A solar panel is a device composed of multiple photovoltaic (PV) cells that convert sunlight into electricity through the photovoltaic effect.
The amount of power produced by a solar panel depends on various factors such as type of solar panel, size, efficiency rate, average lifespan, number of modules. There is also other factors which can affect solar panel output such as the intensity of sunlight, solar panel orientation, and local climate conditions.
The power output of a solar panel is measured in watts (W) or kilowatts (kW). On average, a standard residential solar panel, typically rated between 250 to 400 watts, can generate approximately 1 to 2 kilowatt-hours (kWh) of electricity per day under optimal conditions.
To estimate the power output of a solar panel system, multiply the wattage rating of a single panel by the total number of panels installed. For example, if you have a setup with 20 solar panels, each rated at 300 watts, the total power output would be 6,000 watts, which is equivalent to 6 kilowatts (kW).
However, Commercial and utility-scale solar installations can produce significantly more power per day due to their larger size and advanced technology. Furthermore, you can prepare a strategy to properly utilise excess power in watts produced by an average solar panel.
How Do Solar Panels Work?
There is basic science behind how solar panels work. Solar panels’ build-up of semiconductor materials such as silicon allows the sunlight particles known as photons to strike their surface. This releases the loose electrons from its atomic orbitals that are trapped on the conductors in the form of an electric current.
The conversion process of DC electricity into AC electricity is performed with the help of an inverter. The overall process occurs on a group of solar or photovoltaic (PV) cells. Also, the electricity generated is utilized and preserved by connecting the solar arrays (a combination of multiple solar cells) to the battery storage or electricity grid.
How to Calculate Solar Panel Power Output
Before you understand how to calculate the solar power output, it is important to familiarize yourself with these terminologies:
- Kilowatt (kW): Used to measure the electrical power generated by a solar system equal to 1000 watts.
- Kilowatt-hour (kWh): Power consumption of 1000 watts per hour and 3.6 megajoules contribute to 1 kWh.
- Direct Current (DC): Power generated directly by the solar panels.
- Alternating Current (AC): Power utilized by household appliances.
Let us consider a simple example of a 400-watt solar panel that operates for approximately 5 hours during peak sunlight. The power produced by a solar panel per day can be calculated as shown below:
(Wattage of Solar Panel) x ( Peak Sunlight hours operated)
(400 Watts) x ( 5 hours) = 2000 watts hours (Wh) per day or 2 kWh per day.
Additionally, to find out the energy generated per month, we can multiply 2 kWh by 30 days (remember few months have 31 days):
(2 kWh) x (30 Days) = 60 kWh per month is the power output generated by a solar panel.
How Many Watts of Power Can an Average Solar Panel Produce?
You can find the approximate values of the total wattage power produced by an average solar panel as tabulated below in a proper format:
| Type of Solar Panel | Daily Power Output (kWh) | Weekly Power Output (kWh) | Monthly Power Output (kWh) |
| 4 kW | 16–24 units | 112- 168 units | 480- 670 units |
| 6 kW | 20–30 units | 140–310 units | 600–900 units |
| 8 kW | 35 units | 245–250 units | 980–1000 units |
| 10 kW | 40 units | 280 units | 1200 units |
What Are the Main Factors That Affect the Output of a Solar Panel?
Several factors like Efficiency, location, direction and installation angles, type, number, and age influence the power output of a solar panel.
Efficiency
The efficiency of a solar panel is a metric to represent the percentage of the conversion rate of sunlight into useful electricity, It is a common way to compare a solar panel’s performance.
Usually, solar panel efficiency is calculated by the ratio of power output to the input measured in terms of watts (w). The properly controlled measures under the Standard Test Conditions (STC) are implemented by exposing the solar panels to a controlled light source at a normal temperature of 25 °C and 1kW per square meter in terms of intensity. Typically, commercial panels such as the Monocrystalline modules range between 15% to 23% in efficiency.
In 2022, a group of researchers at the NREL developed a solar cell and created a new world record achieving an efficiency of 39.5% under the 1-sun global illumination.
The advancements in the solar industry have led to the development of Perovskite solar cells having more than 30% efficiency, thereby emerging as a future-oriented solution due to their low production costs and high performance.
Several factors can affect solar panel’s efficiency such as the climate, age and maintenance, type of cells, shading, temperature and many more…
Type of Solar Panels
These are the three main types of solar panels that are available in the market such as:
1. Monocrystalline solar panels are made of single-crystal silicon having an efficiency of 15% to 23%.
2. Polycrystalline solar panels are composed of multiple silicon cells that are broken down and melted together during the manufacturing process. These panels have a lower efficiency of 13% to 17%.
3. Thin-film solar panels are manufactured by depositing a thin layer of semiconductor materials on a substrate like glass or metal, thereby possessing a much lower efficiency below 10%.
However, selecting the best solar panel depends upon every individual’s preference and usage. For example, Monocrystalline solar panels are the ideal choice for users who opt for higher efficiency, lower space and longer lifespan without considering the expensive investment. Whereas, if you’re concerned about the budget, then Polycrystalline solar panels are another alternative that requires high space and has lower efficiency. You can choose thin-film solar panels only for large commercial installations or when flexibility and weight are the prime criteria rather than efficiency.
Number of Solar Panels
The overall power production of a solar system is directly proportional to the total number of solar panels. Since each solar panel has a specific wattage, a greater number of solar panels generates a higher power output.
To determine the optimal number of solar panels, you need to consider factors such as energy consumption, sunlight exposure, availability of roof space, weather conditions, and panel efficiency to generate electricity per unit area.
You can calculate the optimal number (N optimal) of solar panels using the below formula:
N optimal = (V battery / V panel) x (1 + buffer)
Here V battery refers to the voltage of the battery required for charging in volts. Similarly, V panel refers to the voltage rating of your solar panel. Also, the buffer is the criteria or a percentage between 0.10 to 0.20 to consider factors like sudden changes in temperature, shading and several others that can affect the complete performance of a system.
Most importantly, you need to be aware that the N optimal should be altered according to the input voltage limits of an inverter. Also, the final number should be rounded to the closest whole number which assures an accurate estimation of the required energy production.
Age of Solar Panel
The ageing of solar panels leads to degradation that affects PV cells during operation which is a consequence of rainfall, snowfall, excessive temperatures, hail, dust, and other external factors that reduce the efficiency of producing energy per unit area. Typically, the average lifespan of a solar panel ranges between 25 years to 40 years.
It is estimated that solar panels on average degrade upto 0.5% per year whereas in some cases, the yearly degradation rate can reach upto 1.4% or 1.56%.
However, the degradation of solar panels can be avoided by taking several measures to ensure proper maintenance which include:
- Implementing cooling techniques such as water can prevent the PV module from reaching high temperatures, which is an effective method to expand the lifespan of solar panels.
- Regularly inspecting and cleaning the components of solar panels as well as checking for any damages.
- Avoid the accumulation of snow, dirt, and debris on solar panels to enhance the efficiency rate.
- Mainly, invest in high-quality solar panels that are highly resistant to harsh weather conditions and reduce degradation rate.
Direction and Angle of Installation
Installing the solar panels based on Azimuth’s theory of angle and direction helps to harness and generate a majority of solar energy. Roofs that are properly sloped and oriented between the angle of 20 degrees and 40 degrees can capture maximum sunlight and generate plenty of electricity.
Typically, solar panels follow true orientation rather than aligning with the magnetic poles. In other words, the original north corresponds with the Earth’s true axis rather than the North Pole. Also, solar panels positioned towards the east or west generate 20% less energy, whereas the north-facing modules generate 30% less power.
Also, determining the tilt angle based on the location’s latitude plays a crucial role in enhancing solar energy production. It is an angle at which the solar radiation comes in contact with the panel’s surface. You would have understood that an incorrect angle results in diminished energy production that reduces the overall efficiency and increases the payback period.
The best installation angle in the U.S. is between 15 degrees and 40 degrees when the solar panels are faced in the south direction.
Location
The latitude and longitude of geographic locations influence the output of a solar panel as they determine the amount of sunlight received.
Solar irradiance varies according to the different locations in the US, which depends upon several factors such as:
Latitude: Particularly, the solar radiance patterns alter with latitude as the regions closer to the equator receive abundant sunlight. It is because the sun’s rays are more intense and direct near the equator. Whereas the regions with higher altitudes or the northern and southern latitudes receive less sunlight.
Typical weather patterns: Solar panels don’t work effectively in bad weather conditions like extremely hot and cold temperatures.
Seasoned weather: The output of the solar panels varies according to the seasons. In summer, the days are longer and the higher sun angle results in more significant solar energy production. Whereas, in winter, the shorter duration of the day makes a solar panel generate a lower power output due to the reduced sun’s angle.
What Should You Do With Excess Solar Power?
These are the prime reasons for excess solar power production which include:
- A higher degree of mismatch between the electrical energy consumption of a building and photovoltaic production.
- Occurrence of overloading when a solar panel’s DC power exceeds the maximum input rating of an inverter. As a result, it forces the inverter to diminish the input power or restrict the output of AC power. Additionally, it causes a loss in energy production, minimized efficiency and permanent damages to the inverter.
However, you can use excess power wisely by implementing these two different methods:
1. Batteries: Using batteries is one of the straightforward methods to store excess power generated by solar panels. When the batteries are filled, the inverters or charge controllers limit the power output required by the load thereby shortening the maximum potential of solar power systems by not allowing them to further convert the excess energy into electricity.
2. Net-metering: The electric billing tool known as the “Net metering system” allows you to store excess power generated by your solar panels. In this scheme, the unused energy will be credited back to you. Specifically, during cloudy or rainy days, the utility grid feeds your home energy with excess electrical energy produced earlier when your panels aren’t working efficiently. As a customer, you will be charged only for your net energy usage.
Ray is an avid reader and writer with over 25 years of experience serving various domestic and multinational private and public energy companies in the USA.