The key to low energy use in any system is a well insulated box, with a gasketed top-loading lid.
We have had excellent results with our Isotherm
system using the following:
Set the thermostat so the contents are just above freezing in the main section. Once you find the sweet spot, forget about it. I haven't touched our thermostat in two years.
If you don't already have one, install a small biscuit fan to circulate the air inside the box.
Place a piece of 1/2" blue foam insulation
over the area where you store delicate vegs like lettuce to prevent inadvertent freezing.
We have a 6 cu ft box with 5" of closed-cell blue foam. 200 watts solar with MPPT
controller (average input to the batteries
is around 80 AH/day). All lighting
is LED. We have fairly low electronic loads - VHF
plotter, FM radio
. The compressor
runs 2.5 - 3.5 hrs/day @ 7 amps, ~25 AH/day. Our batteries are usually fully charged by mid-afternoon. We do have a high-output alternator/regulator on the engine
, but rarely need to use it.
We resisted installing solar for many years because of the bulky unattractive appearance of aluminum
. We now have 2 semi-flexible panels
mounted on a light mahogany lattice frame on top of the cockpit Bimini
. Most folks have to be told we have solar because the thin panels are almost invisible.
Compared to the inefficiencies of your old system, I'd be worrying most about things like good box insulation
and a circulating fan. Set it and forget it for the thermostat