Home' The Backwoodsman Magazine : May-June 2017 Contents 41
a number of solar cells are connected
together to form a solar panel; two or
more solar panels can be connected
to form a solar array.
Each solar array produces a cer-
tain amount of electricity which is
quantified using the terms “volts,”
“amperes,” and “watts.” There are
scientific definitions for a volt, an
ampere, and a watt of electricity, and
you may know the definitions. It’s
fine if you do, but it’s not really
necessary to make solar power cal-
If you think of volts as the pres-
sure of the electricity, amperes as the
flow rate, and watts as the total
power, you’ll be fine for most solar
purposes. If you multiply the pressure
in volts times the flow rate in amperes
(or amps for short) you will have the
total power of electricity in watts. Following are three
ways of saying that same thing.
1. Volts times amps equals watts.
2. Watts divided by volts equals amps.
3. Watts divided by amps equals volts.
As an example, consider an old-fashioned incandes-
cent light bulb that is rated at 60 watts and is intended to
be powered with 120 volts. How
much current (in amps) will flow
through the bulb? Using number 2
above, watts (60) divided by volts
(120) equals amps (0.5). Most of the
calculations required are also that
Producing electricity from sun-
light has one major drawback: the
sun doesn’t shine 24 hours per day,
365 days per year at any one loca-
tion. In fact, at a given location the
periods of peak sunshine are rela-
tively short. The amount of sunlight
that falls on a given surface are in a
given length of time is called solar
insolation and is often measured in
watts per square meter. (No, insola-
tion is not misspelled; it is a completely different word
In addition to there being no sunlight available at
night in a given location, the period in which the light is
at its brightest is limited to a relatively short period each
day: just before and just after solar noon. Those hours
are called peak sun hours. Of course,
the duration of peak sun hours varies
by the season of the year and by the
latitude of the location. The table
below shows a year round average of
the approximate peak sun hours per
day in each of the 50 states. Note
that some states have a large degree
of variability due to their size, shape,
and terrain. Please see the chart on
the next page.
It’s great to be able to produce
electricity using solar panels, but it’s
even better to be able to store at least
some of it for use at a later time.
Thus, the next thing needed in a
solar power system is a battery
bank. A battery bank consists of
one or more batteries configured to
store electricity and the most common
battery banks are arranged to store it
at approximately 12 volts, although other voltages are
sometimes used. The use of 12 volts relates to the fact
that almost all modern automobile batteries are 12 volts,
or at least that’s what they are called. Fully charged, they
often produce 13.8 volts.
Automobile style batteries are available that use a
number of different technologies, but the most common
is “lead-acid” and that is what is dis-
cussed in this article. Any 12V lead-
acid battery can be used to store the
electricity from a 12 volt solar system,
but some are much better than others.
The key factors to look for are a large
capacity and deep cycle capability.
Deep cycle batteries tolerate being
repeatedly charged and discharged
better than a more common “starting”
batteries for cars, and that is a very
important capability in a solar system.
The battery shown below is often
used for solar power storage as well
as for trolling motors in boats.
There is much more to know
about batteries for solar use, but the
preceding discussion should lay the
groundwork for your further reading and research.
The last required major component in a solar power
system is a controller. This is an electronic device that
performs the following important functions.
u Connects to the solar panel array and senses the volt-
age of the electricity that the array is producing.
This small array consists of two 100-watt
solar panels mounted on a simple wooden
frame. The author plans to remove them
from the frame and install them on top of
the van shown in the background.
The SRM-24 Marine/RV Deep Cycle bat-
tery from Interstate is often used in solar
power systems. Note the presence of
screw terminals for the power connec-
tions; screw terminals are easier to use
than the standard battery post terminals.
Links Archive march-april 2017 july-august 2017 Navigation Previous Page Next Page