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PV cells come in various sizes ranging from 10mm by
10mm to 100mm by 100mm, the most common size being 100mm by 100mm cells.
A single PV cell produces about 1 to 2 watts of electricity; an
amount that is quite insignificant compared to what is required by most
electrical equipment. Two or more PV Cells are built to produce a PV
Module to provide higher wattages as required. For instance, a PV module
producing 50 watts may comprise of at least 25 of 2 Watts output PV cells.
To meet the the electrical need of a home or an industrial setting, PV
Modules are assembled together to form a PV Array that meets the
total energy requirement.
A PVC system design begins with determining
the total energy requirement for a facility to be powered. Next the number
of solar panel units required and other components of the PVC (description
below) are determined. A basic PVC system comprises of the following:
Solar panels generate low voltage Direct Current (DC) electricity. Some appliances (e.g. incandescent lights) may be
powered directly by the energy from the panels as these appliances are DC
compliant. However, most electrical
appliances require Alternating Current (AC) electricity and usually at high
voltages (110V in North America and 230V in most of Europe and developing
world (e.g. Africa)) to function. Inverters are
used to convert the low voltage DC to AC at required voltages.
In summary, the solar cells collect direct
sunlight, converts sunlight into low-voltage DC. Where energy storage in a battery for future use is
required, the DC is stored directly in batteries. A charge controller is
installed between the Solar panels and the batteries to ensure he
batteries are not overcharged. A Power Inverter is
used to convert the DC from battery to AC to power the AC appliances.
PVC System
Other PVC system components that may be
required are: wires and cables (for connection of the components) and
meters and monitors (for monitoring the voltage and reading the currents
of the system.
PV system is a preferred approach for
electricity supply because of its modular features, its
ability to generate electricity at the actual point of use, its low
maintenance requirements and its non-polluting technologies. It is
an attractive option for electricity supply in developing countries where
there is abundant sunlight and large rural population
without the proper infrastructure to develop an electrical grid. In
such countries, PV system can be used to provide electricity to homes,
rural clinics and government/corporate offices.
PV systems are also useful in remote and
isolated locations in developed Worlds (e.g. northern Canadian territories
- Nunavut, Yukon and NWT, arctic Greenland and Iceland and various World
Islands).
PV systems are not
suitable for water heating or other heat related appliances. A solar
heater can heat water more quickly and efficiently than an electric water
heater powered by PV panels. Solar heaters convert up to 60 per cent of
the sun's energy into heat whereas PV cells are
far less efficient and convert only 12 to 15 per cent of the sun's
energy into electricity.
The Size of
a PV system
To size a PV system, follow
these process:
- Determine the amount
of electricity required:
-
Determine the number of devices to be
supported,
-
Multiply the power (in watts or KW) on
each device by the number of hours in a day the device will be used to
obtain the electrical energy required in KWh,
-
Add all the KWhs together to get the
current total energy requirement for the PV system;
-
Allow for expansions to your system.
Depending on your resources, you may want to consider a factor of safety
of 1.3 (i.e. 30% above your current requirement) or 1.5 (i.e. 50% above
your current requirement).
- Size your PV Module and your battery
capacities:
Keep in mind that a PV cell of say 100mm by
100mm cell produces about 1 to 2 watts of electricity. The battery should
be sufficient to store electricity for use during sun-down hours (nights
and cloudy days).
The
Cost of PV system
Sample costs (source:
Solar Energy Society of Canada Inc.):
A
portable PV unit with a 50-watt solar panel, low-power inverter and
battery, are about $700 and can operate three high-efficiency lights, a
small TV and a water pump.
A more
powerful PV system that produces 600 watts and operates several lights, a
TV, stereo, microwave oven and water pump - but not at the same time -
costs about $8,000.
New
production techniques and applications combined with lowering prices for
photovoltaics should increase the acceptance of this environmentally
friendly technology.
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