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Getting the design of the system right is key to ensuring both reliability of
supply and minimum cost. A little time spent in accurate estimation of energy
consumption and planning the installation will pay dividends in the future. The
calculators on this page will help in the process of building the optimum solar
power system for your needs.
Solar Panel Sizing
If you followed the advice in the energy section, you
will have reduced your electrical energy requirements to a bare minimum. The
next stage is to use these to calculate the daily energy requirement. Start the
Electrical Load Calculator
and follow the instructions to calculate your daily energy requirement.
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To use this calculator, first select the type of appliance from the drop down
list, and then insert the number of this type of appliance in the Qty field.
If you know the daily Watt-hour consumption you may enter it directly,
otherwise enter the power rating and daily usage in the appropriate fields. The
value returned is the total daily energy consumption in Watt-hours.
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Next, start the Solar Requirement Calculator. Enter the daily energy requirement and select the seasons you will be using
it in. The result tells you the amount of solar generation needed in Watts
peak. For example, if the answer is 100 Wp, then you need two 50 Watt solar
panels, five 20 Watt panels or any other combination that adds up to 100 Watts.
The actual panels to be used may be determined by their availability, the area
available to you or other considerations.
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To use this calculator, just input the daily energy consumption and select the
seasons the system will be used in. The value returned is the minimum peak
wattage required.
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Now you can size the battery. First you have to decide on the system voltage. A
simple rule of thumb is this: If there are 12 Volt loads or it's a small system
(a few hundred Watts), make it 12 Volt. Otherwise make it 24 Volt. Only think
about 48 Volts if you have telecoms equipment to power or it's a very big
system, at least 1 kW (1000 Watts).
To size the battery, use the Battery Requirement Calculator
. You'll need to use the daily energy requirement calculated earlier.
To use this calculator, just input the daily energy consumption and select the
system voltage and number of days autonomy required. The value returned is the
minimum battery capacity expressed in Ampere-hours at the system voltage.
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Only one big thing left; cable. If the major components are a long way from
each other or the loads, you may need substantial cable to avoid loss of power.
Decide where the components are going and use the Cable Requirement Calculator to work out the size of the major cables.
This calculator returns the minimum size for individual DC cable runs. The
maximum load is entered, along with the system voltage and length of cable
needed.
The result is the minimum cross-sectional area of two-core cable required to
ensure a voltage drop of less than 5% of the system voltage.
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Other Components
Now that the major system components are in place, all that remains is the
simple matter of sizing the:
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Charge Controller and
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Inverter
It is possible to do without a charge controller only if the battery is very
large relative to the solar panel array. An example is the "Battery Saver"
panels designed to plug into a car cigarette lighter. Otherwise, add up the
short-circuit current of the solar panel array and use the next largest
controller.
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