How many square feet of roof space do I need to install solar panels?

How many watts of solar panels per sq foot?

How do I work out which parts of my roof I can use for solar panels?

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The aim of installing a solar power system for most people is to make a profit and provide for your electricity energy needs over the next 25 years in a more cost effective manner than relying just on grid power. The falling cost of solar power and the availability of generous incentives such as the Federal Solar Tax Credit and the Net Metering law make this possible.

To do this you would ideally maximize the yield you would get from your solar panels. However, one thing you can't change is the direction and tilt of your roof and the overall size of your roof space.

What you need to do is work out which parts of your roof will produce the most amount of power. Here is a "discussion on the factors affecting how much power solar panels will produce".

To sum this up solar power production depends on the geographic location of your solar panels and also the direction and tilt of your roof. You can see how much solar energy you will produce given your location, specific roof direction and specific roof pitch by using this "solar power production calculator".

It is quite okay to use parts of your roof for solar panels that produce less power than the ideal south facing unshaded roof but the important thing is to know how much the power output will be reduced by and then to work out if these solar panels being installed on a sub-optimal roof will generate enough power to make the investment worthwhile.

Remember your average rate paid for power is likely to be much more than the base rate you pay for power. The other thing to remember is that utility power will increase over time so your investment return will also increase. You may want to use a higher average power price to reflect this when doing this calculation.

You simply need to decide if you are happy with this return for each part on non-optimal roof space.


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How do I calculate how many square feet of suitable roof space I have for solar panels?

Once you have worked out which parts of your roof produce an acceptable power yield and return on investment by using the solar production calculator for each different roof segment you can then simply measure these roof segments.

You could jump up on your roof and measure these with a tape measure but it is much easier and much safer to measure these roof segments online. In 99% of cases an online measure is accurate enough to determine that a desired array of solar panels will fit on your roof.

Google Earth, Google maps and other online mapping websites usually have scale drawings and you can blow up a picture of your roof.

However, the issue with this is that you are measuring the flat horizontal segment of a tilted surface so that actual space available on the roof will be larger than what it measures in 2D.

The beauty of this though is that you know you will always have more room than the square footage you calculate from a 2D image and that if your array will fit within the square feet, you calculate by this method you will have ample room to install.

However, if you are trying to maximize solar panels on a given roof space you will need to take account of the slope of the roof. You can use basic trigonometry to work out the the size of the roof space once you know the horizontal area and the tilt angle of the roof.

man shrugging question marks
angled roof with solar panels

What affect does roof direction have on solar power output?

The direction and tilt of your roof have an effect on the amount of electricity that solar panels installed on that roof will produce.

You can use our Solar Production Calculator to see the amount of production you will get given your location, the direction of your roof and the tilt angle of your roof.

Includes local incentives


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