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What is the output of a solar panel?

Understanding solar panel output and how it's measured

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The technical answer (bear with us) is that the output of a residential solar panel can be anywhere from 100 to 500 watts, depending on the capacity of the equipment and its operating conditions. Most solar panels on homes today are rated to output between 250 and 400 watts, meaning they can produce between 250 and 400 watt-hours of electricity for every hour they’re exposed to direct sunlight.

However, that answer may not make sense to most people, and it really depends on what you mean by “output” anyway. We’ll explain everything you need to know about solar panel output in plain terms below, so keep reading if you want to learn more and understand the answer above.

Key insights

  • The electricity output of a solar panel is usually measured in watts or watt-hours, depending on the context, but you may see other units if you get deeper into the spec sheet.
  • Solar power is produced at varying intensities throughout the day, month and year.
  • You’ll probably want professional help if you’re looking for the most accurate estimate of a solar panel’s potential output.

Solar panel output explained

Whether you are installing solar shingles, solar panels or any other device that harnesses sunlight to generate electricity, solar output measurements can usually be broken down into voltage, amperage and wattage ratings, which are all just units used to measure different aspects of the flow of electricity.

What you mean by “output” determines the units used to measure it.

Generally speaking, a solar panel’s potential output is rated in terms of wattage (W). That’s why you’ll see references to 300- or 400-watt solar panels as a shorthand for how powerful they are. (As we mentioned before, most homes have solar panels rated to produce 250 to 400 watts these days.)

However, if you’re looking at how much electricity a solar panel actually produces, expect to see the answer measured in kilowatt-hours (kWh). This is the same unit that’s likely used to measure your home’s energy consumption on your electricity bill.

For example, when Chuck, a ConsumerAffairs reviewer from Virginia, went solar, the installer designed a system with “30 panels to provide a 58% reduction of [their] average usage of 1500 kWh. That equates to an [output] average of 870 kWh/month.”

(The same 250- to 400-watt solar panels on most homes produce 250 to 400 watt-hours (Wh) of electricity for each hour they’re exposed to direct sunlight, and 1,000 watt-hours are equal to 1 kilowatt-hour. That means you can calculate how much energy your solar panels can produce if you know their combined wattages and how much sunlight your property gets.)

» CALCULATE: How many kWh does a solar panel produce?

We should be clear — a technical understanding of all of the above terms usually isn’t necessary to reap the benefits of solar power. However, we’ve explained voltage, amperage and wattage in greater detail below for those that have more complicated questions.

While a solar panel is producing electricity, its voltage refers to the rate, speed or pressure at which the electricity can be transported from the panels to the rest of your energy system.

Today, most solar panel systems have a potential output voltage of 12, 24 or 48 volts, representing the maximum speed of the electricity. As you may imagine, higher-voltage systems allow for more solar energy to flow to your home, battery or the electric grid at once.

Solar panel output amperage (or amps) is a measure of electrical current used to quantify the amount of electricity “flowing” from your solar panels. Much like how river speeds are rated in cubic feet of water per second, solar panel amperage is used to measure the amount of electricity that flows out of a solar panel over time.

To use another figure of speech, if solar panel voltage were the speed limit, then solar panel amperage would be the number of vehicles traveling on the road and passing through a certain point. With a higher speed limit (voltage), more vehicles (amps) are able to pass.

Although amperage and voltage are important, wattage is the most common measurement used to predict a solar panel's output because it’s a product of the two. As Daniel L., a licensed electrician with ION Solar, explained to us, “One of the first things they teach you about electricity is that volts times amps is equal to watts.” Basically, solar panel output wattage is a measure of electrical power at a given moment.

Solar panel electricity generation and home electricity consumption are measured in watt-hours or kilowatt-hours (1 kWh = 1,000 Wh) because these are the units used to quantify energy, which is power multiplied by time.

Basically, a solar panel’s wattage is a measure of how much energy it’s capable of producing at a given moment, while kilowatt-hours are used to measure how much energy it actually produces in an hour, day, week, year, etc.

What influences a solar panel’s output?

In practical terms, it can be hard to predict a solar panel’s exact output at any moment because it’s affected by many factors — both internal and external. These include but are not limited to:

  • Temperature: Both ambient and operating temperatures can affect solar panel output. While solar panels can work efficiently in a wide range of temperatures, most solar panels prefer cooler climates and will output slightly less energy on extremely hot days.
  • Panel efficiency: In addition to wattage and voltage, panels are also sold with a solar efficiency rating that measures how well the solar cells can absorb sunlight and create usable electricity. Today’s best solar panels are generally rated at between 20% and 22% efficiency. Solar panels also slowly become less efficient with age, though.
  • Sunlight intensity: Solar panels work best during peak sun hours in the late morning and early afternoon when sunlight is at its most direct and intense. While solar panels can generate marginal amounts of electricity in the early morning and late evening, the majority of solar panel output occurs during the three to seven peak sun hours in the middle of the day.
  • Weather and air quality: A solar panel’s output may also be limited on cloudy days or while covered in snow because there’s less direct sunlight to harness. The same goes for when there’s excessive particulate matter in the air, such as smoke from a forest fire.
  • Solar equipment variables: Before you can use the power generated by your solar panels, the electricity will likely first need to travel through a significant amount of wiring as well as an inverter system. That means your solar panels' total potential output will be affected by the efficiency of the other hardware within your solar energy system.

» MORE: Solar energy pros and cons

How to calculate solar panel output

When looking at solar equipment ratings, you can think of wattage as representing how many kilowatt-hours of energy a solar panel will produce in ideal operating conditions over one full hour. For instance, if you have a 300-watt solar panel receiving full sun on a cool day, you can expect your solar panel to output 300 watt-hours (or 0.3 kilowatt-hours) of electricity for every hour it is actively producing.

Around the country (and seasonally), solar panels can be expected to efficiently produce electricity for three to seven hours per day, depending on your location and the time of year. To illustrate a quick example, let’s say your 300-watt solar panel above was exposed to five peak sun hours during one day in April. With this, you could expect an average daily output of 1,500 watt-hours (300 x 5 = 1,500), or 1.5 kilowatt-hours.

To calculate the potential output of your full solar energy system, we recommend using the PVWatts calculator from the National Renewable Energy Laboratory (NREL) or talking to a solar installer near you. By working with a professional, you can design a solar panel system with confidence in its expected potential output and ability to reduce your energy bills.

» DISCOVER: Best solar energy companies of 2023

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    How much power does a solar panel produce in a day?

    While “power” may technically refer to wattage alone, the amount of solar electricity a panel can produce (measured in watt-hours or kilowatt-hours) depends primarily on the equipment’s specifications as well as the amount of direct sunlight it receives.

    That being said, you could expect a 350-watt solar panel to produce between 1.4 kilowatt-hours and 2.1 kilowatt-hours in ideal conditions with four to six hours of direct sunlight.

    How much power does a solar energy system produce in a day?

    A fairly average-size 6kW system should produce roughly 240 to 300 kilowatt-hours of electricity in a day. Just remember that the amount of energy a solar energy system can produce in a day depends on the number of panels installed as well as the efficiency of the inverter and wiring components.

    How different is a solar panel’s output in the winter vs. summer?

    Solar panel output is generally much lower in the winter than in the summer, largely based on the number of available sunlight hours. The increased amount of sunlight in the summer allows nearly twice the amount of solar energy to be output during the summer versus the winter.

    ConsumerAffairs writers primarily rely on government data, industry experts and original research from other reputable publications to inform their work. Specific sources for this article include:
    1. National Renewable Energy Laboratory, “PVWatts Calculator.” Accessed June 23, 2023.
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