Wattage of a Solar Panel: How Much Power Does It Produce?

The wattage of a solar panel is its power-generating capacity. And solar panel wattage is a critical factor you must consider before going solar.

If you’re interested in residential solar panels, the payback period for solar panels, and how many watts does a solar panel produce, this article is for you.

What Is the Wattage of a Solar Panel?

The wattage of a solar panel, also known as rated wattage, indicates the amount of power it can produce under ideal conditions.

Solar manufacturers calculate the watts of solar panels by evaluating them under Standard Test Conditions (STC). It involves exposing the solar panel to a peak irradiance of 1kW per meter square at 77 degrees Fahrenheit and 1.5 air mass.

So, a solar panel with a 1kW rating has an output capacity of 1kW power under STC. However, STC ratings are instantaneous and are only determined by flash testers. They do not account for the real-world working conditions of solar panels.

In practical terms, the wattage of a solar panel is not a closed rating. It can produce more or less energy depending on various circumstantial factors.

How Many Watts Does A Solar Panel Produce?

You can calculate the output of your solar panel by multiplying the rated wattage of the product with the total number of peak hours of sunlight that your location receives. The higher the solar panel wattage, the more power your solar system can produce. However, this is an average calculation for its total output.  

It’s nearly impossible to predict the exact energy output without accounting for certain factors that affect solar panel watts per square foot. Please note that these are not listed in any particular order of importance—they equally contribute to the overall performance of a solar installation.


Your solar panel’s efficiency refers to how much sunlight it can convert into electricity. And it may surprise you that no solar panel is 100% efficient. Depending on the model and manufacturer, solar panel efficiency usually hovers between 13% to 22%.

The higher the efficiency of your solar panel, the higher its power output.

How Many Watts Does A Solar Panel Produce


The prevailing weather conditions of where you live will affect how much power your solar panels can generate. Exposure to peak sun hours (PSH) and ambient temperature vary widely from one location to another.

Solar panels installed in a sunny state like California (5 to 7.5 PSH/day) will always have greater output than Michigan (4.0 to 4.4 PSH/day), even if they have the same wattage.

Furthermore, increases in ambient temperature lower the output, irrespective of the solar panel wattage. Solar panels perform their best at 77 degrees Fahrenheit and decline by  0.3% to 0.5% in efficiency for every one-degree rise in ambient temperature.

So, sunnier locations may be a boon for you, but hotter climates are not.


South-facing roofs with tilt angles between 15 and 40 degrees provide optimal exposure for solar panels. Position your setup within these coordinates to make sure you can maximize solar panel watts per square foot.

East-west facing roofs are also great for solar setups. However, north-facing roofs will result in markedly lower output than the rated solar panel wattage.

To maximize output, you should match the tilt angle of your solar array to the latitude of your home. It’s a best practice that can give you outstanding results.


Although solar panels can still produce energy in partially shaded conditions, shading significantly impacts their output. Even if one cell in the solar panel is shaded, it can drastically reduce its performance—this is known as the Christmas Lights Effect.

The exact decrease in output can only be determined by the amount and duration of shading. If you want your array to produce power at par with the maximum solar panel wattage listed by the manufacturer, keep a close eye on its placement.

Solar Panel Shading

Type of Solar Cells

The chemistry of the solar cells that make up your panel also affects its output capacity.

As of 2023, heterojunction (HJT) silicon solar cells are the most efficient, with up to 26.07% efficiency in advanced monofacial solar panels. But they could soon be replaced by tandem perovskite solar cells, which are currently in their developmental phase. They have a recorded efficiency of up to 33.7%.

Apart from the wattage of a solar panel, solar cell chemistry also plays a role in its output capacity. The efficiency of each panel depends on the type of silicon used.

Solar panel wattage indicates the hypothetical power your solar panels can produce, but in reality, multiple factors work in tandem to affect their true output.

Why Is the Wattage of Solar Panels So Important?

The power it produces is a critical metric that indicates a solar panel’s performance. Whether you want to lead an off-the-grid lifestyle, reduce your electricity consumption, or ensure backup power during emergencies, everything depends on the solar power your solar installation can generate.

Solar panel wattage estimates the most power produced under ideal conditions. You need this data to determine the size of the ideal solar arrangement for your home.

While it cannot predict the real-time output, you need to know the watts of solar panels to plan your investment. In best-case scenarios, you can produce excess power and store it for future use. If you’re a grid-tied user on a net metering plan, sending power back to the grid can offset your utility costs.

That’s why knowing the wattage of a solar panel is so important.

Why Is the Wattage of Solar Panels So Important?

Go Solar for a Safer Tomorrow

Are you contemplating a solar panel installation in California? AMECO Solar & Roofing is a solar company in California with 50 years of experience in the industry. From a solar panel cost calculator to solar power battery storage and solar panel watts per square foot, there’s so much you can explore with AMECO’s expertise.

Get in touch with us today to learn more about solar panel wattage.