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Thomas Edison began distributing electricity as DC in the NYC area over a hundred years ago, but the line resistances had heavy voltage drops, reducing the voltage at the load. AC power is much more efficient since it is a EM wave that travels across the wires, not the electrons themselves (modern physics can explain the difference) and that is what Nikola Tesla proved. At higher frequency, AC power needs no wires!

Maybe those elevators did need DC power because their motors are DC powered and there is no local AC/DC converter, usually a AC motor coupled to a DC generator before large recifiers were possible. So the utility has to rectify the power then send it as Dc to those clients.

Personally I prefer the AC power and rectify it at the load, just like the Volt and Bolt onboard chargers do.
 

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We have AC as it allows transmissions at high voltage / low current ( current is the cause of the voltage drop ) and uses a transformer to convert down to safe voltages / household needs. There is no DC transformer, that's that only benift
 

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We have AC as it allows transmissions at high voltage / low current ( current is the cause of the voltage drop ) and uses a transformer to convert down to safe voltages / household needs. There is no DC transformer, that's that only benift
A DC transformer would be a D.C. Motor spinning a D.C. Generator of a different voltage.

That's how they used to convert voltage.

In terms of having D.C. Grid power over ac the only benefit would be to solar users, since you could run without a grid tie unit
 

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It used to be difficult to convert DC to different voltages efficiently, but these days, that's no problem. There are already some high voltage long distance DC distribution systems today. Since the loads are all mostly DC, or even in the case of Volts motors, electronically switched from DC, DC distribution will be increasing. Likewise for large appliance electric motors, replacing the "dumb" AC synchronous motors with smart pulse controlled DC motors will increase efficiency. The Tesla vision is an entirely HV DC distribution in the home. Solar panels to HV battery, HV DC to outlets and car, no AC conversion necessary. Will it happen in my lifetime? Maybe not. Energy standards and policy moves slowly!
 

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In NH there's been a "Northern pass" project in planning for quite some time now, that will actually send (over roughly 200 miles) 1GW of renewable power from Canada to the US, using high voltage DC lines.

http://www.northernpass.us/project-overview.htm
 

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The Tesla vision is an entirely HV DC distribution in the home. Solar panels to HV battery, HV DC to outlets and car, no AC conversion necessary. Will it happen in my lifetime? Maybe not. Energy standards and policy moves slowly!
Those policies move slowly because of the need for backward compatibility with old devices. It's been the same in the broadcasting world, which is why HD television took something like 20 years from conception to reality.

But if you bypass the need for compatibility, you can move a lot faster. You can see this in the proliferation of 4K video content which, while it still can't be broadcast, is now becoming widely available via the Internet and UHD discs.

Because they're supplying the power and storage and effectively bypassing the utilities, Tesla may be able to propagate this a lot quicker than would otherwise be the case.
 
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