- steps

- 1. Electric Load Estimation

2. Rating of Solar Panel

3. Battery Sizing

4. Inverter and Charge Controller sizing

5. Cable and circuit breaker sizes

6. Summary of the project

**Off-Grid Solar System Design for Home Application**

**(**Electrical engineer solar opinion and estimate of energy storage and usage limits)

## 1. Electric Load Estimation

The following electrical appliances are considered as a load for the whole design.

Table 1: electrical load

No. | Appliance | quantity | Power(W) | Time (h) | Energy consumption (Wh/day) |

1 | TV | 2 | 36 | 6 | 432 |

2 | Refrigerator | 1 | 75 | 6 | 4500 |

3 | Wall AC | 1 | 900 | 6 | 5400 |

4 | Lighting | 20 | 9 | 10 | 1800 |

5 | Hair dryer | 1 | 1000 | 0.25 | 250 |

6 | Ceiling fans | 2 | 75 | 10 | 1500 |

7 | Blender | 1 | 40 | 0.14 | 5.6 |

8 | Coffee make | 1 | 894 | 1 | 894 |

9 | Dish washer | 1 | 1200 | 1 | 1200 |

10 | Microwave oven | 1 | 1450 | 0.5 | 740 |

11 | washer | 1 | 512 | 0.85 | 435.2 |

12 | Clothes dryer | 1 | 4900 | 0.85 | 2450 |

13 | home computer | 1 | 300 | 8 | 2400 |

14 | Laptop computer | 2 | 60 | 10 | 1200 |

15 | mobile charger | 5 | 5 | 2 | 50 |

16 | Water heater | 1 | 4500 | 2 | 9000 |

17 | Modem/wi-fi | 1 | 10 | 24 | 240 |

Total | 15966 | 32496.8 |

**2. Rating of Solar Panel**

Table 2: Electrical specifications of PV module *

Parameter | Variable | Value |

Maximum Power | P_{max} | 335 W |

Maximum Power Voltage | Vmpp | 42.2 V |

Maximum Power Current | Immp | 7.94 A |

Open Circuit Voltage | Voc | 51.1 V |

Short Circuit Current | Isc | 8.51 A |

- Total DC Amp-hours/Day= Total System Load / System Nominal Voltage

= (32,500Whrs/Day) / 48 Volts

= 677 Amp-hrs/Day

- Total PV Array Current = Total Daily Amp-hr requirement / Design Insolation*

=677 Amp-hrs / 5.0 peak solar hrs

= 136 Amps

- Number of Modules in Parallel=Total PV Array Current/ (Mod. Operating Current)x(DF)

=136/ (7.94 Amps/Module)*(0.95)

= 18.03 modules ≈ 18 modules

**Therefore, 18 modules are connected in parallel.**

- Number of Modules in Series = System Nominal Voltage / Module Nominal Voltage

= 48 Volts / (42.2 Volts/module)

= 1.14 Module

Use 2 modules, **therefore, 2 modules are connected in series.**

**Total number of PV module required = 18×2= 36 modules **

The solar panel size should be selected in such a way that it will charge the battery fully during the one day time. We can assume 5 hours of effective sunlight (December @ Mexico) which will generate the rated power.

- Total power of PV panel capacity needed = 32,500Whr * 1.25 /5hr = 8125W – minimum PV array watts. The 1.25 factor accounts for the battery charge/discharge efficiency losses over the life of the battery.
- Number of modules = 8125W ÷ 335W module rating = 35 modules

Therefore. 38 modules would make the system more reliable and further reduce generator time.

## 3. Battery Sizing

Design Considerations: Desired Reserve Time is one day and Losses and the safety factor is 1.1. Based on these design considerations the Minimum Battery Capacity is calculated in the following way.

=677 Amp-hrs/Day X 1.1

= 745 Amp-hrs/Day

Minimum Battery Capacity = (745 Amp-hrs/Day X 1 Day) / 0.70

= 1064 Amp-hrs

Use TN1000 (1.2V 1000Ah) NICKEL IRON BATTERY

Nominal Voltage = 1.2 Volts

Rated Capacity = 1000 Amp-hrs

=1064 Amp-hrs / (1000 Amp-hrs/Battery)

= 1.064 ≈1 battery

**Therefore, the number of batteries in parallel is one battery **

=48 Volts / (1.2 Volts/Battery)

= 40 Batteries

**Therefore, the number of batteries in the **series is** 40 batteries. **

**The total number of batteries required for this project is 40 batteries.**

## 4. Inverter and Charge Controller sizing

The Peak Load figure is used to size the minimum full power output of the inverter required. Choose an inverter with a power rating above the peak wattage that the loads can draw. The selected inverter is 5000w mppt Solar inverter 230vac 48vdc, this inverter has a built-in charge controller and AC input, so there is no need of calculating another charge controller, and its specification is;

Power: 5000w

Input voltage: 48V Dc

Output voltage: 230v AC

Type: mppt solar inverter

Max. Input voltage: 500vDC

Current: 80A

The number of inverters required is calculated from the maximum load of the project, which is ;

= 9580/5000

= 1.9

**The total** number of inverters required for this project is** two.**

## 5. Cable and circuit breaker sizes

Based on IEEE standards and calculated values in above the circuit breaker/ fuse rating and size of cables in different places look like the following.

No. | Location | Calculated current | Standard rating of circuit breaker | Standard rating of the cable | Number of circuit breaker | Type of circuit breaker |

1 | Solar panel to inverter terminal | 136A | 160A | 50 mm^{2} | 1 | DC |

2 | Battery bank to inverter terminal | 200A | 225A | 120 mm^{2} | 1 | DC |

3 | AC generator to Inverter | 42A | 63A | 10 mm^{2} | 1 | AC |

4 | Inverter to load | 42A | 63A | 10 mm^{2} | 1 | AC |

### 6. Summary of the project

- The total energy consumption (Wh/day) of the project is 32,500Wh/day and the peak load is 9580W.
- Total number of PV module required 36 modules
- Total number of batteries required for this project are 40 batteries.
- Total number of inverters required for this project are two.

Figure 1: Diagram of the project

Figure 1: connection Diagram of the project