Solar Photovoltaic
Frequently Asked Questions
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PV Solar Panel FAQ - Photovoltaic Solar Panels
What is a PV panel?
A PV solar panel, referred to in the industry as a solar module,
is constructed by connecting photovoltaic cells (or PV cells)
to produce electricity. The cells are a semiconductor-based technology
that converts solar radiation into direct current (DC) electricity.
Solar panels for grid-connected home or business use typically
use 60 or 72 PV cells.
What are the benefits of using PV solar systems?
By utilizing PV solar cells, home or business owners are able to generate electricity
from sunlight saving money and avoiding the harmful pollution generated by traditional
methods of generating electricity. This solar generated energy is used to offset
or replace power that would normally be purchased from the utility.
What is Net-Metering?
Net Metering is a useful tool in the field of alternative energy.
For owners of PV systems, net metering provides an opportunity
to sell excess electricity produced to your local utility company.
In North America, forty states currently have net metering policies
in place. Net metering means that the amount of solar electricity
produced (measured in KWh) is subtracted from your overall usage,
meaning you only pay the utility for the difference (the “net” amount).
What are the utility company requirements to connect my solar power
system to the power grid?
The requirements vary depending on the size of the system and the particular
state and/or utility. In some states a special meter must be obtained from the
power company. Information can be found here:
http://www.seia.org/cs/federal_issues/net_metering
http://www.dsireusa.org/
What is a grid-tied solar system?
98% of PV solar panels installed in the USA are grid-tied systems, meaning
that the system is tied to the power grid (local electric power utility company).
The solar power is added to the grid power, reducing the amount of power that
must be purchased from the utility.
What is an off-grid solar system?
An off-grid solar energy system is where there is no connection to the
utility company power grid. This type of installation requires a charge-controller,
a bank of batteries and in most cases an inverter, so that electric power
requirements can be met at night or during cloudy conditions.
What incentives are offered for users of PV solar systems?
Currently, the Federal gives a personal or business tax credit of 30% of the
cost of a PV system. Many states also offer additional incentives for utilizing
PV solar products. Click here
for more information.
What are the different types of PV panels?
There are currently four main types of solar PV panels:
- Monocyrstalline - these are made from cells created by cutting
thin slices from single crystal silicon block and are higher
in efficiency, but also higher in cost per watt. They are easy
to spot because they have a smooth even color, usually black.
- Polycrystalline – these are made from cells created
by cutting thin slices from polycrystal silicon block and are
slightly lower in efficiency, but also lower in cost per watt.
Polycyrstal silicon is the “chicken nugget” of silicon,
made by combining many individual crystals. They are easy to
spot because they have an uneven color, usually blue.
- Multicrystalline – a different term for polycrystalline.
- Thin film – these are made by depositing a thin layer
of very finely powdered silicon (amorphous silicon) or other
photovoltaic material, on a substrate. These are much lower in
efficiency that crystalline cells, and somewhat cheaper per watt.
They are a good choice for large ground mounted utility scale
solar arrays where real estate is plentiful. Their low efficiency
makes them undesirable for commercial and residential applications
because they consume a large amount of roof space compared to
mono or poly panels.
How do I decide how large my PV solar system should be?
Typically the best return on investment is when you target the
average power in watts used during the month with the lowest
electric bill. Most net metering programs do not let you carry
forward a credit, meaning that when you produce more solar electricity
than your total consumption, it is wasted. Actually it is not
wasted, it is just given free to the power company who will sell
it to someone else ;-)
How are solar panels tested and rated?
PV panels installed in the USA must be tested to UL 1703 standard
and in California, also to IEC 61730. They can be tested and certified
by any NRTL (nationally recognized testing laboratory) like UL,
CSA, ETL, TUV etc. For consumer purposes, the main rating to consider
is the watts rating, which is expressed at watts-peak (Wp) which
is the amount of peak power produced under STC (standard test conditions).
What are Standard Test Conditions (STC)?
STC is the main set of conditions used in testing solar PV modules. Conditions
are considered standard when cell temperature is 25C and you have
1000 W/m^2 of direct insolation. STC also assumes a panel is oriented
to the proper angle, elevation.
How much power will a solar PV system produce?
You would calculate the total production of a system by determining
the annual production of a single panel and multiplying it by the
number of panels, then reduce this value to account for inefficiencies.
A professional approach
would be to use a calculator like PVWatts or RetScreen. This approach
will consider the NASA data for insolation at the location, the
expected weather and temperature conditions, the orientation (angle
and azimuth) of the installation and other factors.
Each system will produce a different amount of power based on the
system size, orientation, insolation, etc. A quick look at our solar
insolation map will give you an idea of average annual sunlight
conditions for your area. A quick, free telephone or email consultation
with our sales team will help you be able make a good estimate
of your potential. Just give us a call.
What is insolation?
Insolation refers to a daily total of direct sunlight. In the solar
industry it usually refers to the average daily hours of sunlight
equaling 1000 watts per square meter. On average, locations within
the USA will get between 4 and 6 hours of insolation per day depending
on season and location. Click here to see a zip-code based solar
insolation calculator.
How does shade affect the performance of a PV solar system?
One of the leading causes of power loss in a solar PV system is
when part of the panel or array becomes shaded.
In a panel there will usually be either 60 or 72 cells connected
together. Each cell produces a certain voltage and amperage, the
cells are configured and connected in a combination of series and
parallel connections to produce the correct amount of power. If
any individual cells performance is degraded by shade, the performance
of the entire panel will fall to a point relative to the worst
performing cell.
Likewise, in a string of panels, the entire string suffers performance
reduction to that of the lowest performing panel.
A solar installation should be designed in a way such that none
of the panels are even partly shaded at any point of the day.
How much roof space does a PV system need?
A typical solar panel of 200Wp will measure about 17 square feet.
Depending on installation factors, the required square footage
of roof space will be somewhat larger than simply the area of the
panels. Based on your information, once our engineering department
has determined the required angle, shading factors, etc. we can
give you a more accurate number.
Do solar panels have to be installed on the roof?
Solar panels can be installed on the roof, on the side of a building,
on the ground or on a pole. The most cost effective installation
will usually be on a roof, but if roof or shading conditions prevent
the use of the roof we can help you review other options.
Do installed solar panels have to face a southerly direction?
In the USA, facing south at the correct angle of elevation will
provide the best performance (most KWh per dollar) however solar
panels can also be installed facing towards the east or west as
long as proper considerations are made. Solar panels should not
ever face north.
What about cloudy days?
PV solar panels will generally produce electricity at a reduced
rate under cloudy conditions. Severe clouds will interrupt the
production of power.
How long will a solar panel system last?
Solar panels are known to last 40 years or longer. Typical guarantees
of a solar panel include five years workmanship and materials warranty
and a 20-25 year performance warranty. The typical PV panel performance
warranty will guarantee 90% of rated production for 10-15 years,
and 80% for 20-25 years. Solar panels are designed to withstand
hail, severe wind and weather conditions assuming proper installation.
How do I know if a solar PV system is a good choice for me?
If you live in an area where the sun shines and electricity is
costly, chances are that PV solar panels will make financial sense
for you, especially if there are tax credit, rebates or other incentives
available. Contact our sales team to get assistance in evaluating
your situation.
What are the maintenance requirements or other costs
for a PV system?
For a grid-tied system where no batteries need be replaced, there
is typically little or no maintenance required. You might consider
a periodic inspection to ensure that the panels remain clear of
leaves, dirt, bird droppings etc. Other than that, unless there
is an equipment failure there should be no maintenance required.
What is the warranty on a PV solar system?
Typical guarantees of a solar panel include five years workmanship
and materials warranty and a 20-25 year performance warranty. The
typical PV performance warranty will guarantee 90% of rated production
for 10-15 years, and 80% of rated performance for 20-25 years.
Please look at our products individually to see the specific warranty.
Besides the solar panels, what else is needed for a complete
system?
In a grid-tied system, local power company regulations must be
met, each are is different. Otherwise, the system will include
the panels, mounting hardware, connecting wires, and an inverter
to convert the DC power from the panels into the correct AC voltage.
What are solar inverters?
An inverter is any device that inverts DC (direct current) into
AC (alternating current). In a solar installation, an inverter
is a centralized device that connects to and manages the performance
of the solar panel array; it aggregates the DC power coming from
the panels or strings of panels and inverts the DC power into single
phase (or three phase) AC power at the correct voltage for delivery
into the users electrical system, and provides equipment protection
and safety features. The better inverters on the market also allow
for data logging and web-based remote monitoring of important performance
metrics and power generation.
What are micro-inverters?
In a solar application, a micro-inverter is a small de-centralized
inverter that attaches directly to each panel. The advantages of
micro-inverters are several; they may be safer for the installer
because they eliminate high voltage DC in the system and instead
use household type power; installation may be quicker, and, performance
of the panels or strings can be improved if there are shading conditions
or otherwise poorly performing panels within the array.
Little is known about the longevity of micro-inverters as they
are a new product without an extensive track record. Further, a
failed micro-inverter may be very hard to access and replace if
it is in the center of a multi-panel installation. Micro-inverters
may lower the cost of installation by making it somewhat easier
to wire the array, but they also cost more, per watt, than a centralized
inverter.
At some point it is possible that micro-inverter technology will
reach a point where DYI solar installations may become possible.
For now, only a licensed electrician can commission a grid-tied
system regardless of the type inverter used.
Will my solar PV system include batteries?
When you connect a solar PV system to the grid, you are essentially
using the grid as a battery. When solar power exceeds your usage,
the utility meter spins backwards. When demand exceeds solar production,
the meter sins forward. The utility company grid acts just like
a battery. In a grid-tied system you do not need batteries.
Will the solar electric system function as “back
up” power
when the utility power is not available?
Not in a normal grid-tied PV solar installation. In a grid-tied
system, the inverter will shut off if the power company grid is
not also providing or able to provide power. This is more of a
safety feature than a technical limitation. To have a back-up battery
system, you would need to take the same steps as if there were
no solar involved, i.e., install some type of UPS system. Another
approach would be to install a hybrid on/off-grid system through
the use of a special charger-inverter and batteries.
Can I power my entire building with solarpanels and disconnect
from the utility company?
Yes you can. In an off-grid installation, you must have batteries,
a MPPT charge controller and an inverter – in some cases
the batteries will cost nearly as much as the solar panels and
only last 6-8 years before replacement becomes necessary. Off-grid
solar is achievable, but is very costly and only recommended for
locations where there is no grid to connect to.
What is a charge controller?
A charge controller is a device used to control the voltage and
current coming from a PV solar panel array and into a battery bank. Many
of newer models employ Maximum Power Point Tracking (MPPT) which
looks at the battery bank and configures the PV output to allow
for the best combination of voltage and current to enter the battery
bank. While using a typical charge controller might result
in a power loss of 30%, charge controller using MPPT are 95+% efficient.
What happens if the solar panels are covered by snow?
Some sunlight will penetrate the snow, causing the panels to warm
and eventually melt the snow. Spraying the panels with water from
a garden hose can speed things along. On a single story roof, a
snow rake can be the best option to remove most of the snow allowing
the panel to melt the remainder quickly, we suggest using a model
with a rubber squeegee blade attached to the end of it. Google:
roof rake.
How do the solar panels stand up to hail, wind, hurricanes
etc?
Solar panels themselves are built using tempered glass for durability
and safety and are designed to withstand hail and high winds. Depending
on the wind-load requirements in your area, heavier mounting hardware
may be required.
Will solar panels damage my roof?
Properly installed solar panels will not damage your roof. If your
roof is near the end of its expected life, it might be a good idea
to consider replacing the roof before adding solar panels, because
removing and reinstalling the panels can add to the cost of a roof
replacement.
How long does it take to install a PV system?
A typical residential roof installation can be completed in 3-4
days. The number of panels and type of installation will affect
the installation process.
Can I install the solar panel system myself?
It may be legal to do so depending on the laws in your area. It
is possible for a home owner to install a solar panel system DIY
(do it yourself) however there are many technical and safety issues
to be aware of. If a homeowner is experienced with home improvement
projects and is comfortable working on a roof, it is possible for
a homeowner to do most or all of the work. For most DIY applications
a licensed electrician should be brought in to verify the electrical
part of the installation and initially commission the system.
Is a building permit required to install a PV system?
This varies area to area as far as DIY installations, however
a professional installation will nearly always require a permit.
A call to your local city government (electrical inspector)
would clear this up.
What does a solar PV system cost?
Because of the wide range of variables in system size and installation
requirements it is impossible to state the cost of a system. It
is important to realize that the cost of the panels themselves
usually represent about 1/3 of the total turn-key cost.
How much will I save, how quickly will a system pay for itself?
This will vary depending on the local cost of electricity, state
and local rebates or incentives, and the installed cost of the
solar panel system. The range can be from 3-4 years up to 20 years
depending on these factors.
Does a solar PV system affect the resale value of my
property?
Yes it does. Available real estate property resale value data indicates
that money spent on solar panel installations is recoverable and
may actually increase the value of the home beyond the amount spent.
How do I qualify for and take advantage of state and
federal subsidies, rebates or incentives for solar power?
Each individual situation is different and it is suggested that
you consult with a tax professional. Energy Star has a resource
for federal tax incentives here http://energystar.custhelp.com/cgi-bin/energystar.cfg/php/enduser/std_adp.php?p_faqid=2928
More information is available here http://dsireusa.org/
I rent my building – does it make sense to install
a solar power system?
It may, depending on the length of your lease and other factors.
For tenants interested in a solar installation, some discussion
and agreement with the building owner will be required. In general
it is also beneficial to the owner, particularly if it does not
require any payment on his part.
I live in a condo – will I be allowed to install
a solar panel system?
This will depend on the condo association rules. You must discuss
this with your association.
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