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The following are the basics for roof / ground mounted solar systems
but some parts also apply to mobile solar generator systems.
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1. PV Modules
Photovoltaic Modules are also known as solar panels or solar electric panels.
The PV modules are the individual building blocks for providing power
from the sun.
They are typically made from silicon cells, glass, 'tedlar', and
aluminum. PV modules can vary in type, size, shape, and color. The
common nominal voltages for modules are 12V and 24V, but newer modules
that are intended for grid tie systems, often now have much higher
voltages to accommodate the voltage windows of grid tie inverters.
The mounting system for the PV modules includes the hardware to
permanently affix the array to a roof, a pole, the ground or even
mobile solar generation units (see Mobile).
These fixed mounting systems are typically made of aluminum and are
customized to the mounting surface and the model of module used. It
is important to consider the distance from the roof for flush-type
roof mount installations for PV modules attached to a home or
building.
Restricting airflow under the modules results in higher module
operating temperatures that reduce power output. With pole mounts,
wind loading must be considered and proper civil works must be done
with the foundation for the pole as well as the possible addition of
supplementary wind supports for the array frame.
2. Combiner Box
A combiner box is an electrical box where series strings of PV modules
are then spliced in parallel. This is also the place where the PV
series string fuses or circuit breakers are
located. This allows the installer to bring the separate strings
together and combine them into one positive and one negative
conductor, change wire types and leave the area of the
modules in conduit. They are usually outside and weather rated, so
they can be right next to the array.
3. Charge Controller
A charge controller is a device that regulates the amount of current
the PV modules feed into a battery bank. Their main function is to
prevent over-charging of the batteries, but
charge controllers also block reverse current from a battery bank from
leaking backwards into the photovoltaic array. There are a few
varieties of charge controllers, but the two main types are PWM (pulse
width modulated) and MPPT (maximum power point tracking).
PWM technology is older and more common on smaller solar arrays. With
PWM, the controller is sized based on nominal PV voltage (which must
match battery bank nominal voltage) and the total solar array output
current. PWM controllers typically have two to three stages for
battery charging and maintenance. MPPT controllers can typically take
much higher voltages (but not lower) than the battery bank that they
are charging. They track the performance of the solar array and can
find the maximum power point from a module even when converting excess
voltage to usable current. MPPT charge controllers can allow for a
10% to 25% increase in power sent to the batteries over a standard PWM
controller.
4. DC and AC Disconnects
The DC and AC disconnects are manual switch units that are capable of
cutting off power to and from the inverter. Some inverters have
disconnects integrated into the unit with
switches, others can have them integrated into a power panel assembly,
and some inverters leave you on your own to provide suitable
disconnecting means. The disconnects are used by service personnel or
authorized persons (fire/police/electric workers) to disable power
from a renewable energy system (in this case PV) so that there are no
live electrical parts associated with the inverter, and that no
current is going to the grid that could harm utility employees in the
event that they are working in your area. Using disconnects,
homeowners or authorized personnel can de-energize a system for
maintenance or service. |
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5. Inverter
An inverter takes current from batteries (DC) and turns it to
alternating current (AC) to run any common loads. Some inverters have
integrated AC chargers so that they can use AC power from the grid to
charge the batteries during periods of low sun. Inverters with
integrated AC chargers can also be used in conjunction with
petrol-based generators for battery charging or running very large
loads. Off grid inverters meant for whole home usage must have
appropriate conduit boxes and accessories that enclose live wiring.
Usually, whole home inverters are rated at 2000 watts continuous power
or more. Off-Grid inverters can be modified sine wave or pure sine
wave. Some appliances and many sensitive electronic devices
(computers, stereos, etc) will not function properly on modified sine
wave inverters.
6. Batteries
Batteries store the energy in renewable energy systems. Batteries can
come in different voltages, but the most common varieties are 6 volt
and 12 volt. The three types of batteries that are most common to
renewable energy systems are Flooded Lead Acid, Sealed Absorbed Glass
Mat (AGM), and Sealed Gel Cell.
Flooded lead acid batteries are the most cost effective variety of
batteries. They require maintenance that involves monitoring voltage,
adding water, and equalize charging. Flooded lead acid batteries vent
hydrogen under heavy charging and they must be stored in a ventilated
enclosure.
Sealed AGM batteries do not require maintenance. Since they are
sealed, they do not require watering, nor do they typically vent
gasses. AGM batteries cost slightly more and are more sensitive to
overcharging.
Gel Cell batteries are also sealed and therefore do not require
maintenance and they do not typically vent gasses. Gel batteries are
the most expensive of the three most typical types.
Battery option
With batteries added to a PV system, extra electricity produced by
your system is captured in the high capacity batteries for later use.
This option is a perfect solution for homes or businesses that do not
have easy access to a utility grid or are located in areas that
experience frequent outages.
When your local electrical grid shuts down for any reason, including
rolling blackouts or storm damage, any solar system without batteries
must shut down as well. This safety precaution prevents random surges
of power from traveling the grid and causing injury or damage.
However, if battery backup is included in your system you won't
experience this inconvenience. When a power outage occurs in your
area, your solar system will disconnect itself from the grid and draw
power from the batteries. When grid power returns to normal, the
system automatically reconnects.
7. Cables, Connectors and Brackets
These are everything that are needed to connect all the pieces and
parts together safely and securely.
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