DC Power Revisited

DC power has been proposed for use since Edison debated with Tesla about which should be used.  Ultimately AC has been used more since it allows transmission over long distances which suited having large, centralized power plants.  But with so many of today’s devices and systems using  we see a resurgence of DC power

AC power is everywhere – power grids to commercial buildings and down to the smallest devices.  However, so many of our newest devices require DC power to operate or charge a battery. To provide DC power from the AC feed, the devices rely on power supplies that convert power from AC to DC as well as step the voltage down to the needed level. This transformation introduces a small loss of power due to inherent inefficiencies, no matter the voltages, size of equipment, or power needed.  When those voltage transformations are added to each other, from the source to the end device, the total power lost is much more noticeable.

For DC devices and loads, DC as the power supplied can offer improved energy efficiency and reliability.  If DC power is distributed at the data center room level or further upstream, the power distribution can reduce the number of required conversions and therefore lower the overall energy lost.  In most DC power systems, higher efficiency equipment is used to convert AC to DC power before distribution to the loads.  In the case of data centers, using DC power can help greatly reduce the number of varying transformations before serving the needed loads – which are typically DC powered components in the servers themselves.

DC power can also directly support lighting systems (LEDs), security door locks, actuators, sensors and controls, and more.  DC power can also be more efficiently coupled with renewable energy generation (solar, wind, etc.) and energy storage systems (batteries).

One reason is that DC power is becoming popular again is that Power over Ethernet (POE) has advanced enough to deliver power to multiple systems and equipment which is needed for buildings and controls. POE carries both data at a fast rate and can be managed remotely while delivering power.  Since our data centers are full of equipment that operates on DC power and DC power generation is typically renewable, it would seem that DC distribution would make an efficient approach for improving data center performance by eliminating the conversion losses. 

Although AC power is the most prevalent, the use of DC power in other commercial buildings is widespread and growing to gain those same efficiencies.  Dedicated DC power systems have been installed at workstations to negate the conversion losses for DC equipment.  IT networks, computers, phones, lighting, televisions and more operate predominantly on DC power and eliminating just one conversion from AC to DC for all of those uses adds up to bigger savings overall.  For data centers, the amount of power magnifies the savings.

Facebook and SAP have DC power pilot programs to capture the savings as well as reduce the amount of equipment in their data centers.  Lawrence Berkley National Labs has studied DC power for data centers and estimated that savings could easily be over 20% as compared to AC power. 

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