Page 43 - Solar Power in Building Design The Engineer's Complete Design Resource

SOLAR PANEL ARRAYS 13

qualities of arsenic, the process is very expensive. The main feature of gallium-
arsenide (GaAs) cells, in addition to their high efficiency, is that their output is rela-
tively independent of the operating temperature and is primarily used in space
programs.

Multijunction cell technology This process employs two layers of solar cells,
such as silicon (Si) and GaAs components, one on top of another, to convert solar
power with higher efficiency. Staggering of two layer provides trapping of wider
bandwidth of solar rays thus enhancing the solar cell solar energy conversion
efficiency.

Concentrators

Concentrators are lenses or reflectors that focus sunlight onto the solar cell modules.
Fresnel lenses, which have concentration ratios of 10 to 500 times, are mostly made
of inexpensive plastic materials engineered with refracting features that direct the
sunlight onto the small, narrow PN-junction area of the cells. Module efficiencies of
most PV cells discussed above normally range from 10 to 18 percent, whereas the con-
centrator type solar cell technology efficiencies can exceed 30 percent.
In this technology reflectors are used to increase power output, by increasing the
intensity of light on the module, or extend the time that sunlight falls on the modules.
The main disadvantage of concentrators is their inability to focus scattered light,
which limits their use to areas such as deserts.
Depending on the size of the mounting surface, solar panels are secured on tilted
structures called stanchions. Solar panels installed in the northern hemisphere are
mounted facing south with stanchions tilted to a specific degree angle. In the southern
hemisphere solar panels are installed facing north.

Solar Panel Arrays

Serial or parallel interconnections in solar panels are called solar panel arrays (SPAs).
Generally, a series of solar panel arrays are configured to produce a specific voltage
potential and collective power production capacity to meet the demand requirements
of a project.
Solar panel arrays feature a series of interconnected positive (+) and negative (–)
outputs of solar panels in a serial or parallel arrangement that provides a required dc
voltage to an inverter. Figure 1.6 Shows the internal wiring of a solar power cell.
The average daily output of solar power systems is entirely dependent on the amount
of exposure to sunlight. This exposure is dependent on the following factors. An accurate
north-south orientation of solar panels (facing the sun), as referenced earlier, has a sig-
nificant effect on the efficiency of power output. Even slight shadowing will affect a mod-
ule’s daily output. Other natural phenomena that affect solar production include diurnal