| 1. Determine power consumption demands
The first step in
designing a solar PV system is to find out the total power and energy
consumption of all loads that need to be supplied by the solar PV system
as follows:
1.1 Calculate total Watt-hours per day
for each appliance
used.
Add the Watt-hours needed for all appliances together to get the total
Watt-hours per day which must be delivered to the
appliances.
1.2 Calculate total
Watt-hours per day needed from the PV
modules.
Multiply the total appliances Watt-hours per
day times 1.3 (the energy lost in the system) to get the total
Watt-hours per day which must be provided by the panels.
2. Size the PV modules
Different size of PV
modules will produce different amount of power. To find out the sizing of
PV module, the total peak watt produced needs. The peak watt (Wp) produced depends on size of the PV
module and climate of site location. We have to consider “panel generation
factor” which is different in each site location. For Thailand, the panel generation factor is
3.43. To determine the sizing of PV modules, calculate as
follows:
2.1 Calculate the total
Watt-peak rating needed for PV
modules
Divide the total Watt-hours per day needed from the PV modules (from
item 1.2) by 3.43 to
get the total Watt-peak rating needed for the PV panels needed
to operate the appliances.
2.2 Calculate the number of
PV panels for the
system
Divide the answer obtained in item 2.1 by the rated output Watt-peak of
the PV modules available to you. Increase any fractional part of result to
the next highest full number and that will be the
number of
PV modules required.
Result of the calculation is the minimum
number of PV panels. If more PV modules are installed, the system will
perform better and battery life will be improved. If fewer PV modules are
used, the system may not work at all during cloudy periods and battery
life will be shortened.
3. Inverter sizing
An inverter is used in
the system where AC power output is needed. The input rating of the
inverter should never be lower than the total watt of appliances. The
inverter must have the same nominal voltage as your battery.
For stand-alone
systems, the inverter must be large enough to handle the total amount of
Watts you will be using at one time. The inverter size should be 25-30%
bigger than total Watts of appliances. In case of appliance type is motor
or compressor then inverter size should be minimum 3 times the capacity of
those appliances and must be added to the inverter capacity to handle
surge current during starting.
For grid tie systems or
grid connected systems, the input rating of the inverter should be same as
PV array rating to allow for safe and efficient operation.
4. Battery sizing
The battery type
recommended for using in solar PV system is deep cycle battery. Deep cycle
battery is specifically designed for to be discharged to low energy level
and rapid recharged or cycle charged and discharged day after day for
years. The battery should be large enough to store sufficient energy to
operate the appliances at night and cloudy days. To find out the size of
battery, calculate as follows:
4.1 Calculate total Watt-hours per day
used by appliances.
4.2 Divide the total
Watt-hours per day used by 0.85 for battery
loss.
4.3 Divide the answer obtained in
item 4.2 by 0.6 for depth of
discharge.
4.4 Divide the answer obtained
in item 4.3 by the nominal
battery voltage.
4.5 Multiply the answer
obtained in item 4.4 with days of
autonomy (the number of days that you need the system to operate when
there is no power produced by PV panels) to
get the required
Ampere-hour capacity of deep-cycle battery.
Battery Capacity (Ah) = Total Watt-hours per day used
by appliances x Days of autonomy
(0.85 x 0.6 x nominal battery voltage)
5. Solar charge controller sizing
The solar charge
controller is typically rated against Amperage and Voltage capacities.
Select the solar charge controller to match the voltage of PV array and
batteries and then identify which type of solar charge controller is right
for your application. Make sure that solar charge controller has enough
capacity to handle the current from PV array.
For the series
charge controller type, the sizing of controller depends on the total
PV input current which is delivered to the controller and also depends on
PV panel configuration (series or parallel
configuration).
According to standard
practice, the sizing of solar charge controller is to take the short circuit current (Isc) of the PV array, and multiply it by
1.3
Solar charge controller
rating = Total short circuit current of PV array x 1.3
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