The solar panels are the most important component of any solar power system. The proper sizing as per your load can solve your energy needs. The following points need to be considered before sizing the panels for your solar power system.
(1) Calculating the energy required
Let us understand this with the help of an example:
Please see the load chart below:
Therefore the above electrical appliances need 1700 watt-hours (i) to run during the day.
(2) The battery back required
Let us say, I want a battery backup of 4 hours, that is 350 watt of load is to be backed by the battery for 4 hours. Multiply 350 watts with number of hours of backup required, we get 1400 watt-hours. We need a battery which can provide 1400 watt-hours to run our electrical appliances, (Please read How to size the battery for your solar power system?), Assuming 90% efficiency of the battery (10% is lost when chemical energy stored in battery is converted into DC electrical energy) and 90% efficiency of the inverter (10% of the energy is lost while converting DC electrical energy to AC electrical energy), we get,
1400/ (0.9x 0.9)
= 1728 watt-hours (ii)
You can say like this that 1728 watt-hours from the battery will supply 1400 watt-hours to the load, the remaining 328 watt-hours will be lost during the process of the energy conversion from chemical energy to DC electrical energy to AC electrical energy.
(3) The total energy required
Now, summing the watt-hours required by the load during the day (i) and the watt-hours required by the battery to backup the load (ii), we get,
(1700 + 1728) watt-hours
= 3428 watt-hours
This is the amount of watt-hours which are required as an output from the solar panels.
(4) Sizing of the solar panels
Again solar panels are not 100% efficient; some energy is lost while converting solar energy into electrical energy, also some energy is lost as a heat while transferring through wires. Therefore, assuming 70% efficiency of the panels, we get
3428 watt-hours/0.7 = 4897 watt-hours
Now, we can calculate the size of the solar panels by dividing the above value of 4897 watt-hours by the average solar insolation of the area (It is the amount of the solar radiation falling on the surface of the earth in \(KWh/m^2/day\). A good insolation levels will need less solar panels while poor insolation levels require more solar panels), I am taking the average solar insolation of Delhi/NCR which is 5.5. You can get figures of your area from internet search or you can get it from the website of renewable energy department of your state.
Now, dividing 4897 watt-hours by 5.5, we get,
4897/5.5 = 890 watts
Therefore, 890 watts is the size of the panels that is required which can meet your above mentioned energy needs.
The 250 watts panels are available in the market; therefore you can take 4 panels of 250 watt each to make it 1000 watts.