Calculate How Many Solar Panels Do I Need - 4Steps

how to calculate how many solar panels do I need

Switching to solar energy is an excellent way to reduce your carbon footprint and save on energy bills. One of the most common questions homeowners ask when considering this transition is, "How many solar panels do I need?"

But the number of solar panels required is can vary with your energy consumption, roof characteristics, local climate, budget, and home size.

This blog post will guide you through the steps to estimate the number of solar panels you need as precisely as possible.



Factors for estimation the number of solar panels required

Expected solar power generation

To determine the number of solar panels needed, the key factor is the amount of solar energy that needs to be produced by the system. This depends on your specific solar goal: whether you aim to offset a portion of your electricity consumption, power your entire home, or even generate surplus energy for profit.

In the following explanation, we will use the second scenario—powering your entire home—as an example to calculate the number of solar panels required.


Peak sun hours assessment

A peak sun hour (PSH) is a unit of measurement used in the solar energy industry to represent the amount of solar energy received in one hour at a solar panel's peak performance. It is defined as an hour during which the intensity of sunlight reaches an average of 1,000 watts per square meter (W/m², which is the standard measure of solar irradiance.

Understanding peak sun hours is crucial for designing and sizing solar power systems. It helps in estimating the potential solar energy generation at a specific location, which is essential for determining the required number of solar panels and their placement to meet energy needs. This varies based on your geographical location and the orientation of your solar panels.


Size and dimension of the solar panel

Different solar panel designs offer varying power generation capacities, mainly influenced by their power ratings and efficiency. For instance, PowMr's roof solar panels have power ratings of 410W, 460W, and even 540W. The efficiency of these modules typically ranges from 20% to 22%. The wattage and efficiency of the panels are key factors in determining whether a system needs more or fewer panels.


Calculator of solar panel

You now have a general understanding of the factors to consider when calculating the number of solar panels needed. To calculate how many solar panels you need, divide your average monthly energy usage by the monthly peak sun hours.

Then, divide this result by the wattage of the solar panels you are considering purchasing. The result of this equation will be the number of solar panels you need to meet your energy needs.

Number of the Solar Panel Required = (Monthly Electricity Consumption/Monthly Peak Sun Hours)/Watt of the Solar Panel


Below, we'll list an example of powering an entire home to help you better understand how to estimate the number of solar panels required. Let’s take a closer look at how to use these factors to determine how many solar panels are right for you!


Step1 - See how many hours of sunlight does my roof get

The peak sun hours your roof gets directly influence the duration your solar panels can operate at maximum efficiency. Determine the average number of peak sunlight hours in your area, as this directly influences the number of solar panels required.

For example, in sunny locations like Nevada, a smaller solar panel array may be enough to meet your energy needs. Conversely, in areas with less sunlight, a larger system will be necessary to generate the same amount of energy.

Here's a general overview of peak sun hours across various states:

State Average Daily Peak Sun Hours
Alabama 4.5
Alaska 2.5-3
Arizona 5.7-8
Arkansas 4.5
California 5.2-7.5
Colorado 5.0
Florida 4.9
Georgia 4.6
Kansas 4.6
Kentucky 4.2
Louisiana 4.5
Maine 3.6
Maryland 4.1
Massachusetts 3.9
Mississippi 4-4.7
Missouri 4.1
Montana 3.9
Nevada 5.7-7.5
New Mexico 5.6
New York 3.5-3.8
Texas 4.8
Utah 5.4
Virginia 4.3
Washington 3.6


Step2 - Evaluate how many kwh does your home use per month

According to the EIA, the average energy usage of an American home is about 899 kWh per month. However, electricity usage can vary significantly based on your location and household needs. It's recommended to review your electricity bills from the past year, total your usage, and divide by 12 to get an accurate monthly average.

Additionally, you can calculate electricity bills for peak usage months like summer and winter, ensuring solar panels meet your highest energy demands.

The table below estimates the monthly energy consumption for various home sizes. With the average home size in the U.S. being around 2,000 square feet and the typical household using approximately 900 kWh per month, we can infer that each square foot consumes about 0.45 kWh monthly. This ratio can help estimate the energy usage for homes of different sizes.

Home Size Avg Energy Consumption per Month (kWh)
1500 sq ft 675
2000 sq ft 900
2500 sq ft 1125
3000 sq ft 1350


Step3 - Estimate what size of solar panel system do you need

To estimate the total power of a solar panel system, we can divide the monthly energy consumption (in kWh) by the product of the local peak sun hours per day and 30 (the average number of days in a month), as shown by the formula below:

Size of solar panel system = monthly energy consumption(kWh)/ Peak Sun hours * 30

Based on the home size and corresponding energy consumption, and using an average of 4 peak sunlight hours per day (approximately 120 peak sun hours per month), we can determine the required size of a solar panel system.

Home size Avg Energy Consumption per Month (kWh) Size of Solar Panel System (kW)
1500 sq ft 675 5.625
2000 sq ft 900 7.5
2500 sq ft 1125 9.375
3000 sq ft 1350 11.25


Step4 - Calculate how many solar panels do I need

Finally, you can determine the number of solar panels needed by dividing the total system size by the power output of each solar panel. The higher the power output of a solar panel, the fewer panels you will need.

Number of solar panels = Size of solar panel system(kW) / Power output of each solar panel(kW)

For a rough estimate of the number of solar panels required based on the square footage of your space (assuming 460W solar panels and 4 peak sun hours), refer to the table below.

Home Size Avg Energy Consumption per Month (kWh) Number of Solar Panels (Rounding Up)
1500 sq ft 675 13
2000 sq ft 900 17
2500 sq ft 1125 21
3000 sq ft 1350 25


Additionally, pay attention to the available roof space for solar panel installation when selecting panels of different dimensions and sizes, and adjust the connenction of solar panels accordingly.


Other factors that how many solar panels do you need

Sun Exposure and Climate

Solar panels need sunlight to generate electricity. In sunny regions, fewer panels may suffice. If panels are shaded during the day, their efficiency drops, so you might need more panels or to trim trees to maximize exposure.


Roof Angle and Direction

Panels perform best on south-facing roofs angled between 30-45 degrees for optimal sun exposure. North-facing roofs can still support solar panels, but more panels may be required to meet energy needs.


Roof Size

The size of your roof limits the number of panels you can install. Smaller roofs may need high-efficiency panels to generate more electricity in limited space. If all needed panels don't fit, installing fewer panels will still cover part of your electricity needs.


Your budget plays a crucial role in determining the number of solar panels you can install. If you can't afford a full system, you can start with fewer panels to save on electricity bills, though they might not cover all your energy needs. Additionally, look for solar incentives and rebates in your area to reduce the overall cost of installation.


If you're still unsure about how many solar panels you need, the best approach is to consult with local solar installers. These experts have in-depth knowledge of solar energy systems in your area. They understand the local climate conditions, know which panels perform best, and can assess the specific features of your home to determine the optimal number of solar panels required.

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