Designing a PV system is not very difficult it just needs good understanding of Watts, DC, AC, Amps, Voltage etc. But off course it is not rocket science. Anyone can design a solar system for their specific needs. You really do not need to hire an expert for that. I have written the whole procedure in easy to understand steps, hope you find it useful 🙂
Step 1. Calculate the daily Watt hours requirement. In plain terms first calculate the load which is to be driven , taking in to account the numbers of hours for which it is to run. Example we have to run 2 x 20 W bulbs, 1 x 100 W fan and 1 x 35 Radio receiver.
| Item | Quantity | Watts | No of hours (Daily) | Total Watt-Hour |
| Energy Saver | 2 | 20 | 10 | 400 |
| Ceiling Fan | 1 | 100 | 10 | 1000 |
| Radio receiver | 1 | 35 | 20 | 700 |
| Total | 2100 Watt Hour |
So the total Watt Hour requirement daily is 2100 Watt Hour.
It is advisable to add an overhead of 25 – 30 %. In this case we add 25 %. So total requirement comes to
2100 x .25 = 525 + 2100 = 2625 Watt Hours
Step 2.Workout requirement of PV Modules, depending on whether 12 or 24 VDC system is req.
So we choose 2 x 300 W (24 VDC) solar panels.
Total output = 300 x 2= 600 W
Solar panels are calculated at 20 % less or in other words 80 % efficiency.
So 600 x 0.8= 480 W
If daily sun available is 8 hours, this comes to 480 x 8= 3840 W. Observe that this is more than the daily 2625 Watt Hour req. Generally it should be 20 to 50 % more than the daily req. In this case it is 54%. May be an overkill, but one can work out his/her requirement basing on the money he/she has 🙂 .
Step 3.Now finally calculate the battery system required to run the whole setup.
If we choose 4 batteries of 12 VDC, 200 AHC. Connecting them in series –parallel would give us:
400 AHC, 24 VDC system.
Now calculate the current that this can give: I = W/VDC,
I = 400/24 = 16.6 Amps (This is the peak current that the system can give)
The important thing now to calculate is based on how much hours the sun will be available in a certain area. This is defined by Peak Sunlight Hours (PSH) which varies for every region according to sunlight available daily. You can Google the PSH for a particular place and see its map. It won’t be very detailed but is generally good enough. If we say that PSH is 8 hours (It can never be like 8 hours, I do not know why I chose this value). You can see these links for your area by clicking here, here and here.
So total Amps available is 16.6 x 8= 133 Amp
Now see what load the system can drive.
Power = Amperes x Volts
133 x 24 = 3198 Watts.
Observe that this is greater than our daily Watt Hour requirement (3198 >2625 Watts) and less than the daily power that the panels can give (3198 <3840 Watts). So in effect this means that the battery will be charged by the panels and will give more power than the daily requirement.
Hope you found this post useful 
My Random Ramblings 