Developing Site Plan Drawings

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The following discussion is from a recent thread on SolarPro’s technical forum. Visit to post questions or join the conversation.

Original post from Marvin Hamon, PE:

For nonresidential PV projects, where do you start with your site plan drawing to show the location of PV equipment? Do you start from a blank page, or is there usually an existing site plan showing the property lines, buildings, roads and so forth that you can use as a starting point?

REA: Ideally you contact the developer or architect and acquire CAD files. If CAD files are not available, you try for PDFs. You can then scale the PDF using a known measurement of an object, such as a roofline, parking space line or HVAC unit. If you have not been on-site to obtain a measurement, you can use the free measuring tools available on Google Earth and Google Maps; we have found them to be accurate enough to produce correctly scaled images. We also use the Pictometry ( fee-based service. It’s about as accurate as the Google services but has a much larger tool set, including a way to obtain roof slope and building height. It’s not cheap, though, running about $20 per 10 minutes of use.

If no PDFs or CAD files are available, grab a satellite image of the site and scale it using the method described above. We have found images from Pictometry to be higher resolution than those from Google. Trace the objects in the satellite image to produce the site plan.

You can also do tax lot map searches through the local assessor’s office and obtain PDFs of the site that show the property lines with their headings and lengths. Sometimes the buildings are even shown on these maps.

SteveL: REA pretty much covered it, but we primarily use Google Earth for basic layouts. If we get to a point where we are submitting to the township for land use, we go out and have a surveyor survey the land.

Marvin Hamon: Thanks, REA and Steve. It seems like getting the actual property boundary lines would be the hardest part. For a permit package, how accurate do the locations of everything in the site plan have to be?

SteveL: That depends on your AHJ. In Massachusetts and New Jersey, you pretty much have to provide sealed plans from a surveyor showing locations of everything (usually including trees), and they need to be very accurate. Typically, you can do changes and provide an as-built copy at the end of the project as long as you’re not violating setbacks. If your township has aesthetic requests, it can be a different ballgame.

On one project in New Jersey, a member of the Land Use Board expressed much dismay and disgust at an inverter location. He didn’t want to drive down the major road, look to his left and see an ugly inverter located next to an industrial warehouse. He was one of two who voted against the project at the end. (It still passed, though.) I might have a very biased opinion, since I’ve been told the three worst states for land use are California, Massachusetts and New Jersey.

Marvin Hamon: REA, I had a Pictometry demo the other day and it looked more useful than Google Earth. What has your experience been with it? Have you been using it for design layout or just for site qualification? Are you doing an on-site evaluation to make sure Pictometry got it right?

Ryan: Marvin, John (handle REA) is out of the country right now, so I’ll do my best to answer on his behalf. We have been very happy with the quality of Pictometry. We wish there were some different subscription options, though. We have been using it for design layouts, typically with someone verifying dimensions on-site. The ability to get a clear look for initial assessments has been very helpful. But overall, the measurements have been accurate and reliable.

TennesseeSun: Is an “as-built copy” a record of the changes and revisions to an original set of prints? Is creating this a common practice and do most contractors do this?

Marvin Hamon: The as-built drawings show how the system was actually installed and reflect any changes made to the design during installation. If as-built drawings are not produced, the client will not have a record of how the system was actually installed. Unfortunately, many people see as-built drawings as a waste of money, so it is not always done. I’ve gone into many projects and requested drawings of the existing electrical system only to find that the most recent drawings bear little resemblance to what is actually there. It’s not uncommon for me to have to produce as-built drawings for the existing system just so I can add the PV system to them.

SteveL: It’s not a waste of money. Sadly, some of my company’s first projects didn’t have very good as-built drawings. I’ve gone out to a couple of them for O&M, scratching my head and wondering what’s going on—what’s there doesn’t match my plans. A couple of drawings with red lines marked up from the contractor take no more than an hour to generate, and it takes about 15 minutes to update the CAD files.

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