Aerial Photo Based Solar Site Survey Service

Bright Harvest offers a solar site survey that is based on a model they build of your residence based on aerial photos.

The report provides suggestions on where modules might be placed, what sort of shading modules in each position will face, and gives estimates of yearly production.  The cost for the report is $150.

Mark from Bright Harvest offered to do a report on my house in order to see how it compared with our simple, manual site survey.  I took him up on the offer, and this page shows the results.


The Bright Harvest Report

This is the full solar site survey report for my house...

The report shows three potential PV array layouts for my house.   One is the ground mounted array that I actually use, and the other two are candidate roof mounted arrays.

Here are some highlights from the report -- click on the pictures for full size:

Bright Harvest PV module layout
Overview of house model and all three candidate PV arrays.

3D perspective of model.


Shading analysis
Shading estimates for each panel.

Tabular summary including monthly shading estimates and yearly output.

Some things that impressed me about the report:

- I was impressed by the fact that the report picks up shading due to the mountain range a couple miles to the East.  I did not tell them about these mountains, and did not expect the mountains to be considered, but they caught them and modeled them.

- I must admit that I had not considered that the dormer on the south roof slope would have a noticeable shading effect.  I should certainly have thought about this, but it shows how the report can bring out things that seem pretty obvious in hindsight, but are still easy to miss.

- I had not thought about using the south slopping roof on the north end of the house for collectors.



I had a few questions on the survey that was done for my house.  The questions and answers are listed below.  I was satisfied that the responses were complete and  made sense.

Will the survey typically pick up shading from something like plumbing vents that come up through the roof?

If a panel is partially shaded, is the output from the un-shaded part counted?  How do you handle shading from partial shading objects like deciduous trees?

There was one small shading event missed on the survey:
I'm not saying that this is even remotely a big deal as its a very minor amount of shading, but just wondering if: One should expect that maybe very subtle shading might be missed?  And, if someone alerts you to look for a hard to spot feature like this, will you try to include it in the survey?

I take it that if you do a survey for someone, and they point out that a significant shading item was missed that you would redo the survey for them?

I would just like to add that accuracy in production modeling is limited by a number of additional factors. For example, your module's 215W power rating comes with a -/+3% disclaimer. That's a 6% total range and there's no guarantee that your modules will average out to 215W. Conservative modeling practices suggest using the -3% figure for the whole system. The Enphase monitoring data you're using to compare against estimates also comes with a +/- range. Revenue-grade meters typically have to be at least +/-2% but non-revenue grade is typically +/-5%. Enphase doesn't explicitly state this in their manual but they do say that their low-voltage AC cut-off accuracy is +/-4% (pg. 18 of the M190 user manual). The NREL weather data used for the PVWatts simulation comes with a +/-10% disclaimer... and that's a best case scenario, if your weather site happens to be Class I. Class II and III sites have fewer sensors and fewer years of data gathering so they rely on interpolation and have higher uncertainty values. 

So, we do the best we can with the available data, extract every bit of information from each pixel of aerial image data and in the end the production estimate comes down to an overall accuracy of around +/-10%. 


To Use or Not Use

I would always recommend that you do our simple manual site survey first.  The big advantage of the hand survey is that you will gain a better understanding of how the sun interacts with your house and with the objects around it over all the seasons -- almost everyone finds some things they did not expect.  The hand survey will also make you more aware of what the potential shading issues with your house are.

If after doing the simple survey, you feel that there are still some uncertain areas, then its certainly worth taking it a step further.  Either using the Bright Harvest service, or building a SketchUp model yourself, or whatever is needed to make sure you understand the shading situation well.  One example might be the dormer shading on my house, which would be awkward to get a good handle on with the simple survey.   

Understanding shading is very important -- I get emails quite often from people who are surprised by shading impacts after the modules or collectors are already in place.  So, take whatever steps you need to to make sure you have a good handle on shading.

There is no question that the Bright Harvest survey adds value -- its just a matter of how the fee for the service fits in your budget. 

If you do decide to use the Bright Harvest service, I would be sure to think about any particular PV module arrangements you want them to consider, and to alert them to any shading sources that might be missed.  Providing them with pictures of your house is also a good idea.

I want to make it clear that I don't have any financial or other connection with Bright Harvest.

If you do have the survey done on your house, please let me know how it turns  out, and whether it was helpful (or not).

Free Tool

Bright Harvest also offers a free tool that works with Google SketchUp to help you with laying out PV modules on your roof using aerial photos of your house: 



December 15, 2011