How much do solar panels produce?

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How much electricity do solar panels produce?

kW hours per day

Choose your state to see the complete guide to installing solar panels



Please also note when using the map above that the estimates assume a perfect installation facing due south, at an optimal tilt angle, and unshaded between 9am and 3pm. Click on your state in this map to see our complete guide to installing solar panels in your state.

Geography and Location

Here is a map that shows the average amount of kWh produced by a 1 kilowatt solar power system each day in each state of the USA.

As you can see across the USA daily production per kilowatt installed varies from as little as 2.9 kWh per kw per day to close to 4.7 kWh in very sunny locations. This is because of different levels of solar irradiation available in different locations and is measured in Sun Hours.

Please also note that in some states different parts of the state have very different climatic conditions and so whilst the amount quoted above may be true for some parts of the state it may not necessarily be the case where you live. To see a more accurate estimate for your exact location, our solar production calculator will show you the amount of kWh of production you will get for a certain sized array of solar panels in your zip code. Our database has solar irradiation data for each zip code in America.

 

Find out how much your solar system would produce!

 

house with solar panels and american flag

Seasons

The seasons have a significant effect on solar power production and the numbers quoted above as state averages are the averages across all days of the year. Average production would typically be much lower than this is winter and much higher than this average figure in summer. Here are the results for a 6kw array in Los Angeles demonstrating this:

9,496 kWh per year*
Month Solar Radiation
(kWh / m2 / day)
AC Energy
(kWh)
January 3.93 583
February 4.91 658
March 5.45 806
April 6.14 871
May 6.56 956
June 6.64 933
July 6.92 997
August 6.88 985
September 5.71 791
October 5.07 736
November 4.32 612
December 3.88 567
Annual 5.53 9,495

The tilt and direction of your roof

Because we live in the Northern Hemisphere the optimal direction for your array to tilt towards is south. As most residential systems are installed on an existing roof the roof orientation and the pitch (or tilt) are generally something you have to take as a given when designing a solar system.

However to the extent this orientation is away from south there will be some system losses. Here is the same data from above but this time the direction of the roof was southwest (45% off south):

9,288 kWh per year*
Month Solar Radiation
(kWh / m2 / day)
AC Energy
(kWh)
January 3.59 530
February 4.63 621
March 5.26 779
April 6.09 867
May 6.70 981
June 6.88 970
July 6.99 970
August 6.76 971
September 5.59 778
October 4.85 705
November 3.99 564
December 3.51 512
Annual 5.40 9,288

You can see from this that the change of roof direction from South to South West reduced solar electricity production by 2.2% over the year. If we change the direction of the roof to have the array facing directly west then there is an output loss of 10.9% when compared to a true south facing roof.

To see how this would affect your economics enter your details into the solar calculator below.

You should speak to your local installers about exact production at your specific location and given your specific roof orientation and tilt.

sun shinging on house

Sun Hours

The amount of electricity produced by each kW of solar you install is primarily a function of the solar irradiation that falls on your home or business. Solar irradiation is often measured in Sun Hours. To work out how many Sun Hours falls on each area, meteorologists measure the total amount of irradiation that falls on a place in a day (in mega joules). They then work out what this is equivalent to if it were converted to complete hours when there was 1000 mega joules per square meter of solar irradiation falling on an area, so if there was 500 mega joules falling on average over a 12 hour day then the Sun Hours would be 6. The reason this ties back into the output of solar panels is that solar panels are rated based on the power they produce with 1000 mega joules per square meter of irradiation falling on them.

Other factors affecting power output from your solar panels

Once we have the Sun Hours as a way of measuring the irradiation we can then work out the actual amount of power we will produce by allowing for the many factors that cause real world solar power systems to produce less than their maximum rated output. These de-rating factors include:

  • Inverter inefficiency - most inverters will lose 3-% of electricity in converting it from DC to AC
  • Cable Losses - small amounts of power are lost through resistance in the cables;
  • Dirt - dirt and grime on solar panels will reduce their real world performance;
  • Temperature losses - solar panels are rated based on what they produce at 25 degrees Celsius. As the cells in solar panels get hotter there is more resistance to the flow of electrons across the cells and so their power output reduces compared to when they are getting the same amount of irradiation at a lower temperature.

All up total losses due to these de-rating factors will generally be between 15-20% but when we are working out the real world power of a system we usually use a de-rating factor of around 20%.

person looking at reports and graphs
house with solar using lights at night

Can I cover all of my electricity needs with solar?

There is a significant difference between a grid connect solar system and a stand alone solar system in terms of how they work and what they can do for you.

With a grid connect solar power system there is no batteries and so you can only use your solar electricity if you have an electrical load requiring it at the instant that solar power has been produced.

What this means is that a grid connect solar system cannot provide for your electricity needs at night when there is no sun shining on your panels to generate electricity.

However, that is not to say that a grid connect solar power system cannot meet all of your power needs from an economic standpoint.

Over 30 states now have a net metering law which allows a customer to bank up credits for excess solar that are exported to the utility grid during the day, and then use these credits at night or other times when the sun is not shining and their solar system is not producing electricity.

This law allows consumers with solar systems to get around the fundamental problem they have that electricity is instantaneous and that electricity usage patterns don't necessarily align with solar electricity generation timing.

Essentially, Net Metering law means you can economically cover all of your electricity needs even if you can't physically produce electricity at all times you need it.

In states that have net metering most customers will aim to install a solar power system that will produce the same amount of kWh annually as they consume. This will leave them with something close to a zero electrical bill (other than some fixed charges from some utilities) in states with 1 for 1 net metering.