Inverter load and power estimation calculation

So far so good. Now we will check inverter load and power estimation calculation. Why is this necessary? As a matter of fact this is perhaps the most important section of this training.

For example, if your client tells you that she wants to power:

• 1 x 10 Watt LED bulb used 4 hours per day.
• 1 x 70 Watt fan used for 2 hours per day.
• 1 x 75 Watt refrigerator that runs 24 hours per day with compressor run 12 hours and off 12 hours.

In this case,

1. what capacity of inverter will you use for the installation? So you see why this is important?
2. How many batteries do you need for the system to run for x hours?

Understanding the inverter and battery sizing will distinguish you from thousands of inverter installers out there.  But this system design and calculation will help you understand what you really need and how to achieve the power autonomy you desire.

OK please follow the calculation below to understand carefully how to size your system.

Same Example: A house in Lagos, Nigeria has the following electrical appliance usage:

• 1 x 10 Watt LED bulb used 4 hours per day.
• 1 x 70 Watt fan used for 2 hours per day.
• 1 x 75 Watt refrigerator that runs 24 hours per day with compressor run 12 hours and off 12 hours.

We will power the system with 12 Vdc, 80Wp PV module.

1. Calculate the daily power consumption

2. Inverter sizing
Total Watt of all load = 10 + 70 + 75 = 155 W
To avoid overloadof inverter, the inverter should be considered 25-30% bigger size.
    The inverter size should be at least 195 W or greater.

4. Battery sizing
Total appliances use = (10 W x 4 hours) + (70 W x 2 hours) + (75 W x 12 hours)
Nominal battery voltage = 12 V
Days of autonomy = 2 days

    Battery capacity = [(10 W x 4 hours) + (70 W x 2 hours) + (75 W x 12 hours)] x 2
(0.85 x 0.6 x 12)

Total Ampere-hours required 352.94 Ah Approx 400Ah
    So the battery should be rated 12 V 400 Ah for 2 day autonomy.

Do you understand?

Ok, you should also watch this video to get further clarification.

Do you need further help on this? You can Whatsapp Wavetra Energy in house solar engineer for further assistance.

After COMPLETING this lesson, move on to the next!