Page 67 - Alternative Energy Systems in Building Design

44 SOLAR POWER SYSTEM PHYSICS AND TECHNOLOGIES

UNIT PV CELL CONNECTOR BOX
(−)
DC VOLTAGE
(+) Figure 3.11 Internal wiring of
PV CELL CONNECTION DETAIL a PV solar cell.

Solar Panel Arrays

Serial or parallel interconnections in solar panels are called solar panel arrays (SPAs).
Generally, a series of SPAs is configured to produce a specific voltage potential and
collective power production capacity to meet the demand requirements of a project.
SPAs feature a series of interconnected positive (+) and negative (−) outputs of solar
panels in a serial or parallel arrangement, providing a required dc voltage to an inverter.
Figure 3.11 shows the internal wiring of a solar power cell.
PV solar array installation in the vicinity of trees and elevated structures that may
cast a shadow on the panels should be avoided. The geographic location of the
project site and seasonal changes are also significant factors that must be taken into
consideration.
In order to account for average daily solar exposure time, design engineers refer to
world sunlight exposure maps. Each area is assigned an area exposure-time factor,
which, depending on the location, may vary from 2 to 6 hours. A typical example for
calculating daily watthours (Wh) for an SPA consisting of 10 modules with a power
rating of 75 W in an area with a multiplier of 5 would be (10 × 75 W) × 5 h, which
equals 3750 Wh of average daily power.

Solar Power System Components

PV modules represent only the basic element of a solar power system. They work in con-
junction with complementary components, such as batteries, inverters, and transformers.
Power distribution panels and metering complete the energy-conversion process.

STORAGE BATTERIES
As mentioned previously, solar cells are devices that merely convert solar energy into
a dc voltage. Solar cells do not store energy. To store energy beyond daylight, the dc
voltage is used to charge an appropriate set of batteries.
The reserve capacity of batteries is referred to as the system autonomy. This varies
according to the requirements of specific applications. Batteries in applications that
require autonomy form a critical component of a solar power system. Battery banks in
PV applications are designed to operate at deep-cycle discharge rates and generally are
maintenance-free.