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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.
...albeit this has already happened on a smaller scale before. All you need to do is ask anyone who owns or has owned an RV or Camping trailer.
I dealt with it myself when I had an RV: a bank of huge batteries, an inverter, and a generator. In Tesla's instance, you replace "generator" with "local power grid", but otherwise it's the same routine: Your lights and similar are low-voltage (just like most RVs), but you use an inverter for any general consumer item (TV, computer/laptop, hair dryer, whatever).
I think the only diff would be in the appliances... most RV appliances (e.g. the refrigerator, furnace blower, AC units) are made to run off of 12v DC, but most RV appliances are pretty small when compared to their house-made counterparts.
Maybe ask folks who do the hardcore solar/wind thing?
Quo usque tandem abutere, Nimbus, patientia nostra?
MB is already far ahead, as they actually transmit power from their dams as DC. https://www.hydro.mb.ca/corpor...
"Evil will always triumph over good, because good is dumb." - Dark Helmet (Spaceballs)
Yeah, pretty much. Mains voltage in Oz is 240v AC for similar reasons, we can run a 2400w Clothes Dryer from a single phase, standard 10A outlet. IN the US this requires 2 phases IIRC. Power (in watts) is a function of voltage and current, it's relatively easy to juggle 100-300v on fairly light cable, but there's a good reason car starter motor cables are half an inch in diameter, they need to be to handle the 200plus amp current the starter motor needs at a nominal 12v. Low voltage is fine for lighting and low current applications, but once you get over a hundred watts or so, you need heavy cable or the resistance of the cable becomes a significant source of loss - and heat. This was the problem Edison couldn't solve with DC transmission lines - it was doable for lighting, but even that became a problem when it was all hanging off one mains cable and the current began to build - AC neatly avoids this. It would make sense to use two wiring systems, low voltage DC for lighting (leds by preference) and AC mains voltage for appliances. We have mains voltage standards, we probably need something for DC low voltage systems. 12v is a bit low for more than very light loads over any distance (cars aren't that big) 24v is better, but years and years ago there was a 'Freelight' system that ran on wind generators charging batteries - dates from the 30s and the batteries were just plain Lead Acid, but the system was 32v and there were a lot of small appliances (drills, fans et al) that worked fine at 32v without needing heavy wiring, the same gauge as the lighting was adequate.
Geoff in Oz
With homes having high load devices with large motors(washing machines, compressors in heat pumps, etc) and the large resistive loads like electric heaters, stoves, etc DC just is not the answer. Even with DC there would be a need for DC-DC converters which work by converting to AC... So given how easy it is to move AC voltages around and up/down I would think the question would be how do we optimize the losses in conversions. Maybe we need 5KHz instead of 50/60Hz.
"Anyone who stands out in the middle of a road looks like roadkill to me." --Linus
Absolutely false, ultra high voltage DC is the most efficient way, and smarter countries are building such systems. Brazil is building a system that will have a 1500 mile long line, India is building them too
The USA is running on 220-250V AC for residential (exact voltage varies per locale). It's single-phase with a center-tap neutral, sometimes called "split phase"; Typically, a neighborhood will be on one phase of three-phase distribution system. Split phase allows one get two half-phases of about 120V (typical U.S. receptacle, a.k.a. "power outlet"), but you still have 240V available for large appliances: electric stoves/ranges, furnaces, installed heaters (baseboard or in-wall), clothes dryers, and/or sometimes a welding receptacle in the garage.
Split phase is occasionally incorrectly referred to as "two phase", which actually only exists with one old electrical distribution system near Niagra.
No, most don't. A handful do in fairly specific and limited applications. AC and DC distribution both have their place.
DC in the home, at least for some things, makes a lot of sense, especially if you have local generation... Which is where the tesla powerwall shines.
He's talking about solar DC -> AC conversion: 20% loss, for AC appliances. Then another 20% loss for converting the converted AC back to DC: 40% total loss for connecting to DC appliances.
* Sun generates 12VDC via the solar panel
* Solar panels push power to a battery
* The battery or the solar panel push 12VDC to a DC to AC converter (20% loss of power).
* AC is distributed throughout the house
* Many devices then convert the power BACK to DC (20% loss of power)
* This all seems pretty silly to lose this much power.
I am sure it is less than a cumulative loss of 40 percent power, but when your trying to free yourself of the power company, this really adds up.
Shouldn't there be an option for the battery to generate AC or DC based on the type of appliance that is connecting to it? That would mean 20% conversion loss for DC to AC, for AC appliances, and 0% loss for connecting to DC appliances. The main point is we need both AC and DC sockets connected to this battery.
This is strange. "20 to 40% power loss" seems to be an awfully poor inverter; existing inverters are 4-8 % loss.
Rather than rewire every house in America, wouldn't it make more sense to just design better inverters?
http://www.geoffreylandis.com
DC in the home is only viable due to recent advances in power silicon. AC has its problems, but the genius of AC power is that you can controll it with nothing more than carefully arranged windings of wire and big chunks of metal. Transformers, inductors, capacitors, and resisters can all be made with nothing more than properly arranged and chosen wires and metal blocks. There was no practical DC-DC conversion in Edison's day. Even AC/DC conversion was tricky, often requiring an AC motor with a shaft mechanically linked to a DC generator.
Edison did not have the IGBT
http://en.wikipedia.org/wiki/Insulated-gate_bipolar_transistor
Today, that's different.
You can make tiny, tiny, cheap little AC-DC or DC-DC converters that are dozens of times cheaper and many more times efficient than their counterparts made even a decade ago. What used to require large arrays of MOSFETs and many many pounds of expensive copper windings (And the design/volume/heatsinks/fans to deal with all the waste heat!) is now handled by a much smaller transformer, a handful of inductors, and some advanced switching silicon controlled by a fairly smart processor. You also, thanks to increased efficiency, don't need to overbuild with expensive heat tolerant components so much. (Heat shortens component lifetimes, particularly caps)
And they're already deeply commoditized because, guess what, the chinese are big in to solar. (They know they are going to need it. They're quite aware that traditional energy can't economically fully meet their future demand.)
DC has very rapid power loss over any kind of distance.
No it doesn't. Losses are related to current, not AC vs. DC. A higher current in the same sized conductor equates to higher loss. You can get around this by raising the voltage (traditionally easier with AC), thus transferring the same amount of energy with less current, or you can increase the size of the conductor. DC can actually transfer more energy than AC on a similar sized conductor because it doesn't have to deal with skin effect.
I could link all of these terms to applicable articles for you but I'm feeling lazy and this is all common knowledge stuff anyway.
I want peace on earth and goodwill toward man.
We are the United States Government! We don't do that sort of thing.
Running both AC+DC works but they both still add up to the same tolerable breakdown voltage before it arcs over in an undesirable manner.
HVDC works well for long trunk lines between a distant large power source and a population center, but it much less useful for a grid system with many interconnect points. That's why the primary usage has been between hydro plants and distant cities and for international interconnects (especially where the local grids of the two sides do not share a common standard).
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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.
This is why there are only a handful of DC transmission lines in the world
How big are your hands? Wikipedia has a "few" (200+) examples of HVDC transmission lines. And a here's a cool map showing the inverter stations.
I do this for a living as an facilities electrical engineer who works closely with electricians. The phase between lines on the primary side of a single-phase stepdown transformer is irrelevant to the secondary side. Indeed, sometimes the distribution lines are Y configuration rather than delta, so the inputs to the single-phase transformer is sometimes line-neutral instead of line-line. In most systems worldwide the single-phase transformer has two poles on the secondary side, one of which is grounded locally and is connected to the neutral conductor, the other pole is connected to the "hot" conductor or "line voltage". There is typically about 240V between hot on neutral. A main electrical panel for residential will have 2 bus bars in this case.
In the U.S., the transformer is typically has a three-pole secondary with a center-tap connected to the center of the secondary coil. The center tap is connected to local ground as well as the neutral conductor, and the other two poles at opposite ends are each hot conductors. Since there is only one coil on the transformer secondary this results in two hots that while measured against neutral are 120V, but each 180 degrees out of phase with the other for a result of 240V between lines. A main electrical panel will have 3 bus bars in this case. You can confirm this with a voltmeter. (If they were 120-degrees out of phase, you would measure a SQRT(3) ratio of V_lineline/V_lineneutral.
Occasionally in a commercial or industrial facility, you may find a 2-pole electrical panel that is a sub-circuit to a three-phase Y-configured panel (120/208V Typical configuration). These tend to be remodel conversions from when the building mains were swapped from single-phase to three-phase. In this one case, you will get the 120-degree difference between lines. When this is the case you have to be extra careful when connecting loads to the subpanel, because the difference in line-line voltage is less than what you would expect at first glance, and some equipment may fail to operate, or operate in a degraded state, because of that.
There's two main sets of losses, as I understand: Resistive losses and radiative losses. You can get into other issues, such as power factor and phase error related losses. The two biggies that hit you almost before you get started are resistive and radiative losses, though, if you just consider a single transmission line driving a resistive load.
You combat resistive losses by going up in voltage, so you can send more power with less current. Since resistive losses are proportional to the square of current, each doubling of voltage reduces your resistive losses by a factor of 4. That's why long haul transmission lines are high voltage.
Radiative losses are different. Whenever you accelerate a charged particle, you generate an electromagnetic wave. With respect to wires carrying current, that corresponds to changing the amount of current. (Current measures the rate at which electrons flow, so changing current means accelerating or decelerating electrons.) That's how radio transmitters works, for example.
In an AC system, that current is continuously changing, so those transmission lines are continuously radiating away some amount energy. But that's not all. If there are any conductors nearby, those E-M waves can induce a current in those conductors, and the resulting E-M waves from that induced current can drag on the AC line further. This mutual induction is how transformers work. But, along an AC transmission line, unwanted coupling results in transmission losses. So, an AC system has a built in, inherent source of losses in the alternating current itself.
In a DC system, with a fixed, perfectly resistive load, the current doesn't change, so there's no radiative losses. In the real world, though, the loading on the system is continually changing, so the actual current demand on the DC system will vary over time, and some energy will be radiated away. To some extent that can be filtered, but that's limited by the amount of storage you can put near the ends of the transmission.
The reason AC won out over DC in the early days is that we didn't have practical means to step DC voltages up and down. But, we had just invented the first practical transformers, and those can step AC to higher and lower voltages trivially.
HVDC is practical now since we've had 100 years to develop better technology for converting DC voltages on the grand scales required.
Program Intellivision!
Well, that doesn't seem to be completely true
1999 Darwin Awards - Resistance is Futile
and that was only a 9v battery.
The parasitic losses of DC over long distance is reason enough that it's not done
Siemens quotes 3.5% loss per 1,000km for +-800kv DC vs 6.7% for 735kv AC systems, exactly the opposite of your claim. I think I'll trust one of the biggest names in power over someone with a free bitcoin scam in their signature.
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