Everybody is mad about Nikola Tesla these days, claiming that he was a greater inventor than Edison. They even name cars after him. Certainly, Tesla was a genius; he and Westinghouse won the first round of the Current wars, and most of the world has been using alternating current for the last century. But Thomas Alva Edison had something to celebrate on his 165th birthday this weekend; He lost that first battle, but has won the war. It's like William Gibson said; The future is here, it's just not very evenly distributed. Five years ago, when I first said Edison was right, I got pounded in the comments, but now the evidence is incontrovertible, and even that car with Tesla's name on it runs on DC.
High Voltage Distribution is Doing It in DC
It is a common misconception that high voltage AC is better for long distance transmission than DC; it's not. What matters is the voltage, and in Edison's time there was no easy way to transform direct current, while simple transformers could change AC. In fact, DC transmission has lower line losses and doesn't need such high towers, because it is less likely to arc to ground. Siemens is building the world's largest HVDC system in China, 1400 kilometers carrying 5,000 megawatts. They are planning the world's largest underwater cable, to run from Australia to Tasmania, all HVDC.
Offices are Doing It In DC
In the commercial world, The EMerge Alliance has agreed to a 24 volt standard, and the industry is producing an expanding line of hardware that anyone can install and change, no electrician required. It is quick, easy, safe and green; according to the alliance, the new system will:
- Promote interoperability through reuse of system devices that plug-and-play mobility and simplicity.
- Promote sustainability with simpler system devices that have less materials (no AC-DC conversion components)
- Reduce energy consumption through state-of-the-art device controls and solid-state lighting.
- Facilitate the direct connection and use of energy from solar, wind, or other alternative energy sources.
- Provide improved energy efficiency through integrated load and source management
The current in a circuit is limited to 4.1 amps; it won't run a hundred watt lightbulb. But it won't electrocute anyone either, and will run just about everything we use today in our day to day lives. It doesn't need metal jacketed wires and doesn't need a ground, so it is cheaper to install. Since LED lighting and electronics use DC, they will be more efficient because there are no vampire loads and losses from the transformation and rectification.
Data Centers are Doing It in DC
A recent study by the Electric Power Research Institute showed that use of direct current increased efficiency in data centers by an average of 15.3%. it is easy to understand why; you don't have millions of power supplies converting AC to DC, with their fans running. The basic equipment is more efficient, and the overall cooling loads, a huge cost in data centers, are reduced significantly. As Caleb Garling pointed out in Wired recently:
Data centers typically convert AC power from the grid into DC power to charge their uninterruptable power supply (UPS) batteries — which provide back-up power when there’s even the flicker of an outage from the grid. But that DC current must then be converted back to a lower AC as it enters the center’s power distribution units (PDU), and then it returns to DC when it hits the server racks.
That's why Facebook built its huge new Prineville, Oregon data center around direct current. You just get rid of all that stuff.
Pretty Soon Your House Will Be Doing It In DC
Look around at what you use every day, and it is almost all DC; when LEDs become cheap and common in the next few years, about the only time you will plug anything in that AC is for your vacuum cleaner, and as Roombas scale up, even they will be able to dine on a DC diet. It's just the big stuff, the washing machine and fridge and air conditioner, that use the big power now.
According to to EPRI, the electric power research institute, the House of Tomorrow might well be DC. The output of solar panels and wind turbines is DC and is stored in DC batteries; every time you put it through an inverter you lose energy. Every time you plug in a wall wart to convert back to DC, you lose energy. In fact, according to EPRI, you might not plug in your electronics at all, because induction chargers might be built into the fabric of the house.
While the big loads, like air conditioners and fridges still exist, they can run even more efficiently on direct current, thanks to electronic variable frequency drives (VFDs).
Use of VFDs is on the rise, since controlling the speed of the motor to match demand can not only save energy but also optimize function. For example, being able to fine tune the motor speed of an air conditioner, and thus functions such as fan speed and air flow, can make room temperatures and conditions more comfortable.
As motor-operated loads become increasingly controlled through VFDs –very little will remain in a house that really needs AC power.
There are so many advantages, including the facilitating of the move to renewable and independent power sources.
Perhaps the biggest advantage of DC powering is that most of the distributed generation and energy storage sources—whether solar panels or fuel cells or microturbines or batteries—are inherently DC sources. You can connect your rooftop solar panel to a home’s DC wiring. And when you can finally buy that plug-in hybrid electric vehicle at the local dealership—why not plug that in to your DC outlet? Your car can either be charged—or be run as a generator to power the house.
But I think changes might go even further than that. Wiring is now installed in our houses like plumbing; it is permanent and put in when the house is built by electricians. Because nobody knew how people were going to lay out their furniture, outlets are mandated to be every 12 feet along the walls, with cords on lamps six feet so that dangerous extension cords are not used. That means that many of those outlets are completely superfluous. They all have a third copper wire in them too, to ground them for safety. Between the extra wire and the extra outlets, probably half of the copper in a house is superfluous. Then we face issues of child safety and the EMF radiated by alternating current.
But if it is low voltage and low amperage, wiring might stop being part of the fabric of the home; You might end up buying your whole electrical system at Home Depot or IKEA and just tape it onto the baseboards and lead wherever you want it.
None of this will be news to the off grid, RV or tiny house people; they have been living a DC life for years. But I suspect that once LED lighting becomes more affordable, the last reason for maintaining the dangerous and expensive 220/110 volt distribution system in our houses will be gone.
And who knows, we might even be driving Edisons instead of Teslas.