Page 82 - Solar Power in Building Design The Engineer's Complete Design Resource

52 SOLAR POWER SYSTEM DESIGN CONSIDERATIONS

Figure 3.4 Stand-alone hybrid solar power system with standby generator.

a cycle. Additional waveforms with higher cycles, when superimposed on the base
waveform, add or subtract from the amplitude of the base sinusoidal waveform.
The resulting combined base waveform and higher harmonics produce a distorted
waveshape that resembles a distorted sinusoidal wave. The higher the harmonic con-
tent, the squarer the waveshape becomes.
Chopped dc output, derived from the solar power, is considered to be a numerous
superimposition of odd and even numbers of harmonics. To obtain a relatively clean
sinusoidal output, most inverters employ electronic circuitry to filter a large number of
harmonics. Filter circuits consist of specially designed inductive and capacitor circuits
that trap or block certain unwanted harmonics, the energy of which is dissipated as
heat. Some types of inverters, mainly of earlier design technology, make use of induc-
tor coils to produce sinusoidal waveshapes.
In general, dc-to-ac inverters are intricate electronic power conversion equipment
designed to convert direct current to a single- or three-phase current that replicates the
regular electrical services provided by utilities. Special electronics within inverters, in
addition to converting direct current to alternating current, are designed to regulate the
output voltage, frequency, and current under specified load conditions. As discussed in the
following sections, inverters also incorporate special electronics that allow them to auto-
matically synchronize with other inverters when connected in parallel. Most inverters, in
addition to PV module input power, accept auxiliary input power to form a standby gen-
erator, used to provide power when battery voltage is dropped to a minimum level.
A special type of inverter, referred to as the grid-connected type, incorporates syn-
chronization circuitry that allows the production of sinusoidal waveforms in unison
with the electrical service grid. When the inverter is connected to the electrical service