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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.
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.
With houses as big as they are, we ( USA ) need to think about going to 220v to save on copper.
Besides, inverters are easy to build, soon you'll beable to buy a Raseberry Pi kit to run a 10kw inverter.
Forgive me if I have this wrong, but if we start wiring houses for low voltage DC, won't this mean huge fat copper cables to deal with the current implications of a washing machine or oven pulling tens, even hundreds of amps because of Ohms law?
If we were starting out then maybe, but there are just so many things that can be plugged into an AC socket. It's pretty amazing that you can take anything from the last 50 years or more that has the right plug on it, shove it into a wall socket, and off it goes. The current system is a very good standard, and it will be hard to change things. Further, one of the original reasons Tesla (Nikola) won out is that the induction motor is an extremely good motor design (safe, reliable, quiet). Lots of things still have AC induction motors (heatpumps, your fridge) and these require, well AC. If you don't have that then you need a motor driver for them (or brushes I suppose) which is just a three-phase inverter anyway.
Also 20-40% power loss is crazy. More like 5-10% with modern semi-conductors and getting better/cheaper all the time.
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.
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
I'm not sure that home batteries will drive a switch to low voltage DC. There's a ton of inertia to overcome. The cost of retrofitting the wiring to handle the higher amperage of using lower voltage alone will be thousands of dollars for every single house, apartment, and office. A simple 20A 120V circuit changed over to 12V will draw 200A. You're going to need to upgrade to 4 or even 2 gauge wire at a minimum to handle that kind of current. And that's a lot of money.
The switch from AC to DC inside the home might be feasible but there's no way you can convert the entire grid. You'd have to rebuild the whole grid from scratch to convert from AC to DC. The transformers to step the voltages up or down simply don't work unless they're pushing AC so how do you handle industrial level supply being stepped down to household voltages at the neighborhood transformer? And who's going to pay for the switch? And what about the industrial users who don't need to run low voltage DC? How do you satisfy their demand?
Then you have to deal with how a substantial number of appliances are built. Many are designed for AC current and won't work with DC, regardless of the voltages. Sure, you can swap out the power supply in your desktop PC to take a DC feed without a lot of trouble. And if electronics retailers had a standard DC wall voltage to work with, you'd see most consumer electronics move to those standards. But how do you deal with a cable modem that needs 12V and a home router that takes 9V? Who wants to go out and replace all of their equipment that is running just fine right now? Who has the money to do that?
And here's the kicker. What real benefit do we gain from a switch over to low voltage DC in the house? Sure, some of the consumer electronics we use won't need that big wall vampire to supply them with power. And sure, we don't really need to run our lights from 120V when 12V can still drive enough light from LEDs without any trouble. But what about the appliances in the house that really draw the bulk of the power in the house? The 240V electric stove or the heat and AC systems? What about your refrigerator and your washer/dryer? Hell, can you imagine the amperage draw trying to recharge your electric car with 12V? And are you going to just skip using those appliances when you're running on battery power?
So if you're going to have to keep your 120V AC based house wiring for your major appliances, do you really want to spend all the money installing a low voltage subsystem for a few consumer electronic devices to supplement the wiring you already have? I know I wouldn't want to.
Like everything else that is poised to "fundamentally change the way we do things", the dreamers never consider the practical reality of actually making the change. In reality, I think we're going to have to deal with the inefficiency of converting from DC battery power to 120V AC for the home. There's just too many things to overcome for little to no benefit.
Seems premature to me. An awful lot of things have to work out just right for whole-home battery systems to make much sense.
Even then low-voltage DC plants don't make much sense. Your microwave oven consumes 1100+ watts. Know what amperage that is at 5 volts DC? You'd barely be able to wrap your hand around the power cord.
Even at 48 volts DC, the power plant in a telephone company central office is really something to behold.
Also, AC/DC conversion isn't as dire as stated. Sloppy cheap converters do indeed operate at around 75% effeciency with the remaining 25% lost as heat. But look at the "80+" computer power supply standards. The "80+ platinum" standard requires 95% efficiency. Those power cost twice as much but "pure science" does not prevent their operation. They work as promised.
Moderating "-1, Disagree" is simple censorship. Have the guts to post your opinion.
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.)
All of that info is very good and informative, however, the whole premise of rewiring a home for DC to accommodate renewable sources is, well, folly at best and corporate FUD at worst. They make inverters for a reason. Sure, there is some loss doing the inverter DC to AC conversion, but that loss is negligible (even over the lifetime of the system) compared to the cost of rewiring a home. Note, that you would also have to buy new appliances and such that ran on DC, and currently there aren't any suppliers of home appliances that run off DC, they are all RV or marine appliances.
The whole rewiring premise is stupid! The linked article is nothing but FUD to drum up business for electricians from idiots that know nothing about power electronics.
There is a dead elephant to prove it.
If he had simultaneously ran DC to a 'control' elephant and it remained unharmed, you might be on the way to proving something.
I do not want your cheap brainburning drugs. They are useless for work. And I am a working man today.
We need to use HIGH voltage DC at about the same voltage as your house is now, forget about going "low voltage" DC.
No, we don't.
120v AC will kick you off of it if you touch exposed wires.
120v DC will cause you to clamp down if you grab onto a wire or device that electrocutes you, and worse still, it'll kill you at much lower voltages than AC.
On that alone, HVDC is stupid in the home.
Thats ignoring things like how circuit breakers and switches behave under DC verses AC.
AC has a ridiculous number of safety advantages that are not present in DC, which is why you RARELY see high voltage DC.
Couple in the resistive losses of DC and HVDC suddenly looks really stupid to anyone with a clue.
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Someone is pushing some other agenda here.
I've fallen off your lawn, and I can't get up.
I can see AC to the doorstep a big efficient whole house power supply that has 12vdc and 48vdc rails that are distributed thorough the house and battery backed, and few 220v "appliance circuits" off the AC.
48V and 12V lines are far too low to be sage and/or sensible. Remember that the power used is equal to the voltage times the current and that the heating of the wire carrying the current goes as the square of that current. Typical house wiring is good for ~30A of current and supplies several plugs in a room typically. With a 12V circuit you limit the power of all the devices connected to this circuit to 360W vs. the 6.6kW you get now (or 3.3kW if you live in North America). Even with a 48V circuit you only get 1.44 kW.
The result is that either you need to rewire the entire house with massively thick, and therefore expensive, cables to carry the far higher currents or you need to use a higher voltage for transmission. Even the factor of two reduction between Europe and Canada/US is noticeable for some devices: electric heaters are far punier than their European counterparts, kettles take far longer to boil, and Electric lawnmowers are practically useless etc. If you drop the voltage by another factor of 2-10 below even Canada/US then almost all devices will be impacted.