Page 34 - Solar Power in Building Design The Engineer's Complete Design Resource

4 SOLAR POWER SYSTEM PHYSICS

is lost (up to 50 percent) when these devices are used. This characteristic is evident
in many of today’s electronic devices that have internal converters, such as fluores-
cent lighting.

ALTERNATING AND DIRECT CURRENT: 1950 TO 2000
The discovery of semiconductors and the invention of the transistor, along with the
growth of the American economy, triggered a quiet but profound revolution in how we
use electricity. Changes over the last half-century have brought the world into the era
of electronics with more and more machines and appliances operating internally on dc
power and requiring more and more expensive solutions for the conversion and regu-
lation of incoming ac supply. The following table reflects the use of ac and dc device
applications of the mid-twentieth and twenty-first centuries.

AC DEVICES—1950 DC DEVICES—2000

Electric typewriters Computers, printers, CRTs, scanners
Adding machines CD-ROMs, photocopiers
Wired, rotary telephones Wired, cordless, and touch-tone phones
Teletypes Answering machines, modems, faxes
Early fluorescent lighting Advanced fluorescent lighting with electronic ballasts
Radios, early TVs Electronic ballast, gas discharge lighting
Record players HDTVs, CD players, videocassettes
Electric ranges Microwave ovens
Fans, furnaces Electronically controlled HVAC systems

As seen from the preceding table, over the last 50 years we have moved steadily from
an electromechanical to an electronic world—a world where most of our electric
devices are driven by direct current and most of our non-fossil-fuel energy sources
(such as photovoltaic cells and batteries) deliver their power as a dc supply.
Despite these changes, the vast majority of today’s electricity is still generated, trans-
ported, and delivered as alternating current. Converting alternating current to direct cur-
rent and integrating alternative dc sources with the mainstream ac supply are inefficient
and expensive activities that add significantly to capital costs and lock us all into archa-
ic and uncompetitive utility pricing structures. With the advent of progress in solar
power technology, the world that Thomas Edison envisioned (one with clean, efficient,
and less costly power) is now, after a century of dismissal, becoming a reality. The fol-
lowing exemplify the significance of dc energy applications from solar photovoltaic
systems: first, on-site power using direct current to the end source is the most efficient