Green Collar Careers - Solar
Component Design Review
- Solar PV Panels
- Solar Panel Mounting Racks/Rails & Clamps
- Tracking Systems
- Connectors & MC Cables
- Combiner Boxes and Lightning Arrestors
- DC Disconnect
- AC Panel
- kWh Meter
- System Diagram
- Battery Bank (Off Grid)
- DC Charge Controller (Off Grid)
Solar PV Panels have a footprint of about 40"
x 60" and are in the 200 Watt DC range. Consisting of an
array of 50-60 individual polycrystalline silicon cells, a metal
backing/frame and a non-reflective glass cover these panels
typically weigh about 40 Lbs each.
are about a dozen key manufacturers and each has similar sizes and
specifications, but not exactly the same. Some use higher
voltages and lower currents and may have slightly different foot
prints. In most cases mounting provisions and power cables
will use the same hardware.
are used to support solar PV panels. These rails are
usually an aluminum extrusion with a clamp that fits in a set of
slots or flanges depending on the rail. Clamps attach to the
solar panels and rails attach to the structure. Rails can be
attached with screws, threaded rods and several other ways.
There are hundreds of specialized extruded rails designed for
modular frame structures, and each have some special benefit.
Tracking Systems can boost the production by as
much 1/3 over that of a static mounted system. Azimuth axis
tracks the sun through the day from sun up to sunset giving the
largest gain. Elevation axis tracks the sun through the year
as the elevation changes with the season. Tracking systems
are generally much more costly then just adding extra panels so
they are rarely used when cost benefits are the primary concern
with system design.
Connectors and cables manufactured since
2008 must conform to the new NEC code requires the shrouded bayonet
style latching connectors, as shown in the picture. Solarline MC4
and Tyco Solarlok are the primary connectors in use since 2008.
Some older stock panels have the SL1/MC3 type connectors and some
have the new SL2/MC4 latching type.
it is possible to make these cables in the field, its better to
buy them already to length. Standard lengths are 15, 20, 25,
30, 40, 50 feet. There are also 30 & 30 foot extender
cables. Each panel will need two cables + & - .
Combiner Boxes serve as a junction point for the
power cables exiting the solar panels. They come in various
configurations and may allow series and parallel connections to
establish the DC voltage output. Most include positions to
add fuses and/or circuit breakers.
Lightning protection is a mandatory component for all solar PV
installations. Both the DC side and AC side need protection.
Protection begins with an effective ground such as a copper rod at
least 8 feet deep with 1/0 or larger cable to the DC and AC
grounding points of the system. The Lightning arrestor is a
special silica device that below a certain voltage threshold is an
insulator, and above that voltage becomes a conductor.
DC Disconnect box requirements are usually dictated by local codes.
Generally a conventional four position AC service panel with DC rated
breakers will do. Most kits do not include these boxes so you
will need to check your local code requirements and purchase them
separately, generally less then $100. Locate this panel next to
the inverter for easy service.
|Inverters take the DC
power from the solar panels and invert that to AC power. A
clean AC power signal is a must; for a refresher on
inverters review Section
309. Grid Tied systems must use an inverter approved by
the local utility. Grid Tied requirements are more stringent
to assure a clean output is generated, that proper surge and
protection is implemented, and that the output power wave is
synchronized with the commercial AC side.
Inverter placement should be located indoors, near the AC Power
Panel, and preferably in an environment free of excess dust and
heat. Some inverters have fans which may require annual dust
AC Power Panel is the same thing as the main power panel for your
home. The output from the inverter should pass through an AC
disconnect box (strongly recommended) and local codes need to be
checked for requirements. Generally something similar to the DC
disconnect will apply. A dedicated AC Disconnect will provide
the best location for AC surge and lightning protection devices for
the solar electric system.
Kilowatt-Hour Meters provided by the utility company may be
sufficient, however most utilities will require a separate meter just
to measure the volume of electricity produced by the solar electric
system. These separate kWh monitoring units (Cumulative kWh
Meters) are often not included in the kit and are generally under
$100. They make a great feature for homeowners to visually see
the value of the system they purchased.
|System Diagrams should
indicate component placement in the home and property.
Because the MC cables are pre-formed you will want to have a
connection chart that identifies run designations for each cable
routing points and run lengths.
Panel mounting requirements will vary with the structure and local
code. While most rack systems are fairly modular the rack
design will likely require approval by local code authorities.
Most of the time local codes will specify the requirements in a
way that most people can easily interpret them.
95% of the solar PV installations are Grid Tied with no battery or
generator backups. Off grid systems will almost always require a
backup system or there is no power when the sun is not shining.
The main component differences between a Grid Tied System and Off Grid
system are Battery Banks and Charge Controllers.
Every Off-Grid system will have a dynamic set of complexities so
we'll only touch on a few key points.
Battery Banks use lead-acid batteries that differ from your car in
sizes and voltage. Each cell of the battery provides 2 volts so
a 6 volt has 3 cells, and 12 volt has 6 cells. Storage batteries
are designed for "Deep Cycle" service meaning they will typically
cycled between 100% charge to 15% charge. Car batteries aren't
designed for deep cycle service and won't last very long under home
Batteries are sized as Voltage x Amp hours.
Section 305 has brief
summary about DC electricity, but to simply, multiply the volts x amps
to get the watt hours. So a 600 Amp hour 6 volt battery would
store 3600 watt hours. Typically battery storage is sized at
about 6 times the DC Watts of the system operating for 1 hour.
For example, a 3000 Watt DC solar panel array at 1 hour is 3000
Watt-Hours; Battery Capacity may be sized about 18,000
Watt-Hours. Again, the complexities of the specific application
will determine the sizing of battery storage.
DC Charge Controller is required to maintain an adequate charge level for the batteries. Some Charge Controllers are connected to the
DC Disconnect to feed the batteries, and some Inverters may have an
integrated Charge Controller.