Plenty of lorry night heaters on the bay of fleas that use very little diesel but can put out a great deal of heat. It's the initial start up that kills the battery, once running they use very little battery powerA diesel fired heater hooked to a thermostat and ignited by a battery topped off from a solar panel would be best i should think.
A solar array big enough to capture enough energy in winter to run an electric heater wouldnt be cost effective.
How about running a waterpipe through a muck or compost heap?
No it won't.Will a solar trickle charger keep a battery full running some sort of fan heater?
Waste oil heater. We manufacture them and run 3 of them in our workshops, parents house. We have 4 in green houses locally in place of their water heating for frost protection.
No it won't.
You need to be burning something if you want a heater, diesel, wood, coal etc. But be aware that the fumes from fossil fuels will likely kill your plants or at least the sulphur in them will.
Are you trying to heat it or just keep the frost off?