Solar Panel Performance Calculation: Accurately Determining System Capacity

When designing a solar panel system, one of the most crucial steps is accurately determining its performance. This defines how much energy the system can generate and how efficiently it will operate. An undersized system may not produce enough electricity for a household or business, while an oversized system can lead to unnecessary expenses. To select the right-sized solar system, it is essential to consider panel performance, dimensions, the number of sunshine hours at the installation site, and other factors affecting energy production.
In this article, we explain how to precisely calculate solar panel performance, explore different methods for measuring the energy output of a single panel or an entire system, and highlight key considerations for installation and planning.

To calculate solar panel performance, the first step is to determine the type of panel used in the system, as different models vary in capacity and size. The Tongwei Solar 440Wp N-type panel, for example, has a peak output of 440 Wp under optimal conditions. Its physical dimensions are 1762 × 1134 mm, covering a total surface area of 2 square meters. This means that under ideal sunlight conditions, the panel can generate approximately 220 W per square meter. To calculate the total output of a solar system, we need to consider the number of installed panels and their orientation and tilt angle to ensure maximum efficiency.

Why Is It Important to Calculate Solar Panel Performance Correctly?

Accurate performance calculations are essential for proper system sizing, as they determine whether the system can meet energy consumption needs.
For example, if a household consumes 4,000 kWh of electricity annually, the solar system must be capable of producing this amount. In Hungary, the annual sunshine hours range between 1,100 and 1,300, depending on location. A 1-kilowatt peak (kWp) solar system can generate approximately 1,100–1,300 kWh per year under these conditions.

If using Tongwei Solar 440 Wp panels, each panel provides around 0.44 kWp. To produce 4,000 kWh per year, the system must have a capacity of 3.5–4 kWp, which requires approximately 8–9 panels.

Measuring Solar Panel Performance: Per Panel or Per Square Meter?

Solar panel performance can be assessed either per panel or per square meter, depending on the evaluation criteria.
For instance, the Tongwei Solar 440 Wp N-type panel has a peak output of 440 Wp, meaning that under ideal conditions, it can produce this amount of energy at a given moment. With a surface area of 2 m², its output per square meter is around 220 W/m².

This calculation helps estimate how many panels can fit on a given roof space and the total capacity achievable within that area.

Daily and Annual Energy Production: How to Calculate the Output?

The amount of energy generated by a solar system primarily depends on the installed panel capacity and the number of sunshine hours. In Hungary, the annual sunshine hours range between 1,100 and 1,300, depending on the region. If a system uses Tongwei Solar 440 Wp N-type panels, each panel has a nominal capacity of 0.44 kWp.

If a household installs 10 of these panels, the total system capacity will be 4.4 kWp. To calculate annual energy production, this capacity is multiplied by the annual sunshine hours. If a location receives 1,200 sunshine hours per year, the 4.4 kWp system will generate approximately 5,280 kWh annually (4.4 × 1,200 = 5,280 kWh).

To determine daily energy production, the system's capacity is multiplied by the number of sunshine hours on a given day. For example, on a sunny summer day with 5 hours of full sunlight, the 4.4 kWp system will produce 22 kWh of energy (4.4 × 5 = 22 kWh). Seasonal variations cause daily production to fluctuate, with lower values in winter and higher values in summer.

What Factors Affect Solar Panel Performance?

The performance of solar panels depends on various external and internal factors that influence the amount of energy the system can generate. One of the most critical factors is the intensity of solar radiation, which varies based on geographical location and season. In Hungary, for example, sunlight is stronger and lasts longer during the summer months, while in winter, days are shorter, and the angle of sunlight is less favorable.

Panel orientation and tilt angle also impact efficiency. For optimal performance, panels in Hungary should generally be installed facing south with a tilt angle between 30 and 35 degrees to absorb the maximum amount of sunlight throughout the year. If the orientation or tilt angle deviates from this optimal range, performance can drop by 10–20%.

Shading has a significant effect on performance as well. Even if a single panel is partially shaded by a tree, building, or other obstruction, it can reduce the efficiency of the entire system. This is because traditional solar systems use series-connected panels, meaning that a shaded panel can limit the power output of the entire string. To prevent such energy losses, it is worth considering the use of optimizers, which allow shaded panels to operate independently, preventing them from affecting the performance of the rest of the system.

SolarKit Tips for Accurate Solar Performance Measurement and Planning

When selecting the right solar system, it is essential to consider the specific conditions of the installation site and the expected operational environment during the planning phase. SolarKit experts recommend accurately assessing the household's or business’s annual energy consumption in advance and selecting the number and capacity of the panels accordingly.

To maximize efficiency, special attention should be paid to the proper orientation and tilt angle of the panels. In Hungary, south-facing panels with a tilt angle of 30–35 degrees are recommended for optimal performance. If the roof’s tilt angle differs significantly, a mounting structure may be needed to optimize the panel positioning. Additionally, it is crucial to account for shading from surrounding buildings, trees, or other objects, as these can lead to significant performance losses. In shaded environments, it is advisable to use optimizers, which allow individual panels to function independently, preventing shading from reducing the overall system performance.

To accurately determine the system’s expected output and minimize potential losses, using a monitoring system is recommended. This enables continuous tracking of daily production data. A well-designed and optimized solar system ensures stable and reliable energy generation in the long run.

Still Have Questions?

1. How can I calculate how many solar panels I need?

• The number of panels required depends on your annual electricity consumption.
• For example, if a household consumes 4,000 kWh per year and uses Tongwei Solar 440 Wp panels, each panel generates approximately 528 kWh annually under average Hungarian conditions.
• To meet a 4,000 kWh yearly demand, you would need around 8 panels (4,000 ÷ 528 ≈ 7.57, rounded up to 8).

2. What affects solar panel performance the most?

The performance of solar panels is primarily influenced by the number of sunshine hours, panel orientation, tilt angle, and potential shading. A south-facing orientation with a tilt angle of 30–35 degrees ensures optimal energy production, while shading can significantly reduce efficiency, which can be mitigated by using optimizers.

3. How much does performance drop on cloudy days?

Solar panels generate energy even in cloudy weather, but their performance can drop by as much as 70–80% compared to sunny conditions. Diffused light still allows panels to function, but with significantly reduced energy output, which is why it is important to consider weather variability when sizing the system.

4. Should I oversize my solar system?

Oversizing is only beneficial if excess energy can be utilized, such as with energy storage or a grid feed-in system. If surplus energy cannot be used, an oversized system results in unnecessary investment costs, making accurate performance calculations essential.

5. What maintenance do solar systems require?

Solar systems require minimal maintenance, but it is advisable to periodically check the cleanliness of the panels and electrical connections. Dust, leaves, or bird droppings can reduce efficiency, so cleaning the panels at least once a year is recommended. Optimizers and monitoring systems can help track performance continuously and quickly detect any issues.