On September 4, 1882 the great inventor Thomas Edison turned on America’s first power plant, Pearl Street Station, in downtown New York City. It supplied power in the form of direct current (DC) to 85 wealthy and influential customers in lower Manhattan including JP Morgan, the NY Stock Exchange, and some of the country’s most powerful newspapers.  However, one hundred years on and the vast majority of the global power system is fed with alternating current or AC power despite the fact that all the digital devices that make up our modern lives run on DC. Why this happened and why this may change is the topic of this blog.

In 1882, Thomas Edison’s DC power complex was a marvel – a complete generation and distribution system that supplied safe, reliable electricity at competitive prices. In the following years, DC power quickly became the standard in the U.S. power industry, while Edison’s incandescent bulb illuminated a growing number of households, businesses, and industries. However, Edison’s DC systems were technically only capable of sending electricity a little more than a km. Furthermore, separate electrical lines had to be installed to supply power to the various appliances requiring different voltages which all meant that Edison’s power systems were more complex and expensive compared to the AC alternative which was pushed by a former employee of Edison, Nicola Tesla and George Westinghouse.

The turning point in what became known as the “war of the currents” was the opening up of the Niagara Falls hydropower station and the AC system which enabled that cheap power to be transported over 300 km to New York. Edison’s reaction was to set off a fierce smear campaign in the press to discredit AC by linking it to the dangers of electrocution and death. It did not help. The technically more advanced, more versatile and cheaper AC system won over Edison’s DC system.

And for over a century nearly all devices in our homes and businesses across the whole world used that AC power. But today all of the digital devices that make up our modern lives, from mobile phones to computers, to televisions, to LEDs, all need direct current to power them. The result of this is that nearly all of these digital devices need a little black box called a transformer for changing the AC power which is delivered to our homes into DC.  However, one of the issues with these boxes is that they also suffer energy loss through heat (5%–10%) during the conversion process, which is why they are warm to touch.  So the big question now is why we don’t just move to DC? Surely it is more efficient and thus cheaper?

One of the issues is that we already have a huge investment in the AC system. It would be extremely expensive to retrofit our whole power transmission and distribution system for DC. However, bypassing the grid for select customers such as data centres and for off-grid solutions is already economically and technically feasible, and this trend will only intensify as more of our electricity demand requires DC power. Electric vehicles will also require DC at stations to recharge, since AC stations are just too slow, and again, there is the issue of losses. DC to DC means higher efficiencies, lower power losses and thus lower costs. Finally, it is not a stretch to imagine new buildings constructed to use both currents.

Another driver for DC will be the move to decentralised power. Solar PV, fuel cells, and batteries all produce DC power. Currently, the power from solar panels needs to be converted into AC using inverters before it can be delivered into our residences and workplaces, or fed into the grid. The DC to AC conversion losses may only amount to 3%, but then that AC power is re-converted back to DC for our digital devices where the losses are often as high as 10%. To cap it off, these inverters are expensive and would be unnecessary if our homes and buildings ran on DC. Plus, if we switch to DC we could do away with the myriads of plugs used in different countries. Instead, we could use a simple USB connection, which is actually what we already do when we connect our mobile phones to our laptops with USB cables to recharge them.

In developing countries already DC solutions are the cheapest way to bring power to these people. They will most likely directly utilise the DC power from solar panels together with highly efficient batteries. This is what companies like Mobisol are already doing by offering solar and battery solutions to African homeowners.  And for the long distances thee countries will most likely use DC transmission and DC distribution equipment which is what Brazil and China are already doing. This begs the question, whether we in Europe and North America will be left with an uncompetitive power infrastructure as power supply comes increasingly from DC sources such as solar and demand for DC power thanks to all those digital devices such as iPads continues to grow?

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  • Tags:
  • AC ,
  • alternating current ,
  • automobile ,
  • DC ,
  • DC transmission ,
  • direct current ,
  • George Westinghouse ,
  • grid ,
  • inverters ,
  • low-carbon transition ,
  • Niagara Falls ,
  • Nicola Tesla ,
  • solar pV ,
  • Thomas Edison ,

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