DC Data Centers: A Necessary Paradigm Shift for Sustainability and Savings
DC power supplies enable leaner, more powerful data center system architectures that — through skillful planning — can also mitigate total system cost. But first, we must make a paradigm shift. DC data centers
Vast amounts of unused electricity simply disappear in data centers, lost to tedious, continuous, and ultimately unnecessary conversion and transformation processes. But switching the prevailing alternating current (AC) power supply to direct current (DC), which would effectively eliminate a significant percentage of these losses, will require a massive paradigm shift. DC data centers
The benefits of the energy conservation that switching data center architectures to DC power supplies would elicit extend well beyond ecological sustainability, though. DC power supplies enable leaner, more powerful data center system architectures that — through skillful planning — can also mitigate total system cost and the time and effort invested into installation and upkeep. So, enduring the growing pains of a shift in the status quo will be a worthwhile endeavor.
If AC is Less Efficient, why is it the Norm?
The fact that any mention of primary voltage electricity almost certainly refers to AC power doesn’t mean that will always be the case. During the War of the Currents at the end of the 19th century, AC advocates Nikola Tesla and George Westinghouse pitted themselves against Thomas Alva Edison, who made a strong case for direct current (DC), in the world’s first formal format war. We know now how the story ends, but the outcome wasn’t so clear at the time.
Direct Current: Non-Standard, but not Non-Existent
Thankfully, Edison’s defeat in the fight for a standardized source of primary voltage electricity didn’t amount to the end for DC. In fact, there are a lot of DC-powered electronics in the digital age, including entertainment devices, industrial IT equipment, communication technologies, electric vehicles, and more. At the generation end of the energy supply chain, technologies are quickly evolving to mimic the AC primary power chain in alternative energy equipment that generates direct current, such as photovoltaics, fuel cells, and wind turbines. There is also an important exception to the otherwise prevailing use of alternating current as the standard for power transmission: high-voltage, direct-current (HVDC) transmission systems, which enable the low-loss bulk transmission of electrical power over long distances.
So, despite having lost the battle over standardization well more than 100 years ago, more and more electricity is now supplied in DC form in at least one segment of the power supply chain, which is comprised of energy generation, transmission, and storage equipment and, at the far end, powered devices. Although DC to AC conversions can be required to reduce voltages for certain technical reasons, AC voltages and frequencies are — in many cases — largely still used due to the prevalence of existing infrastructure built to support standardized AC power. However, these conversions always result in fairly significant power losses and sums of wasted energy and always generate unnecessary heat, which also negatively affects electronics systems and could easily be avoided by switching power supply systems to DC.
Energy-Guzzling Data Centers
According to an independent British report from 2016, data centers consume approximately 3% of the world’s electricity and account for 2% of total greenhouse gas emissions, which, considering the vast expanse of electronic systems and devices currently in existence, is pretty significant. In fact, the global ecological footprint of data centers is roughly equivalent to that of the airline industry, which is often vilified for its environmental impact. Globally, data centers have consumed an annual average of 416.2 terawatt hours (TWh) of electricity for the past several years, while the entire United Kingdom — which is home to more than 66 million people and consistently ranks amongst the top 10 world regions with regard to gross domestic product (GDP) — only consumed an annual average of about 300TWh in the same span. So, it’s safe to say that today’s data centers are real energy guzzlers.
The metric typically used to evaluate data center efficiency, the Power Usage Effectiveness (PUE) value, compares the total amount of data center energy consumption to the amount of energy consumed by its computers. For example, a PUE value of 1.3 means that 30% of the energy consumed was dissipated as heat rather than utilized. This may sound like a lot, but it’s actually considered an excellent PUE value. Values of around 2 or higher are more the rule than the exception.
Why do These Losses Occur?
Power losses occur all over the place — in processors, in cooling devices, in distributed power systems, and more. Traditional data centers draw their energy from a medium-voltage AC line. This alternating voltage is first transformed down and converted to DC in order to feed the batteries in the uninterruptible power supply (UPS) systems that provide data centers with enough stored power to support continuous operation for at least a span in the event of a serious power outage. The voltage is then converted back into AC and supplied to data center’s power distribution units (PDUs), which feed individual server power supplies before being converted back to DC to power the servers themselves, which work off of DC. During each of these many conversions, energy is dissipated in the form of heat loss. To maintain the efficient operation of the various data center systems, this heat loss must be cooled and discharged, which requires additional components, like fans and heatsinks, and — you guessed it — more power.
The DC Approach to Data Centers
Since every AC to DC conversion results in power losses and heat generation and data center servers already work off of DC power, providing data centers with DC power and continuing to use it as consistently as possible throughout the power chain makes perfect sense. To make this change by using as much existing infrastructure as possible, the incoming medium-voltage AC would be transformed down and converted to DC using a high-power rectifier. The DC power would then supply the batteries for the UPS before being transferred to DC switchgear for further distribution to new DC server power supplies and, finally, to the servers, which already use DC supply voltages. An even more effective model could also swap out the traditional AC grid power for direct DC power supplies generated by alternative energy systems, including solar- and wind-power systems.
Advantages of DC Data Centers
The DC approach to data center power architecture employs significantly fewer components than the current AC approach. Fewer components take less time to install and service, reduce the potential for errors, increase system reliability, and mitigate installation and maintenance costs, which makes the DC approach a cost-effective solution as well. According to a study conducted by Nippon Telegraph and Telephone (NTT), data center system reliability can be expected to experience a tenfold increase simply by virtue of being less complex. In addition, according to calculations and studies by companies including ABB, Amstein + Walthert, and Stulz, eliminating the various power transformations and conversions achieves a 10% boost in supply-to-server efficiency, reduces infrastructure investment costs by around 15%, and slashes the amount of space required by around 25%.
DC data center architectures also improve the quality of the power supply. They eliminate problems with unwanted harmonic waves and harmonic distortions, as well as the need for phase compensation, synchronization (for coupling the various sources and networks), and even rectifiers and inverters since the batteries are directly connected to the DC supply.
Plus, since data centers are almost exclusively located in rural areas due to the higher cost of more densely populated land, it’s much easier to integrate renewable energy sources such as photovoltaics, fuel cells, or wind turbines, especially since they already supply electricity as a direct current.
There are already some DC data centers in China, Japan, the United States, Germany, and Switzerland. However, there are not yet any binding standards to adhere to. The International Electrotechnical Commission (IEC) has set out to create the missing link with standardized plug and socket devices according to TS 62735. The IEC TS 62735-1 standard for power distribution systems up to 2.6kW was adopted since August 2015 and IEC TS 62735-2, for power distribution systems with outputs of up to 5.2kW that can no longer be separated under load, was approved in December 2016.
The next step is to approve a device-side equivalent. Several different approaches to DC connectors have been brought to market, but none have been able to prevail due to the current lack of standards. As such, various providers are working with the IEC’s standardization body to create an internationally recognized standard for DC plug connections based on the previous AC standard IEC 60320.
The global conversion of data center voltage supplies will need to be a gradual one to prevent all of the powered devices from needing to be switched from an AC to a DC supply all at once. However, solutions in support of this sea-change, including equipment that can feed data center devices with both an AC and a DC supply, are actively being sought. The power supply units of these devices can process both supply voltages, but an internationally effective solution must also ensure that all safety-related precautions are accounted for.
Where there is light, there is also shadow. This universal maxim also applies to DC data centers. Compared to the prevailing AC system architectures, there are still relatively few DC data center architectures. As such, there is a lack of data regarding their long-term performance and benefits. The availability of DC components is still in its infancy as well, and these components will not only require standardization but will also require a new systems approach to DC supplies with integral planning from the grid to the chip. For instance, since losses occur in every power system, DC data centers still experience losses like heat loss and, as such, will also require cooling systems with a DC supply. They will also need DC air conditioning systems, fire protection systems, access control systems, and building control systems, amongst others.
Mass market cooperation between all of the manufacturers, suppliers, engineers, designers, standards organizations, operators, and other members of the power supply chain will be necessary to achieve this massive paradigm shift in an efficient manner and share in the many benefits of DC data center system architectures.
Data centers based on DC power supplies have enormous potential. Benefits include considerable energy savings, as well as significant savings on operating and infrastructure costs, physical space requirements, and the amount of time required for installation and maintenance. Since they use fewer components, they also offer higher reliability performance. DC data centers also have the ability to directly harness DC power from renewable energy sources without additional transformation or conversion processes, which would further boost efficiency, overall systems cost, and sustainability. Finally, the quality of DC power is unequivocally better than that of AC. As such, connectivity component suppliers like SCHURTER and international standards organizations like the IEC are actively working together to realize the great potential of DC data center architectures.
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