Director, Telecom Products, Analog Mixed Signal Group
Power over Ethernet (PoE) is an increasingly important technology for utility executives. The high-power version, as defined by the IEEE802.3at-2009 standard, allows simultaneous delivery of power and data on CAT5e and above cabling, which eliminates the need for electrical outlets in difficult-to-reach locations, and offers a number of network-enabled energy-management options.
Devised originally to support the industry’s earlier IEEE802.3af-2003 specification as a method to power low-power devices such as IP phones and WLAN Access Points, PoE recently got a boost in capabilities, and now can also power devices such as high-definition (HD) network cameras, IEEE802.11n access points and thin clients.
In practice, the PoE standard defines a method for any device requiring up to 25.5W to be powered over Ethernet using two out of the four pairs of wires existing in a CAT5e cable. The voltage range that PoE supports is 50V to 57V, with a maximum ongoing current of 600mA.
Unlike the earlier IEEE802.3af-2003 standard, the more recent IEEE802.3at-2009 specification does not preclude utilizing all four pairs to source power, which means a maximum power of 51W may be delivered to powered devices, as required.
Additionally, the latest PoE specifications include mechanisms for device detection, classification, disconnection, and protection from overload/short conditions, while also adding many new advanced, “smart” energy-management capabilities.
- Powered Device (PD): the device being powered.
- Endspan Power Sourcing Equipment (PSE), or PoE Switch: an Ethernet switch with built-in PoE capabilities, directly connected to a powered device
- Midspan PSE, or Midspan: a piece of equipment placed between a non-PoE switch and a powered device, which enables a network to be upgraded to PoE capability without requiring any changes to the existing switch infrastructure.
There are two primary reasons that IT managers deploy PoE. First, PoE offers an ideal way to implement centralized power backup. By delivering power to devices from a central location over CAT5e cables, PoE offers a very simple and straightforward way to back up devices such as IP phones that require 99.999 percent availability.
All that is required is a single Uninterruptible Power Supply (UPS) in order to back up 24, 48, or hundreds of phones connected to a single switch room. Second, PoE simplifies the deployment of the electrical infrastructure because it is a Separated Extra Low Voltage (SELV) technology (<60V) and handles detection and classification at voltages below 30V.
This means PoE can be deployed without the need for a certified electrician, and in wet areas. It is ideal for deployments in locations in which AC outlets are not present, and/or are hard to reach or inconvenient to maintain, such as ceilings, attics and rooftops.
A third benefit of PoE PSEs is that, in many cases, they can be remotely managed, which makes remote re-sets and scheduled shutdowns possible. Taking advantage of this benefit can result in electrical-bill savings of as much as 73 percent, since devices like IP phones can simply be set for operation from 9 a.m. to 5 p.m. on weekdays, instead of 24/7.
Thanks to these benefits, PoE is rapidly growing in popularity. According to market analysts, over 30 percent of all Ethernet switches deployed in the enterprise are now PoE-enabled. It is estimated that 53 million PoE ports were shipped in 2008, about 45 percent (or 24 million) in the U.S.
At 10W per port, this means PoE is the delivery mechanism for approximately 2,102,400 MWh of energy consumption every year in the U.S. alone (and doing so much more efficiently than alternative approaches for generating DC power from AC).
PoE opportunities for Electric Utilities
PoE presents electric utilities with an unique opportunity for incentivizing customers to make investments in PSEs that can save thousands of MWh per year. The biggest savings would be realized from deploying equipment that can be programmed to be shut down at pre-determined times, which could reduce power consumption by over 70 percent.
There are challenges, however – first, there is no way to enforce PoE utilization, and second, because PoE deployment requires manufacturers to invest in material costs, this is not something utilities would be normally inclined to create incentive programs for. Utilities have already struggled with this situation using traditional approaches to power efficiency; i.e., making sure every conversion in a system is done in the most efficient way, which, similarly, is normally associated with costs for the manufacturer.
Incentivization becomes much more practical, however, when there is a way to measure and predict return on investment. For this reason, Microsemi created its Green PoE Certification Program, which addressed the challenges faced by the PoE switch industry because there was no un-biased way to test PoE switch efficiency.
While many firms like Miercom perform Ethernet Switch efficiency testing, these tests related only to the power consumed when sending data packets, without any PoE loads. While this is useful for non-PoE switches, this measurement is meaningless for PoE switches, for which approximately 90 percent of the power is used to power PDs, and 10 percent to power the data switching components.
Microsemi’s Green PoE Certification program changes the picture, by providing a simple way to test efficiency. The data is not tested at all — only the efficiency with which PoE power is delivered. The ratio DC out/AC in is measured in two states: full power and half power load for the complete switch.
This also serves to automatically normalize the test according to the number of switch ports being tested, and allows comparison between 16, 24, 48 or any other number of ports in a system. Finally, this method also allows for the testing of midspans, which are an increasingly important platform for deploying PoE in a highly cost-effective and flexible manner.
Microsemi’s Green PoE Certification criteria for “Green-ness” is also straightforward: the top 25 percent of switches in terms of efficiency are green. The others are not. In discussions with utilities, most agree that it is a very appealing proposition to give incentives to IT managers who deploy green PoE PSEs, knowing that there will be substantial savings realized from deploying a green switch or Midspan as compared to equipment without PoE capability.
This value proposition extends to the smart grid, as well. As PoE is deployed in the emerging smart grid, it will be possible for low-priority users to be shut down in case of demand peaks, and one can conceive of a solution that integrates Smart Grid controls and PoE controls.
This would allow utilities to potentially instruct users to shut down their lowest-priority PoE devices to save power, rather than implementing complete shut-down plans. This capability can allow systems to survive natural catastrophes and tough summers in a much better shape than today.
Whether in the data center or in the smart grid, PoE is emerging as a technology that can be used by electrical utilities to increase the level of control that their customers have over power consumption. Additionally, PoE offers a powerful new way to incentivize customers to save power and reduce the need to build more energy production capacity.