What is Photovoltaic?
The PV effect is the direct conversion of solar energy into electricity. This process
does not generate heat like solar domestic hot water or solar pool heating systems do. It also differs
from the process used in solar thermal power plants, where concentrated solar energy is used to
produce steam that activates a turbine connected to an electric generator.
PV power systems do not have any moving parts. They are reliable, require little maintenance
and generate no noise or pollutants. PV systems are modular - the building blocks (modules) come
in a wide range of power capabilities, from a fraction of a watt (e.g. solar watches and pocket calculators)
to more than 300 W. Modules can be connected to achieve the power that your application requires.
PV systems are classified into two,
off-grid and on-grid. The off-grid system in an autonomous system
that operates independent from municipal or the local electric
company while the on-grid is usually connected to the municipal or
local electric supplier, thus making the private PV an integral part
of the national grid. Customers with on-grid PV systems can usually
sell the excess electricity generated by their solar system to the
local electric company. From the cost point of view, on-grid systems
cost more to install due to the additional equipment needed to
integrate the PV into the grid.
How does PV work?
PV cells are normally fabricated using special semiconductor materials that
allow electrons, which are energized when the material is exposed to sunlight, to be freed
from their atoms. Once freed, they can move through the material and carry an electric current.
The current flows in one direction (like a battery), and thus the electricity generated is termed
direct current (DC) The energy generated by PV modules can be
used immediately or stored in batteries for later use. Normally,
the excess energy generated in autonomous PV systems during
sunny periods is stored in batteries. The batteries then provide
electricity at night or when there is not enough solar
radiation. For these applications, the number of watts in the
array and the capacity of the batteries are carefully sized to
give optimum performance.
PV systems generate DC electricity only,
usually at the rate of 12 and 24 Volts. Therefore, and in order
to operate the household appliances that usually require 110
or 220 AC the system deploys a device called inverter to change
the 12 or 24 Volt DC power generated by the PV into AC power of
the required 110 to 240 volt. Charge controllers are used
to control and optimize the amount of current flowing into the
system from the PV solar panels.
Performance of PV systems
Performance of PV systems is calculated by taking 8% inverter, 3% wiring and
4% soiling losses into account. Array temperature compensation
is based on 25 degrees Celsius. Lower temperatures will improve
performance and Higher temperatures will reduce performance.
