Anyone seriously considering installing a solar panel system at some point faces the question of calculating solar panel battery and inverter. Adequate and precise calculation is very important because oversizing or undersizing your solar system can decrease its efficiency or impose unnecessary waste of your budget.
Therefore, we will explain the most important elements for determining the size of the solar storage system and help you design a setup that matches your electricity needs perfectly.
How to Calculate Solar Panel Battery and Inverter
The best way to learn how to size solar panel battery and inverter as well as other solar system components is by understanding your solar energy needs.
We will guide you through each step of determining your system's size. Let’s start!
#1. Determine Your Power Consumption Needs
Before making any decision about solar panels, batteries, or inverters, it is essential that you calculate your power consumption needs. This calculation is what your entire solar system plan should be based on.
To calculate your power consumption needs, first list all the appliances you plan to power, along with their wattage. Also, consider the daily operating hours for each appliance.
So, the formula could look like this:
Appliance Wattage x Hours Used = Daily Watt-Hours (Wh).
Example:
Cooker: 3000Wx3h = 9000Wh
Refrigerator: 150Wx24h=3,600Wh
Computer: 50Wx8h=400Wh
TV: 100Wx4h=400Wh
Total daily Wh needed: 9000Wh ₊ 3,600Wh₊400Wh₊400Wh =13,400Wh
#2. Calculate Solar Panel Capacity
When you have your total daily energy consumption calculated, the next important step is to calculate the solar panel capacity that would match your needs. The formula for this calculation includes the total Wh needed, which is divided by the average sunlight hours, and the result indicates the solar panel wattage required.
So the solar panel wattage calculation formula is:
Total Watt-Hours Needed ÷ Average Sunlight Hours = Required Solar Panel Wattage.
So, if your total daily Wh needed is 13,400 and your location receives 5 hours of peak sunlight per day, you need 2,680 watts of solar panels.
13,400Wh ÷ 5 hours = 2680 watts.
The manufacturer always states the maximum peak power of the solar module in the technical data (Wp refers to peak watts). However, this value can only be achieved when the sun shines on the module at an angle of 90 degrees. In case of cloud cover and bad weather, the shading can reduce the output.
Plus, when the lighting or angle doesn’t match, the module output will drop. In practice, it has been established that during an average sunny summer day, solar modules provide approximately 45% of their peak power in a period of 8 hours. This means you should always add a 20% to 25% buffer to account for these losses.
#3. Determine the Size of the Solar Battery
It is important to consider your usage patterns when sizing your solar battery storage. If you experience frequent power outages or rely on solar energy as your primary source of electricity, you may need a higher capacity battery.
In addition, if you plan to use solar energy to power high-energy devices such as air conditioners or electric vehicles, you’ll need to consider those usage patterns when sizing your battery storage.
Now, let’s see how to calculate the size of the batter. So, the formula for calculating the size of solar battery is:
Total WH needed ÷ Battery Voltage = Required battery capacity (Ah)
As for the battery voltage, your choice depends on your overall system design and compatibility with the inverter. Generally, common voltages for solar systems are 12V, 24V, or 48V. Let’s assume you choose a battery voltage of 24V.
Based on the example we used in previous sections, the calculations would look like this.
13,400 Wh ÷ 24V = 558,33Ah.
Let’s not forget to consider the Depth of Discharge (DoD) in different types of batteries:
- Lead acid batteries have a DoD of around 50% which means you can only use half of their rated capacity. If you use more, that would significantly affect their lifespan.
- Lithium batteries typically discharge up to 80-90% of their capacity.
So, in order to be precise and accurate, the calculation for the size of the solar battery needs to account for the differences in DoD.
The adjusted calculation would, therefore, look like this:
-
For lead acid: the required battery capacity ÷0.5
- For lithium: the required battery capacity ÷0.8
Finally, you also need to account for inefficiencies, unexpected loads, and cloudy days, meaning you need to adjust the solar power system calculation by incorporating the safety margin. The safety margin typically means taking 20% to 15% of the battery capacity.
So, to get the final battery capacity for solar panels that you need, we will multiply the required battery capacity with the DoD accounted for by 1.2.
#4. Choose the Right Inverters
The right choice of inverter is crucial for ensuring the optimal efficiency of your solar power system. Therefore, you need to calculate the size of the inverter correctly to avoid system disruptions. Here’s the formula:
Total Watts Needed × Inverter Efficiency Factor (typically 1.2-1.5) = Inverter Size (W).
Example:
If you have the devices that together consume 1000W when running simultaneously, multiply that value with the inverter efficiency factor, which is typically between 1.2 and 1.5. So, the calculation would look like this:
1000W x 1.2 = 1200W
A few things to consider when choosing the inverter size are also the difference between its continuous and surge power. The surge power refers to the maximum power the inverter can supply for a short duration, which is usually needed for starting up devices. So, your inverter’s surge power rating should match the startup power of your devices.
Another consideration is whether you’ll use an inverter for sensitive electronics. In this case, you should choose pure sine wave inverters that produce a smooth, consistent waveform similar to grid power. Another option is a modified sine wave inverter that produces a stepped waveform. These are better choices for simpler devices like lights, heaters, and basic tools.
Now that you know how to size an inverter for the solar system, let’s combine all the calculations.
#5. Putting it All Together
Let’s illustrate these calculations with an example of powering a small home or an RV. Here are the data we start from:
Daily consumption: 1850Wh
Sunlight Hours: 5h
Battery Voltage 12V
Devices running simultaneously: 500W
To calculate the solar panel wattage, we’ll divide the daily consumption needs by the sunlight hours, and we get 370W, which can be translated into two solar panels of 200W.
Using the formula Total WH needed ÷ battery voltage = Required battery capacity (Ah), we get that the capacity that would suit these needs would be 231Ah.
The next step is to calculate the size of the inverter using the formula Total Watts Needed × Inverter Efficiency Factor (typically 1.2-1.5) = Inverter Size (W), which indicates that the inverter size should be 625W.
Keep in mind that you should also account for seasonal changes, which may require you to add a backup solar generator for winter or cloudy periods. In addition, regular solar panel maintenance is also important to ensure long-term solar energy efficiency.
4 Common Mistakes to Avoid When Calculating Solar System Size
Avoiding common mistakes when calculating solar panel battery, inverter, and system size will help you ensure a proper design of your solar setup and a maximum return of investment. So, let’s take a look:
#1. Undersizing or Oversizing the System
Both undersizing and oversizing the solar system lead to unnecessary expenses. While undersizing means you’ll have to ensure electrical energy supply during critical times, oversizing means bigger upfront costs and wasted energy.
Therefore, you need to calculate your daily energy consumption and peak power demand carefully while accounting for seasonal variations in sunlight hours. The best way to avoid this mistake is to add a 20-30% safety margin to your calculations to account for inefficiencies and unexpected loads.
#2. Ignoring Battery Depth of Discharge
It is essential that you understand what DoD is and size your battery based on usability, not total capacity. Otherwise, you’re risking premature battery failure or insufficient backup power. So, the best battery for a solar power system is the one that matches your needs, not the one that is the most expensive or well-advertised.
#3. Not Considering the Inverter Surge Capacity
Keep in mind that the surge power rating of an inverter is just as important as the continuous power rating. The solar inverter of your choice needs to be strong enough to support the startup surge of your largest appliance, so let that be one of your inverter sizing guide points.
#4. Overestimating Sunlight Availability
Sunlight hours can vary significantly due to different factors. However, it is always better to assume less than more sunlight hours to avoid undersizing your solar power system.
So, make sure you’re basing your calculations on reliable solar insolation data for your area, take seasonal, shading, and weather conditions into account, and use conservative estimates for sunlight hour calculations.
Final Thoughts
By following the guidelines outlined in this article, you can quickly learn how to calculate solar panel battery and inverter and thus maximize energy production and savings.
Of course, it is also possible to subsequently increase or decrease the power of the solar power system. You can increase the system by adding more solar panels and replacing the inverter if the power becomes insufficient to support the increase of the system.
Keep in mind, though, that while modifications of your solar system aren’t necessarily complicated, they can cause significant costs. Therefore, use the calculations we provided carefully, and feel free to consult our experts to ensure you plan your solar system well.
How to Calculate Solar Panel Battery and Inverter FAQ
#1. How to calculate the number of solar panels and batteries required?
To calculate the number of solar panels, you need to divide the daily energy needs by the hours of sunlight. For batteries, you need to divide daily energy needs by battery voltage and adjust for DoD.
#2. How do I match my solar panels to my inverter?
To match solar panels to your inverter, you need to ensure that your solar panels' total wattage doesn’t exceed your inverter’s maximum input.
#3. What happens if I undersize my solar system?
Suppose you underestimate the size of your solar system. In that case, you will not have enough electricity to meet your energy needs, which may result in power outages, especially during periods of high usage or on cloudy days. Additionally, solar batteries might deplete, requiring you to depend on the grid or backup power more frequently.
#4. Can I expand my solar panel system later?
Yes, you can expand your solar panel system later by adding more solar panels, but you also have to ensure that the inverter, charge controller, and battery bank can handle the system expansion.
Disclaimer: The content on Portable Sun is for informational purposes only. Electrical work can be dangerous—always consult a qualified professional. We are not liable for any injuries, damages, or losses from installation or use. Always follow local regulations and safety guidelines when handling electrical components.