DC POWER: TWO ENERGY BIRDS, ONE SHINING STONE

November 6, 2017 § Leave a comment

Energy resiliency, especially in relatively isolated communities, can largely be achieved by local production and distribution. In the mid to low latitudes, solar intensity will favor solar electricity. And it is getting cheaper by the day. A recent winning tender for utility scale solar in India came in at around 3.6 cents per kWh. That is cheaper than many coal plants, certainly any newly constructed ones.

To really take advantage of solar electricity, note the fact that the electricity is output as DC. Conversion to AC, transmission, and then reconverting to DC at each device such as LED lights, computers and cell phones, is wasteful. Furthermore, useful equipment, such as fans and compressors, use less electricity for the same output, when running on DC. A DC powered “brushless motor” fan consumes between 40% and 70% less energy than one running on AC. Compressors are the workhorse of those two other common household appliances: refrigerators and air conditioners. However, these last two are currently not mass manufactured in DC use mode; they ought to be. Curiously, the latest refrigerators do use DC in the critical components, even though the input power is AC. DC fans are well on their way in India; a trade partnership could have them delivered here. For rural communities, DC powered well pumps exist, with dozens of manufacturers in India.

A possible architecture in a community could have the following features:

Small solar farms attached to each development, commercial or residential. Since people love trees around the homes (especially in low to mid latitudes), and solar panels prefer absence thereof, rooftop solar is contraindicated. Furthermore, on-ground solar is lower cost to install and maintain, and can take advantage of tracking of the sun.
DC microgrids to conduct the power to the users. For long distance transmission, AC is preferred. That is pretty much why Edison lost out to Westinghouse about a century ago. But for the short distance of a microgrid, DC works just fine. Preferably, the homes and establishments ought to be wired for both DC and AC, as are data centers today. The DC wiring would feed the current DC devices. Eventually, homes ought to convert to all DC devices. In the meantime, the AC portion would be fed from one single DC/AC converter at each home junction box, at relatively high efficiency. All this is compatible with grid power, which should increasingly be deemphasized. Again, in this instance we are discussing moderately or totally remote communities. A military base would qualify as well, for additional reasons of energy security.
Community waste to biogas is simple to execute (landfills, animal waste or water treatment plants). The biogas can be used as fuel for many purposes, but also for generators with DC output.

In short, solar electricity, combined with a DC microgrid could serve the purpose of resiliency. At the same time, the proper use of the attributes of DC power could also cause less energy to be used for the same utility. This checks both the resiliency and energy efficiency boxes. Resiliency may be viewed as a measure to adapt to climate change. This approach, to a degree, simultaneously addresses mitigation.

Vikram Rao

Research Triangle Energy Consortium