How Much Energy Does a Solar Panel Actually Produce? Electricity Output Explained

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power output of a solar panel

Power output or wattage is an important factor to consider when comparing solar panel options. You may hear your solar installer say, “it’s a 255 Watt panel” or “the panel I am recommending is has a wattage of 300.” Or, when you are reading a quote from a solar installer, you might see numbers like 245W, 300W, or 345W next to the name of the panel. They are all referring to a solar panel’s wattage, capacity and power output.

How much energy can a solar panel produce?

Available sunlight will vary depending on where you live but for the sake of an example, if you are getting 5 hours of direct sunlight in a sunny state like California you can calculate it this way: 5 hours x 290 watts (a wattage of a premium solar panel) = 1,450 watts or roughly 1.5 kilowatt-hours (kwh). Thus each solar panel in your system would produce a little over 500-550 kWh of energy per year.

All solar panels are rated by the amount of DC (direct current) power they produce under standard test conditions. Solar panel power output is expressed in units of watts (W), and represents the panel’s theoretical power production under ideal sunlight and temperature conditions. Most home solar panels on the market today have power output ratings ranging from 250 to 400 watts, with higher power ratings generally considered preferable to lower power ratings. Pricing in solar is typically measured in dollars per watt ($/W), and the total wattage of your solar panels plays a significant part in the overall cost of your solar system.

Why does solar panel output matter? How to calculate panel wattage

Power output is an important metric for your home or commercial solar panel system. When you buy or install a solar photovoltaic (PV) energy system, the price you pay is typically based on the total power output of the solar panels in the system (expressed in watts or kilowatts).

Solar panel wattage represents a solar panel’s theoretical power production under ideal sunlight and temperature conditions. Wattage is calculated by multiplying volts x amps where volts represents the amount of force of the electricity and amperes (amps) refers to the aggregate amount of energy used. The financial savings you derive from the solar system is a result of the electric energy that it generates over time (expressed in kilowatt-hours).

Size vs. quantity: typical solar panel ratings and capacity

Power output on its own is not a complete indicator of a panel’s quality and performance characteristics. For some panels, their high power output rating is due to their larger physical size rather than their higher efficiency or technological superiority.

For example, if two solar panels both have 15 percent efficiency ratings, but one has a power output rating of 250 watts and the other is rated at 300 watts, it means that the 300-watt panel is about 20 percent physically larger than the 250-watt panel. That’s why EnergySage and other industry experts view panel efficiency as being a more indicative criterion of solar panel performance strength than solar capacity alone.

big power output means big solar savings

In practical terms, a solar panel system with a total rated capacity of 5kW (kilowatts) could be made up of either 20 250-Watt panels or 16 300-Watt panels. Both systems will generate the same amount of power in the same geographic location. Though a 5kW system may produce 6,000 kilowatt-hours (kWh) of electricity every year in Boston, that same system will produce 8,000 kWh every year in Los Angeles because of the amount of sun each location gets each year. (Read our blog on how electricity production and electricity prices you pay to your utility impacts your savings.)

The electricity generated by a solar PV system is governed by its rated power output, but it’s also dependent on other factors such as panel efficiency and temperature sensitivity, as well as the degree of shading that the system experiences and the tilt angle and azimuth of the roof on which it’s installed. As a general rule of thumb, it makes prudent financial sense to install a solar system with as much power output as you can afford (or that your roof will accommodate). That will ensure you maximize your savings and speed up the payback period of your solar energy system.

Find out more about average prices for solar across the country for 3kW,4kW5kW6kW, 7kW8 kW and 10kW solar systems.The EnergySage Solar Marketplace makes it easy for you to compare your savings from solar panels with various power output ratings.

How many watts of energy does a solar panel produce?

The two graphics below present different views of power output from the leading manufacturers who supply solar panels to the U.S. market. Because panel manufacturers often produce more than one line of solar panel models, the power output of most company has a significant range. Figure 1 illustrates the range of power outputs offered by each manufacturer’s panel products, and Figure 2 lists the minimum, maximum, and average power outputs of the solar panels within each manufacturer’s portfolio.

Solar panel electricity production by manufacturer

Figure 1:   Range of power output of solar panels manufacturers

Figure 2: Electricity output (in Watts) of solar panel manufacturers


Solar Panel Manufacturer




Canadian Solar225345291
China Sunergy290320306
ET Solar250340295
Green Brilliance230300266
Hanwha Q CELLS245340295
Itek Energy270370319
REC Solar240350286
Renogy Solar250300268
Trina Solar Energy245345284

Three Tips for Solar Shoppers

  1. Homeowners who get multiple quotes save 10% or more

    As with any big ticket purchase, shopping for a solar panel installation takes a lot of research and consideration, including a thorough review of the companies in your area. A recent report by the U.S. Department of Energy’s National Renewable Energy Laboratory (NREL) recommended that consumers compare as many solar options as possible to avoid paying inflated prices offered by the large installers in the solar industry.

    To find the smaller contractors that typically offer lower prices, you’ll need to use an installer network like EnergySage. You can receive free quotes from vetted installers local to you when you register your property on our Solar Marketplace – homeowners who get 3 or more quotes can expect to save $5,000 to $10,000 on their solar panel installation.

  2. The biggest installers typically don’t offer the best price

    The bigger isn’t always better mantra is one of the main reasons we strongly encourage homeowners to consider all of their solar options, not just the brands large enough to pay for the most advertising. A recent report by the U.S. government found that large installers are $2,000 to $5,000 more expensive than small solar companies. If you have offers from some of the big installers in solar, make sure you compare those bids with quotes from local installers to ensure you don’t overpay for solar.

  3. Comparing all your equipment options is just as important

    National-scale installers don’t just offer higher prices – they also tend to have fewer solar equipment options, which can have a significant impact on your system’s electricity production. By collecting a diverse array of solar bids, you can compare costs and savings based on the different equipment packages available to you.

    There are multiple variables to consider when seeking out the best solar panels on the market. While certain panels will have higher efficiency ratings than others, investing in top-of-the-line solar equipment doesn’t always result in higher savings. The only way to find the “sweet spot” for your property is to evaluate quotes with varying equipment and financing offers.

For any homeowner in the early stage of shopping for solar that would just like a ballpark estimate for an installation, try our Solar Calculator that offers up front cost and long term savings estimates based on your location and roof type. For those looking to get quotes from local contractors today, check out our quote comparison platform.

big power output means big solar savings

20 thoughts on “How Much Energy Does a Solar Panel Actually Produce? Electricity Output Explained

  1. Raxit

    Hello, I had installed 2.01KW Solar Rooftop System. It consists of 6x335W Waaree Monocrystal Solar Panels and using 3KW Capacity Growatt 3000TL inverter. However, my system is only producing units between 5-6 per day. I am seeing that during the peak hours, the wattage doesn’t go beyond 1200watts and between 10.30am to 1.30pm it hangs in between 950watts to 1200watts. I am not able to understand the cause for this, as even after considering weather and efficiency factors, It should produce around 1700watts or so during the peak hours. Can you provide any suggestions? I was told it should produce 8 units a day and it will go up to 11 or 12 during the summer. Thank you.

  2. ERNEST Smith

    my system is 8 monocrystalline panels never produces much the size is 1700 watts and all i get in lancashire is just enough to run a light bulb and its grid tied, so i think ive been sold down the river.two microinverters 500 w and two at 360 w. the cost was 2000 pound.

  3. AK

    In response to the first comment left by Raxit and to set the article straight:

    The performance of your system is probably quite normal.

    I will have to bite: Please do not take the calculations on this article as your baseline for calculating power production. It is by far an oversimplification, and probably not a helpful one. If a panel has a nameplate rating of 290 Watts, that does not mean that this is the output you will see, real world output is quite far from that, but a system must be designed taking all parameters into consideration to meet the production target, so this is pretty old news for any solar PV designer.

    The panel rating refers to the DC output at Standard Test Conditions (STC) which this article gets right. However, the standard test conditions are 25 degrees celsius and 1000Watts per square meter, which is a fairly high irradiance value and way cooler temperatures than most rooftops anywhere in California during production hours. Power output decreases with temperature. A slightly more helpful value is PTC rating, which is an approximation of what a panel will produce in real world conditions, then you can multiply this for the number of panels and efficiency of the inverter, which is typically between 96-97%, giving you the CEC-AC rating, which is what utilities use as a quick rule of thumb to calculate how much power a system might produce. This is not even factoring in the pitch of the roof, orientation and shade, all which have great influence the production of a PV system.

    The PTC rating in California for a 290 Watt panels is around 267 watts in good light conditions, with a typical inverter of 97% efficiency, this leaves you with 258 watts of production at peak times in perfect light conditions and and the sun perfectly perpendicular to your array. Local weather and average annual radiance MUST be taken into consideration as well.

    Man that was long… hope it was at leas vaguely helpful to moderate production expectations.


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