How Many Solar Panels Do I Need For 1000 kWh Per Month?
How Many Solar Panels Do You Need For 1000 kWh Per Month?
How Do I Calculate How Many Solar Panels I Need?
Here are the steps you need to follow to calculate the size of your solar panel system:


 Estimate your home’s energy usage in kWh per day
 Find the irradiance value in kWh/m2/day (peaksunhours) for your location
 Calculate the theoretical size of the solar system needed in kW
 Adjust the system size to account for losses
 Divide the final kW solar system size by the individual solar panel watts
 Add another 10% to account for periods of bad weather

A home consuming 1000 kWh per month would need 27 solar panels, each rated at 300 watts. This assumes an average irradiance of 4 kWh/m2/day (peaksunhours) and does not include PV system losses of up to 23%. Good practice is to add 20% to 25% more panels to account for system losses.
Video – How to calculate how many solar panels you need for 1000 kWh per month
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How Many Solar Panels Would I Need For 1000 kWh Per Month?
Every solar calculation begins with the load, in this case 1000 kWh. You begin by working out how many kilowatts of solar power would be needed, before calculating the number of solar panels.
It sounds easy, but there are a few things you need to know.
First of all, solar panels don’t put out the same power in every location – it depends heavily on the irradiance, or sun’s energy, in your geographic location.
Secondly, the theoretical power output from a solar panel array is never what you actually get! This is because there are losses in all solar power systems. These losses can be around 23% of the total output, so not insignificant.
Infographic – Solar Panel Sizing Takes 10 Major PV Losses Into Account
By far the biggest factor affecting solar panel output is irradiance, and this varies by geographic location.
The two worked examples following show the difference in the number of solar panels needed for a home using 1000kWh per month in San Francisco, Ca and Glasgow, UK.
How Many Solar Panels Do I Need For 1000 kWh Per Month In San Francisco, Ca?
 City: San Francisco
 Home energy use: 1000 kWh per month
 Solar system losses: 23% (same as multiplying energy needs by 1.4)
 Solar energy required per month: 1000 kWh x 1.4 = 1400kWh/month
 Solar energy required per year: 1400 kWh x 12 = 16800kWh
 Irradiance at San Francisco, Ca = 2089.1 Peak Sun Hours/year
 Solar system size required: 16800kWh/2089.1 PSH = 8.042kW
 How many 300 watt solar panels required?: 8042 watts/300 watts = 27 solar panels
What is the solar system payback period in San Francisco?
Installation costs for a solar power installation in SF is about $2.5 per kW, so the cost of an 8.042kW system would be about $20000.
In the calculation below, I’ll work out how many years it will take to recover that capital cost:
 San Francisco residential electricity cost per kWh = 25.7 cents/kWh
 Yearly savings = energy usage x electricity cost = 12000kWh x 25.7 = $3084/year
 Solar payback time San Francisco = solar cost/yearly savings = $20000/3084 = 6.5 years
How Many Solar Panels Do I Need For 1000 kWh Per Month In Glasgow, UK?
There should be a big difference in the number of solar panels required in Glasgow, because the irradiance is much lower than in California – see the screenshot from GlobalSolarAtlas.info below:
The Direct Normal Irradiation 678.8kWh/m2/year (also called PeakSunHours) in Glasgow is more than 3 times less than in California. Now let’s do the calculation again:
 City: Glasgow, UK
 Home energy use: 1000 kWh per month
 Solar system losses: 23% (same as multiplying energy needs by 1.4)
 Solar energy required per month: 1000 kWh x 1.4 = 1400 kWh/month
 Solar energy required per year: 1400 kWh x 12 = 16800kWh
 Irradiance in Glasgow, UK = 678.8 Peak Sun Hours/year
 Solar system size required: 16800 kWh/678.8 P.S.H = 24.75kW
 How many 300 watt solar panels required?: 24750 watts/300 watts = 82 solar panels!
Clearly, this is a huge difference and it probably isn’t worth it to install solar in Scotland.
How Much Power Does An Average House Use?
1000 kWh is not far off the US monthly average for a typical home, which is 900 kWh/month. This equates to about 30 kWh per day.
How Do I Calculate kWh?
It is possible to estimate a home’s energy needs in kWh, but it isn’t very accurate. You would have to add up all the wattages of ‘normal’ appliances (you’ll see what I mean by ‘normal’ later on in the post.)
You also need to guess how many hours per day a particular appliance would be used. As you can see, the approach isn’t too accurate.
What I call ‘normal’ appliances are those with a constant wattage i.e. you switch it on and it takes a constant amount of power in watts.
Some appliances aren’t like that. If an appliance uses a compressor, such as refrigerators, heat pumps, freezers and air conditioners (AC), then it isn’t so obvious what the average power consumption is.
These types of appliances run in cycles. That is, sometimes they are running, sometimes stopped and other times starting up. Compressor motors are subject to surge current.
For the above reason, it’s often difficult to estimate average watts. The best way is to simply take last year’s energy usage from your utility bill, which will be a good estimation of what you use.
Is 50 kWh A Day A Lot?
Yes, 50 kWh is quite a lot. The average home energy usage in the US is 11000 kWh per year, which is 916kWh per month or just over 30 kWh per day.
So 50 kWh is almost 1.7 times more than the US home average.
How Many kWh Per Day Is Normal?
‘Normal’ depends heavily on the kind and size of home you have, and the location.
Homes in very hot or very cold locations will probably use more electricity, expecially if using reversible AC units. The US average is about 30 kWh per day but the usage per state can vary wildly.
Table – Compare kWh usage per day for 20 US States
State 
Average kWh used per month 
Ave kWh used per day 
1211 
40 

632 
21 

557 
18 


723 
24 
1078 
35 

1088 
36 

1005 
33 

1273 
42 

551 
18 

1220 
40 

860 
28 

629 
21 

602 
20 

1205 
40 

1142 
38 

602 
20 

1124 
37 

1174 
39 

894 
29 
How Many kWh Does A Solar Panel Produce Per Day?
Solar panel output is determined to a great extent by the irradiance at a particular location. Once you know this irradiance value, it’s quite easy to work out how many kWh any size panel will produce each day.
Power output = solar panel size in watts x peaksunhours
Table – How many kWh does a solar panel produce per day in different locations?
City 
New York, NY 
Birmingham, UK 
Lisbon, PT 
Brisbane, AU 
Nairobi, KN 
Irradiance (peaksunhours/day) 
4.086 
2.165 
5.163 
5.275 
3.955 
100W solar panel output per year (kWh) 
149.1kWh 
79kWh 
188.5kWh 
192.5kWh 
145.8kWh 
100W solar panel output per day (kWh) 
408.6 watts 
216.5 watts 
516.3 watts 
527.5 watts 
395.5 watts 
How Much Does A 1000 Kw Solar System Cost?
Installation costs for domestic solar are reducing all the time, spurred on by healthy competition, but there are still differences between the US States. Here’s a list of several States, with average costs per solar kW installed:
Solar installation cost per kW installed by state




 Arizona – $3.61/kW
 Colorado – $2.44/kW
 Florida – $2.61/kW
 Idaho – $2.52/kW
 Kansas – $3.07/kW
 Maine – $2.88/kW
 Missouri – $2.96/kW
 New Mexico – $3.22/kW
 Ohio – $2.82/kW
 South Dakota – $2.39/kW
 Texas – $2.74/kW
 Washington – $2.69/kW



How Many kWh Does A 12kW Solar System Produce?
The exact amount of kWh generated by a 12kW solar power system depends mostly on the irradiance in the installation’s location.
How Many kWh Does A 12 kW Solar System Produce In San Francisco, Ca?
The irradiance value in San Francisco is 2089 peaksunhours per year, so the calculation is:
Energy generated 12 kW solar in San Francisco = 12000 x 2089 = 25.68 kWh per year (68.7kWh/day)
How Many kWh Does A 12kW Solar System Produce In Glasgow, UK?
In Glasgow it’s a very different story, as the irradiance is very low at 678.8 peaksunhours/year.
Energy generated by 12 kW solar in Glasgow = 12000 x 678.8 = 8.1246 kWh per year (22.3 kWh/day)
How Many Solar Panels Does It Take To Make 2000 kWh A Month?
This depends heavily on your location, because the sun’s energy varied according to geographic location.
For example, in Las Vegas the irradiation is 7.492 kWh/m2 per day, or put another way, 7.492 Peaksunhours. 2000kWh per month equates to 65.75 kWh per day, which is a lot of power!
The solar power required = 65,750 watthours/7.492 peaksunhours = 8.776 kW
How many 300 watt solar panels to make 2000 kWh/month in Las Vegas?
8776 watts/300 watts = 28 solar panels of 300 watts each.
How many 300 watt solar panels to make 2000kWh/month in London, UK?
London’s irradiance is 2.398 Peaksunhours, so the equation becomes:
The solar power required = 65,750 watthours/2.398 peaksunhours = 27.418 kW
As you can see, this is a massive difference!
Number of solar panels required = 27418/300 = 91 solar panels, each 300 watts.
Solar Panel Sizing Calculator – How Many Solar Panels To Run A House?
Table – How Many 300W Solar Panels Needed for Monthly Loads Between 300 Watts and 1500 Watts.
The following table assumes an average irradiance value of 4 peaksunhours and individual solar panel size of 300 watts.
Home load in kWh 
Number of 300 watts solar panels required (irradiance of 4 peaksunhours) 
How Many Solar Panels Do I Need For 300 kWh Per Month? 
8 solar panels of 300 watts each 
How Many Solar Panels Do I Need For 400 kWh Per Month? 
12 
How Many Solar Panels Do I Need For 500 kWh Per Month? 
14 
How Many Solar Panels Do I Need For 800 kWh Per Month? 
24 
How Many Solar Panels Do I Need For 700 kWh Per Month? 
20 
How Many Solar Panels Do I Need For 1500 kWh Per Month? 
42 
How Many Solar Panels Do I Need For 20 kWh Per Day? 
17 
How Many Solar Panels Do I Need For 100 kWh Per Day? 
83 