As far as the electric
heaters are concerned there is one thing nobody has mentioned.
You have a battery
bank of 690 AH - 230 x 3. That is measured on a 20 hour rate, meaning you have 690 AH only at a usage of 34.5 amps. If you use only 20 amps your bank is much larger. But if using the 150 amps it takes to power a 1500 watt heater through an inverter
you will only effectively have a battery
bank of a much smaller size - somewhere around 450 to 550 AH at a guess. You would reach the low voltage cutoff point of the inverter
Also, engine charging
is only effective until the batteries reach 80 - 85% capacity. No matter how large the alternator
the last 15% or so to a full charge will take 6 to 8 hours as the batteries internal resistance increases and they accept less and less current
can make up the difference if you have a large enough array and the sun is shining.
This is why water
heaters, any kind of room heater, or air conditioners should not be run off of 12 volts and an inverter with very few exceptions.