A Case for the Return to DC Power

Lucas Hamilton

As we have seen many times, tides change and we return to previous processes because they are actually more efficient.  So why shouldn’t this be true of electric current?

If we look at onsite power generation for buildings like photovoltaics (PV) we see that they are generating Direct Current (DC). In order to move toward more sustainable solutions like photovoltaics there will need to be a return to Direct Current (DC) for our power.

We are seeing a resurgence of DC into our lives through items like lighting, with the switch to LEDs, and computers. These are two of the biggest power consumers in our commercial buildings and they run on DC.  When we convert Alternating Current (AC) to DC power 20 percent of the power is lost in that transference.  Feel the heat coming off your computer power plug. That heat is energy loss. Now imagine you have a building with PV on the exterior generating a fixed amount of DC current. If you invert the DC to AC in order to put it into the grid (-20 percent) and then plug your computer power cord into an outlet to get that power back, you loose 20 percent again. With the technological limitations we have with PV efficiencies, limited surfaces upon which to install the cells, and ever increasing demands for power within our buildings, how can we afford to keep loosing power to these inversions?

It is time to reevaluate DC in our lives! As we move toward more renewable energy, like photovoltaics (and they will play a larger part in our lives moving forward) we should consider how many of the appliances we use could be run on DC.  At the same time, if you are planning a new home or building and will be employing photovoltaics, consider keeping more DC current available throughout the building. Keeping things that are DC as DC and not plugging them to AC circuits makes sense.  Maybe it’s time for a second plug in the room.  A DC plug.

Lucas Hamilton is Manager, Building Science Applications for CertainTeed Corporation

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  • Mike:

    Our group has invented a device that converts 220 to any DC voltage your specify. This DC voltage then can be bussed and tapped into by various loads like LED Lamps and anything else that runs on DC.
    Mike

  • EP:

    Why not just make the conversion of AC to DC and DC to AC more efficient? It’s been done with gasoline car engines. Distributing DC is no picnic. They used to think gasoline engines could never be efficient AND powerful but look now.

  • I think your 80% conversion efficiency numbers are a bit conservative. Real world conversion efficiencies in both directions currently range from 85 to 95%. But the reason for not deploying DC on a large scale is voltage drop. If you put solar panels on top of a tall building and then try to run low voltage DC throughout the building, the cost of the copper wire be astronomical since you would need to size it to account for voltage drop.

    Early solar powered homes did use DC wiring and cigarette lighter sockets were common in the 1970s and into the mid-1980s. Solar advocates moved away from this once inverter eficiencies moved beyond 85%, partly for convenience and partly for safety. It was also more cost effective

    In terms of using energy for interior lighting it is far more cost effective to use daylighting strategies than DC powered lighting systems.

    • Guy,
      Thanks for the very insightful comment. You clearly have solid experience in this area and I, for one, welcome learning from all sources. Looking at your website, you have a great deal to offer regarding solar technology and sustainability. I hope our readers will take the time to visit your website http://www.arttec.net as well.
      Lucas