When selecting a solar electric
system for your cabin or offgrid home, it is important to know
how much power you will be consuming in a single day's worth of
available sunshine. This information is critical because it is
important to replace the power that you've taken out of your
battery pack each day or you will run into a deficit which will
eventually damage your battery pack.
We once had a customer that
called, wanting to order a single 120 watt solar panel, a charge
controller and a 1000 watt inverter. He wouldn't accept any
technical support from us, saying that he was an engineer and
"Knew what he was doing" About a week after we shipped him his
order, he called saying that his system had stopped working !
After questioning him we learned that he properly connected his
solar system and inverter to a large 180 pound 12 volt truck
battery. The problem started when he plugged his big screen TV
into the inverter. The inverter powered the big screen TV just
fine, the problem was he that was taken more energy out of his
truck battery than what he was putting back in with his solar
His TV was drawing about five
hundred watts and we was watching it for about 4 hours per day.
That's 2000 watt hours of consumption per day. His solar panel
was rated at 120 watts, and in 6 hours of full sunshine per day
was producing 720 watt hours per day.
Well, needless to say, like a
bucket of water that's being drained faster than it's being
filled, the battery's energy content was emptied and you can't
run a 500 watt TV off of a 120 watt solar panel, so his inverter
simply shut down.
This is why it's important to
match your daily consumption with your solar system's daily
production. To correctly sized a system for you cabin or remote
home, you must first determine the wattage of each item that you
wish to power and you also need to determine how long each item
will run per day. For example a 60 watt light bulb that is used
for 5 hours will consume 300 watt hours. Watts multiplied by
time is equal to watt hours. A microwave oven that consumes 800
watts that runs for 15 minutes, consumes 200 watt hours, 800
watts times .25 hours equals 200 watt hours.
So to correctly size a system
for your cabin or offgrid home, simply make a list of each item
that you intend to run. Next to each item write down it's power
consumption in watts and next to that write down the amount of
time that the item will run per day, then multiply the watts of
the item by the amount of time that it will run and write that
number down in the last column. After you have calculated the
watt hour consumption for each item, simply add each item's watt
hour rating together and you'll have your total consumption for
the day. For example:
Once we have this information,
it's a simple matter to match the number of solar panels,
inverter and batteries that you will need in order to produce
and store enough power for what you consume.
The above description assumes
that you do not have a generator. If your cabin or remote home
is equipped with a generator then the amount of solar panels
needed could be reduced. But remember the less number of solar
panels that you install will mean the longer you will need to
run your generator per day to meet your electrical needs.
Sizing the wattage rating of an
inverter for your cabin or remote home is a simple matter of
determining the total number of appliances that you would
typically be operating on a concurrent basis, and adding a
buffer of at least 500 watts. In other words if there was a
possibility that you would have your 600 watt microwave, a 200
watts coffee maker and a 200 watt stereo running at the same
time, you would be drawing 1000 watts, then you should choose a
1500 watt inverter. An inverter should never be run at it's
maximum rating for prolonged periods of time, doing so will
shorten the life of the inverter.
Another issue to consider is
the amount of surge current that your appliances draws. Any
appliance that uses a transformer, motor or other magnetic
device draws what is known as surge current at startup. These
devices are otherwise known as inductors. Inductors appose the
flow of electrical current.
When an inductor is first
energized there is a great degree of inertia that must be
overcome for the magnetic field which surrounds the inductor to
reach it's maximum field. Just as it's difficult to initially
push a car by hand that is at rest and gets easier to push as it
gets going. Initially starting an inductor takes a great
deal of current to get it started but backs off on the current
after it gets going.
Devices such as microwave
ovens, refrigerator compressors, fan motors and large
transformer based appliances can draw from 3 to 6 times it's
normal wattage in an initial surge of current. This initial
surge of current typically only lasts milliseconds but it's
enough to shut down an inverter if it's not sized properly. Thus
it's important to choose an inverter that has enough surge
capacity to start such appliances. For example a meager 600 watt
microwave oven will typically require a 2000 watt inverter just
to get it started.
If all of this
information seems a little overwhelming, don't worry our
friendly knowledgeable staff are here to help you every step of
And finally, be cautious when
purchasing a solar system for your cabin or offgrid home over
the Internet. Get to know who you're dealing with. Many of the
cabin solar kits that are available on the Internet are actually
home made configurations. Many websites on the Internet that
would appear to be large reputable companies are actually home
based affairs that operate from an impossible to trace POB
(PO Box). Remember,
you're about to give this individual your personal information
and more importantly your credit card number.
Is his company solvent ? Does
he have liability insurance ? Does he really have the
items that you're about to purchase in stock ? Does he
have any stock ? With the advent of the energy crisis,
dozens of home based dealers with little or no formal training
or experience have cropped up on the Internet.
Even if you don't live nearby, ask the dealer if you can get
directions to his place of business so you can stop by and take
a look at some products. If you can't get directions or a
straight answer from him, then in our opinion, steer clear !
It's important to remember that it takes only minutes to upload
a website to the Internet and only seconds to take it down.
would like to learn more about protecting yourself when shopping
on the Internet