Page 78 - Solar Power in Building Design The Engineer's Complete Design Resource

48 SOLAR POWER SYSTEM DESIGN CONSIDERATIONS

Solar Power System Components

and Materials

As described later in this chapter (see the section entitled “Ground-Mount Photovoltaic
Module Installation and Support Hardware”), solar power photovoltaic (PV) modules
are constructed from a series of cross-welded solar cells, each typically producing
a specific wattage with an output of 0.5 V.
Effectively, each solar cell could be considered as a 0.5-V battery that produces current
under adequate solar ray conditions. To obtain a desired voltage output from a PV panel
assembly, the cells, similar to batteries, are connected in series to obtain a required output.
For instance, to obtain a 12-V output, 24 cell modules in an assembly are connected
in tandem. Likewise, for a 24-V output, 48 modules in an assembly are connected in
series. To obtain a desired wattage, a group of several series-connected solar cells are
connected in parallel.
The output power of a unit solar cell or its efficiency is dependent on a number of
factors such as crystalline silicon, polycrystalline silicon, and amorphous silicon mate-
rials, which have specific physical and chemical properties, details of which were dis-
cussed in Chapter 2.
Commercially available solar panel assemblies mostly employ proprietary cell man-
ufacturing technologies and lamination techniques, which include cell soldering.
Soldered groups of solar cells are in general sandwiched between two tempered-glass
panels, which are offered in framed or frameless assemblies.

Solar Power System Configuration

and Classifications

There are four types of solar power systems:

1 Directly connected dc solar power system
2 Stand-alone dc solar power system with battery backup
3 Stand-alone hybrid solar power system with generator and battery backup
4 Grid-connected solar power cogeneration system

DIRECTLY CONNECTED DC SOLAR POWER SYSTEM
As shown in Figure 3.1, the solar system configuration consists of a required number
of solar photovoltaic cells, commonly referred to as PV modules, connected in series
or in parallel to attain the required voltage output. Figure 3.2 shows four PV modules
that have been connected in parallel.
The positive output of each module is protected by an appropriate overcurrent device,
such as a fuse. Paralleled output of the solar array is in turn connected to a dc motor via
a two-pole single throw switch. In some instances, each individual PV module is also