the vanes.
The size shown can heat a small office in the dead of winter as long as the sun is shining or you can build smaller units to distribute around your house.
My block heater is stock as far as i know.
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For caravans a diesel tank must be installed but for the majority of motorhomes the heater can source its diesel fuel from the existing diesel fuel tank.
The biggest problem with a diesel in winter is just pure cranking power also with adding a trickle charge from the solar panel you will also slightly warm the batteries so they will perform better 2 fold.
De longhi mica thermic panel heater full room quiet 1500w freestanding easy install wall mount adjustable thermostat 2 heat settings black hmp1500 4 1 out of 5 stars 2 794 92 32 92.
Over the course of a sunny day this system can heat a room at zero cost.
You can build a very effective solar space heater for around 400 in parts.
There are no pumps fans or moving parts.
Order engine heater block universal for your vehicle and pick it up in store make your purchase find a store near you and get directions.
Unit is powered using only one solar panel.
It draws 378 watts according to my special plug in watt meter and heats the engine enough to melt a doughnut ring of snow around the valve cover area.