THE MATH OF A SOLAR SYSTEM
Calculate your energy needs, and the number of solar modules and size of battery bank they require.
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This and other solar system information is available
from Siemens Solar P. 0. Box 6932,
Camarillo, CA 93011 ( http://www.siemenssolar.com ).
SOLAR AREA FACTOR MAP
Please keep in mind that every solar installations is
unique and is affected by many factors, such as local
weather patterns, which vary greatly even within a small
geographical area.
Sizing Principles
In addition to the electricity used by appliances, the
system itself also consumes some power. For example: you do
not get back all the energy you put into a battery. Each
day a battery is left unused (and without any additional
charge), it can lose 1% to 2% of its charge, and even a
properly charged battery is still not 100% efficient. An
inverter also uses some energy to convert electricity from
DC to AC, and voltage is lost as electricity travels
through wires. To be on the safe side, system design should
assume 30% DC waste and 40% AC waste.
Solar modules should be installed at the correct
'tilt-angle' to achieve the best year-round performance.
Generally, this is an angle equal to the site's latitude
plus 20%, with modules facing south in the northern
latitudes and north in the southern latitudes.
BATTERIES
Batteries are a major component in solar systems. A number
of different types and capacities are available. Many small
to medium sized systems can use photovoltaic or marine
grade batteries. These are designed to be deep-cycled
(discharged and recharged) many times and are generally
maintenance free. They are available in capacities of about
120 Amp-hrs.
Batteries must be able to store enough energy for daily
operations. A reserve should be considered so you will have
additional capacity to operate the loads during anticipated
periods of cloudy, sunless weather. This reserve capacity
is referred to as system 'autonomy' and is rated in clays.
The amount of autonomy needed varies. For critical loads
such as telecommunications, you may want 10 or more days of
autonomy, for a residence perhaps five days, and only a day
or two for a vacation cabin.