# How to design a solar system

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. 