Off-grid power: Does it still make sense to have DC appliances?

In ye olden days of off-grid and home-power generation (AKA solar, wind, etc.), it was accepted that the best way to get the most from your system (which typically supplies power, either from the cells/turbine or battery bank, via DC) was to wire your house for DC use and use DC-native appliances. Converting DC to AC involved lots of losses, and inverters were expensive and not very good.

Today, however, high-quality DC-AC inverters are really cheap. Does it even make sense anymore to go with DC-native appliances, lights, wiring, etc.? Or should you just convert the DC to AC immediately and supply your house and appliances with only AC?

There’s probably not a simple answer to this, as it depends on a variety of factors.

The main question I would ask is this: What’s the voltage coming off the system? If it’s low (less than 50 V or so), then I would seriously think about converting it to AC and boosting the voltage using an inverter. Otherwise, you’ll need big copper wires to deliver power. Another thing is motors… AC motors are more efficient than DC motors, which is another reason to immediately convert the power to AC.

But an AC inverter has drawbacks. There has traditionally been a trade-off between efficiency and harmonics. High efficiency inverters simply modulate the DC using MOSFETS, thereby creating lots of nasty harmonics. These harmonics can overheat and/or damage certain appliances. LP filtering certainly helps, but it also reduces the efficiency.

Another thing to keep in mind is energy storage. Most PV systems need a basement full of batteries to supply energy at night. This energy must be stored as DC.

So I don’t know… I guess if I were PV building a system I would be very tempted to install the best inverter I could afford and run most things off AC.

Above 48VDC is rare. Typical home power generation is 24 or 48VDC (straight 12VDC less frequently, b/c of the wiring issues–usu. this is just for reaaaallly small cabins or RVs).

Putting this (DC power source and batteries before the AC inverter) is pretty typical, I think.

This is my gut feeling, but I haven’t seen recent articles confirming that this is a good idea.

I’m with Crafter Man. Given the cost and efficiency of inverters these days it’s pretty hard to justify the expense of going with all DC devices. You might want to run some or all of the lighting off of DC, but everything else I would run off of an inverter.