To anyone who has a passing knowledge of the History of Electrical Engineering (yes there really is such a thing), the 1888 War of Currents figures as one of the most prominent events. It was Thomas Edison and DC vs. George Westinghouse and Nikolai Tesla championing AC. As you know, DC, or direct current — something you use with anything electronic, especially battery operated — presents a constant voltage level on the line. On the other hand, AC–or alternating current — something you use whenever you plug a cord into a wall outlet — presents a sine wave that alternates between plus and minus 169 volts 60 times a second, or +/-325 volts 50 times a second, depending on where you are in the world. [BTW, if you don't recognize those voltages, it's because, by convention we talk about the Root Mean Square (RMS) voltage which is the peak voltage divided by the square root of two, or 120 VAC and 230 VAC.] At the time it was a no-holds barred, knock down – drag out standards fight that would make WWE wrestling promoters blush over the promotional ethics used. Thomas Edison went around to state and local fairs zapping everything from dogs to elephants with AC to “prove” that AC was unsafe. He went so far as to invent the Electric Chair as a way of saying AC was so unsafe that it could be used to reliably execute criminals.In the end, AC won out because of two inventions — the transformer and the synchronous motor. The transformer solved the transmission distance problem of the day of getting power more than a mile away from the generating station. It did it by using the first secret of energy efficiency – using as high a voltage as you can. Being before the invention of electronics, DC didn’t have a technical answer. The second invention, the synchronous motor, allowed you to use the alternating current directly at the load — a motor to convert the electrical power to mechanical power, and now at the point of use without belts and pulleys. With the clever invention of the Electric Utility and government-sanctioned Monopoly model, AC and the power grid went on to become the Top Engineering Achievement of the 20th Century, and never looked back. 122 years of tradition, unchanged by progress And that’s pretty much the way we have left it ever since, or as I like to say: 122 years of tradition unchanged by progress. But consider this from the Center for Power Electronic Systems (CPES): by the end of 2010, power electronic systems are expected to control 80% of all electricity used. If you look under the covers, you actually find that it’s a lot worse than that. While AC is used between systems and components because it’s been the standard for over 100 years, internally, lots of things convert to or from DC. In fact, anything with a logic chip in it or consumer electronics is using DC. And when you look at alternate energy production, Photovoltaic, wind turbines, water pico-turbines, they are almost always DC. Now if you are asking “so what?” I’ll tell you what: energy efficiency. Maybe it’s time to really question our assumptions; what if everything we “know” is wrong? The two secrets of energy efficiency are using the highest voltage you can and doing the least conversions. In fact, we at Intel Labs followed a natural progression into our new Energy Systems Research Lab because we started out trying to optimize energy efficiency for Intel. We started with the processor. But today, the processor in a laptop running typical office applications constitutes only 5% of the total power used by the system. Thus, optimizing the last 1% of efficiency here is well beyond the point of diminishing returns. So we have expanded our view over the last five years to the system and then to the enterprise. DC – An idea whose time has come and gone … and come again In 2006 we participated with Lawrence Berkley Lab in a study of power for the datacenter. The published, peer- reviewed findings are that you save an astounding 28% over the current North American AC power distribution practices by using DC. This kind of energy efficiency improvement simply does not exist at the component level any more. In 2008 we teamed up with EYP Mission Critical, an HP Company, and Emerson Network Power to examine how DC power distribution for a datacenter stacks up against high-efficiency AC (called 400Vdc before the new standard proposed by EPRI) powerpoint slides and white paper. Looking at a 5.5MW datacenter expansion as an engineering study, we found that even high-efficiency AC is still at least 7% less efficient than 380VDC. Even the Green Grid, which has members who are heavily invested in the current AC distribution, agreed the efficiency savings are significant. In fact two years ago, the Intel Eco-Tech Office held the first IT “Great Debates” and the first of three was AC vs DC in the Datacenter. Thus, the main benefits from 380VDC distribution for the datacenter are: - 7% Energy Savings vs. High-Efficiency 415VAC; 28% vs Current Typical 208VAC - 15% Less Capital Cost - 15% fewer PSU components - 33% Datacenter Space Savings - 200% Reliability Improvement, which goes to 1000% if you directly connect the battery bus - Elimination of harmonics and inherently immune to other AC power quality issues - Natural affinity to alternate energy generation (Photovoltaic, and wind are ~400Vdc internally, and you actually lose energy & efficiency when you are forced to convert to AC) So with all these advantages, who wouldn’t jump all over this? Turns out lots of folks are wading into the DC waters. Japan is out in front with their Green IT initiative that started in 2009. In December, they proposed a standard for what is now being called 380Vdc. The Electric Power Research Institute (EPRI) has DC Power Partners group that is working through a lot of the details of a 380Vdc Standard. They have just elected to fold under the EMerge Alliance which has been championing low-voltage DC for the office. The DC Power Partners has proposed a voltage/time envelope to match the well known CBEMA spec for AC-powered IT equipment at 110VAC. Connectors have been defined for power supplies and are available in production quantities, as well as connectors for rack interconnect using the existing IEC connector and standards. A +/- 190 VDC distribution wiring scheme is being proposed to address human safety and is actually safer than Vac distribution (lower voltage and lower human hazard). All of these technologies were reviewed at the latest TC38 working group meeting in Tokyo, Japan. The neatest thing is that other industries are starting to align around the 380Vdc standard – Photovoltaic panels and Hybrid Vehicles and Florescent lighting are already using these kinds of voltages and are snapping to this standard. In New Mexico, Intel Labs just opened a new lab, the New Mexico Energy Systems Research Center (NM ESRC) for collaborative research, with the participants in the New Mexico Green Grid. One of the first projects in the NM ESRC is to connect up a DC microgrid between the existing 10kW Photovoltaic Array, DC-powered servers (working with Intel IT) and then expand the microgrid to include an interface to energy storage (DC), high-efficiency office lighting and power (also DC … think laptop plugs in without a power cube), and then grid-tie it to the AC power on campus. To borrow the WWI doughboy’s battle cry: Thomas Edison, we are here!
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