newsHow to Calculate Solar Panel Battery and Inverter? – 5 Easy Steps

July 8, 2021by NGLE0

Solar panel systems are rapidly becoming a common source of clean and renewable energy. As the world is inclining more towards renewable resources to meet the energy demands solar energy is playing a great role to provide sustainable and clean energy. 

A solar panel system is designed to harness sunlight and then convert the solar energy into usable electricity. A solar panel system comprises several components that must be connected with each other and must be compatible for the system to run effectively and efficiently.

Sizing the components is a very important step in the design of a solar panel system. Improper sizing can make the system work inefficiently or not at all also. Sizing of the batteries, solar panel size, inverter size, and the charge controller size are custom to each application and therefore must be accurately determined prior to purchase the system for a site. 

The sizing of the components depends on the location of the solar panel system, the load it needs to supply and other site associated factors. Usually these calculations are carried out by the solar companies who are installing the system or professionals, but the calculations are not that difficult and is you are planning to install a solar panel system on your own then you can easily determine the sizing through the following process:

How to calculate solar panel battery and inverter?

1st step (Determining the load wattage)

The first step in order to determine the size of the components is estimating the amount of load that needs to be supplied and the time of its use plus the extra storage that you need to have for emergency needs or when the solar system is not producing electricity. Estimating the accurate load wattage is highly important as this value will mainly determine the size of all the components.

The load that needs to be supplied is basically the amount of electricity used by the number of appliances at your home (in most cases; however, it can also be the amount of electricity used by certain appliances only that you want to run on solar energy). This is the first step in determining the size of the components. 

Add up the wattage of all the appliances that you need to operate through the solar panel system. After determining the wattage of the appliances, now you need to find the operating time of each appliance and multiply with the respective wattage to determine the energy used. Lastly, add up all the energies in Watt-hours to determine the total energy that you need the solar panel to produce. 

For instance, a 400W machine runs for 2 hours and a 100 W bulb needs to be run for 5 hours in a day. The energy can be determined as:

(400 x 2) + (100 x 5) = 1300 Watt-hours.

This is the ideal value of energy that will be needed from the solar system. In actuality there are efficiency losses and some machines require greater starting energy. To cater to this issue we can multiply the ideal amount with an adjusting factor like 1.5. This value now will be a more accurate estimate of the load energy and the amount of energy that is required from the panel.

2nd step (Determining the dimension of the solar panel system)

The size of the solar panel system determines the amount of energy that it can produce. Energy production also depends on the number of hours effective sunlight falls on the panel. For summers this can be as high as 10 -11 hours and in winters it can reduce to 4-5 hours. The load value can be used to determine solar panel rating, and the number of solar panels required. 

The size of the solar panel is determined by its rating in watts. For determining the solar panel size the following formula can be used:

The actual amount of watt-hours determined from the first step/ no. of hours of sunlight = Watt of solar panel.  

 It is better to use the least number of hours of sunlight so that the solar panels can work effectively even on the least bright days.

3rd step (Determining the battery size)

Next, you need to determine the battery size or the storage capacity that you need in order for the system to have a backup and work efficiently and smoothly. A deep cycle battery is recommended to be used for a solar panel system. This kind of battery has been designed to sustain rapid recharging and discharging to low energy for a number of years. 

It is important for the battery storage capacity to be large enough to cater the energy on days when the solar panel is not producing sufficient energy or no energy at all. Batteries are rated in Amp Hours or h rating. Let’s see how Ah rating can be determined.

Batteries are available in different voltage ratings. You have already determined the watt-hour needed from the solar panel. Ah rating can be determined by:

  1. The actual amount of watt-hours determined from the first step/voltage of the battery = Amp Hours of the battery needed.
  2. However, this is not the correct value. For efficient use, we include 20% tolerance in the battery capacity. For this, we will multiple the Amp Hours value with 1.2.
  3. The battery should be designed to provide double the normal use of load. For this, we multiply the last result obtained with 2 and then multiply it with the number of days for which the storage is being designed. The value thus, obtained will give you the final value of the Ah rating of the battery. 
Determining the battery size

Multiple batteries can be used to meet the Ah rating. These batteries can either be connected in series or parallel according to the need of the situation. You can achieve different capacity loads and varying voltages by opting for different configurations. 

4th step (Inverter size)

An inverter is the most essential component of the solar system as it is used to convert the DC electricity produced by the solar panels into AC electricity that can be used by the appliances.

The inverter size is easy to determine but is extremely essential to do so. The size of the inverter can be determined if you know the maximum load of your home or the peak load of the home. For this you simply need to add up the wattage of all the appliances in your house or the wattage of the load that needs to be supplied from the solar system. The sum of the wattages will give you the inverter rating. The inverter size could have easily been determined in the first step.

It is also to be made sure that the battery voltage rating and the inverter voltage rating are same so that they are compatible with each other.

5th step (Determining charge controller specifications)

Determining charge controller specifications

A charge controller is also an essential part of the system. The power generated by the solar panel system is highly fluctuating and goes to a peak value and also drops to a very low value. You need a device that can smoothen the power fluctuation. For this a charge controller is used. 

Moreover, it is also very important that the batteries connected for extra storage do not overcharge because overcharging of batteries can severely damage the batteries. Preventing reverse current to flow from the battery to the solar panel is also necessary; this reverse current can usually flow at times when the solar panel itself is not producing any current. Using the charge controller helps in solving all such issues.  

The factors that need to be taken into account for determining the charge controller include amperage specs or the current of the solar panels. This rating can be determined by:

Solar panel wattage / battery voltage = current

This value of current can be slightly rounded off to consider the losses but too much tolerance can result in overcharging of the batteries.


The formula and method of determining the accurate size of each and every component of the solar panel system have been discussed in detail. The formulae are quite simple and one with a basic understanding of the things can also determine the sizing of the system.

It is very important that the accurate size for all the components are determined before the purchase is made. And on top of that, it is essential to determine the correct ratings of the components so that the system can work efficiently at all times and you can enjoy clean energy without stressing.


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