The average solar panel has a power output rating of 250 to 400 watts (W) and generates around 1.5 kilowatt-hours (kWh) of energy per day. Most homes can meet energy needs using 20 solar panels, which typically have an installed system capacity of six to eight kilowatts (kW).
Solar panel wattage is determined under laboratory conditions, but the actual output constantly changes once installed. The exact power output of your system will depend on the type of photovoltaic (PV) solar panels you use and external factors like sunshine and ambient temperature. Read on to learn about factors that affect performance and how to maximize your solar generation.
How Is Solar Panel Power Production Measured?
The wattage of a solar panel measures how much energy it produces under standard testing conditions. While solar system size is measured in kilowatts, the amount of electricity a solar array generates is measured in kilowatt-hours.
All manufacturers use the same Standard Test Conditions (STC) to determine the nameplate wattage of a PV module:
- The panel is exposed to an irradiance or light energy of 1,000 W per square meter.
- Solar cell temperature is 25°C (77°F) at the time of testing.
- The light spectrum used during the test represents sunlight crossing the atmosphere at an angle of 48.19°. This is known as the “air mass 1.5 spectra” or AM1.5.
The output measured under laboratory conditions determines the rated wattage of a solar panel. This testing also dictates the solar panel efficiency rating. For example, if a PV module generates 220 W per square meter, it is 22% efficient.
As of June 2023, Canadian Solar produce the most efficient solar panels in the industry — the company have reached 22.8% efficiency. However, many other brands make solar panels with an efficiency of over 20%.
Solar panels are manufactured in standard sizes, and wattage increases with size. Smaller, 60-cell panels are common in residential installations, while 72-cell panels are normally used in commercial and industrial installations. You can find other sizes, but 60-cell and 72-cell panels are the most common.
Factors Affecting Solar Panel Power Capacity
The nameplate wattage of solar panels is determined under ideal conditions that do not reflect real-world applications. For example, a 360 W panel may operate closer to 300 W when installed on a rooftop with average sunlight conditions. Below are some of the factors that affect the energy production of a solar panel.
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Manufacturers use specific laboratory conditions to determine solar panel wattage, but the actual output of your system will vary depending on factors such as sunlight exposure and local temperature conditions
Amount of Sunlight Exposure
Solar panels generate more electricity when they get more hours of direct sunlight. Assuming you compare PV systems of the same size, you can expect higher productivity in sunny states like California. You can use the World Bank Global Solar Atlas for an idea of the sun hours available in your location.
Ambient Temperature
Increased sunshine makes solar panel systems more productive, but high ambient (air) temperatures can have a detrimental effect. High heat can temporarily reduce the ability of PV cells to convert sunlight into electricity.
Solar panels have a temperature coefficient, which describes how much power their cells lose per Celsius degree as the panel heats up. Most solar panels have a temperature coefficient of around -0.3% to -0.5% per °C. This means a temperature rise of 10°C will cause a power loss of around 3% to 5%.
Solar Battery and Inverter Efficiency
A solar panel system includes other components, such as inverters and batteries. The inverter is necessary since it converts the DC power (direct current) generated by solar panels into the AC power (alternating current) used by home appliances. Battery storage is optional in grid-tied solar systems, but necessary for off-grid systems.
These devices waste some of the power your system generates since they are not 100% efficient, but you can find inverters and battery systems with an efficiency of over 95%. Although this represents a small loss, it is worth considering when designing a solar energy system.
Estimating the Potential Power Output of Solar Panels
The amount of power a solar array can generate depends on sunshine and weather conditions. To determine a system’s exact power output at any given time, you must measure it directly. But you can use the Global Solar Atlas to estimate how much energy your system will generate annually:
- Using the Global Solar Atlas, click on your location and look for a value called specific photovoltaic power output or PVOUT.
- This value estimates the annual productivity of solar panels in your location, measured in kilowatt-hours generated per kilowatt of peak capacity (kWh/kWp).
- For example, if the Atlas shows a PVOUT value of 1,500 kWh/kWp and you have an 8 kW system, you can expect to generate 12,000 kWh of electricity per year.
- Say you have an electricity tariff of 16 cents per kWh, you could save $1,920 in annual electricity bills.
- To determine the energy production of each panel, divide the total output by the number of panels. For example, if you have an 8 kW system with 20 panels that generate 12,000 kW total, each panel should generate 600 kWh of energy per year.
Power Output by Solar Panel Type
The main factor that determines panel power output is the type of solar cell: monocrystalline (most efficient), polycrystalline (intermediate) or thin-film (least efficient). The following table compares the typical power output you can expect when comparing types of solar panels.
| Solar Panel Type | Typical Power Rating* |
|---|---|
| Monocrystalline | 320 W–380 W |
| Polycrystalline | 250 W–300 W |
| Thin-film | Less than 200 W |
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*Power estimates reflect typical wattages for residential solar panels with a size of 65 inches by 40 inches (or similar), which is common in home installations. Power output ratings will increase or decrease with solar panel size.
As you can see, high-efficiency monocrystalline panels can generate more watts of power compared to thin-film and polycrystalline panels. Homeowners with limited space can use monocrystalline panels to achieve the highest possible electricity output.
Maximizing Solar Panel Power Generation
Solar panels have a rated wattage and efficiency, but their actual performance depends on many external factors. You can achieve higher efficiency by following these recommendations:
- Install your solar panels in an unshaded area.
- Clean your solar panels regularly to prevent dust and dirt from accumulating and blocking sunlight.
- Monitor the daily electricity output of your solar panel system. Many inverters have a built-in monitoring app you can install on your smartphone. Contact your solar installer if you notice any dips in system performance.
We recommend a professional installation if you plan to go solar. Solar panels that are not wired properly can suffer from low productivity or even permanent damage. Incorrectly installing your system can also void your manufacturer’s warranty. The best solar companies ensure proper solar panel installation and help you troubleshoot any issues over time.
The Bottom Line
The average residential solar panel has a power output rating of 250 to 400 watts, and generates approximately 1.5 kWh of electricity per day. Manufacturers use specific laboratory conditions to determine solar panel wattage, so the actual output will vary depending on factors such as sunlight exposure, temperature conditions and how much energy is lost by other system components. You can maximize solar production by using high-efficiency monocrystalline panels, opting for a professional installation and keeping your panels free of dirt and debris that could block sunlight.
Your solar installer can calculate the ideal system size for your home based on your electricity usage, energy needs and site conditions. Since companies test solar panels under the same conditions, you can compare power output directly when shopping for panels. Installers also use rated wattages to size solar power systems and estimate electricity production.
Frequently Asked Questions About Solar Panel Energy Output
The average solar panel generates 1.5 kWh of energy each day. Solar panel productivity largely depends on rated wattage and local sunshine conditions. Electricity production will be higher on sunny days with clear skies and lower during cloudy weather or on short winter days.
You can estimate solar panel power output by multiplying a panel’s efficiency rating by your location’s peak sunlight hours, which you can find using the Global Solar Atlas. For example, a 400 W panel in an area with 4.3 watt-hours of peak sunlight would generate 1,720 watt-hours or 1.7 kWh of energy each day.
The average cost of a home solar system is $2.85 per watt, which equals $17,100 for a 6 kW system or $22,800 for an 8 kW system. You can lower your system cost by claiming the federal solar tax credit and other solar incentives. High-wattage solar panels are more expensive but may qualify for higher incentives. For example, since the federal solar tax credit equals 30% of total project costs, you would see a higher credit with a more expensive solar system.
Solar panels generate renewable energy by collecting sunlight using PV cells on their surface, which is then converted to electricity to power your home. A solar panel’s efficiency rating measures how much sunlight it can absorb and convert into usable electricity. Learn more about how solar panels work.
Most residential solar panels have a wattage between 250 to 400 W. You can reach 2,000 W (or 2 kW) of capacity by using five 400 W panels. A 2 kW solar system can generate over 3,000 kWh of energy per year under favorable site conditions. So considering the average home uses 10,632 kWh per year, a 2 kW system would cover around 28% of energy usage in a typical home.
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