Green DC for Datacenters, Why Not Homes Too?
Posted by Bob Warfield on December 19, 2007
There are some posts up about how much greener DC power is for datacenters. Phil Windley says a single server may have a larger carbon footprint than a 15 mpg SUV. That was an amazing statistic for me to hear. CNet reports there is a startup called Validus that is working on the idea of supplying DC within datacenters instead of AC to help combat the waste.
The idea is that converting AC to DC is wasteful of energy, particularly when it is done over and over again inside every digital box. Whether we’re talking wall worts for small boxes or full-on PC power supplies (or worse) for bigger boxes, it is wasteful. I don’t find that hard to believe. All these power supplies get warm to the touch. Heck, my PC supply has a big fan built right into it. This leads me to ask: If this is a good idea for datacenters, why isn’t it a good idea for homes too?
I wonder what percentage of the power we use in our homes would be better off DC rather than AC? Most electronics immediately want to convert to DC. All of our computers and home entertainment electronics are in that category. Many things with motors are not currently in that camp, but they could be with DC motors. I’m speaking of refrigerators, for example. It’s not clear to me that something like an electric range or water heater really cares one way or the other. Certainly anyone that has built a PC can see that it would be easy enough to give up the power supply. The principle issue is simply providing cabling with the right voltages. It’s the same cabling that comes out of your power supply today. One issue would involve those voltages. It’s very easy to change voltages in the AC regime with a simple transformer. DC is more problematic. Unfortunately, even PC’s like several different voltages to be available. A typical PC power supply offers -12V, -5V, 0V (ground), 3.3V, 5V, and 12V. Phew, that would be a lot of outlets on the wall! I wonder what the chances are we could get by on fewer voltage options.
The other interesting thing is that DC is ideally suited for batteries and solar power. As it stands, those who wish to employ solar power have to run the DC output from their solar panels into an inverter to convert it to AC. Of course this costs energy through losses to make the transformation. If we had more of a DC-based economy, life would be better.
So why doesn’t the power company just provide DC instead of AC? There was an epic battle fought between Thomas Edison, a DC proponent, and Nikola Tesla, the father of many early AC inventions, that Edison ultimately lost. It turns out to be cheaper to generate AC with rotating machinery, and cheaper to transmit it over long distances. If we’re going to go DC, we need to do so at the “last mile”. It remains an intriguing idea. I’ll be on the lookout for an “appliance” power supply that will run multiple computers and save power.