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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 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 Photovoltaic System will
comprise of one or all of the following:
-
Photovoltaic or
Solar Cell, Module or array
– collects visible light from Sun and
converts it to electricity (direct current
(DC));
-
Battery
(rechargeable) – Stores solar energy up to
provide electricity for sun-down periods (nights and cloudy days). It must be able to discharge and
recharge. Usually a little pricey than the disposable battery.
-
Charge
Controller -
feeds
electricity from the solar panel to the battery in a manner that prevents
the solar panel from overcharging the battery. The charge controller also
protects the solar panels from electrical damage.
-
Inverter –
converts the low-voltage direct currents
(DC) from the battery to 110 Volts of alternating current (AC) required by
most household appliances.
PV systems generate low voltage Direct Current (DC) electricity whereas most electrical
appliances require Alternating Current (AC) electricity and mostly 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.
Modern
Charge Controllers come with in-built Inverters.
Where energy storage in a battery for future use is
required, the DC is stored directly in batteries and the Inverter will be
used to convert the DC from battery to AC to power the AC appliances.
Some appliances (e.g. incandescent lights) may be
powered directly by the energy from the panels as these appliances are DC
compliant.
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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