Today: AC, Tomorrow: DC?

[nwdiver]

Given the huge imbedded capital in our existing AC transmission and distribution grid, it seems most likely that the first step would be in-home centralized DC. Still, as @FlasherZ points out, different devices use different voltage; how many parallel DC systems would you want in the house? Manufacturers would also need to standardize plugs, etc.

Well, I guess to answer the original question... no, I don't think we'll be seeing DC circuits in our homes, ever. Overcoming the legacy costs would not be worth the benefit. The keys on my keyboard are arranged so as to prevent MECHANICAL entanglement... how long has it been since that was an issue?

 

[austinEV]

Johan I have had the same thought in your OP for quite a while. For the reasons already covered, long-distance transmission will probably stay AC, but about 80% of what we use in the home is now converting from AC to DC. Go look under your desk, assuming you are oldschool and have a PC. If you are like me, you have about 6 wall-wort DC converters (ethernet switches, pc speakers, printer, external drives, router, laptop charger, LCD monitors, cable modem...). Then my media cabinet is similar (switches, routers, nas storage, tivo, etc). Heck, a lot of things which have AC plugs are just doing the conversion for you, like PC's, large printers, tv's etc.

A DC in-house, or even small-area standard wouldn't be so hard. Laptops should be getting one eventually to standardize charging, IEC announces new standard for future universal laptop chargers | The Verge

I think the standard would be 24V, and inexpensive regulators in the devices would knock it down to 12, 6, 5, whatever. It would be one plug, different from any nation's current AC standard (no chance of making a mistake) and it would probably have an actual active communication protocol where the new device enumerates for 100mA and asks for a power budget (this is what USB does). If the 24DC plug has capacity the power is supplied. That way you could save power because you would only have one AC to DC conversion (instead of dozens) and the plugs would be small, neat and cheap. Money is saved because you don't keep re-buying wall worts and a lot of e-waste is eliminated. (raise your hand if you have box of orphaned power converters).

Part of the reason I think this hasn't caught on is that the power savings is minimal. The AC to DC converters are actually pretty efficient which undercuts the need a bit.

I have had thoughts of just doing an ad-hoc version for my desk setup. Build a custom desk with a single 12V AC to DC supply. Virtually all your little gadgets take 12V. Then you could get a fairly modest solar panel at 12V, and a 1kWh of li Ion batteries and go digitally off-grid... It pains me that I have 85kWh of capacity mainly loafing in the garage!

 

[freds]

\ It pains me that I have 85kWh of capacity mainly loafing in the garage!

My understanding is that the current DC to DC converter is relative a fairly low power device; considering how thick the cables that feed it are. They appear from the pictures to be the same size as to the motor and charger; given in super charger feed though mode it can handle 120KW and 150KW or more to the motor ; I wouldn't surprised if something became available for off grid or heck work related energy peeks.

Maybe the factory workers would have their cars supply peaks during the work day? Employee purchase program?

 

[Robert.Boston]

Cycling an EV's battery to avoid using grid power is an economically bad idea except in extreme situations. Batteries degrade with cycling, so there's a finite number of cycles you have available before the range drops below an acceptable threshold. If you amortize the cost of the battery replacement over those cycles, you'll find that power out from the battery has a value above $100/MWh (plus the purchase price of the power that went in, after round-trip losses).

There's a reason that Tesla didn't include any means to draw much power out of the Model S battery (other than driving).

 

[stopcrazypp]

This is not true of all battery types, although it is true of Tesla's. Some battery types have extremely high cycle life, such that it makes sense to cycle the battery.

 

[DITB]

One issue with DC, assuming we are talking 5, 9, 12 and 24V DC, is that it's only good for quite short distances. The higher the voltage, the lower the loss (for the same cable gauge). It is ideal to keep AC for grid distances, while DC is something I myself have considered inside a house. So many devices now use USB power, which is great for commonality. Imagine a USB "bus" from a 6V battery, which can be fed from AC, solar PV and more. Just plug in anywhere to 5 (6), 12 or 24 (19). I think MacBooks need at least 19V DC if you want to power them with DC, possibly similar with other notebooks.

There are lots of efficient appliances made for camping and RVs, even fridges and freezers. One disadvantage about solar PV is that for a normal grid tied system (which isn't able to run in island mode), the system is totally inoperable if the grid is down. Imagine looking up at your solar PVs during a blackout, on a nice and sunny day, and you cannot even operate your razor or charge your phone. THAT is a bit silly, and need to be solved.

One way using existing tech is to look at Victron and their chargers/inverters made for ships - there is a high degree of flexibility there ...

 

[William13]

We are forgetting very high voltage DC transmission lines which are likely to help smooth out wind and solar power generation over the entire country with very little loss as opposed to high loss with low voltage DC current.

 

[DITB]

We are forgetting very high voltage DC transmission lines which are likely to help smooth out wind and solar power generation over the entire country with very little loss as opposed to high loss with low voltage DC current.

They were not forgotten, see some of the previous posts ("HVDC").

Both AC and DC has it's place, and I agree with the OP, it makes sense to look at DC again, although in my opinion, mainly for very short range (within a typical house for instance).

 

[igotzzoom]

At least from an end-user standpoint, I think the next step will be these:

And ultimately, these: