Looking at the specs for the 10KW Generac generator, I can see why it was burning the propane so readily.

@half load (5kW) - 4.73 litres per hr - 405 Kg per week.
@full load (10kW)- 7.31 litres per hr - 626 kg per week.

No load (just turning over) will probably be around 10-15% of full load fuel consumption rate so will consume around 60-90 kg per week. With 35% left after 5 days I would assume that the tank size was in the 150-200 kg range, i.e 300-400 litres in size. That is a lot of propane and would be very expensive to run. Running a heating (cold winter) or cooling system (hot summer) continuously (say 2kW continuous load) would mean that the emergency electrical system (tank+generator) would last around 75-100 hrs or about 3-4 days.

If you power a single 100W incandescent light bulb continuously with this setup using the 10KW Generac generator + full propane tank, the light bulb would burn for about 16-21 days.

If you power a 100W (light output) gas powered lantern it would burn 200kg of propane in around 140 days.

Efficiencies matter and Solar PV makes sense to power low powered highly efficient lighting (LEDs) and electronic devices.