Use Google Earth to Size Your Solar System

Posted by admin on January 13, 2009

Using Google Tools for Estimating Solar Installations Tutorial

Want to know how much solar you can get on your roof without breaking out the ladder and tape measure? Google Earth is the perfect tool for estimating how much solar you can get on your roof. And, best of all, from the comfort of your desktop of laptop.   I have used Google Earth along with Google Sketchup to produce very accurate reports for companies and municipalities that wanted to know EXACTLY how many Photovoltaic panels they could get on their rooftop or vacant land.

How accurate is this?  I was talking on the phone one day with a PV installer that happened to mention he had just got back from sizing a solar system for one of his clients.  He was telling me that he is getting too old to be going up and down the ladders all the time just trying to get information to bid out a PV system.  I thought this was a perfect time to test my system.  I asked him what the address was of the building he had just measured.  While he was still on the phone, I looked up the address and measured off the roof space, did a little math and said,” It looks like you can get 52 KW on that roof.”

He came back with “What?  Have you already put a bid in on this building?”  He had come up with 51.6KW.  He worked directly on the roof using his measurements.  I was in my office using a satellite through Google Earth.

So, here’s how you do it. Just click on the images to enlarge them.

Step 1.
Download and install Google Earth.  It is free.  http://earth.google.com/ If you already have Google Earth, then go ahead and open it.

	Step 2. In the upper left-hand corner insert your address into “Fly Me,” then click the little magnifying glass and Google Earth will fly you to your address of choice.
	Step 3. Now that Google Earth has found your address, it is time to zoom in.  You can zoom in by double clicking the screen.  Zoom in as close as you would like.  Unfortunately, Google Earth is bound by the military to only allow only a satellite image from a certain height.  You can still zoom in, it just won’t be a clear as you would like.
	Step 3. Now that Google Earth has found your address, it is time to zoom in.  You can zoom in by double clicking the screen.  Zoom in as close as you would like.  Unfortunately, Google Earth is bound by the military to only allow only a satellite image from a certain height.  You can still zoom in, it just won’t be a clear as you would like.
	Step 4. Now that you have your home or building zoomed in, click on the Ruler in the top tool bar. Here you will have a choice of options which I’ll set out as follows:
	Step 5: Pick-Line then-Feet Note: Google Earth Pro has the ability to measure square footage.  With the free version, you have to do the math yourself.
	You will notice you now have a little box with dashes on the side.  This is your measuring tool.  Place the measuring tool on your roof and hold the left mouse bottom down while you move horizontally across the roof.  You will see the distance in feet.
	(Our example has 165.43 feet.) Now, hit the clear tab and lets do this again vertically.
	You can see that in our example we have 215.19 feet. Now this is where a little math comes in.  It is really simple.

You multiply your horizontal figure by the vertical figure to get your square footage.  I always round the numbers down to make it easier.

(Example:  165 ft X 215 = 35475 Square feet)

Now the rule of thumb in the solar industry today is that you get plus or minus 10 watts per square foot. So, we take the square foot and multiple it by 10 watts.
(Example: 35475 sq ft.  X 10 w = 354750 watts) 
A kilo watt is 1000 watts. So Divide 354750 by 1000.
(Example: 35470 / 1000 = 354.74 kilo watts)

The building in this tutorial has room enough for us to place 300 kilowatts on the roof.  This does not mean the roof can physically hold this weight; it just means that you have the potential.

There are quite a few factors you have to look at besides having the room to put 300 KW on a roof.

In the next tutorial I will show you how to use Google Sketchup to place panels on the roof.  Sketchup is also a wonder tool for finding shading problems.

If you have questions, just place them in the comments as I will answer all that I can.