Find out how much electricity solar panels will generate for your home based on your location, direction and roof pitch
Find out how much electricity solar panels will generate for your home based on your location, direction and roof pitch
Last updated by Author Andrew Sendy
How much electricity do solar panels produce per day in each state?
Kilowatt hours (kWh) per Day per Kilowatt (kW) of solar panels installed
Choose your state to see the complete guide to installing solar panels
The map above showing kilowatt hours per kW of solar panel system capacity assumes a perfect installation facing due south, at an optimal tilt angle, and unshaded between 9am and 3pm. Click on your state to see our complete guide to installing solar panels in your state. You can calculate kWh per month by multiplying the average kwh per day by the monthly kwh multiplier in the table below if you want to know how many kilowatt hours a solar system installed on your home will produce in a specific month.
How much electricity does a single solar panel produce?
One way to answer this question is to look at the wattage of a single solar panel.
Residential solar installations typically use 60 cell solar panels that produce between 260 and 300 watts at standard test conditions. However, the wattage of the panel can be seen as the maximum amount it can produce and in practice standard test conditions don’t happen often and instantaneous electricity generated by a single solar panel is usually lower than its peak DC rating.
What most people want to know is how much a solar panel will produce over a year.
Given solar panels have different wattage ratings it is more convenient to answer this question by asking how much 1 kW of peak capacity of solar panels will produce over a year. This allows you to compare the electric usage on your electricity bill with the power output of a planned system to ensure it is the right size for your home. Given that net metering pays you retail rate for excess power it is then easy to calculate how many solar panels you need, whether you have enough square feet of roof space to fit them, and collect solar quotes from the best solar companies near you.
How does geography and location affect the amount of power generated by solar panels?
At the top of this page 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 while 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.
How does the kilowatt hours of electricity produced by solar panels change with the 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 6 kW array in Los Angeles demonstrating this:
| 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 |
How does the tilt and direction of your roof affect the kilowatt hours of power your solar panels will generate?
Because we live in the Northern Hemisphere the optimal direction for your array to tilt towards is south. To the extent your roof 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):
| 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.
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.
How much power do solar panels produce on a cloudy day?
There is no one answer to this question because to put it simply it depends on how cloudy it is. However, what we can say is this. Solar panels produce less electricity the more cloudy it gets because the clouds block some of the solar energy from reaching the panels. However, it can also be said that I have never seen solar panels during the day producing no power because of clouds. Usually the electricity production is reduced by around 60% in full cloud compared to what the same solar array would be producing in full sun.
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%.