Knowing how to calculate the number of solar panels is the first step for anyone who wants to transform their electricity consumption into a more economical and sustainable source.
While the process involves technical factors such as average consumption, solar radiation in your area, and equipment efficiency, it can be simplified with data you already have, such as your electricity bill.
Throughout this article, you will discover, for example, that the same house may need 8 or 12 solar panels depending on the city where it is located.
Understand how these factors directly influence system sizing and learn how to make a reliable calculation to make your decision confidently!
How to calculate the number of solar panels?
To correctly size a photovoltaic system, you need to understand three factors: how much you consume, how much sun your region receives, and the generation capacity of the chosen modules.
The process is technical, but it can be simplified with basic data and straightforward calculations. Learn more in the following topics:
Know your average consumption
The starting point for any solar project is knowing how much electricity you consume on average per month.
This data is available on your electricity bill, usually in the “consumption in the last 12 months” field.
Ideally, you should average the last 6 to 12 months to account for seasonal variations (such as air conditioning use in the summer or heating use in the winter). This ensures the system is sized with adequate margin.
For example, if the consumption of the last six months was: 480, 510, 470, 530, 490 and 500 kWh, then the monthly average will be:
(480 + 510 + 470 + 530 + 490 + 500) ÷ 6 = 496,6 kWh
This average is the consumption that the system must compensate for monthly.
Estimate your daily consumption
Since photovoltaic systems generate energy daily, average monthly consumption must be converted to daily consumption. To do this, simply divide the value by 30 using the formula:
Daily consumption (kWh/day) = Monthly consumption (kWh) ÷ 30
Returning to the numbers in the practical example we are working on, we would have to:
496,6 kWh ÷ 30 ≈ 16,55 kWh/day
This value will serve as a basis for defining the required system power.
Check irradiation and efficiency
To know how much energy a solar system can generate, it is essential to consider the solar irradiation in your region, that is, the amount of sunlight available per day.
For example, in a city like Goiânia, the average daily solar radiation is around 5,0 kWh/m²/day, a very favorable value.
But not all of this energy turns into electricity. Some is lost in the process, whether due to dirt on the panels, heating, cables, or the inverter itself. Therefore, an efficiency factor of around 85% is typically applied to well-installed systems. Doing the math:
5,0 × 0,85 = 4,25 kWh/day per installed kWp
In other words, every 1 kWp of solar panels installed in Goiânia generates, on average, 4,25 kWh of energy per day. This number is crucial, as it will be used in the next step to calculate the system's total power.
Determine the number of plates
Now, in the final step, with the total system power determined, simply calculate how many solar panels will be needed. To do this, divide the total power by the power of each module. Here's the formula:
Number of plates = System power (W) ÷ Power of each plate (W)
Returning to our example, we saw that the home consumes, on average, 16,55 kWh per day, and we know that, in Goiânia, each 1 kWp installed generates approximately 4,25 kWh per day. With this, we can calculate the system's required power:
System power (kWp) = Daily consumption ÷ Generation per kWp
Power = 16,55 ÷ 4,25 ≈ 3,89 kWp
Now, to know how many solar panels will be necessary, we will need to consider modules with a power of 410 W (or 0,410 kWp), which are quite common in the residential market.
Number of boards = System Power ÷ Power of Each Module
Number of plates = 3.890 W ÷ 410 W ≈ 9,5 plates
Since it's not possible to install "half panels," it's best to round up. Therefore, 10 410W solar panels will be needed to meet this home's average monthly consumption, based on Goiânia's climate conditions.
This calculation is an estimate and may vary depending on the roof pitch, possible shading and other design details.
But with simple data and a few steps, it is possible to have a clear idea of what to expect when investing in solar energy.
Does the number of solar panels needed change depending on the region?
Yes, and this is one of the most relevant variables in sizing. Brazil has a wide range of climates, and solar radiation varies considerably between regions.
Therefore, the same energy consumption may require fewer panels in the Northeast and more panels in the South, for example.
Below, see how irradiation directly influences the number of plates in each region of the country:
North East Region
With an average solar irradiance of 5,5 to 6,5 kWh/m²/day, the Northeast region boasts the highest solar potential in the country. States such as Piauí, Bahia, Ceará, and Pernambuco lead the rankings for photovoltaic generation.
This means that systems installed in the region require fewer panels to generate the same energy, making projects leaner and more economically viable.
Northern Region
Despite its proximity to the equator, the North Region is heavily influenced by rainfall, cloud cover, and high humidity. Average irradiation ranges from 4,5 to 5,5 kWh/m²/day, depending on the state.
Generation is good, but climate fluctuations must be considered, especially during the rainy season. The use of systems with monitoring and preventive maintenance is highly recommended.
Midwest region
With an average irradiation of 5,2 to 6,0 kWh/m²/day, the Central-West region is one of the best locations for solar generation. The low urban density and large available areas facilitate installations of all sizes.
Goiás, Mato Grosso and Mato Grosso do Sul have high potential, with excellent annual consistency of solar radiation.
Southeast
Average radiation in this region ranges from 4,5 to 5,5 kWh/m²/day. States like Minas Gerais stand out for offering excellent radiation, with good stability throughout the year.
Dense urban areas, such as São Paulo and Rio de Janeiro, may have greater shading, requiring extra care in the design, such as microinverters or optimizers.
South
It is the region with the lowest solar radiation in the country, varying between 3,8 and 5,0 kWh/m²/day, especially during winter.
The number of panels to generate the same amount of energy tends to be higher, which can increase the initial cost of the system.
However, it is still possible to obtain excellent results with a well-designed project, considering the correct orientation of the plates and technologies that maximize production.
Does the type of roof influence the calculation?
Yes, the type of roof has a direct impact on both the sizing and the feasibility of installing a solar system.
The slope, orientation, material and available useful area are essential factors that can increase or reduce the efficiency of the system.
Ideally, solar modules should face north (in the southern hemisphere), with an inclination that approximates the latitude of the location.
This combination optimizes solar radiation capture throughout the year. East- or west-facing roofs are also viable, but may require a larger number of panels to compensate for losses.
Elements such as water tanks, chimneys, trees, and neighboring buildings can cast shadows and significantly impact energy generation throughout the day.
Good design identifies these obstructions and, if necessary, adopts solutions such as microinverters or optimizers.
Additionally, ceramic, metal, or fiber cement roofs are common in Brazil, and each requires specific fixing methods.
In some cases, structural reinforcements are necessary to ensure the safety and durability of the installation.
Roofs with small, fragmented or poorly oriented areas can limit the number of panels and directly influence the generation calculation.
Therefore, assessing the roof's characteristics is a fundamental technical step, which must be carried out using measuring equipment and simulation software.
Which professional should perform this assessment?
The correct sizing and safe installation of a photovoltaic system requires specific technical knowledge.
Ideally, the assessment should be conducted by an electrical engineer or technician specializing in photovoltaic systems, preferably with recognized certification. This professional will:
- Analyze consumption history and estimate the customer’s energy profile;
- Carry out a technical visit, evaluating the roof, structure and possible shading;
- Design the system based on local radiation, equipment efficiency and concessionaire standards;
- Use simulation software to forecast annual generation and financial return on investment;
- Issue ART (Technical Responsibility Note), when necessary, ensuring technical and legal support.
Reputable integration companies have this type of professional on their team and offer comprehensive support, from design to approval by the energy distributor.
Relying on this technical support is the best way to avoid undersizing, failures or future problems.
Is it worth having solar panels?
Yes, in most cases, investing in photovoltaic solar energy It is a financially advantageous and environmentally responsible decision.
Return on investment (ROI) typically occurs between 4 and 7 years, with systems having an average lifespan of 25 years or more. Key advantages include:
- Significant reduction in electricity bills, which can reach 95%;
- Property valuation, as properties with solar energy are more attractive on the market;
- Low maintenance cost the modules only require periodic cleaning and basic inspections;
- Sustainability, because solar energy is clean, silent and reduces CO₂ emissions;
- Energy independence, that is, less exposure to increases in concessionaire rates.
Even in regions with lower radiation, solar energy remains a solid alternative, especially with the constant increases in electricity bills and incentives for distributed generation.
Why count on the Canal Solar?
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- Updated and reliable articles;
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Conclusion
Calculating the number of solar panels involves more than simply dividing monthly consumption by the panel's power. It's an analysis that considers local conditions, system efficiency, and even the installation type.
By understanding these factors, you ensure a well-designed system capable of meeting your needs economically and sustainably. Whether for residential, commercial, or rural use, solar energy is a viable and increasingly affordable alternative.
And remember: having qualified technical guidance makes all the difference in the efficiency and durability of your solar investment.
An answer
It kicks off with powerful stats—Brazil has reached 30 GW of installed solar through self-generation and R$146.4 billion invested since 2012—setting a strong foundation for why marketing matters