Category: Uncategorized

AC/DC

The voltage from a standard wall jack is alternating current (AC), and the voltage from a battery is direct current (DC).  There are very few things that we use that are designed to use AC voltage directly without a conversion to DC.  The two main exceptions are incandescent bulbs, which can use either AC or DC power, and some electric motors. 

Electric motors can be designed to use AC directly or DC power directly, so some electric motors are AC, like the one that runs the fan in the heating and air conditioning unit in your house.  Other motors are designed to use DC current like the Tesla Model 3. 

So why are most power outlets AC if most things have to convert the power back to DC to use it? 

Back in the nineteenth century, when Thomas Edison invented the light bulb, his idea was to us DC power to power his light bulbs.  But there was a problem: Edison’s DC power system could not be transmitted over a few miles. This meant a power station would have to be built every few miles –a lot of power stations. 

Fortunately, an employee of Edison’s, Nikola Tesla, developed a way to use AC power to transmit

power cost effectively over many miles. Edison was against using AC power. Nikola Tesla quit after a disagreement with Edison and went on to work with George Westinghouse to provide electricity to households and businesses using AC power transmission lines and equipment. 

Tesla patented a number of inventions that had to do with AC power that are still being used today to produce and transmit electricity over longer distances. Tesla Motors, Inc. was named after Nikola Tesla.

Solar Power

Now we are starting to have a new problem. Solar panels generate DC electricity.  We often convert this to AC current only so we can plug in the power adapter of electronic devices that change it back to DC.

In a house powered entirely by solar power it would make more sense to use the DC power directly since the solar panels and the batteries that store their power in both use DC power, and converting between AC and DC or DC and AC is less efficient since you lose energy in the process.

How Solar Energy Works

Electric Today

Today, we have some long distance high voltage DC transmission lines but they are actually only cost efficient over much longer distances.

An overhead  cable run with HVDC would need to be between 600 and 800 kilometers to be cost efficient —  that is between 375 and 500 miles. 

Underwater and underground HVDC cables become cost efficient at about 30 miles or so.  So HVDC is often used  in long distance undersea cables. So even now, AC power is generally a better choice for the transmission distances we  need.

—Dean McIntyre, June 18, 2020