We live in a rural 250 year old colonial that was wired for ceiling and wall sconce electric lights sometime in the mid-1940s. In the early 70's outlets were added, then updated to Romex when a central heating system was installed.

We are updating to solar thermal for heating and want to add some solar PV just to put the lights off-grid, in case of another hurricane or blizzard.

The original lights are on two isolated circuits on for second floor, one for third, and I think they are just in series.

I remember doing the potato battery experiment with an old fashioned ceramic ceiling fixture years ago, and I wondered ... is there a way to use the existing wiring to go directly to DC and simply switch to DC LED edison screw lightbulb? Instead of a whole inverter, just for lights?

The DC-AC inverter is the expensive part. If I can figure this out, we'll run another USB-PD circuit for all our other power brick devices.