DC power supply to homes

[Danijel Gorupec]

One quick question... What drawbacks do you see if our homes are supplied by DC voltage, instead of AC? That is, imagine that about 100 years ago we opted for DC, not AC and that everything is engineered accordingly. Would now our homes appliances cost less or more, overall?... Please, don't consider power distribution problems at first. I am only interested about possible drawbacks once the current is delivered to a home.

 

The problem I see is about replacing AC motors with DC motors - DC motors being either more expensive or less reliable (washing machine, compressors for refrigeration, water pumps, fans...). On the other hand, powering various electronics (TV, computer...) seems a bit cheaper as today these are usually powered by switching-mode power supply.

[John Cuthber]

What voltage are you planning to use?

Too low and it won't deliver enough power without needing impractically thick cables.

Too high and it's no use for running consumer electronics.

And, since it's AC you can't easily convert it from one voltage to another efficiently.

[Danijel Gorupec]

I think, the same RMS voltage as it is now (230VDC in Europe). This will in fact allow somewhat thinner cable insulation because voltage never goes as high as with AC (Vpp). It might also allow somewhat smaller copper area because there is no reactive current component and no skin effect.

 

The converting from high voltage level to low voltage level (24VDC, 12VDC, 5VDC...needed for most electronics) is done using switching-mode supplies anyway. Therefore, today we do not benefit from AC in our home.

Edited August 30, 2013 by Danijel Gorupec

[EdEarl]

Some transmission lines now use DC instead of AC.

 

High-voltage direct-current (HVDC) technology is used for greater efficiency in very long distances (typically hundreds of miles (kilometres)), or in submarine power cables (typically longer than 30 miles (50 km)). HVDC links are also used to stabilize against control problems in large power distribution networks where sudden new loads or blackouts in one part of a network can otherwise result in synchronization problems and cascading failures.

At one time AC was used because transformers could change the voltage and current when necessary. That technology is less important today, and perhaps one day most of our power distribution will be DC.

[studiot]

 

What drawbacks do you see if our homes are supplied by DC voltage, instead of AC? That is, imagine that about 100 years ago we opted for DC, not AC and that everything is engineered accordingly. Would now our homes appliances cost less or more, overall?...

 

Drawbacks?

 

How much do you think it cost to create the existing power grid? £ Billions?,£ Trillions?

 

If all this was torn down and replaced with another system that also cost £billions? £trillions?

 

Who would pay?

 

Why the consumer of course.

 

Do you have any idea how much higher our bills would have to be to make such a change?

[John Cuthber]

I'm not saying that DC power transmission is a non-starter.

There's a perfectly reasonable DC link between the UK and France for example.(AC would be amusing)

But for local grid transmission it' not a viable option unless, for some reason, someone pays to provide a second set of power cables for the duration of the changeover.

[EdEarl]

I'm not saying that DC power transmission is a non-starter.

There's a perfectly reasonable DC link between the UK and France for example.(AC would be amusing)

But for local grid transmission it' not a viable option unless, for some reason, someone pays to provide a second set of power cables for the duration of the changeover.

If it happens, I suspect it would be on the Solar City model. A company puts PV on your roof, and you are running on DC, with a DC to AC converter in your house to grid connect so you have power 24x7 and sell excess to the power company. Then, someday, the power company runs a DC line down your street and connects you to it. When everyone on the street is connected to DC, they remove the AC lines on that street. Then they work on the next street over.

 

Rewiring a house for DC would be expensive, so you'd probably keep AC appliances. New homes might be powered by DC only.

 

IDK if it will ever be a good economic decision to replace AC by DC, but it wouldn't have to be done everywhere at once.

 

Edison and Tesla fought over whether AC or DC would be used to power the world, and Edison died thinking he had lost that battle. He may have been right.

[Enthalpy]

50Hz or 60Hz transformers are still the state of the art from medium to high to medium to "low" 230V voltage. No-one considers to replace them by electronics and smaller transformers up to now, unless the transmission through sea or huge distances demands DC. Since most electricity uses at home are light bulbs, I doubt DC would be sensible, even if there were no compatibility issues.

 

Even to supply current very locally, 50Hz transformers are used. Within a school, a plant... If 1MW consumption is spread over 200m, you typically have a 24kV transport and one or two transofmers to 230V. So if you imagine a new small city powered by Sunlight far in a desert, it will have several voltages, preferibly with standard transformers between. Worse, imagine when the city grows...

 

Electric motors for sure. Squirrel cages run so well! Some fluorescent lamps and many halogens need AC. Some older power electronics needs AC: thyristor bucks for DC motors, cycloconverters...

 

One more: electrocution is much worse with DC. AC leaves you more chances to survive, since the muscle tetany isn't so radical. I survived once to 110V 60Hz under very bad conditions; with DC through the thorax I'd be dead.

[Danijel Gorupec]

Well... I would leave the current transmission (and production) systems as is, at first - I would only convert to DC at the last step (last substation) or even inside a home (if the customer wants both, AC and DC). But eventually, the DC network should spread to the entire block(s) of houses. This is to address problems with the changeover.

 

The local small PV power stations should be connected to such DC networks - I hope to avoid 50/60Hz inverters (DC/DC converters could still be needed to increase voltage, so I am not sure if the solution will be much cheaper).

 

I hope that electric cars in future will have rapid charging batteries/capacitors. Our local charging stations will have large batteries/capacitors to store the energy that will be poured quickly into our cars. These large batteries/capacitors will be filled from the DC network during the night (at lower price). During the early evening (highest power load), any residual energy from these large batteries/capacitors can be returned back to the DC network.

 

... hmm... electrocution problem... I never thought about this one... It will be more of problem here in Europe where we don't like to electrocute people

[Enthalpy]

Photovoltaics vitally needs converters.

 

Fast-charge batteries exist and are little worse than slow ones: have a look at a store for model hobbyist.

 

Quicker car operation just replaces the empty battery with a full one, so the car doesn't wait.