Page 33 - Solar Power in Building Design The Engineer's Complete Design Resource

A BRIEF HISTORY OF THE PHOTOELECTRIC PHENOMENON 3

Tesla: “How will the dc power a 1,000 horsepower electric motor as well as a single
light bulb? With AC, the largest as well as the smallest load may be driven from the
same line.”

Edison: “The most efficient and proper electrical supply for every type of device
from the light bulb to the phonograph is Direct Current at low voltage.”

Tesla: “A few large AC generating plants, such as my hydroelectric station at
Niagara Falls, are all you need: from these, power can be distributed easily wher-
ever it is required.”
Edison: “Small dc generating plants, as many as are required, should be built
according to local needs, after the model of my power station in New York City.”

EARLY AC DOMINANCE
After Edison introduced his dc power stations, the first of their kind in the world, the
demand for electricity became overwhelming. Soon, the need to send power over long
distances in rural and suburban America was paramount. How did the two power
systems compare in meeting this need? Alternating current could be carried over long
distances, via a relatively small line given an extremely high transmission voltage of
50,000 volts (V) or above. The high voltage could then be transformed down to lower
levels for residential, office, and industrial use.
While higher in quality and more efficient than alternating current, dc power could
not be transformed or transmitted over distances via small cables without suffering
significant losses through resistance.
AC power became the standard of all public utilities, overshadowing issues of safety
and efficiency and forcing manufacturers to produce appliances and motors compatible
with the national grid.

THE 100-YEAR-OLD POWER SCHEME
With ac power the only option available from power utilities, the world came to rely
almost exclusively on ac-based motors and other appliances, and the efficiencies and
disadvantages of ac power became accepted as unavoidable. Nicola Tesla’s develop-
ment of the polyphase induction ac motor was a key step in the evolution of ac power
applications. His discoveries contributed greatly to the development of dynamos, vac-
uum bulbs, and transformers, strengthening the existing ac power scheme 100 years
ago. Compared to direct current and Edison’s findings, ac power is inefficient because
of the energy lost with the rapid reversals of the current’s polarity. We often hear
these reversals as the familiar 60 cycles per second [60 hertz (Hz)] hum of an appli-
ance. AC power is also prone to harmonic distortion, which occurs when there is a
disruption in the ideal ac sinusoidal power waveshape. Since most of today’s techno-
logically advanced on-site power devices use direct current, there is a need to use
inverters to produce alternating current through the system and then convert it back
to direct current into the end source of power. These inverters are inefficient; energy