How to Calculate Solar Panel Battery and Inverter

How to calculate solar panel battery and inverter Overview

The solar panel is a device that converts sunlight into electricity using photovoltaic cells. It can be used as a standalone power source, but it’s more common when combined with batteries and inverters.

An inverter changes DC from Solar Panel into AC which we use every day like light bulbs etc. Batteries are needed because of the low voltage output of solar panels, so they store energy during day time and release it at night.

So you need both these devices together to make your home fully self-sufficient. But how do you know what size of solar panel will work best? What kind of batteries should I buy?

These questions may seem simple, but there are many factors involved in choosing the right equipment. This post explains everything about calculating solar panel batteries and inverters.

  1. Calculating Battery Size :
    Battery capacity depends on the number of hours per year you want to run appliances. For example, If you have a small house, you don’t need a large battery bank. You need enough battery to last few days. On the other hand, if you live in a big city where you get less sun than ordinary people, you might require a larger battery bank. The most popular type of battery bank available today is deep-cycle lead-acid batteries. They provide a long life span and high reliability. However, their cost is higher compared to AGM batteries. Another option is AGM batteries which are cheaper but not very reliable. There are also hybrid systems combining both types of batteries.

Battery Bank Capacity Number of Hours / Year * 100%
Example – A 10Ah Deep Cycle Lead Acid Battery has a capacity of 1000Whrs/year.

That means it can supply power for one hour each day for 365days.
So if you plan to run lights 24hours a day, 7 days a week, you would need a 10 Ah battery bank.

If you only plan to run lights 8 hrs a day, 5 days a week, you could go with a 6 Ah battery bank.

AGM batteries are a good choice if you plan to run the appliance for a short period, such as microwave ovens, coffee makers, etc.

If you plan to run a refrigerator all day long, you must consider buying a bigger battery bank.

  1. Calculating Power Output of Solar Panels :
    The amount of wattage produced by solar panels varies depending upon location, weather conditions, angle of Sunlight, the efficiency of PV cells, and its age. Most manufacturers give average numbers for different locations.
    To calculate watts generated by a solar panel, you multiply the area of the solar panel times intensity of sunlight received by that area. The intensity of sunlight is measured in Watts per square meter. To find out how many wattages you generate daily, you divide the total wattage by 12.
  2. Calculating inverter Voltage & Amperage :
    An inverter is basically a circuit breaker. When connected between two poles of the battery bank, it breaks down direct current into alternating current. An inverter provides a constant frequency of 60Hz. Its rated ampere rating determines maximum load current. Maximum load current Rated Amps + 20%.
    To calculate volts provided by the inverter, you take input voltage divided by the resistance value. The resistance value is determined by dividing amps by volts.
    For example, if you connect a 3Amp load to a 15Vdc battery, the inverter needs to produce 18 Volts.Tips on how to choose the right solar inverter and battery
  3. Choose Inverter based on your application requirements.
    You should know what kind of loads will be running at home during peak periods. Will they be using more electricity like washing machine, dishwasher, air conditioner, etc.? Or will there be no use of AC except occasional lighting? Etc.
  4. Consider inverter output capability.
    Most modern inverters come with built-in protection circuits. They have overcurrent, Undervoltage, reverse polarity, and thermal shutdown protections. These protectors shut down the inverter automatically once certain limits are exceeded. If these limit values are not met, the inverter shuts itself down before damage occurs. This protects both the inverter and the battery bank. If you want to avoid shutting down the system due to overload, make sure to select an inverter that comes with higher ratings than those mentioned above.
  5. Select the appropriate size of battery pack.
    Battery capacity directly affects the cost of installation. The larger the battery pack, the greater the initial investment. But when appropriately installed, large packs last longer. A good rule of thumb is to buy enough power to meet all expected usage plus 10% extra. So if you expect average consumption of 100W / hour, get a 200Whr battery.
  6. Check whether the inverter has proper grounding.
    Inverters need to be grounded so that they don’t cause electrical shock hazards while connecting them to the grid. Most inverters sold nowadays come with ground wire already attached. However, if yours doesn’t, you may attach one yourself. It’s recommended to install a separate ground rod near the house because most houses are made of metal materials. Ground rods help prevent electric shocks caused by lightning strikes.
  7. Do not forget to check the charging port specifications.
    Inverter manufacturers specify minimum and maximum charge rates. The minimum charge rate specifies the lowest amount of time needed to recharge the battery fully. The maximum charge rate indicates how fast the battery can accept current. Some inverters allow only full discharge followed by recharging. Others allow partial discharges followed by complete recharge. Always refer to the manufacturer’s manual for details.


Knowing the amount of solar energy available from the sun helps us plan our daily activities accordingly. It’s important to match the correct type of batteries and inverter with each other and the applications we intend to run.

We also need to consider the location where we wish to place it. All these factors play a vital role in determining the performance of the whole setup.

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