Solar Off Grid System Design with Manual Calculation

 Load Estimation :-

In the solar off grid system firstly we will find all the appliances which is operated by solar power. After finding all the appliances we will calculate total energy consumption by all the appliances with total wattage of all appliances.The methods of total watts and total load consumption is given in fallowing table.

This system is design for a petrol pump which is located in Hyderabad Telangana India:

            The design Layout of solar off grid system like Module Mounting Structure & Module Installation is Shown In Fig 1 & 2 which are given below.

Fig -1 

Fig - 2

Appliances are mentioned below

1.     LED Tube Light,18 W 

2.     Mobile Charger,15 W

3.     Out side LED Light ,20 W

4.     Fan  60 W

Load Estimation: Calculation of AC & DC Loads As per Customer Requirement -

S.No.	Appliances	Load Wattage	No. of Appliances	Total Watts	Operating Hour’s	Total Consumption (Watts)
1	LED Tube Light	18	7	126	12	1512
3	Out Side  Light	20	10	200	12	2400
4	Fan	60	3	180	12	2160
5	Wi-Fi Router	15	1	15	12	180
6				521		6,252 Watts

Total Daily Watt Hour (Wh) Per Day = 6,252 Wh

Electronics Component Selection:

(A) Inverter Capacity Selection 

Load			Inverter
Total Wattage of Load (W)	Efficiency (%)	Out Put Wattage (W)	Inverter (VA)
521	88	521	Output (W) X 100 / Efficiency (521 X 100)/ 88 =  592 ≈ 600 VA

 (A)Solar Inverter Capacity Selection: 

Total Energy (Wh)	Efficiency (%)	Total Energy (Wh)
6,252	88	6,252X (100/88) ≈ 7,104 Wh

  (B)Solar Charge Controller Selection: 

Energy (Wh)	Wattage	Voltage	Maximum Current (A)
7,104	521	24 V	521/24 = 21.70 ≈ 22 Amps

                Here, The System Voltage is 24 V 

Energy (Wh)	Wattage (W)	Voltage	Maximum Current
7,104	600 W	24 V	22 Amps

We need to Supply 8962Wh energy to the input of the inverter with system voltage 24 V, Now we are calculate reacquired Ah capacity 

                            Ah Capacity = Wh ÷ V

                                                 = V X I X H ÷  V

                                                 = 7,104 ÷ 24

                                                 =296 Ah, ≈ 300Wh This Energy is required on a Single Day 

Day of Autonomy: The Battery in this system store energy to supply the power to the load during non-sunshine hours. In this situation like rainy or winter session, it is possible that the sun is not available one or two days.

Here we are considering 2 days of autonomy days, one day for today and another one day for tomorrow (Next Day).

Battery Sizing:

            The battery use for Solar PV system must be rechargeable ,allow to deep discharge should have long life span ,easily serviced and have high capacities and low self-discharge 

(A) Battery Capacity:- Battery has certain parameter Like DoD which is consider here 50%

We are assume 24 V, 200 Ah battery on this system 

Energy (Wh)	System Voltage (V)	Battery Capacity (Ah)	DoD (%)	Actual Battery Capacity (Ah)
7,014	24 V	7,014÷ 24 = 296 ≈ 300	50	300 ÷ 0.5 = 600

 (B) Standard Battery Capacity Available 

Here we are consider two days of Autonomy  

Actual Capacity After DoD (Ah)	Numbers of day of autonomy	Finel Required Battery Capacity  (Ah)
600	2	600 X 2 = 1200 ≈ 1200

Actual Capacity After DoD (Ah)	Slandered Battery Capacity In (Ah)	Total No. of Battery
1200	200	1200 ÷ 200 = 6

• No. of Battery = 6
• system Voltage =24 V
• Standard Battery Voltage = 24 V
• Series Connection = 24 ÷ 12 = 2
• Parallel Connection = 6÷2 ( battery in parallel ) = 3

Thus total battery capacity will be 

                    72 X 600 Ah = 43,200 Ah 

                                               = 43,200 watts or 43.2 Kwh 

Means this system can release 43 unit electricity on  daily basis. If we are see on monthly basis then it will be generate 1,920 unit electricity per month.

Note:  One thing to note here is that if we are increasing Autonomy Day, then the number of batteries and the power are increasing accordingly.

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Here we are proceed with two day of autonomy day

Solar Photovoltaic Module Sizing:

(A) Energy Calculation 

Total Energy (Wh)	Battery Efficiency	Energy From SPV Module (Wh)
7,104	88%	7,104 ÷ 0.88 =8,072 ≈ 8,000

(B) SPV Module Wattage Estimation 

Energy from SPV Module	No. of Sun Shine Hours (h)	SPV Module Wattage (W)
8,000	5.5	8,000 ÷ 5.5 = 1467 ≈ 1500

(C)Standard Module Capacity:

Actual SPV Module Capacity In (W)	Standered SPV Module Capacity In (W)	Total No. of SPV Module
1500	250	1500 ÷ 250 =  6 ≈ 6

(D) No. of SPV Module Series & Parallel Connection:

No of SPV Modules	System Voltage (V)	Standard SPV Module Voltage (V)	Series Connection	Parallel Connection
6	24	24	24  ÷  12 = 2	6 ÷  2 =  3

Summary:-

1.     Solar PV Module 24V,300Wp - 6No's

2.     PCU Inverter 600VA - 1 No's

3.     Battery 24V,150Ah-6 No’s 

4.     Other miscellaneous Equipment- As per site requirement

* Such Type system are suitable for village areas or remote & hilly area where the proper electricity transmission and distribution are not possible.

System Backup Time:-

Load	2300 W	1200 W	600 W	300 W	150 W	100 W
Duration	Hrs. mint	Hrs. mint	Hrs. mint	Hrs. mint	Hrs. mint	Hrs. mint

** In this context i want to said that the above backup time calculated on the behalf of 50% DoD

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