DIY Solar Site Survey

One of the most important steps when deciding to install a Solar Energy System is to determine whether your site has the appropriate solar resources available. Because, if the site does not have enough sunlight, then your new Solar System could be a large waste of money.

To Evaluate Your Site for Solar Energy, there are two questions that you need to answer:

  1. Does your location get enough sun?
  2. Do nearby obstacles (trees, buildings, etc) at your location block too much sun?

The first question is a simple, quick one to answer. Essentially, this requires only a little bit of research to determine how cloudy your weather is. The best resource for this is to use a solar resource map. Please see the USA Solar Map for the solar resources that are available at your location.

*please note that any level of 3 or above is considered acceptable for solar energy uses. However, the higher the number, the better your solar energy system will perform.

To answer question number 2 you will need to complete the following site survey. It can be a little time-consuming, but fun none-the-less. And, even if you are certain that you get good sun, please do a survey anyway…you may find some major surprises.

The Science: The path of the sun across the sky changes with the time of the year. This is why is it absolutely critical to do an obstacle survey for your intended solar site, and not just stick your head out the window and see if the sun is shining.

At the two equinoxes, the sun rises at due East, and sets due West. At Solar Noon on the equinoxes, the altitude of the sun is 90 degrees minus the local latitude. For example, in Denver, CO, with a latitude of 40 degrees, the altitude of the sun at Solar Noon on the equinoxes will be 90 degrees – 40 degrees = 50 degrees. The length of these days everywhere on the Earth is 12 hours, and they occur on March 21, and September 21.

The Winter Solstice is the shortest day of the year, and occurs on December 21 in the Northern Hemisphere, and is also the day of the lowest solar altitude at any given place.  On this day the sun will rise well South of East, and will set well South of West.  The solar altitude on this day is 23.5 degrees lower than it was on the Equinox.  Our Denver example looks like this:  50 degrees – 23.5 degrees = 26.5 degrees.

Conversely, the Summer Solstice is the longest day of the year, and also day of the highest solar altitude.  The Summer Solstice occurs on June 21 in the Northern Hemisphere, and on this day the sun will rise far North of East, and set well North of West.  The Solar Altitude for the Summer Solstice will be 23.5 higher than it was on the equinox.  In Denver, the Summer Solstice calculation looks like this:  50 degrees + 23.5 degrees = 73.5 degrees.  This is the highest in the sky that the noon sun will be all year.

When planning to install solar collectors it is important to ensure that the sun will be shining down on them during all parts of the year that you want it to.  This site survey is designed to make sure that that happens.

What you will need:

Please print out two copies of the Solar Elevation and Azimuth Guide. You will use both.

Step 1: Make the Elevation Guide

  1. Paste one copy of the Solar Elevation and Azimuth Guide onto a piece of cardboard
  2. Trim the cardboard along the Site Line (you will site along this edge for elevation measuring)
  3. Put a small nail through the reference circle where the lines meet
  4. Tie one end of a light string to the nail, and the other end to a small weight (a nut or bolt is fine)

Step 2: Make the Azimuth Guide

  1. Paste the second copy of the Solar Elevation and Azimuth Guide onto a piece of cardboard
  2. Find a thin, straight piece of wood ( a wood pencil) and drill a small hole near one end.  You will site along this pointer to measure azimuth angles.
  3. Put a small nail through the drilled hole, and then through the center of the reference hole

Step 3:  Doing the Survey

  1. Set up a reasonably level surface (card table) about where your collector will be
  2. Tape the azimuth guide to the table so that the 180 on the blue azimuth scale faces true south.
  3. Measure the azimuth and elevation angles for each of the high points along your horizon
    1. Start Northeast and work your way around through South to Northwest
  1. To measure the Azimuth Angle of an object:
    1. Site along the pointer you attached to the Azimuth Guide
    2. Move it till it is lined up with the object
    3. Read the Azimuth Angle where the pointer passes Azimuth Angle Number Scale
  2. To measure the Elevation Angle of an object:
    1. Site along the Site Line on the Elevation Guide
    2. Read the Elevation where the string crosses the elevation angle scale
  1. Mark each Azimuth and Elevation on the SunChart (see image below) by making a dot
  2. Draw your actual horizon line by connecting the dots together in a continuous line (see image below

Sun Chart

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