For small Solar Power Systems you can increase efficiency by running lights and equipment directly from the DC output of the batteries. Usually this is only done with 12V battery banks. The calculations of watt-hours etc. is the same as for AC loads, but you don’t have the 15% or so loss in the inverter.
You will still have losses in DC-DC converters if you need to bump the voltage up or down, for instance 19V DC for a computer or 5V USB output for a tablet. In a 12V DC system you can have very substantial losses in the copper wiring unless the wire runs are very short or the wires are very thick. The “engineering toolbox” website has a couple graphs showing how far you can run various gauge wires here: https://www.engineeringtoolbox.com/12-volt-wire-loss-chart-d_1689.html
Steca and Sundanzer make very efficient refrigerators & freezers that run on 24V or 12V DC, and are reason enough to consider staying with a DC system, since they will use a lot less power than any AC powered counterparts.