Why is it we do not use a DC electricity service in our homes?

Answer 1

The transmission losses are enormous for DC. It is much more efficient to use AC.

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Apart from the reasons why, instead of using direct current, alternating current is used for distributing electricity from power generation stations to consumers, it is worth considering the fact that many different types of electrical equipment are used in today's homes, offices and factories, but they don't all run at the same voltage.

For example, in North America many types of large household appliances - such as range cookers, water heaters, washing machines, clothes dryers and air conditioning units - need 240 volts.

Lights, hair dryers and other small appliances need 120 volts.

Electric razors, personal computers, flat-screen televisions, radios, hi-fi units and personal music players, etc. need low voltages such as 3, 5 or 12 volts.

If the main incoming electricity service to a building were dc (direct current) there would be only two ways in which such a wide range of voltages could be produced:

1) by using a different in-line resistor for each appliance, to drop the incoming service voltage to the correct amount that the appliance needs.

Doing that would produce a lot of heat from all the various in-line resistors and that heat would just be an expensive way of heating the surrounding air in the room...

(In the 1940's and '50s, after World War II, that system was actually used for ac appliances as a way to allow US-made 120 volt ac radios, etc. to be used in Europe and other countries where the incoming service voltage was around 240 volts ac. Those voltage-drop resistors were commonly known as "line cords".)

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2) by using lots of electronic voltage regulator units - but that method was totally impossible at the time the first electric power distribution services and networks were invented in the 19th century because, to be able to build those units you need lots of cheap semiconductors, but such semiconductors were not actually invented until around the middle of the 20th century!

So it's quite a clever idea to use ac (alternating current) for the incoming main service because it is then very easy and efficient - and relatively inexpensive - to produce the actual voltages that are required by each different appliance. All you need for each appliance is an appropriately-sized "power supply unit" which includes a small transformer and rectifier to produce dc.

Ever since low-cost semiconductors were invented, power supply units have been made in very small sizes by using miniature Transformers and/or electronic voltage regulators and invertors.

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Most places in North America use AC at 120v which has been transformed down from a much higher voltage using transformers. Transformers do not work with DC.

However solar panels put out DC which is converted to AC at the house.

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Answer

In fact, DC transmission losses are significantly lowerthan AC transmission losses. Which is one of the reasons that DC is often used for long-distance overhead transmission lines. For underground cables, the closeness of the cable's cores make them highly capacitive, which means that an AC cable will draw far more current than a DC cable -for this reason, undersea cables are often DC.