Power from the Sun by Dan Chiras

Author:Dan Chiras
Language: eng
Format: epub
ISBN: 9781550926248
Publisher: New Society Publishers
Published: 2016-03-18T04:00:00+00:00

FIGURE 6.4. Electricity.

The graph in Figure 6.4a indicates the voltage over an extremely brief period. The voltage shift from 0 to +120 volts then back down to 0 takes 1/120 of a second; the voltage shift from 0 to −120 takes another 1/120 of a second. Together, one complete cycle is 1/60 of a second or 60 cycle per second electricity.

The basic H-bridge circuit found in some older inverters produces an almost perfect square wave. What that means is that the voltage jumps from 0 to +120 instantaneously, remains there for a short period, then instantly drops back to 0. Unfortunately, square wave electricity does not match the type of electricity produced by power plants. They produce sine wave electricity, shown in Figure 6.4d. Square wave electricity is not a very usable form of electricity. However, if this square wave is modified so that it pauses at zero volts briefly before reversing direction, the result is modified square wave electricity, shown in Figure 6.4b. Although doesn’t appear to be much different, it is closer to a sine wave, the kind used in most homes. It can be used in off-grid homes, but has some serious shortcomings.

The problem with square wave and modified square wave electricity is that they contain harmonics. Harmonics are waveforms at frequencies that are multiples of the desired frequency. What that means is that there are electrons that cycle at different frequencies—besides the fundamental 60 cps.

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