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How much electricity does a solar panel produce?

Electricity sparking

The amount of electricity a solar panel produces depends on three important factors: the size of the panel, the efficiency of the solar cells inside, and the amount of sunlight the panel gets.

We’ll break down what you can expect from a typical solar panel, and how that power output compares to the power you need for the gadgets and appliances you use inside your home.

How big are solar panels?

When we say “solar panel,” what we’re talking about is a typical silicon photovoltaic panel for residential use. These days, most solar panels are about 5 and a half feet tall and a little more than 3 feet wide:

If you look closely at the solar panel in the image above, you’ll notice 60 little squares. These squares are actually individual solar “cells,” which are linked together by wires. The cells are where electricity is made, and the wires carry the electricity to a junction box where the panel is hooked into a larger array.

Why does solar panel size matter?

The more solar cells working in tandem, the more power they’ll create. That’s why the size of the panel matters if you’re trying to calculate how much electricity a panel makes.

Solar panels have been about this size for decades, but modern panels make more electricity than in the past. That’s because panel manufacturers have found ways to improve cell efficiency over time.

Comparing solar panel efficiency from 1954 to 2018

How efficient are solar panels?

Solar efficiency relates to the amount of available energy from the sun that gets converted into electricity.

Back in the 1950s, the first solar cells were capable of taking 6% of the energy from the sun and converting it into electricity.

If they were configured to be the same array of 60 cells you see in the image above, that would have created a current of about 20 watts electricity, about a third of what would be needed to light up a 60 watt incandescent bulb.

When we originally wrote this page in 2012, solar cells could convert 15% of the energy hitting them from the sun into power. As of 2018, the efficiency of the most advanced solar cells is closer to 23%, while average solar cells for residential use are around 18.7% efficient.

If you combine the efficiency of the cells with the size of the panel, you get a number called the “power rating.” In the solar industry, we say “that panel is rated to produce X watts.”

What’s the power rating for an average solar panel?

As of 2018, a typical solar panel produces around 320 watts of power, but panels come in many different wattage ratings, and finding one that produces exactly 320 watts is rare. The top 10 residential solar panels for 2018 includes panels rated to produce anywhere from 290 watts to 360 watts.

More efficient panels are a little more expensive, and are usually only needed if you have limited space on your roof.

Your solar installer will work with you to figure out how many panels you need to produce enough energy for you to use.

It generally matters less how much each panel can produce than how well the whole array performs.

How is a solar panel’s rating calculated?

Your solar panels will have a number listed on the back that indicates how much power they will pump out during ideal conditions. This is called the Standard Test Condition rating (STC for short).

Here’s what a label looks like on the back of the solar panel:

A rating label on the back of a solar panel

To determine an STC rating, solar labs test the panels under ideal conditions called “peak sun,” or 1000 watts of sunlight per square meter of surface. That’s approximately equal to the power of the sun at noon, on a sunny day, at the equator.

In the picture above, the label shows an STC rating of 250 watts for the panel. If that panel received full sun for one hour, you’d get 250 watt-hours of electricity. With 4 panels, you’d get a kilowatt hour. Click here to read more about the difference between a kilowatt and a kilowatt hour.

The Top 10 Solar Panels for Home Use in 2018

California is a great place, full of sunshine and people who love to capture it for their own use. The state does one amazing thing right when it comes to solar power, and that’s collect an archive of data about every single installed solar system in the state. From that data, which includes nearly 50,000 home solar systems installed in 2018, we pulled a list of the the top 10 solar panels used.

The table below shows the most popular solar panels in 2018, in order of number installed. As an interesting side note, the top 2 panels on this list represent 25% of all solar panels installed on homes represented here. All together, the 10 panels below represent 64% of home solar installed in California in 2018.

RankManufacturerModel No.Rated Output (watts STC)
1SolarCitySC325325
2SunPowerSPR-X22-360-D-AC360
3Jinko SolarJKM290M-60B290
4SunPowerSPR-X21-335-BLK-D-AC335
5SunPowerSPR-X21-345-D-AC345
6SunPowerSPR-E20-327-D-AC327
7Mission Solar EnergyMSE295SQ5T295
8LG ElectronicsLG330N1C-A5330
9Jinko SolarJKM290M-60290
10REC SolarREC285TP2 BLK285
Based on data from California Solar Statistics for 49,453 solar systems under 16-kW in size, for which permits were approved in 2018.

Where can you buy home solar panels?

Like we said above, the panels we’re talking about here are meant for residential rooftop solar installations. You can’t just go buy them on Amazon—though Amazon does have some great solar panel kits that use lower-wattage panels (Full disclosure, as an Amazon Associate, Solar Power Rocks may earn a commission from qualifying purchases).

No, the panels described above can are meant to be installed in a larger array on a rooftop by professional solar installers who are licensed and insured to design and install a solar system that can power your home and either feed extra extra energy back to the grid or store it in batteries.

If you’re an electrician or roofer who wants to go it alone, these panels can also be purchased from a wholesale solar supplier and installed in an on- or off-grid configuration with or without batteries. You can DIY a solar installation, although we don’t recommend it, or you can purchase the equipment wholesale

Solar panel output calculator (kWh)

Even if you live at or near the equator, you can’t expect to replicate these ideal conditions. The amount of electricity solar panels produce depends on average sunlight over the course of a year. If it’s historically more cloudy in your area, there’s less available energy from the sun to convert into electricity.

The first step to figuring out how much electricity your solar panel can produce in a year is to find your place on the globe. If you live in the United States, you can figure out how to calculate the amount of electricity a solar panel produces and how much you can save using our simple solar calculator:

If you live outside the United States, check out Weather Underground’s solar calculator. You can enter your address into it and get specific details about how much sunlight hits your house on average. The calculator also gives the option of entering a specific model of solar panel and the square footage of the panel coverage on your roof.

Solar panel output per day and per month

Using the example above of a 250-watt STC rated panel, if you multiply the 250 watts the panel produces by the number of hours of full sun you get in a day, you’ll get the amount of kwh that panel produces per day. Multiply by 30 days and you’ll get mothly kWh output for the panel.

The average roof in the United States gets about 4 hours of usable sun per day. We know the sun shines more than 4 hours, but “full sun” is a measurement that combines all the parts of the day when the sun is lower in the sky into one number.

Using 4 hours of full sun, gives you this equation: 250 watts x 4 hours. That’s 1 kWh (1,000 watts) in a day per 250-watt panel.

If you multiply 1kWh per panel by 30 days in a month, you’ll find that each 250 watt rated panel will produce about 30 kWh in an average month.

How much energy does a solar panel produce per square foot?

Solar panel output per square foot

The average-sized solar panel takes up an area of 17.6 square feet and produces 265 watts under direct sunlight. That translates to just over 15 watts per square foot.

How many solar panels are needed to power an average house?

Sizing a solar panel system to your home’s electric usage can be done by taking look at your energy bills over a year.

Most utility companies provide information about your last few months of usage on your bill, but you can probably get more on their website. A few lucky customers get a year and a half like this:

a sample energy bill before solar panels with usage details

We’ll spare you the trouble of averaging that column, and tell you that this house uses about 2,200 kWh per month. That’s quite a bit higher than the national average, which means the homeowner could really be helped by solar power!

Typically, homeowners in the United States use about 900 kWh a month on average. So, take 900 kWh and divide by the amount of kWh one solar panel produces over the course of a month (30kWh), and you get a 30 panel installation. 30 panels x 250 watts per panel equals a 7,500 watt system (7.5kW).

Again though, these are just rough estimates. It’s best to connect with a solar expert we trust who can appropriately size a system and help take advantage of all the local incentives to get it done right and as affordably as possible.

How much power do my devices use?

There’s huge variation in power use between households depending on what you own and how often you use everything. People in the South and West United States tend to use more electricity for heating and air conditioning, whereas people in the North and East tend to heat with gas or fuel oil.

One basic old-fashioned lightbulb uses 60 watts of electricity; a CFL uses 18 watts. Laptops often use about 45 watts, and desktops can run between 150-300 watts. Window air conditioning can range between 500 and 1500 watts, and central air conditioning can use 3500 watts.

The average home in the US uses about 1,000 kWh of electricity per month. All those little devices add up to big usage, with variations by season. Usage also varies between day and night. Unless you work at home, most of your electricity usage probably happens at night.

On or off the grid?

Since solar panels only generate power as the sun shines, you’ll need a way to store the energy. Though it’s possible to use a battery for storage, the easiest (and cheapest) solution for most people is to stay connected to the grid.

If your solar panels are producing more energy than you’re using—when you’re at work, on vacation, or just not running many devices—excess power will flow back into the grid. In many locations, utility companies offer a program called “net metering” that can compensate you for extra power you produce.

At night, or anytime you need extra power, you’ll pull it from the grid. With a grid-connected system, you’ll never need to worry if you happen to need more power than your solar system has been sized to provide. You may also choose to supply only part of your average electricity bill with solar, and use the grid for the rest.

Your solar installer will talk to you about all of the options. Interested in getting a quote? Sign up with us to get a free consultation.

Last modified: February 11, 2019

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Mehran
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Mehran

I have a house with suite in the basement. I use electric heat for the basement and my electricity is very high, specially during the winter it’s close to 4,000 kWh per month. Can I use the solar system to cover that or at least part of it or it’s just not for me. We live in northern side with shorter days in the winter and longer days in the summer, and cold winter.

mike
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Priorities: 1. Lower heat transfer :: insulate walls with fiberglass R-11 to R-13 on wall, cover with sheet rock. 2. Cut infiltration losses – spray foam insulation in leaky windows, doors, gaps. 3. Reconsider electric heat; consider gas heat or solar hot water on roof to storage in basement if sunny in winter.

r burry
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r burry

I think your numbers are wrong there. Going of the percentages the second generation is less than 3x as effecient. Yet on your wattage number you have it 10x. Something must be off, unless there is some solar concept I dont understand

T Satyanarayana
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T Satyanarayana

Does the present solar panels convert heat energy also into electric energy under very hot conditions in places like North India using Peltier Modules. What are the technical and financial constraints.

Dan
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Dan

I am using 3 electric pumps for irrigation of 65 hectares of land .Due to high electricity costs, I want to shift to solar energy. The power requirement for the 3 pumps are 160 , 76 and 200 kilowatts. Sunshine hours are an average of 7 to 8 hours per day. How many solar panels should i installed and what would be the estimated cost.Thanks

Jijo Pazhayattil
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Jijo Pazhayattil

Are you sure about the kilowatt rating of the pumps you use? A 200KW pump is going to pump some serious volume of water!!!

gasper
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gasper

more over, in the solar calculator page you refered to earlier, the dimensions in which standard? meter, inch, feet? all of them are mentioned so i wouldnt get a good figure there

gasper
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gasper

hi, i have installed 4 x 250 panels, 4 x 200 amhr batteries, MPPT inverter/charger of kW, my consumption is 300 w more or less, and this is supporting the grid when its power goes off, so first question, 300 w on mppt panel means 300 x 3600 (seconds) to get W-hr? that would be way too high, please correctme

Mike
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Mike

Assuming the solar panels in different years are the same sizes, then the efficiency calculations cannot make sense. If a 1954 panel was 6% efficient, whereas a 2012 panel was 15% efficient, then one would expect that the solar energy harvested would increase by a factor of 15% / 6%, i.e. 2.5. However, it varies by a factor of 10! (200W / 20W). Therefore some of the measurements cannot be correct. Similarly, the 2018 panel was 18.7% efficient, which, compared to the 2012 panel, is an increase by a factor of 1.2467. Therefore if the other numbers are correct the… Read more »

Alan Edwards
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Alan Edwards

Although solar energy is one of the cleanest and most abundant renewable energy sources available, the space required to install solar systems can be a barrier to its implementation.

Anonymous
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Anonymous

One GW in the Atacama desert in Photovoltaic is equivalent to GWh/year

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