AC v DC: The power struggle over electric current outputs

Thomas Edison launches AC electricity transmission in the 1890s. Photo: Shutterstock.

Thomas Edison launches AC electricity transmission in the 1890s. Photo: Shutterstock.

The famous current war that was fought between Thomas Edison on one side and George Westinghouse and Nikola Tesla on other side was a war of two electricity transmission methods.

Alternating current was declared the victor over direct current when Edison's company was wrapped up into General Electric in 1892 and the world moved forward with AC.

While many argued that DC had various superiorities, not the least of which was safety, DC was crippled by transmission losses.

DC was used at 110 volts both in transmission and to power light globes.

At such low voltages, the transmission losses meant that you had to be located within 800 metres of a power station.

The advantage of AC was that a relatively simple low-loss transformer could step the voltage up for transmission and then back down for usage.

More lifestyle:

Westinghouse systems used 500 volts for transmission and 100 volts for usage.

Using Watt's Law, if you increase the voltage by five times, you decrease the current by five times.

Then combining with Ohm's Law, the power loss is proportional to the square of the current so the net result was that, at 800 metres, the single voltage DC system would lose 36 per cent of its power in transmission compared to the AC system which only lost 2 per cent.

That was then. This is now.

The world's longest subsea power cable has just been switched on.

Hydropower in Norway is now powering homes in Great Britain via a pair of 15-centimetre diameter, 724-kilometre long cables.

This interconnector is the sixth connection from Great Britain to European nations with 9 per cent of all power consumed in the UK coming via interconnectors to countries including France, the Netherlands, Belgium and Norway.

Great Britain has a desire to reduce its current level of 46 per cent of fossil-fuelled power and one of the strategies to ensure a smooth supply of power is to increase connectivity with its neighbours.

While these interconnectors are typically used to import power, Great Britain's current level of 28 per cent of renewable power will increase to the point that, by the year 2025, the same interconnectors will be used to export power.

And what type of electricity is used on the interconnector?

You guessed it. DC, 515kV to be exact.

Specifically with subsea installations but also with long terrestrial interconnectors, such as the 3300 kilometres recent installation at 1100kV in China, DC is now the preferred option.

Somewhat ironically, General Electric has been one of the companies pioneering more efficient methods to convert DC to high voltages to make it superior to AC for long transmission runs.

In 2009 I wrote an article and calculated that we only needed 1000 square kilometres of solar panels to provide all the power Australia needed.

I said that with 176,500 square kilometres of Simpson Desert in Australia, we could use some parts of Australia to not only provide for our needs but export power to our neighbours.

At the time I was dreaming but now with breakthroughs such as the North Sea Link, I can see a day when we will generate renewable power for our neighbours. Indonesia currently has 87 per cent of power generated by fossil fuels.

PNG is at 75 per cent. Singapore: 97 per cent. Philippines: 75 per cent. Malaysia: 86 per cent.

For so long Australia has dug up earth and sold it to the world but one day we will reach the bottom of the hole.

Creating an export economy with renewables should meet with very low resistance (sorry - couldn't help that one).

  • Mathew Dickerson is a technologist, futurist and host of the Tech Talk podcast.
This story AC v DC: The power struggle over electric current outputs first appeared on The Canberra Times.