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The figures indicate the average
(over the course of the year) amount of insolation (full sun hours) for
these zones. These figures are based on the yearly average; consequently,
systems based on these figures will provide more power in summer and less
in winter. Winter figures for daily solar gain may be from 25% to 50%
LESS than these average figures, determined by site latitude and
seasonal climate characteristics.
The second question addresses
the amount of energy required. In order to accurately size a system, you
need a fairly accurate idea of the applications average daily power consumption.
This is critically important to the size of the system. Overestimate will
artificially inflate the cost and underestimate will result in a system
that is too small, leading to a greater chance of shortening battery life.
The third question requires
analysis of how efficiently the application uses the energy generated
by the ST product. Note what appliances or equipment use a large amount
of power, and replace them with more efficient devices. Switching from
incandescent lights to LED or compact florescent lights and switch to
propane appliances such as the dryer, stove, water heater and space heating.
Replace a refrigerator with a more energy efficient model. Eliminate phantom
loads by putting anything with a remote control on power strips, including
devices with a clock such as microwaves.
How much will it cost? The
more accurately you assess the energy needs, and the more energy efficient
your application is, the more cost efficient your design will be.
To begin sizing an ST system,
determine the power consumption demands. Make a list of the appliances
and/or loads required to run and find out how much power each item consumes
while operating. Most appliances have a label on the back which lists
the wattage. Specification sheets, local appliance dealers, and the product
manufacturers are other sources of information. Appliances and other devices
are rated in a variety of ways. Some are rated by energy cost based on
kilowatt-hours per year and utility rates, while others are simply rated
in Watts or horsepower.
The goal is to determine a
weekly Watt-hour demand requirement that the ST system must support, and
the maximum demand rate at which it must deliver AC power. Solar cycles
are diurnal, meaning they occur daily, but the system has battery energy
storage which evens load demands out over time so that is the basis for
our calculations.
As a general rule, most electrical
devices do not consume power 24 hours a day, they operate intermittently
or on-demand over the course of a day or even decades. We need to reduce
everything to it’s worst case probable weekly requirement. If for
example, a pump activates once a week, but runs for several hours, the
SOLAR PANEL ARRAY is sized to support that and all other loads
(in Watt-hours) added up over the course of the week. You divide that
value by 7 to get the energy the solar array must harvest daily. Preferentially
calculate this value using lower winter solar energy availability for
a worst case determination.
DC loads can also be factored
in for equipment running directly off the batteries. Simply add their
Watt-hour requirements to the AC loads.
The INVERTER needs
to be sized to handle the worst case AC power demand that could happen
when multiple loads are applied at the same time. Resistive loads such
as incandescent lights and inductive loads such as electric motors have
a high initial surge current associated with them so the inverter must
be able to supply that.
The following calculator provides
Watt-hours per day based on weekly loads. Multiply that value by 1.25
to 1.5 based on winter sun availability. Divide that result by the average
sun availability in hours based on your location. The answer provides
the solar panel array size you will need.
The BATTERY bank size
will be the result of the number of days of autonomous (no sun) operation
multiplied by the average daily Watt-hour usage, times 2. Divide that
number by the DC system voltage to arrive at the battery array amp-hour
capacity you'll need. Batteries connected in series sum voltages based
on the number of batteries. Batteries connected in parallel sum current
(amps). Divide the required amp-hour capacity by the battery rating for
the number of series banks you will need. A series bank is determined
by the system DC voltage. For example, if you are using 6-volt batteries
in a 24-volt system, they must be arranged in series banks of 4. Each
bank connected in parallel with the next bank adds it's amp-hour capacity
to it.
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