Page 329 - A Comprehensive Guide to Solar Energy Systems

334 A CoMPreheNSIVe GuIDe To SolAr eNerGy SySTeMS

FIGURE 16.1 Form of available PV technologies (A) PN-junction and its implementation as a PV cell, (B) a PV module
(containing 36 identical cells), and (C) a PV array (containing 6 modules).

and inverters) depend on primarily application requirements as well as the total
cost. DC–DC converters shown in Fig. 16.2B have two main purposes: to match load
characteristics and to obtain maximum power from PV module under varying solar in-
solation levels and/or load conditions. In addition, stand-alone inverters are sometimes
used which cannot connect to the electrical grid but operate as isolated generators only to
power AC loads (Fig. 16.2C and D) like refrigerators.
energy storage (Fig. 16.2C and D) is frequently required either to store the produced
electrical energy for use when sunlight is insufficient and/or to reduce/eliminate the im-
pact of instant variations of solar irradiance, which is due to uncontrolled environmental
factors. Traditionally, energy storage is done by lead acid batteries, but recently these have
been replaced by lithium battery like liIonP as they offer higher energy density and at an
acceptable cost.
The grid-connected (grid-tied) inverters (Fig. 16.2e and F), which are the most common
inverter systems, can supply energy not only to local loads within the household, but can
also supply power to distant loads connected elsewhere on the electrical grid (as the grid
acts as an infinitely large energy storage system!). This occurs when there is a surplus of gen-
erated energy. When the PV power generation runs short of supplying the local household
however, power is either sourced from a local battery storage, if it exists, or from the grid.
In the absence of a grid voltage (i.e., an electrical blackout) a conventional grid-tied
inverter system disconnects from the grid, which aims to protect personnel working on
power lines that are assumed to not be live. In addition, such inverters also disconnect
from the grid when the grid voltage level becomes outside inverter’s settings, which is usu-
ally defined by acceptable voltage standards. however, high penetration of distributed re-
newable energy supplies like PV systems may also cause disconnections due to excessive