How much output do you get from solar panels?



How much output do you get from solar panels?

‘How much power do solar panels produce?’ is a question we often receive from consumers. In our experience, they could be asking about either of the following two things: 

  • Solar panel power output rating: This is the output capacity of an individual solar panel, measured in watts. It varies from model to model.
  • Solar panel production at a specific place (like your roof): The energy production of an individual solar panel over a time period, installed in a specific place (measured in kilowatt-hours kWh).

These are both crucial things to know for anyone interested in, or already using, solar power. The good news is that both of these concepts are closely related and relatively easy to understand. 

Once you understand solar panel output, we can move on to asking the big question: How much electricity will solar panels produce on my house, and how many modules do I need to cover my electricity bill?

Calculate the solar panel power output you need to power your home

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    What is the power output rating of a solar panel?

    The power rating tells you how much power a solar panel was designed to produce. It measures the wattage of a panel when it is operating at standard test conditions.

    “Standard test conditions” is when there is a cell temperature of 77F° (25C°), and 1 kilowatt per square meter of solar energy shining on the panel. 

    In other words, a solar panel’s power rating measures how much electricity an individual solar panel will produce under ideal operating conditions.

    What is the standard power output rating of home solar panels in 2023?

    Solar panels used on homes in 2023 generally have power output ratings between 350 and 450 watts of DC power per module.

    Solar panel wattages have steadily increased over time. Just consider the fact that 400-watt solar panels are now commonly-used in home solar panel installations. The first residential panel with this level of power output, 400 W, only came out in March 2019 (it was released by SunPower, and it was very expensive); at that point, many homeowners were still installing solar panels that were between the 250 W and 300 W mark.  

    The reason for the growing power wattages of solar panels is due to improvements in solar panel efficiency. Higher efficiency means that you can produce more power in the same amount of space. 

    Higher efficiency solar panels are especially important when you are looking to install a residential solar power system on your home, but you have limited roof space. You can use fewer high efficiency panels to produce the same amount of energy as you could if you had used more lower efficiency panels.

    What determines the power output of a solar panel?

    The amount of electricity produced by a solar panel can vary based on three factors:

    1. Efficiency of the solar cells
    2. Number of solar cells it contains
    3. Type of solar panel

    Solar panel efficiency 

    Even though the average size of solar panels hasn't changed in decades, their efficiency ratings have improved drastically. When first used in the 1950s, solar panels could only convert one-twentieth of the sun's energy into electricity. At that percentage, a standard-sized solar panel would only produce about 20 watts of electricity, hardly enough to power a small light bulb.

    By contrast, modern solar panels are capable of absorbing around one-fifth of the solar energy that hits them, allowing a single solar panel to reach 400 watts of output or more. 

    The power rating of each panel is determined by combining cell efficiency with the size of each solar panel. This means that each panel is rated to produce a certain amount of wattage.

    Solar panel size: 60-cell vs 72-cell

    In terms of power output, it is best to separate solar panels into two categories: 60-cell solar panels and 72-cell solar panels.

    60-cell solar panels are typically 5.4 feet tall by about 3.25 feet wide and have a power output in standard test conditions of between 350 watts to 400 watts, depending on the exact efficiency of the cells in them. 

    72-cell solar modules are physically larger because they have an extra row of cells, and will usually have a power output of between 400 watts and 450 watts. These are less often used for rooftop solar because they are difficult to handle on a roof; they are more commonly used for utility-scale solar farms.

    Type of solar panel: mono vs. poly vs. amorphous 

    Modern solar panels are made from silicon solar cells, which are either monocrystalline or polycrystalline (sometimes called multicrystalline) silicon solar cells. 

    Both are similar in terms of energy output, although panel efficiency is typically slightly higher in monocrystalline solar panels.

    There’s also a third, less common type of solar module: amorphous solar panels. They are cheaper, but also produce much less power. 

    Monocrystalline solar panels 

    These are the most expensive and efficient panels on the market. The cells contain pure silicon and undergo a complicated process of growing long crystal silicon rods as they’re being constructed. The rods are sliced into nearly translucent wafers and formed into cells.

    Polycrystalline solar panels 

    These panels are composed of multiple polycrystalline cells. They're slightly less efficient, but more affordable. The cells are processed differently, giving them the appearance of shattered glass. This product is also cut into very thin slices.

    Amorphous solar panels 

    The cells are not crystals, but rather a thin layer of silicon secured to a base material such as glass or metal. While these panels are the least expensive, they also produce far less electrical power. 

    This means you'll need more of them to equal the power output of either of the other panels; otherwise they will not produce enough energy. The real benefit to creating amorphous solar panels is being able to form the material into long sheets that can be applied like roofing materials on south-facing roofs or other surfaces.

    How much power does a solar panel produce over a month or a year?

    When we measure a solar panel’s output over time, we use the unit kilowatt-hour (kWh). One kilowatt-hour is equivalent to 1,000 watts (1 kW) of continuous power production over one hour.

    Here’s how much solar power output you can expect from different sized solar panels, and how many of them you would need to build a typical 6 kW system:

    Solar panel output by power output rating
    Rated output Average monthly output* Average yearly output # panels for 6kW system Example panel
    350 W 42.6 kWh 511.3 kWh 18 Silfab Solar SLG
    375 W 45.6 kWh 547.9 kWh 16 LG Neon R
    400 W 48.7 kWh 584.4 kWh 15 SunPower Maxeon 3
    *Based on an average of 4 peak sun hours per day (typical for many parts of the US) and average month length of 30.4375 days. Expect power output to vary over the year due to day-to-day changes in weather and seasonal changes in climates.

    The above table is useful in helping you get an idea of how many solar panels you need to reach a desired power output. It allows us to answer the following questions: 

    How much power does a 400-watt solar panel produce?  

    A 400-watt solar panel will produce, on average, 1.6 kWh of electricity over a day, and 48.7kWh of electricity per month.

    How many solar panels do you need to produce 1,000 kWh per month?  

    To produce 1,000 kWh in a single month, you would need 21 solar panels rated 400-watts each.

    Why solar system output can vary from place to place

    Solar power ratings are based on how much power they produce in ideal sunlight and temperature conditions (AKA standard test conditions). This is defined as the “maximum power rating”.

    The problem is that actual sunlight conditions aren't always at their peak. This means that the amount of electricity your home's solar panels will actually produce on any given day depends on several environmental factors, including:

    • The average amount of sunlight your roof might get daily or annually
    • Whether recurrent shading, which could be from wind-blown tree branches, obscures direct sunlight from constantly hitting your solar panels
    • The size of your solar panels and the level of efficiency the solar cells operate at converting energy into electrical power

    Do solar power panels generate more electricity in certain states?  

    Yes, solar panel power generation varies with the climate of the state, the number of sunlight hours, and the sunlight intensity that the panels are exposed to. 

    Learn more: Power output from solar panels in each state, per day and per year

    Can you increase a solar panel’s output or efficiency?

    There’s no way to increase the solar panel output and efficiency a solar panel was designed to achieve. 

    What you can do is make sure that the solar panels are performing as efficiently as possible; this is achieved by performing routine cleaning. Dust, debris, and snow can lower the efficiency of the panels, so you’ll want to keep them clean.

    How many solar panels will my home need?

    Calculating the number of solar panels needed to power your home can easily be done online using our solar panel calculator. The calculator will take into account:

    • The size of your home
    • Location of your home
    • The amount of power you typically use every month
    • The rate charged by your utility for electricity

    All of these factors influence how much solar power you need to maximize your savings where you live.

    The calculator will then provide an estimate for all the key solar information you need:

    • The solar panel output needed to wipe out your electric bill
    • The actual number of solar panels required to achieve that output
    • The cost to install a solar panel system of that size 

    The next step is to talk to local installers. They can conduct a detailed assessment of your roof and provide an actual quote and timeline for the installation of a complete solar panel system for your home. The calculator makes this process easy by allowing you to choose how many solar installers you would like to receive quotes from. 

    Find out how many solar panels you need for your home

    Key takeaways

    • The ‘power output rating’ tells you how much electricity a solar panel can produce under ideal operating conditions.
    • Right now, most residential solar panels have power output ratings of between 350 and 450 watts of DC power per module.
    • Three factors determine how much output a solar panel is capable of: its efficiency, its size (60-cell vs 72-cell) and the type of panel it is (mono, poly, or amorphous).
    • A 400 watt solar panel will produce 48.7 kWh of electricity per month on average.
    • Many factors can affect the real-world output of solar panels, including the weather conditions and whether or not there’s any shade on them.
    • To figure out how many solar panels you would need for your home, use our advanced solar panel calculator.
     - Author of Solar Reviews

    Andrew Sendy

    Solar Industry Expert

    Andy is arguably the most qualified rooftop solar expert in America. He is in a unique position, having founded a large solar company but now being independent of any particular company. He has appeared on CNBC, has been referenced in public hearings concerning the rooftop solar industry ( such as the recent CPUC NEM 3 decision) and has been referenced by many major publications such as the Wall Street Journal, Business Week and many others.

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