My MoBo thread - keeping engine warm in winter ...

[Refueler]

Too much power. Would cost a fortune to run. Look at what Refueller's 80 Watts is achieving.

But if the power can be free - solar - and not from yard mains supply ... then why not ...

My household electric bill before I had the Solar installed was over 500 euros a month ... yes you read that correct. I have become miserly on power demands ..
The 80W .. I am seriously considering adding another on other side of engine .... thinking that at 160W - that is still workable from inverter ... with moderate Solar to charge up batterys ... but thats if I dont have mains availasble. This boat is at home - so not a problem for power but our marina bans heaters to keep electric consumption down to enable us to have if free. I have another boat there.. The experiment with the towel rail has proved successful - so could be installed in that boat as well ... if I also add a temp switch .., I could cut the power demand to maybe 80W x 12hrs ... less than 1kw a day ...

 

[NormanS]

We have a theoretical 180w of solar, but at this time of year when the days are so short, and the sun is so low, the output from the panels wouldn't be enough to give any useful amount of heating.

 

[William_H]

Interesting question re solar powered heating. I would suggest connect solar PV panels directly to heating pad. Angle the solar panels to best sun angle.
You need a heating pad whose resistance matches that of the solar PV panel. So 100w 20v (12v) panel will have a source resistance of 5 ohms (at full power) perhaps closer to 10 ohms low power in winter. That means an element resistance of 10 ohms needed. So something like a 12v 12 watt heating pad. Now that gets correct resistance for max power transfer but of course could get over loaded in summer. ( 100w gives 20 v into 12 ohm gives 1. 66 amps is 33 watts which would cook your heating pad.) (local heating) So perhaps better, safer to make your own heating element from resistive wire. Nichrome is best but a single strand of 1x19 rigging wire could be cut to make 12 ohms then wound on something heat proof but insulating to make a resistor (element) that could handle the higher power. Make it physically big and long.
All very tricky and then you only get heating when sun shines which probably is not much good for ice protection. ol'will