There are several things to consider when buying an off grid inverter, such as KW rating, capacity of inverter, input voltage range and needed power output.
How to choose the right off grid inverter for an off-grid solar system?
If you are looking for an inverter that is most suitable for your solar system, you are sure to step into the market and find yourself buried under technical questions – size of inverter, KW rating, capacity of inverter, input voltage range, needed power output, etc.
Truth is picking the right inverter is fairly easy. In a few steps you will learn how to size an inverter yourself.
To start with, you need to make a rough estimation of your power needs. Here are some simple steps for the calculation:
STEP-1: Determine your power needs
Let us assume that there’s no grid connection and you completely rely on your own off-grid solar system.
The following electrical equipments are required to be run simultaneously:
Two tube lights (60 Watt each)
Two fans (80 watts each)
One television (120 Watt)
One CFL (15 Watt)
Now let us calculate the total power needed. Which is the sum of the watts for all equipment
Total Power Needed = [(2 X 60) + (2 X 80) + (1 X 120) + (1 X 15)]
= 415 Watt
STEP-2: Determine your off grid inverter capacity
In ideal conditions, if there are no losses, the Total Power Needed (calculated in Step-1) should be the inverter capacity.
Unfortunately this is not the case because there is a difference between power which is specified in Watts and VA rating of electrical equipments.
Power in Watts is the real value i.e. the real power drawn or supplied by equipment.
Power in VA is the apparent power i.e. multiplication of voltage and current drawn or supplied by equipment
Mathematically, this can be written as –
Power (VA) = Power (Watts) / efficiency of inverter/equipment
Now let us assume that the efficiency of inverter is 0.8,
The required power (VA) for the inverter will be calculate as below:
Power (VA) = 415 / 0.80
= 518.75 VA
Hence, the minimum required VA rating of your inverter is approx. 520 VA.
Which type of inverter will fit my needs?
An inverter converts direct current (DC) to alternating current (AC).
Off-Grid inverters can be categorised into 2 types:
Pure Sine Waveform Inverters
Modified Sin Waveform inverters
I would always suggest to use pure sine waveform inverter as it has numerous advantages over Modified sine waveform inverter.
Pure sin wave inverters can run all the electrical home appliances, efficiently and effectively. They are more durable and keep appliances safe.
On the other hand, modified sin wave inverters are less expensive and most commonly used in houses. But the major drawback is: they are not compatible to all devices and may create excessive heat in appliances which will reduce durability and lifetime.
Also, Modified Sine Wave inverters create more noise and power surging can lead to malfunctioning of home appliances.