Hi I’m Amy from the altE Store.
I’m going to show you the difference between
60 cell solar panels, and 72 cell solar panels.
Other than the obvious difference of 12 solar
cells, there are pros and cons to using each
of them in different solar power systems.
First a little background. Solar panels are
made from blocks of silicon ingots that are
cut into square cells.
Those are the squares that you see that make
up the solar panels. Each solar cell produces
about a half a volt.
They then wire multiple cells in series, plus
to minus, to make a solar panel.
Wiring the cells in series increase the solar
panel voltage to a usable level.
The more cells that are wired in series, the
higher the voltage.
For example, if 36 cells are wired in series,
you get an output of about 18 volts.
Now, solar first got its start in the battery
based off grid world, where solar panels were
built to charge a battery bank.
The 36 cell solar panel that outputs 18V is
perfect for charging a 12V battery bank, since
you need a higher voltage to charge a battery.
So a 36 cell solar panel is called a 12V “nominal”
panel, as it is designed to charge a 12V battery.
Likewise, a solar panel with twice as many
cells, 72 cells, outputs about 36 volts, and
it is great for charging a 24V battery bank.
So it is called? You got it, a 24V nominal
solar panel.
If you have a 48V battery bank, there aren’t
many companies that make 48V solar panels.
So, in that case, what do you do if you need
to charge a 48V battery bank?
You would wire multiple solar panels together
in series, either four 12V panels or two 24V
panels to output 72V,
Which will efficiently charge a 48V battery
bank, even in very hot weather when the voltage
of silicon panels drops low.
For an example of the effect that heat has
on solar panels,  check out this
video we did on temperature and silicon solar
panels.
So all was well and good with figuring out
what nominal voltage solar panels to use,
just make them match the nominal voltage of
the batteries, when along came two different
technologies that added an interesting twist
to the mix.
The first was grid tie solar.
With a grid tie inverter, you could now convert
the DC voltage from the solar panels directly
into AC to power your house, no batteries
required.
So the restriction of 12V, 24V, and 48V went
away.
This allowed the solar panel manufacturers
to use however many cells they wanted to.
For solar panels up to about 300W, the industry
settled on 60 cells.
Using the terminology from the battery world,
that’s a 20V nominal panel.
With an Open Circuit Voltage, or Voc, of around
38V, grid tie solar systems were able to string
up to 12 or 13 60 cell solar panels in series
and stay within the Electrical Code restriction
of staying under 600V DC, even when taking
cold temperature into consideration.
If they were using 24V 72 cell panels, they
would be limited to only 11 in series in cold
environments, limiting their system size.
The second change was still in the battery
based world, with the solar charge controllers
that are used to manage putting the power
from the solar panels into the batteries.
Early on, the shunt or Pulse Width Modulated
(PWM) charge controllers had to match the nominal
voltage between the solar panels and the battery bank.
Maximum Power Point Tracking (MPPT) solar charge controllers came onto the scene and
allowed you to take
a higher voltage solar input and reduced the
charge controller voltage output to correctly
charge a battery bank, while increasing the output current,
eliminating any power loss due to forcing
solar panels to operate at whatever voltage
the battery bank was actually at.
This opened up the ability to use any cell
count solar panels, as long as the voltage
was higher than the battery bank.
Although some specialized charge controllers
allow you to charge with a lower voltage solar
panel, most of them require higher voltage.
Since 60 cell “grid tie” solar panels
are so common now, their price per watt has
dropped much lower than the nichy 12V panels,
making them an attractive option to charge
battery banks.
Just remember you have to use a more expensive
MPPT charge controller to do it.
Also note that you cannot use a single 60
cell solar panel to charge a 24V battery bank.
You need at least one 72 cell panel or two
60 cell panels in series to have a voltage
high enough to charge 24V.
If you are in a cold environment, most 150V MPPT solar charge controllers limit you to
up to only two 72 cell panels in series, but
you can do up to three 60 cell panels in series,
and still stay within that 150V limitation.
So, what about the 72 cell 24V solar panels
for grid tie solar systems?
Well, technology and codes move forward, and
newer revisions of the electric codes now
allow for 1000V strings for grid tie commercial
and utility scale systems.
Also, grid tie inverters are getting bigger
and bigger, allowing for extremely high wattages
getting inverted.
Since watts equals volts times amps, a way
to increase the wattage of a solar panel is
to increase the voltage by adding additional
cells.
Adding 12 more cells generally adds an additional
foot of length to the solar panel.
With larger commercial and utility scale projects,
larger panel sizes are able to be used.
So 72 cell panels give them a way to regularly
make solar panels well over 300W.
Higher wattage solar panels reduce the number
of panels that are needed in the system to
reach your target wattage,
which can decrease the labor needed to install
them. Higher wattage panels may also reduce
the amount of balance of system equipment
needed, including racking, wire, and in some
cases, electronics themselves, if they are
using microinverters or DC Optimizers. Note
that not all microinverters will support 72
cell solar panels, so 60 cell is still the
only option in some cases, mostly for home
systems.
Most 72 cell panels still weigh less than
the 50 lb restriction set by OSHA, so can
be carried by one person,
although their size can make it awkward to
handle alone. The smaller 60 cell solar panels
can be easier to handle.
So, what size solar panel you should use for
your project depends on a lot of criteria.
Are you building an off-grid or a grid tie
solar system? If it is off grid, what voltage
battery bank are you trying to charge?
Do you have physical size restrictions that
would limit the size of the panel? Will the
equipment you want to use support the solar
panel?
Will a higher voltage panel restrict the number
of panels you can use in a system?
These are all questions you need to ask to
determine what size panels are right for you.
Give us a call at the altE Store, and we’d
be happy to help you get what you need.
I hope this was helpful, if so give us a like
and a share, and subscribe to our channel
so we will notify you when we release a new video.
And be sure to check out our selection of
solar products at altestore.com, where we’ve
been making renewable doable since 1999.
