Advice on small off grid system for mountain cabin

Re: Advice on small off grid system for mountain cabin

Most non-filament lighting (CFL, LED, Florescent, Neon, etc.) needs some sort of ballast/voltage conversion/current control/etc... So once you leave Edison's light, there is really no "native voltage" (very big simplification/over generalization). Same for electronic loads--A computer may have 4 or more voltages generated internally to support the various power requirements.

So, that really leaves wiring losses and conversion losses as the main variables. Obviously, low voltage/high current creates problems/expenses with the wiring (I²R losses--double the current, 4x the losses on the same wire).

If we assume 3% wiring losses and 15% AC inverter losses--The AC inverters (or even DC-DC converters like 48 volt to 12 volt) are an added cost to the system. But between a 12 volt and 120 Volt system, you need ~100x as much copper (by weight/$$$ amount) to deal with the 10x higher currents to have the same wiring losses...

Assuming wire runs are short and not too many circuits--You can probably do it with 12 volt wiring.

However, as soon as you add more circuits and longer distances, the ~15% hit by the AC inverter vs the issues of low voltage DC wiring--The AC inverter (for me) is usually the better solution (more reliable, longer distances, higher power appliances--if needed).

If most of your loads are 12 volt native loads--Then 12 volts makes more sense--But be sure that these are 12 volt loads that can run from 10.5 volts to 15+ volts DC.... Many 12 volt loads are optimized to operated from ~12.5 to 14.2 volts (automotive typical voltages)--And will not function well, or may even fail when operated on a full off grid DC power bus with the full voltage range (and temperature range) that your battery bank can experience.

I much prefer to have a single AC inverter be the "only DC appliance" I have to worry about.

So--Is a 15% larger solar array and battery bank plus the cost of an AC inverter (recommend TSW if possible) vs wiring 12 volt circuits (using Anderson connectors is a "standard" for HAM radio gear DC power). There is the issue that a low wattage load on an AC inverter can have much worse efficiency (i.e., a 6 watt AC load on a smaller inverter with 6 watt tare loading--Gives you 50% efficiency).

I will also add that I believe that AC power (even at the higher votlages) is safer regarding fire. Lower current flow, cheap/plentiful circuit breakers, GFI devices, and even Arc Fault, even transformer isolation if needed. (excluding actual hot to neutral/ground electrical shock).

You have to send 10x the current to do the same job on 12 VDC (10x larger breakers, etc.).

You do have less of a shock hazard (12 volts is pretty unlikely to shock somebody in normal operation.

However, you are likely to weld your wedding ring to a 12 volt battery bus because of the very high available current. Not usually going to happen on a 120 VAC circuit.

There is the ground loop issue too... DC radios/appliances frequently use the DC Chassis as the ground and return electrical connection. With modern 120 VAC appliances, the AC Hot/Neutral are isolated from earth ground--So, you don't have ground loop current issues.

-Bill