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Use of DC Power Can Save Energy




By Bruce Graham

In a recent opinion piece in the Wall Street Journal, the Institute for Energy Research laid out the huge costs involved in transforming the electric grid in the United States to run on clean power. This transformation is possibly decades away. 

As operators and constructors of buildings that consume energy, we need not simply wait for that transformation if we want to reduce energy use and emissions. Instead, we should look at how we use power. And when I say use, I don’t mean “conserve” power in the sense that we need to turn off/dim the lights when we are not in a room. We have great building automation systems that have been controlling our “conservation” of power for a long time, and we now even have economical solutions to provide the same for the home. What I mean is actually how we use electric power at the apparatus, no matter what it is. In general, all transistorized equipment, lights, and electronically commutated motors run on direct current (DC) electrical power. The batteries, of all sizes, we use daily are direct current. When we create native power via solar, wind, or kinetic energy harvesting, it’s in the form of direct current. And when we store power for demand response, emergency back-up or portable use, we store it in direct current. Do you see the connection?

There has been much back and forth between the advocates of alternating current (AC) and direct current (DC) over the years. But since the recent commercial development of power electronics, including high current (IGBT) transistors that can convert voltages more efficiently than traditional coil transformers, direct current use has started to make more sense than ever at many levels in power systems.  So while there’s no question that alternating current is still adequate for long distance transmission of power produced at large scale utility plants, it’s becoming less than adequate for end of the line use, and even far less adequate for end of the line distributed power creation and coupling.

Think of your office floor or home as a “nano” or “micro” power grid. Here, your power consumers like lights, blinds, motion detectors, security sensors, ceiling fans, etc., all run on DC power, which is brought to each directly. (Just like our personal devices, some apparati, like lights, are so efficient that they have built in batteries that charge when power is available and then use the battery power when it is not). In our spaces now we bring alternating current to each and then very inefficiently transform the power to direct current, wasting energy and dollars and creating unwanted and unplanned for heat. Think of the charger you have for your portable devices like your laptop. When you charge you actually waste a lot of energy and it is evident by the heat of the charging brick. Today we can bring direct current power directly to these apparati so efficiently the power loss and heat gain are negligible.  Also, in this line of direct current power, we can add power supplied from wind, solar, etc., at any location without the DC/AC/DC transformation and the need to synchronize to the alternating line current in the middle. (Some analysis of the DC/AC/DC transformation has shown losses of energy greater than 14 percent).

In fact, there is a similar example that we are all familiar with. It is called the Internet, though instead of a network of power, the Internet is a network of data. It connects many devices that are consumers of data (search and retrieve) and many devices that are suppliers of data (posts and store) — noting that these devices can be nearly anywhere and even moved around in the network and operate either connected or disconnected from the network for periods of time. A DC nano or micro power grid works the exact same way — we can plug in power consumers (i.e., lights), or power suppliers (PV, wind, or even your hybrid vehicle) anywhere. Like the Internet, the possibilities for improvements on both the supply and demand side provided by a mesh network of interconnected nano or micro power grids and macro (utility) grids is nearly unlimited and can be extremely cost effective. And battery storage at a small scale is manageable if needed. Brian Patterson, president of the EMerge Alliance, a non-profit hybrid ac/dc microgrid advocacy and standards group,  has used the term coined by Bob Metcalfe, father of the Ethernet,  as the “Enernet” (energy network ) to describe such a system.

Part 2: Advantages of In-Building DC Power Use


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posted on 8/31/2015