Would we have a DC Grid? A system where high voltage DC would be
transmitted over grid we have today, inverting power to AC when required
by the occasional motor or AC load?
Perhaps, but in any case, today we have an AC grid, with a zillion little
rectifiers loitering at its edges. Yes - a zillion. Every television,
computer, cellphone, microwave, fluorescent lighting ballast, cordless
phone - a zillion. And they're each sucking up a watt or two, often 24 hrs
a day. Arthur Rosenfeld, head of the California Energy Commission, calls
them our "Energy Vampires."
And what's more, near the 'edge of the grid' where these rectifiers
convert from AC to DC to power our electronics, we're installing DC
generators; solar photovoltaic cells, wind generators, fuel cells, and
batteries. Each of these produces clean direct current, which we spend
energy inverting to alternating current, synchronizing, avoiding
islanding, and sending it into a transmission and distribution system that
is rife with losses.
Finally, before it's used, this inverted power is rectified again, back to
its original DC form. This round-trip journey to nowhere is expensive.
The rectifiers were built with only economy in mind. They're cheap, hot,
and inefficient.
So what's going to happen?
First, centralized rectification. One rectifier, probably at the
building's service entrance, will provide DC power through a separate, or
even the same electrical systems. Currently, commercial fluorescent
lighting systems powered by DC have a separate DC wiring system. It's easy
to convert the AC lighting system wiring to DC. In the future, we'll see
wiring systems that provide AC through the hot and neutral wires, DC
through the neutral and ground - the patented outlet for this already
exists.
The Nextek Power Gateway is such a centralized rectification system that
takes power first from its DC buss, powered by locally generated energy
(like solar photovoltaic), then, as needed, from the AC grid, rectifying
only what's needed when clouds pass overhead or at night. An additional
advantage of this architecture is that the system is not subject to
anti-islanding laws and can continue to power the load during a power
failure (see related links, following article).
Second, the Universal Transformer. In development now are several designs
for a solid state transformer that will provide whatever power is needed,
at whatever frequency. The efficiency and flexibility of this device will
cause dramatic improvements in the energy profile of the grid (see related
link following article).
Next, the DC Grid? The feasibility and the necessity of a DC transmission
system is an unresolved topic but there are significant benefits involved.
These will be better outlined in an upcoming white paper soon to be
released by EPRI.
The battle between AC and DC was originally fought by Edison and
Westinghouse at the turn of the century. The invention of the AC
transformer allowed Westinghouse to build the power plant at Niagara Falls
in contrast to Edison's backyard generators. Westinghouse won, but "Edison
was Right."
About the author...
Mark Robinson is VP Sales & Marketing for Nextek Power Systems of Long
Island, NY. He is a licensed master electrician and a Microsoft Certified
Engineer. Nextek Power Systems provides their Gateway for Power to
commercial buildings to power lighting systems and Variable Frequency
Motor Drives with clean DC from locally generated sources.
The information and views expressed in this article are those of the
author and not necessarily those of RenewableEnergyAccess.com or the
companies that advertise on its Web site and other publications.
