Can Edison still win the power wars?

[andrewducker]

Back at the dawn of human electricity use there was a fight between Edison and Tesla over whether it should be delivered as AC or DC.

Tesla won. AC was more efficient for transmitting long distances.

But, nowadays, electricity is frequently transmitted long distances using High Voltage DC. And more and more devices are powered by DC (either by batteries or increasingly by USB).

The local grid that connects to your home is still AC though, and the complication and expense of running a whole separate set of cables to your home probably isn't worth it, when you can do the conversion in lots of little boxes internally.

Although maybe we will start to get central converters in people's homes that then power all of their USB sockets. And slowly Edison will take over your power supply from within!

Not this week though - USB tops out at 240W, which isn't enough for a washing machine. And the maximum cable length is 4m, which isn't going to let you mow the lawn. It'll be a while before DC can do everything, if it's ever feasible (or desirable).

Comments

[doug]

Interesting!

I thought the HVDC interconnects worked out better than AC because they're mainly used for transmission between separate power grids, which won't be synced. Since you need that separation anyway you don't make the savings in easier step up and step down that AC gives you.

Until recently, almost all electricity started life as AC, since it comes from actually-rotating generators - whether the rotation was driven by wind, water, or steam (from coal, oil, gas, or nukes). Alternators (rotation to AC) are cheaper, more reliable, and more efficient than dynamos (rotation to DC, needs a moving commutator). The question then is at what point in the transmission chain do you rectify to DC, and 'as late as possible' is a good choice because it lets you have transformers along the way, and also lets you use AC in loads directly where you can, which is more efficient.

But now we have significant solar PV generation, and will increasingly have batteries as a power-smoothing source, which perhaps opens up other options.

[sobriquet9]

AC is not more efficient for transmitting long distances. It's slightly less efficient because some of the AC power is radiated by transmission line acting as large antenna.

AC is easier to convert to high voltage and back with a transformer. High voltages are more efficient for transmittion long distances, because for the same power the current is lower, therefore less power is lost on heating the wire.

Now that we have more cost efficient ways to convert DC voltages using solid state devices, DC may be making a comeback. Incidentally, DC-DC converters still use AC internally, just at much higher frequency that would be impractical to transmit.

[andrewducker]

I did not know that was how they worked!