How many kWh does a solar panel produce?
Understand the energy production potential of your solar panels
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Calculating how many kilowatt-hours (kWh) a solar panel can produce might seem intimidating, especially if you don’t have any prior electrical knowledge or experience. Using a few basic pieces of information, however, it’s fairly easy to come up with a decent estimate of how many kilowatt-hours your solar panels can produce each day.
Before we get into the nitty-gritty details, here are three very important principles to keep in mind when finding the number of kilowatt-hours your solar panels can produce.
- Solar panel capacity is rated in watts; solar production is measured in watt-hours.
- Panel wattage is related to potential output over time — e.g., a 400-watt solar panel could potentially generate 400 watt-hours of power in one hour of direct sunlight.
- 1,000 watts (W) equals one kilowatt (kW), just as 1,000 watt-hours (Wh) equals one kilowatt-hour (kWh).
How much energy does a solar panel produce?
There is no single figure for the amount of energy a solar panel can produce because it mostly depends on two factors (among dozens of other variables):
- The panel’s wattage
- The intensity of the sunlight you expose it to
Although it almost goes without saying, solar panels produce the most electricity when exposed to full sunlight. When obstructed by shade or dense rain clouds, solar panels exposed to partial sun generate electricity at much lower levels.
Assuming your solar panel is operating in ideal conditions, the easiest way to estimate how much solar power a panel can produce is to multiply its wattage by the number of peak sunlight hours per day in your location.
Let’s say, for example, you have a 200-watt solar panel in a location that receives five peak sunlight hours per day. Here, your 200-watt solar panel could theoretically produce an average of 1,000 watt-hours (1 kilowatt-hour) of usable electricity daily.
In this same location, though, a larger-wattage solar panel would be able to produce more electricity each day with the same amount of sunlight. A 400-watt solar panel would generate 2 kilowatt-hours there, and a 500-watt solar panel would generate 2.5 kilowatt-hours.
» LEARN: How do solar panels work?
How many kWh does a solar panel produce per month?
Depending on its wattage, an average solar panel may produce anywhere from 25 kWh to 60 kWh per month. To calculate a solar panel’s monthly production in kilowatt-hours, multiply its expected daily output by the number of days in a month.
Statistically speaking, the average number of days per month is 30.4.
For example, let’s say your 350-watt solar panel produces an average of 1.4 kilowatt-hours per day. Multiplied by 30.4, this would equal an average of 42.5 kWh per month — or just about 510 kWh per year.
Just be aware that potential solar power production varies from month to month. In the United States, most solar energy systems are able to generate the most kilowatt-hours per month from April through September, thanks to the extended number of daylight hours over the summer.
What affects solar panel output?
Although calculating a solar panel's theoretical output is relatively simple, there are many real-world factors that influence the amount of power generated at any given moment.
While researchers everywhere continue to make new breakthroughs in solar power potential, here are the most prominent variables that affect solar panel output today:
- Sunlight intensity
- So far in this article, we have talked a lot about peak sunlight hours, which represent the amount of time in a day when solar panels work most efficiently. During peak sunlight hours (usually from the late morning through the afternoon), sunlight is at its most intense and direct.
Although solar panels still work outside of peak sun hours, it's much more difficult to generate effective amounts of solar power during the wee hours of the morning or late in the evening.
- Solar cell efficiency
- Not all solar equipment is equal, and some panels are more efficient at converting sunlight into usable electricity than others. Also, solar cells slowly lose efficiency over time, so older panels are often less efficient than when they were new.
- Whether cast by a neighboring chimney, a nearby tree or the clouds in the sky, even partial shade can dramatically affect the power output of a set of solar panels.
In some cases, you can trim back branches, tall bushes or other foliage to decrease the shade on your solar array. Other times, things outside of your control, like particulate matter from pollution or smoke, can also prevent your solar panels from working at maximum efficiency.
- Ambient outside temperatures
- Solar panels heat up while they generate electricity, which can sometimes cause them to lose efficiency on extremely hot days.
It may surprise you, but most solar panels produce their maximum amount of electricity per hour in cooler weather conditions. Consider looking for solar panels designed specifically for hotter regions if you live somewhere with high temperatures.
- Installation angle
- The angle at which solar panels are installed relative to the sun’s position in the sky affects their potential output. While plenty of residential roofs are tilted at angles conducive to harnessing direct sunlight, the “ideal” angle for solar panels is technically equal to your property’s latitude.
- Photovoltaic (PV) system losses
- You need more than just solar panels to generate and use solar power. However, you can expect to lose some energy as the electricity generated by your panels travels through the wiring and other components of your solar energy system, with none more important than your inverter. (To minimize energy losses, you should use high-efficiency inverter equipment and follow general best installation practices.)
In the worst-case scenario, all the power generated by your solar panels may be temporarily out of reach if a central inverter is offline. Such was the case for Paul, a ConsumerAffairs reviewer from California, who claimed, “My ~6kW system has been generating 0 power for months due to a bad inverter.” Thankfully, Paul’s installer read this review and took the necessary steps to solve the issue.
» MORE: Solar panel efficiency
How to calculate a solar panel’s energy production
If you want to know the amount of solar energy your panels can generate in a year, follow these steps to calculate a strong estimate:
- Determine your panel wattage. Your panel's wattage should be clearly labeled on the equipment itself as well as in your product manual. When using multiple panels, simply add their wattages together. For instance, two 250-watt panels would provide 500 total watts of solar capacity.
- Find your average peak sunlight hours. We recommend using a tool such as the PVWatts Calculator from the National Renewable Energy Laboratory to find the average number of peak sunlight hours in your location. Although peak sunlight hours vary throughout the year, using an annual average makes it easier to estimate an expected yearly production. Most areas in the U.S. have between three and six peak sun hours per day.
- Multiply your wattage by your peak sunlight hours and 365. If you have 500 W of solar power and five hours of peak daily sunlight, that would equal 2500 watt-hours (or 2.5 kWh) of solar energy produced each day. Multiplied by 365 (for each day of the year), your annual solar production would max out at just over 900 kWh per year.
Alternatively, if you’re trying to decide what your solar energy system’s total capacity should be, you should start by looking at your property’s annual electricity consumption and work backward from there. John Ytterberg, a former residential solar consultant, explained it to us like this: “Most solar panel systems are designed to produce approximately the same amount of electricity or slightly more than the home consumes each year.”
Just bear in mind that these estimates assume ideal conditions, and the real-world factors that affect solar generation, such as weather patterns, ambient temperatures and other constantly changing conditions, will likely make your daily solar energy production vary quite a bit.
Thankfully, once you add solar panels to your home, your installer will likely provide a way for you to track your system’s daily solar energy production. So, depending on your inverter, you may be able to see your system’s performance at the end of the day or in real time on your laptop or smartphone.
How much energy do solar panels produce hourly?
The amount of energy solar panels produce hourly depends on a lot of factors, including the panels’ wattage and the intensity of the sunlight. In general, you can calculate the peak hourly energy production of a solar panel by looking at its wattage, though.
For example, in peak operating conditions, a 400-watt solar panel could theoretically be expected to generate 400 watt-hours of solar energy.
How many kWh does the average home consume in a year?
According to the U.S. Energy Information Administration, the average American household consumes about 10,632 kilowatt-hours (kWh) of electricity per year.
How much energy do solar panels produce across their lifetimes?
Solar panel lifetime energy production varies, but if you have a solar panel that produces a daily average of 500 watt-hours of electricity (or 0.5 kWh), that could translate to as much as 5,475 lifetime kilowatt-hours over 30 years.
Just remember that different solar panels’ lifetime energy production numbers vary considerably. Think of it this way — a solar panel’s daily production can vary quite a bit, and when you multiply that out over the years, the range opens up even more. (Solar panels can last a long time, producing electricity at slowly diminishing rates for 30 years or longer.)
- Article sources
- 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:
- U.S. Energy Information Administration, “Most utility-scale fixed-tilt solar photovoltaic systems are tilted 20 degrees-30 degrees.” Accessed May 18, 2023.
- National Renewable Energy Laboratory, “PVWatts Calculator.” Accessed May 18, 2023.
- U.S. Energy Information Administration, “How much electricity does an American home use?” Accessed May 18, 2023.
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