I have devices that run on 6 vdc, 12 vdc, 15 vdc, 18.5 vdc and a few other voltages. I use 1.5 vdc and 9 vdc batteries.

I own nothing that charges from a USB port.

I see no trivial solution.

Requires 0 changes to the grid or to generation plants.

DC voltages are mostly standardized already. That’s why you can charge everything from a USB port.

Even in an existing structure (house) changing the wiring to provide DC would be fairly trivial. Run a line from PV to breaker box. Hook it up to whichever circuit you choose. Change the standard outlet box to a USB outlet box.

Several rooms in my house have 2 separate AC circuits. Change 1 to DC, leave the other standard AC.

That should be a miniscule additional charge to the installation costs of your PV system. An extra hour, maybe, to the time an electrician spends there? So, $50? $100?

Lighting is more problematic. Maybe you would have to add an AC to DC converter and 3 way switches, so you could choose PV/off/grid or something.

There’s a topside boundary on the number of cars sold per year. I think the fleet turnover is around 15 years which would mean that about 7% of all cars are replaced each year.

If we get range and low purchase price we might see a more rapid fleet turnover for the first round of EVs.

The last time I heard the chess-board rice grain story, it ended very badly for the inventor: Once the King figured out the cost, he had him executed!

Inverters are about 98% efficient. Power supplies, the ones now used for most low voltage DC devices are 80% to 90% efficient.

You are correct that by the time power gets from your solar panels to your laptop there has been as much as a 20% loss. One trip through an inverter, one through a power supply.

Now, what would it take to change augment our grid to provide a parallel DC line in order to avoid the small amount of electricity lost. Remember, your laptop is not an energy hog. Most of the electricity you use runs the big stuff like your refer, washer/dryer, electric range, microwave, water heater, dishwasher, …..

We’d have to string a new set of wires on the grid.

We’d have to install a new set of wires and outlets in each building.

We’d have to standardize DC voltage for all the stuff we now run on DC.

We’d have to take grid AC and convert it to low voltage DC. Otherwise we’d have to establish as separate free-standing DC grid with its own generation and storage. If we were to convert grid AC to DC then all the savings disappear.

What would that save? Say 20% for a 9 watt LED. 1.8 watts. Same for a 35 watt laptop, 7 watts. It would take quite a bit to get up to 1 kW of savings and at $0.11/kWh payback for the infrastructure would take a long time.

Probably better to spend the money at the supply end and install more solar panels and wind turbines.

The exception is server rooms. Some are starting to wire all DC and use one big power supply to convert for all. Not sure that saves any power, just cuts down on the wiring.

And your new light bulb obviously contains one in the base. That’s 2 trips thru inverters. Even if they are 98% efficient. Though most desktop power supplies were 80% last time I built a machine though ‘silver’ 85% PS and ‘gold’ 90% PS were readily available for some extra dough. That’s just off the top of my head, it might have been 85%, 90%, 95%.

Still, the point is if you have PV you are converting to AC and then converting back to DC for many of your end uses.