Exactly how much power does a solar panel generate?

You, like many Americans, may be considering going solar and wondering if it makes financial sense. When there’s a power outage, would solar panels keep your lights on? If you don’t have a battery, then probably not. In the long run, will installing solar panels save money? (The precise amount and rate of improvement are context-dependent.) What percentage of my home’s energy needs can a solar panel on my roof meet, anyway?

The information regarding your solar panels, your home’s location, and any obstacles between your panel and the sun are necessary to provide a satisfactory answer to the last question.

You may get an estimate of your solar system’s electricity production from any reliable solar contractor. Some companies are even promising guaranteed output. But if you’re interested in learning more about how much power solar panels may generate for your home, here’s everything you need to know.

Solar panel output calculation

To calculate how much energy a solar panel can generate, all you have to do is multiply the panel’s area by the amount of sunlight it receives.

According to Brighter way Solar’s vice president in Florida, Neil Gallagher: “To calculate how much output a solar panel generates, consider the wattage and solar irradiance the panel receives.” The wattage rating indicates how much power the solar panel is capable of producing under optimal conditions. The amount of energy from the sun that actually hits the solar panel is called “solar irradiance.”

Standard wattages for residential solar panels are around 400 watts. Solar irradiance maps for each month of the year, covering both North and South America, are available from the National Renewable Energy Laboratory. Worldwide maps are also available.

“There are several free resources on the internet that may be used to calculate solar irradiance. Multiply the solar irradiation by the solar panel’s wattage rating to get the amount of electricity produced. The calculated figure represents a daily estimate of energy production in kilowatt-hours. Keep in mind that temperature, panel degradation over time, and system losses can also affect daily energy output,” Gallagher said.

The PV Watts tool on NREL’s website will also run the calculations for you. Simply enter in your address information.

Production factors for solar cells

How much electricity solar panels generate can rise or fall depending on a number of environmental factors. Here are the most important variables that can change how much electricity a solar panel generates.


Cloud cover in particular can have a major impact on the output of solar panels. When there are lots of clouds in the sky, such on gloomy days, the solar panels receive less of the sun’s rays and hence produce less energy. Solar panels may still generate electricity during overcast days, however at a lower rate and efficiency. This is especially the case when the day is punctuated by brief cloud cover.


A location’s latitude provides information about its north-south orientation on Earth. The equator marks 0 degrees, whereas the North and South Poles mark 90 degrees. More solar energy is produced at latitudes closer to the equator because of the greater amount of sunlight available there throughout the year. Due to the sun’s lower inclination, solar irradiance is diminished at locations with greater latitudes. This causes less energy to be generated from the sun since light has a longer distance to travel through more of Earth’s atmosphere. Solar panels have been installed and are functioning from the equator to the poles, but if you want an accurate estimate of how much energy your panels will generate, you need to account for latitude.


When sunlight is blocked from reaching a solar panel, hotspots form due to the increased internal resistance. When a solar panel develops hotspots, efficiency drops, power output drops, and there’s a risk that the damaged cells or the entire panel will fail in the long run. Install solar panels in regions where there is little to no shade to get the most out of them.

Installers of solar panels often mount panels with bypass diodes or microinverters to reduce the impact of shade when it cannot be avoided. However, there are new companies making solar panels that can function nearly as well in partially shaded areas.


Solar panel performance might decrease in hot environments. Although solar panels will produce the most electricity when exposed to direct sunshine, their efficiency will decrease if the ambient temperature is too high. Solar panels, according to the experts, perform best in mild climates. The effectiveness of solar panels decreases by 3% for every degree the temperature rises beyond 25 degrees Celsius (77 degrees Fahrenheit).

Can I keep the power my panels produce in a battery?

Your solar panel system’s output may exceed your daily electricity needs, depending on the details you’ve provided. However, the solar panels won’t be able to supply all of your energy needs once the sun goes down. While a battery can be used to store some of your extra solar power for later use, you will need to draw energy from the grid to make up the difference.

Solar batteries provide a reliable backup power source for your solar array and grid tie-in. In the event of a blackout or when solar panels aren’t producing enough energy, these generators will keep you powered. However, battery systems may be pricey, with a 10 kilowatt-hour module costing around $10,000. That’s why it’s so important to weigh the costs and benefits of a home battery unit installation carefully.

Brighterway Solar’s Gallagher stressed the need of having your solar installer or vendor evaluate your electricity consumption prior to deciding whether or not to include a battery in your solar system. Professionals can advise you on the viability and cost-effectiveness of installing a battery unit after analyzing your energy consumption.

If you don’t have batteries, should you invest in solar panels?

Although solar systems with batteries connected are becoming increasingly common (almost 9% in 2021) for homes, most installations still occur without them. Since California revamped its net metering program, investing in batteries has become a more financially viable choice. The way you are charged for electricity, the amount your utility is willing to pay you for your excess solar energy, and your own energy consumption will all factor into your decision about whether or not to invest in a battery.

In areas where “1-to-1” net metering credit is in place, the utility provider will pay you the same amount per kilowatt hour as it charges the customer. According to Gallagher, purchasing a battery could be beneficial if the electric company’s credit is less than the amount they charge on your bill.

Batteries can be a more cost-effective option than using the grid directly because of time-of-use tariffs, which charge more for electricity at specific times of the day.

If you want to know if adding a battery to your solar system would save you money, consider your electricity usage, net metering, and time-of-use rates.

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