Solar Panel Guide: Step by Step Procedure

Jun 18, 2017
5 min read

After reading this solar panel guide, You will be able to; → To calculate the no of solar panel (with rating) → To calculate the rating of Solar panel

→ To calculate the rating of batteries for Solar panel system → To calculate the back-up time of batteries → To calculate the charging current for batteries → To Calculate Charging time for batteries → UPS Rating for load requirement and much more…

Before starting, I recommend you to read this Article about Solar panel installation and Photovoltaic Pane Selection for Residential or Commercial.

PV: Types of Solar Panel and which one is the best PV Panel

Let’s starts:

Suppose. Load = 800 Watts

Inverters Rating =?

Required Backup time for batteries = 3 Hours

Required No of Solar Panel =?

No of batteries =?

Solution:

Inverter should be greater 25% than the total Load

800 x (25/100) = 200

800+200 = 1000 Watts

This is the rating of the UPS (Inverter)

Now the required Back up Time in Hours = 3 Hours

Suppose we are going to install 100Ah, 12 V batteries,

12V x 100Ah = 1200 Wh

Now for One Battery (i.e. the Backup time of one battery)

1200 Wh / 800 W = 1.5 Hours

But our required Backup time is 3 Hours.

Therefore, 3/1.5 = 2→ i.e. we will now connect two (2) batteries each of 100Ah, 12V.

If the number of batteries given, and you want to know the Backup Time for these given batteries, then Use this formula.

1200 Wh x 2 Batteries = 2400 Wh

2400 Wh / 800 W = 3 hours.

So this is a 12 V inverter system, Now we will install two (2) batteries (each of 12V, 100 Ah) in Parallel.

Why Batteries in Parallel, not in Series?

Because this is a 12Vinverter System, so if we connect these batteries in parallel, then the Voltage of batteries (12 V) remains same, while it’s Ah (Ampere Hour) rating will be increase

(Remember: In parallel Connection, Voltage will be same in each wire or section, while current will be different i.e current is additive e.g. I1+I2+I3…+In = 100Ah +100Ah = 200Ah

In Series Circuits, Current is same in each wire or section while voltage is different i.e. Voltage is additive e.g.V1+V2+V3….Vn..

For The above system if we connect these batteries in series instead of parallel, then

The rating of batteries become V1+V2 = 24V while the current rating would be same i.e.100Ah.

We will now connect 2 batteries in parallel (each of 100Ah, 12V)

Therefore for 2 Batteries,

200 Ah 12V,

Now Required Charging Current for these two batteries.

(Charging current should be 1/10 of batteries Ah)

200Ah x (1/10) = 20A

Now the required No of Solar Panels

P = VI

P = 12V x 20 A

P = 240Watts

This is our required watts for solar panel (only for battery charging, and then battery will supply power to the load)

Now

240W/60W = 4 Solar panels

Therefore, we will connect 4 Solar Panels (each of 60W,12V,5A) in parallel.

This was only for battery Charging (and then battery will supply power to the desired Load) i.e. for those electrical appliances, which will get power through inverter (from charged batteries)

Now suppose there is some (Directly connected to the panels through inverters (without battery) load about 10A, which we have connect directly to the solar panel (No batteries required)

In this case, required current (20 A for Batteries Charging and 10 A for direct connected load through Inverters during sunshine only but batteries will be also charging while panel supply power to the direct connected load.

In this case, total current,

20A + 10 A = 30A

Now I = 30 A, then required Power

P = V x I = 12V x 30A = 360Watts

(This is for both Direct Load and Batteries Charging)

Now,

360/60W = 6

Therefore, we will Connect 6 No of Solar panels (each of 60W, 12V,5A)

And We use Charge Controller about ampere rating i.e, the charging current for 200Ah battery is 20-22 Amperes (22A (For Battery Charging)+10A(for direct DC Load)…So we can use a charge controller about 30-32 Amp.

Note: this calculation is base on ideal case, so it is recommended to always choose a Panel some bigger then we need. Because when Solar Panel charges the battery so it is wasting some power on charging too.

this is another Circuit Diagram for the above Calculation for Solar Panel Installation

Cost of a Solar Plant

Above mentioned three items will cost according to the electricity requirements we may have depending on our needs.

As a reference, let’s assume following situation:

We need to run following items on solar energy:

2 Fans
2 Energy Savers
1 laptop
and few chargers

Here’s the corresponding load we will need:

2 Fans: 110 x 2 = 220 Watts
2 Energy Savers: 20 x 2 = 40 Watts
1 laptop = 20 Watts
and few charges = 10 Watts
Total: 270 Watts

Ideally speaking we will require 270 Watts of energy to be produced by solar system that we are going to deploy in our example case.

Practically, we will deploy 540 Watts panels, because when on Solar energy – during day time – we need to power our appliances with 270 watts, plus we need to charge our batteries too for usage during load-shedding in the night.

Here is the corresponding cost for 540 Watts of Panels:

Solar Panel: Rs. 100 per watt = Rs. 100 x 540 = Rs. 54,000
Inverter – we will need 1KW inverter = Rs. 26,000
Batteries: 2 x 200 Amp batteries: Rs. 13,000 x 2 = Rs. 26,000
Total Cost: Rs. 54,000 + Rs. 26,000 + Rs. 26,000 = Rs. 106,000

Note:

You can use one battery instead of 2, but that will store lesser amount of electricity – which will give shorter back-up time during nights. Same as we deal with UPS batteries — more the battery power will mean more back-up time.
With two batteries and the load requirements in our example case the back-up time will be around 4-6 hours during night.
Please note that during day time you won’t require batteries, so technically speaking – you can run this solar plant for assumed load for whole day (as far as the sun is up).
Since the load is 540 Watts, 1KW inverter will do the job. If load was 2400 Watts then you would have to use 3KW inverter.
Price’s of bigger inverters are given below.

So you need to spend Rs. 106,000 for the solar plant to power up 2 fans, 2 energy savers, one laptop and few chargers for seamless up-time.

Here are few things to note:

Price of solar plant may differ. Above mentioned price of Rs. 100 per watt solar plant is market average rate for premium quality Chinese plants
You can get European (German) solar panels for Rs. 150 per watt, but that’s just additional cost as Chinese panels work fine.
If your load exceeds 500 watts then you will have to use high-voltage inverters, that is 2 KW, 3kW or above. Here are estimated prices for bigger inverters:
1 KW Inverter: Rs. 26,000
2 KW Inverter: Rs. 35,000
3 KW Inverter: Rs. 45,000
4 KW Inverter: Rs. 60,000
5 KW Inverter: Rs. 80,000
10 KW Inverter: Rs. 200,000
P.S. Prices of inverters also vary, depending on the quality and made. Prices mentioned here are for good quality Chinese inverters
Number of batteries will also depend on the load you may require to store. Here’s the desi formula for calculating back-up timing of a battery:
Amperes of battery x number of hours with sun-shine / load = Back-up time in hours
Example: (200Amp + 200Amp) x 10 hours / 540 Watts = around 7 Hours

Amount of batteries required in your solar plant can be determined by using or re-arranging above desi formula:

Back up time = Amperes of Battery x Number of Hours with Sun-shine / Load
Amperes of Battery = Back up time required / Number of hours with Sun Shine x Load

Furthermore:

Life of solar panels is around 25 years, however, with time the efficiency or electricity-production ability of panels lessens
Life time of dry-battery is around 5-7 years
Life time of liquid-battery is around 2 years
Solar panels work fine below 45 degree Celsius
Solar panels work well even in hilly areas.