Making a Solar Map

If soil testing weren't enough of a good time, I am also preparing to create a solar map for the two potential building sites on the property I am attempting to purchase. What is a solar map, you say? A solar map is an important tool for anyone planning to use solar design in their building project. It can also be informative for people purchasing an existing home or for people interested in determining the feasibility of passive solar "fixes" in their existing homestead. It is also important for people trying to determine the best place on their property for a garden. There are all kinds of uses for a solar map. It is also tons of nerdy fun.

The solar map provides two very important pieces of information. First, it lets you know where the sun is in the sky at different times of day on different days of the year. It also tells you what and when different features in the landscape obstruct the sun from the area on which you are focusing. I learned about solar mapping by reading Building Green (2009) by Clarke Snell and Tim Callahan. This book is highly recommended for anyone interested in eco-friendly methods of building.

The first step in the process is creating your own graph for the mapping. If you are going to do it manually, you will need some graph paper. The horizontal axis will represent the east to west orientation (azimuth). The vertical axis will represent altitude. Intervals will be marked at 20 degrees. On this graph, you will mark the azimuth and altitude of the sun as it passes through the sky each hour on at least the summer and winter solstices. Now, don't freak out. You don't have to be a math or astronomy wizard for this. You just need Internet access.

This website will provide you with an altitude/azimuth table for your location. You just need to Google your latitude and longitude using your zip code. Below is an example table:

Astronomical Applications Dept.                                                U.S. Naval Observatory                                                         Washington, DC 20392-5420                                                      NASHVILLE, INDIANA                                                                o  ,    o  ,                                                                W 86 15, N39 13                                                                Altitude and Azimuth of the Sun                                                Jun 21, 2012                                                                   Eastern Standard Time                                                                          Altitude    Azimuth

h  m         o           o 

05:00       -3.9        55.2 

06:00        6.3        64.6 

07:00       17.0        73.3 

08:00       28.3        81.8 

09:00       39.9        90.8 

10:00       51.5       101.5 

11:00       62.4       117.0 

12:00       71.4       144.3 

13:00       74.0       190.9 

14:00       67.9       229.8 

15:00       57.8       250.6 

16:00       46.5       263.5 

17:00       34.9       273.3 

18:00       23.4       281.9 

19:00       12.3       290.4 

20:00        2.0       299.3 

21:00       -8.0       309.2

Astronomical Applications Dept.            

h  m         o           o                                              

08:00       -1.0       119.9 

09:00        8.6       129.9 

10:00       16.7       141.2 

11:00       22.9       154.3 

12:00       26.6       168.9 

13:00       27.3       184.3 

14:00       24.9       199.4 

15:00       19.7       213.1 

16:00       12.4       225.3 

17:00        3.6       235.8 

18:00       -6.7       245.1

Once you have this information, you can start plotting it on your graph. 

If you are as lazy as I am, you can let an online calculator do it for you. Here are some online resources for that:

http://www.builditsolar.com/References/SunChartRS.htm 

http://solardat.uoregon.edu/SunChartProgram.html 

When all is said and done, you should have something that looks similar to this:

This concludes Part I of Solar Mapping. We'll address mapping of landscape features another time.