Environmental Engineering Reference
In-Depth Information
module or array will produce more electricity. PV modules are rated on the
basis of the power delivered under Standard Testing [4]
Conditions (STC) of 1 kW/m² of sunlight and a PV cell temperature of 25
degrees Celsius (°C). Their output measured under STC is expressed in terms
of ―peak Watt‖ or Wp nominal capacity [5]. A typical crystalline silicon
module consists of a series circuit of 36 cells, encapsulated in a glass and
plastic package for protection from the environment. Although PV modules
are warranted for power output for periods from 10-25 years, they can be
expected to deliver amounts of energy (voltage and current)for periods of 40 to
50 years [6].
3.3.2.2. Invertors
Inverters have the task of DC/AC conversion. There are two main
categories of grid-tied inverters. Line-commutated inverters derive their
switching signals directly from the grid line currents. The low switching
frequencies produce harmonic currents that need to be filtered out. In the case
of small single-phase inverters the bulky and expensive filtering networks are
not practical. In the case of large three phase-inverters, multiple units could be
connected through a multi-phase isolation transformer at the utility output to
filter any unwanted currents; the transformers should be rated to withstand
additional heating due to harmonic current copper losses [7]. Self-commutated
inverters derive their switching frequencies from internal control units as they
monitor grid conditions, in particular frequency and voltage.
Figure 9. Photo-voltaic Power Plant.
