We are some distance from the tipping point, but it looks as if we may soon find that a household DC supply may be quite desirable. LED lighting and motor control by PWM may make it more convenient to have a DC source for all appliances and lighting.

With more efficient motors and such, something like 48 volts could be distributed through existing building wiring, saving both time and money, although segregating runs for existing mains AC voltage could be a challenge. Wall outlets and light switches would need replacing, too.

Wonder where to invest some ground floor money?

 

Anything like this will always come back to one thing - how much will cost to implement - and this is irrespective of the practical benefits it may bring. Across the board the costs might very well be intangible.

Has something recently been published discussing this?

Dave

 

Just extrapolation from growing usage of DC devices.

 

I'm certainly no expert on power engineering (I did one 12 week course on it in University!), but the issue is IIRC is transmission losses, and the current infrastructure is geared towards this and hence AC because of the benefits it presents (correct I hope?!). To change this en-masse would be hugely complex and expensive - impossible probably. I would imagine it could only be implemented locally where the complexity issues and costs would be manageable. Then the question is what are the benefits of a local implementation over what exists. Maybe someone who knows might be able to offer some input on this.

If there were financial benefits to changing, the commercial world might be interested. Furthermore if there were environmental benefits governments might take an interest to promote it as an alternative.

It's an interesting question, and one I have nothing more than a cursory understanding of. As a slight tangent I recall there was a discussion here on AAC some time back about an inaccuracy in the e-book regarding Tesla and Westinghouse an their involvement in promoting AC transmission technology.

Dave

 

Would it be a cheaper more efficient method if standard AC voltage was used to charge an array of cells in the house and then these cells could then be used to light house and drive dc motors at 48V. Would that be a cheaper approach or would an array of cells in a domestic envoirnment be considered too damgerous??

 

That may not be the way to go. Even assuming 48 volts is a good voltage to work with, you have to consider how much resource gets tied up in those batteries. Lead-acid is most definitely not the way to go, but I have no idea about the economics of turning out a zillion or so lithium ion or lithium polymer cells - not to mention all those chargers.

The distribution system for AC is pretty well developed, so it may make sense to stay with that. I can't say at what point there might be enough appliances in a home to make a DC system economical or desirable. Part of my speculation is the growing use of solar panels to make some household power. That means those homes have AC and DC sources present.

Maybe the advance will come when a refrigeration compressor gets developed running with PWM control. having DC in the house makes charging the electric car a bit easier, too.

 

Would a digitally controlled outlet that gives DC voltages be feasible? Inverters seem to have issues with efficiency, so the future homes with DC power from Solar Panels may be possible if no conversion to AC is required. Also what would be wrong with having DC switchboards in every room behind the wall that routes DC power based on the request of the device being plugged in (possibly done through wireless).

This is all assuming technology advances to a certain level.

 

What would be wrong with having DC switchboards in every room behind the wall that routes DC power based on the request of the device being plugged in?

Well, nothing except cost. Folk will pay my employer about $90 per hour for me to install them, and then pay someone else about $200 per wall to cover them. Then someone will need to paint.

As Dave said - it all boils down to costs.

 

Where will AC to DC conversion take place in the appliance, or outside at the DC switchboard, or after the distribution transformer.

HVDC has lower transmission losses but what about the losses at the AC to DC convertor?
What about its(converter and inverter) capacity?
And unless we connect dozens of DC generators in series we can't step up the voltage.
so AC can not be eliminated.
And yes the cost will be huge.
Then we have to convert this DC back into AC using invertors to step it down (again losses, cost,capacity?) unless we want 400KV in our houses.
Otherwise DC transmission has LOTS of advantages.

So after all this, if we convert AC back to DC after distribution transformer..what about existing appliances and the existing AC distribution system.

The best solution for existing systems IMHO would be:
To have a converter inbuilt into the appliances for existing systems.
To take the idea into consideration when a new scheme is being planned.

 

Edison promoted Edison. Much of 'his' inventions were done by others. His electric 'vision' would have had coal and oil burning DC power plants for every mile of wire. Us poor folk would still be living with wood, gas or oil lighting and choking on the fumes of the DC plants while the wealthy lived in the 'clean light'.

Progress would have been retarded and would have probably kept us at 1800s tech for the next 100 years. Without efficient power generation and distribution we'd not have the technology or the society that we now have.

The man who really brought us out of darkness died a pauper.

 

I have never doubted that Tesla was a much greater intellect than Edison. The world would be way less advanced if Edison had managed to force DC power distribution.

My point is that if most AC voltages have to be converted to DC in the home, meaning the end of the fixed-speed AC motor, then Having a central DC distribution system in the home may be more cost effective than many rectifier/regulator duplicates.

 

The man who really brought us out of darkness died a pauper.

It is easy to bash someone who is dead. Edison was a great businessman -- no different the the current generation of billionaires.

However, since we seem to be in a Edison-bashing mood, let me point out that he promoted the use of AC for executions in the US, not because it was better for that purpose, but because he felt it would make AC and George Westinghouse look bad. In fact, DC is better and presumably more humane for electrocution.

John

 

The other day I came across an article which stated something like:
The problem with modulated supplies and drives is that the cause harmonic currents to flow due to non linearity of load(change in impedance with voltage)..This caused overheating and other problems which resulted in lowering the PF and thus the efficiency of motors etc.
(Of course the efficiency might still be higher than in other cases, I think).

Also AC motors can still be controlled by VFD (having only inverter stage if there is only DC available) and since they have their own advantages maybe they will coexist with DC motors.

 

Not the end of AC by any means.

There is no existing means to transfer electrical power over long distances via DC current. There ARE efficient dc-dc converters available nowadays, but not cost effective at the rate we're using power.

Even if most household appliances eventually are run from DC, it'll still be AC supplied right up to the point of the meter.

Whatever you do with it after that point is your business, and your electric bill.

 

Not the end of AC by any means.

There is no existing means to transfer electrical power over long distances via DC current. There ARE efficient dc-dc converters available nowadays, but not cost effective at the rate we're using power.

Even if most household appliances eventually are run from DC, it'll still be AC supplied right up to the point of the meter.

Whatever you do with it after that point is your business, and your electric bill.

You kind of gesture towards my point a little here, that the existing AC-focused infrastructure would preclude any wide spread usage of DC (irrespective of benefits in the short term at least). Once it gets stepped down to 11kV at the local level (I'm using UK ratings here so this may differ from locale to locale) then is there scope for looking at DC-distribution? I'm not the man to answer that question.

Funny you mention DC-DC converter because a colleague of mine is currently doing some commercial-focused research into this field, primarily aimed at electric vehicles, but it will be interesting to see how this moves forward in years to come.

Dave

 

There is an interesting article about this:
http://www.americanscientist.org/template/AssetDetail/assetid/56694;jsessionid=aaaa8v7FzYJnYf

 

In keeping with the article nanovate links to, I recall a Swedish reactor that used the condensed steam from the turbines to heat houses and even heat several really big greenhouses so the community could enjoy fresh produce all year.

Of course, this flies in the face of the modern (at least modern American) pressures to consolidate as much as possible

Perhaps it will be AC in the summer to keep the air conditioners running, but DC in the winter so we can stay warm basking in the rosy glow of our household dropping resistors.

 

DC current is harder to convert than AC current. If you are using AC current, you just need a cheap transformer, a rectifier, a capacitor and a regulator to get a very decent DC supply. Converting DC current is a challenge, as you will need to PWM it first, and if you are converting it to AC, you really need a decent harmonic signal generator, as a square wave won't do.

Plus, multi kilowatt induction motors have to be triphasic, and a full AC current will be really needed.

 

Actually, it was the large increase in the cost of transformers that caused me to start thing about this. Copper's price has gone up quite a bit. It will continue to do so until a new copper mine is discovered. Price increases tend to drive innovation.

 

The prices on copper and nickle are becoming like gold. Maybe rather than going to DC, we will be going back to the iron age....no stainless steel, no high-strength aluminum alloys, etc. Obviously, that's an exaggeration, but it was a shock the first time I tried to buy some nickle foil. John