18/09/2023
STEPS ON HOW TO SIZE A SOLAR POWER SYSTEM
Assuming you have the following appliances;
1 plasma TV(55W)
1 decoder(18W)
1 ceiling fan(70W)
1 home theatre(35W)
4 LED bulbs(5W each)
The total power of these appliances is 198W and their total energy consumption for 12 hours is 2,376Wh or 2.376KWh.
To design a solar system that will power these appliances for 12 hours every day with a 1.5KVA/1500VA inverter, you will;
Step 1: Divide the energy consumption by the inverter efficiency. High quality inverters have efficiency of more than 90%. We will use 90% for this calculation.
These will be 2,376Wh/0.9=2,640Whr.
Step 2: Add the value above to the inverter standby consumption (this is the energy consumed by the inverter every day when it is on).
2,640Wh+360Wh=3,000Whr
3,000Whr is the total energy demand of the solar system. For the solar system to function efficiently, the solar panels need to generate 3,000Whr of energy and store in the batteries every day when there is sunshine.
Step 3: To size the battery bank, divide the total energy consumption by the system voltage. Using a system voltage of 24V, this becomes
3,000Whr/24V=125Ah. It is not a good practice to completely discharge the batteries. We will divide the value above by 50%(0.5) DoD (depth of discharge)
125/0.5=250Ah
Step4: To calculate the number of solar panels needed, divide the total energy by 0.65. Ideally solar panels don’t perform up to their rated values due to shading, temperature and other effects that we cannot control.
3,000Whr/0.65=4,615Whr
Divide again by the peak sun hours (the amount of sunshine available in a particular location for an average day). Here we will use 4.5hr
So 4,615Whr/4.5hr=1,026Wp
To know the number of panels needed, divide by the power rating on the solar panel. Solar panels comes with different ratings. In our example, we will use 250W
1,026/250= 4.104
We need 4 solar panels rated at 250Wp.
Step 5: The size of the charge controller(we will use a PWM SCC) will be 50A. The size of charge controller depends on the amount of current the panels will generate when connected in parallel or series.
Therefore we will need;
1.5kva/24v inverter
4 solar panels of 250w
2 deep cycle batteries of 12v/150ah connected in series
50amps PWM charge controller
Cables, breakers, cable lugs, SPDs, change over, battery rack, solar panel mounting rack.
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