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How Tesla Batteries Will Force Home Wiring To Go Low Voltage
CIStud writes with a story at CEPro suggesting that solar power and home batteries like Tesla's PowerWall "will force the reinvention of home wiring from primarily AC high voltage to DC home-run low voltage to reduce power conversion loss," writing "To avoid the 20% to 40% power loss when converting from DC to AC, home wiring will have to convert to home-run low-voltage, and eventually eliminate the need for high-voltage 110V electrical wiring." As a former full-time Airstream dweller, I can attest to the importance of DC appliances when dealing with batteries.
You'd think the fight between Edison and Tesla would have ended long after their deaths. Clearly not. It is a good thing their graves aren't near each other, if they were, there would surely be lighting bolts going back and forth.
Kind of ironic. Nikola Tesla fought to champion AC power, and the company named after him will bring Edison's dream of DC-sourced homes to reality.
This is a very poorly researched article. They talk about getting 12V from a solar panel. No modern home-scale solar system runs at 12V. The power loss due to resistance is much too high until you use wires that are much too large.
The real solution would be to standardize on some type of home HVDC distribution in the 150-300VDC range. This would help keep the DC/DC conversion in roughly the 2:1 voltage ration range, which helps efficiency. It would also help keep the wire gauge reasonable. I'm not sure how the article's author envisions running things like a modern HE washing machine with build in heater from, say, 12V. It would take about 100-150 amps and require about 2/0 gauge wire to keep the losses manageable.
Just because we're all dim bulbs doesn't mean we're low voltage. There is a lot of resistance around here.
Faster! Faster! Faster would be better!
Low voltage is not going to happen, if only because the costs for copper wire would be astronomical. If you take your standard 1500w electrical outlet, at 120v it only needs #14 gauge wire to run 54 feet @1800watts because it's only 15 amps. If you take that down to 24V, you need #2 gauge wire to run the same distance, and you are only getting 1200watts, at 50 amps! #14 wire is about $0.17 per foot, where as #2 wire is (from what I could find) about $7.50 per foot.
-Xoltri
This is largely what I was thinking.
As it currently stands, commercial buildings often have 277V lighting circuits (this is in the US) because it involves installing less copper in the ceilings.
From this, one can intuit that lowering the voltage will significantly increase the amount of copper, but let's take an example and make it more solid.
Let's say, for the sake of example, that we were considering 48V DC as an alternative to 120V AC (I personally would not want to consider anything lower than 48V in a home environment). If you need to deliver 1200W from point A to point B, it will require 10A at 120V, and 25A at 48V.
That 10A could be safely delivered on a 14 ga. wire in most domestic contexts, but will probably be delivered on 12 ga. For 25A, however, you're going to need 10 ga.*
A 250' roll of wire is ~$43 for 14 ga, $95 for 12 ga., and $138 for 10 ga. See the problem?
For the next challenge, you will also need to use different, more expensive switches and circuit breakers, or drop back to using fuses. This is because an AC arc self-quenches in half a cycle or less, and won't re-establish until the contacts are brought close enough together. The DC arc, on the other hand, is continuous, and requires additional effort to quench. Just for the record, there is an arc every time that a circuit breaker or switch is opened under load. This is the reason why you will often see switches and breakers labelled "AC Only".
Now, this is not to say that these problems won't be overcome or that a different variant might come about. Who knows? Maybe they'll gravitate towards 120V AC or some such, in which case it will be 1915** all over again.
(*For the non-Americans and uninitiated, US wire gauge is backwards: larger numbers are smaller wires. 14, 12 and 10 gauge are ~2.1, 3.3 and 5.3 mm^2, respectively)
(**There is nothing special about 1915, but I live in a house that was built in 1915 and was electified from day one. It would have had DC delivered to it in those early days, courtesy of Mr. Edison's various efforts in my current home town of Schenectady.)
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> If you're using somewhere near the inverter's peak output, then you can get as much as 90% efficiency
These days inverters are much better than that. To use a random product that is currently shipping, an SMA Sunny Boy 5000 runs at 95.5-97% efficiency. Bigger inverters are even better with some commercial scale monsters at 98% efficiency.
The original article is pure nonsense. There are already three port inverters on the market. Those ports are: your 120V AC, your solar array, your battery bank. If the energy is going from the solar array to the battery there is simply no intermediate conversion to AC. With a three port inverter, there is only ever a single conversion from DC to AC. And, as I previously mentioned, will only get hit with a 3-4.5% loss. There is simply no way the world is going to change how electricity is delivered to avoid that.
Since the Tesla Power Wall is pretty much for sure going to be a high volume product, there are inverter manufacturers falling all over themselves to design and build three port inverters specifically optimized for the Tesla product.
Someone is pushing some other agenda here.
I've fallen off your lawn, and I can't get up.