As power density increases, data center operators and service providers need to take advantage of every opportunity to reduce power consumption and improve power efficiency. Nowadays, most data centers use alternate current (AC) power distribution system. Recently, however, the data center industry is exploring another choice — direct current (DC) power distribution system.
Direct Current (DC) Power refers to a form of power that is most commonly produced by sources such as solar cells and batteries. As its name suggests, direct current (DC) means the current is linear and direct. It always flows in the same direction and does not oscillate between positive and negative terminals.
DC power can be used in many scenarios, from the charging of batteries to large power supplies for electronic systems, motors, and more. High-voltage direct current is used to transmit large amounts of power from remote generation sites. Common applications with DC power also include portable solar systems and other off-grid appliances in the solar industry.
Compared to AC power, which can transmit power over thousands of miles with very little loss, DC power plants can only transmit power up to a few miles. That's why today's industrial world is dominated by AC power. But in a data center, the energy transport is confined to the data center facility itself. Therefore, the consideration of transport loss when using DC in the data center is less critical. Plus, advances in DC power technologies have made it more efficient and easily regulated.
As there has been a growing interest in moving to DC for power distribution within a data center, DC power certainly comes with its fair share of benefits. Let's take a holistic view of the pros and cons of data centers with DC power.
Compared to the current AC approach, the DC power approach is less complex and uses significantly fewer components. Fewer components take less time to install and maintain, and mitigate the potential for errors, thus reducing installation and maintenance costs.
DC power distribution takes up less space as it uses less copper than a comparable AC system, and does not require the use of rectifiers when stored power is distributed during power interruptions. This means more floor space for server racks and cooling equipment.
The DC power distribution also improves the quality of the power supply. With AC power, there are losses of power every time the current changes directions. While DC eliminates problems with unwanted harmonic waves and distortions, as well as the need for phase compensation and synchronization.
Modular and scalable
Energy storage devices like batteries can be placed directly on the existing DC power architecture, and loads can be added as needed without having to change the current power network. This adds up to faster installation and upgrades as the facility grows and the load increases.
Integration with other sources
It’s well documented that a DC system makes it easy to integrate on-site energy sources like solar panels, fuel cells, or wind turbines that also produce DC power. This has become increasingly appealing as more data centers are moving to green data centers.
Despite the long list of benefits of DC power, there are some limitations to consider.
Lack of standard
There is no industry-defined standardization for a DC power data center yet. DC power systems are still missing an agreement on a standard for electrical voltages and electrical connectors.
If you plan to change the existing AC power architecture to support DC power, there is certainly a cost involved which the industry may try to avoid.
Limited DC power resources
A DC power data center will also need DC air conditioning systems, fire protection systems, access control systems, and building control systems (as well as DC power-consuming equipment like DC servers, networking switches, etc.). However, there is a limited number of those infrastructure on the market that run on DC power supplies. It makes DC power distribution system a difficult choice for data centers.
Lack of knowledge
Compared to the prevailing AC system in data centers, there are relatively few DC data center architectures. It means a lack of data about their long-term performance and benefits. Thus, data center owners and operators have limited knowledge and experience when it comes to running a DC power data center.
Just as there are centralized and distributed UPS systems, there are centralized and distributed DC power distribution systems. In a centralized DC power architecture, the power is distributed from a central location at the user voltage. While in a distributed DC power architecture, power is not converted to DC until it is close to the equipment consuming the power.
Compared to a centralized one, a distributed DC power architecture has some unique advantages. To start with, power doesn't have to be distributed from a central place at user voltage. So there are no safety concerns with higher voltage, and cables do not need to bear high currents. Power can be transferred to power-consuming equipment using smaller cables thus incurring lower losses.
Additionally, with hot-swappable and replaceable modules for rectification and battery storage, a distributed DC power architecture is more modular and makes the system more maintainable.
As is mentioned above, there are a few hurdles standing in the way of wider adoption of DC power systems in data centers.
First, there is a lack of industry-defined standards, which will be needed for DC to be a viable choice. The cost involved in retrofitting the existing AC systems also makes it a challenge to opt for DC power.
Moreover, there is a limited selection of indispensable resources such as DC power supplies for servers, air conditioning units, fire protection gear and building controls that run on DC.
The greatest challenge of all is lack of knowledge among data center owners and operators. They have to face questions like where to put the AC-to-DC conversion, and how to engineer an energy storage device on DC systems. Obviously, it takes some time for the industry to be more familiar with the long-term performance of DC systems.
Despite some obstacles on the way, DC power data centers still have great potential because of all the benefits they offer, such as significant savings on operating and maintenance costs, and physical space, better power quality, and easy integration with other sources.
However, before switching to DC power systems, data center owners and operators have to look closely at their existing networking and power infrastructures to decide whether they should make the switch.
International standards organizations like the IEC are actively working on ways to unleash the enormous potential of DC power architectures in data centers. With the development of data-heavy, next-generation technologies, it may not be long before DC power becomes the new normal.