A virtue

A virtue - Electrifying the non electrified. In Pakistan there are more than 50,000 non electrified villages. Only in Peshawar more than 2500 schools are non electrified. I believe these people (surviving without electricity) are more hard working than any one else. What if this hard work is utilized in development of country by providing them the very basic need of electricity? Isn't it a virtue? 

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Solar is Cheaper

Solar is Cheaper - In Pakistan commercial unit of electricity costs you 27 rupees/unit. Solar PV Systems can surely give you big savings now. Let me explain you with an example

Lump sum price of a long life solar pv system is 180,000 for 1kva system. This system generates 5 units per day (on average), and 150 units per month. 


Per month electricity savings = 150 * 27 = 4050 PKR

Savings in the 1st year= 4050 * 12 = 48,600 PKR

Annual inflation > 11%

Savings in the 2nd year = (48,600 * 0.11) + 48,600 
                                   = 53,946 PKR

Savings in the 3rd year = (53,946 * 0.11) + 53,946 
                                  = 59,880 PKR

Savings in the 4th year = (59,880 * 0.11) + 59,880 
                                  = 66,466 PKR

Total savings in 4 years = 48,600 + 53,946 + 59,880 + 66,466
                                   = 228,892 PKR

Hence a payback of less than 4 years. From there onwards you will enjoy free electricity. 

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Solar Capacity

The sun generates 370 trillion watts per day. Which is equal to 370,000 billion watts per day and further equals to 3,700,000 million watts per day. The average of solar radiation that reaches the earth is equal to 5KW/h per square meter. If we use 2% of the deserts of the world for solar PV plants this can generate electricity for the whole world.

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PV technology classes

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DC components of a solar PV Plant

DC system of a solar PV plant comprises of the following:

• Array(s) of PV modules.
• DC cabling (module, string and main cable).
• DC connectors (plugs and sockets).
• Junction boxes/ combiners.
• Disconnects/ switches.
• Protection devices.
• Earthing.

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200kW Off-Grid Solar PV System Design -1 hour Battery Backup - Hybrid

Project Requirements:

• Total load = 200kW
• Battery backup time = 1 hour
• Primary source = Solar PV
• Secondary source = Grid
• Tertiary source = Battery Bank

System Design:

1. Solar Panels:

Wattage of single panel = 235Wp

No. of solar panels = (Total load x 1.4) / 235

                                = (200,000 x 1.4) / 235
                                = 1192 (rounded value)
     2.  Inverters:
Company = SMA
Two types of inverters (built in charge controllers) will be used.
a). Sunny Tripower     b). Sunny Island (Grid Inverter Or Battery Inverter)

a) Sunny Tripower:
Requirement for sunny tripower = 280,000W*
* 200,000W x 1.4 = 280,000Wp
Suitable sunny tripower (according to the requirement) = STP 20,000 TL
No. of sunny tripower used = 14 

STP 20,000 TL

b). Sunny Island

Requirement for sunny island = 200,000W*
* Sunny island runs the load, so its rating depends upon total load. 

Key functions of Sunny Island:

• In case public grid goes down then Sunny Island generates its own grid and do not let your system go down. 
• In order to keep the Sunny Island running, a battery bank is a must.

Suitable sunny island (according to the requirement) = SI 5048
No. of Sunny Islands = 36*
*One can connect maximum of 36 sunny islands in one system. 36 sunny islands can support 300,000 W load for 1 minute (With suitable battery bank)
230,000 W load for half an hour (With suitable battery bank)
200,000 W load for 1 hour (With suitable battery bank)

SI 5048

Below design is in process    

 3. Solar PV array design:
According to the data sheet of STP 20,000 TL, the input DC voltage capacity of STP 20,000 TL is 750V. It has four inputs of solar PV arrays. The input voltage of one array must not be greater than 90 % of 750V. 
Since the open circuit voltage of one solar PV panel is around 34V. Connecting 15 solar panels in series will give us (15*34) 510V DC which is smaller than 675V (90% of 750V).
So we can make two solar PV arrays, having 15 panels each. All the 15 solar panels will be connected in series in one array.

     4. Battery Bank:
Battery rating is defined in terms of Ampere Hours (Ah). We can find out the Ah for battery bank according to the load and backup time.
Ah = (Load x backup time) / (DOD x PF x System Voltage)
Now
   load = 5000
   backup time = 1 hour
   DOD (depth of discharge) = 0.6
   PF (power factor) = 0.8
   System voltage = 48V
So
Ah = (5000 x 1) / (0.6 x 0.8 x 48)
      =  217.01
So now we need 217Ah @ 48V for battery bank.
Rating of single battery = 200Ah @ 12 V
Connecting four batteries of above rating, in series, will give us 200Ah @ 48V.

System Topology:

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How to design an Off-Grid (hybrid) solar PV system using SMA solar inverters

Information required:
Load =?
Backup time =?
Connection type = single phase or three phase?

 

Design steps:

Step 1

How to decide the battery bank?
Lets say my backup time requirement is 2 hours Then battery capacity (Ah) can be calculated using the following formula
Ah = (Total Load x Backup hours)/(DOD x P.F x SV)
Where

• DOD - Depth of discharge
• P.F - Power factor
• SV - System voltage

So

Ah = (5000 x 2)/(0.6 x 0.8 x 48) = 434.02 Ah approximately equal to 400Ah
Now my battery bank will consist of 8 batteries having 200Ah @ 48V capacity each.

Step 2

How to decide quantity of solar panels?
a) No. of solar panels for running the load directly through solar grid.
Load = 5kW
No. of panels = 5kW x 1.4  --> 7 kW --> 7/235Wp = 30 panels (235 Wp each)
Peak solar hours in worst month of the year = 4 hours (considering the design is for Lahore Pakistan)
so solar PV grid will suport the 5kW load for 4 hours a day. Before and after these four hours, the solar PV grid will give low yield. This low yield will then be compansated by Battery bank and public grid.
b) No. of solar panels for charging the battery bank
400 Ah @ 48V battery bank acts as a 1kW load for solar grid and public grid. (real time observation)
So for a 1kW load we would need 1000 x 1.4 = 1400Wp of panels
No. of panels = 1400/235 = 6 panels
c) Total no. of solar panels
36 + 6 = 42 panels

Step 3

How to choose the inverters?
For choosing the inverters we need to know about following specs of the inverters from its data sheet

• Maximum output power
• Maximum input DC voltage
• Maximum input DC current
• Maximum input Power

Lets say I want to use SMA inverters (Sunny Boy and Sunny Island) then I would choose following inverters
SMC 9000 TL (Solar Inverter)
SI 5048 x 2 (Grid Inverter)

You may also visit
Circuit Diagram for 5kW Off-Grid Solar PV System
5kW Off-Grid Solar PV System Design

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