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What Makes a Good Solar Site?

Before anyone installs a solar system on their home or property, the question first crosses their mind, “Do I have a good site for solar?” Although designing a great solar system requires expertise, figuring out if you have a good solar site is really simple. Many solar installers will offer free site assessments but it doesn’t hurt to take a look for yourself. The three basic factors to look for when determining whether you have a good solar site are:

  1. Orientation
  2. Tilt
  3. Shading

Orientation

“Orientation” simply means the direction your solar system is facing (i.e. north, south, east, west). Here in the northern hemisphere, the basic design rule is that you want to point your solar modules due south. In the southern hemisphere, it is opposite so there they point their modules to the north. If your house has a big south facing roof, that bodes well for your future solar installation. Even if your roof faces southeast or southwest you will only lose about 5-10% of the production you would achieve from due south. If your roof face is pointing east or west you will lose 15-20% of the production you would obtain with south facing modules so may want to consider a ground mounted system in that case.sunpath.png

Tilt

The “tilt” of your solar array is the angle between your solar modules and the ground. Solar modules at a tilt of 0 degrees would lie flat on the ground (i.e. horizontal) while a module at 90 degrees would be straight up and down (i.e. vertical). Since the sun’s path changes throughout the year and your modules produce the most electricity when hit directly by the sun’s rays, it is best to have your modules tilted at an angle in-between 0 and 90 degrees. The optimal angle to tilt your modules is equal to your latitude in the northern hemisphere. Chicago, Illinois is at 42° N latitude while Dallas, Texas is at 33° N latitude which means a solar module in Chicago should be tilted at 42° while a module in Dallas would perform better over the year tilted at 33° (see diagrams).

lat-long-us-map.jpgtilt_and_orientation_angle4.jpg

Solar-Array-Tilt-Angles-300x141.jpgIf the solar module is going to be fixed throughout the year and you want maximum overall production, set your solar module tilt angle to your latitude. If your solar module is movable for seasonal variation you can achieve higher production by raising the module more towards vertical in the winter and laying it more flat during the summer (see diagram).

array_orientation.gifNormally you will install your solar system flush with your roof so you will not be choosing your tilt angle unless you are installing a ground or pole mounted system. If your roof is not tilted at the same number of degrees as your latitude in the northern hemisphere, don’t worry, the loss in production due to small tilt variation is minimal. Here is a chart that shows you what percentage of optimal production will be achieved based on different orientation and tilt angles for a site at 35° N latitude.

Shading

Is your potential solar site completely without shade from trees, chimneys, surrounding buildings, etc? It is important to do a shade analysis of any potential solar site since it can be surprising what ends up being shaded at different times of the year. Although you can get a good idea by a cursory site examination, it is important to be forward thinking and plan ahead. What if those trees that are currently 20 ft tall are at 40 ft in 15 years?

There are two specially made tools which solar professionals use for shade analysis in site assessments. The Solmetric SunEye and Solar Pathfinder are both widely accepted as industry standard professional shade analysis tools. By using one of these devices, a solar professional will be able to position your system so that shade will not be an issue and there won’t be any surprise shadows at different parts of the year.Solmetric_SunEye.gifSolar_Pathfinder.jpg

                Solmetric SunEye                                                                       Solar Pathfinder

Part of the reason it is so important to do shade analysis is that any shading of a solar module or array can disproportionately affect output. If you shade 25% of a solar array the output could go down as much as 75%. Although shading concerns can always be mitigated by the use of microinverters, when you make an investment in a solar system you want to make sure it produces as much energy as possible throughout the year.

 A Few Other Factors

  • Roof Age and Material
  • Electrical Service and Utility
  • Current Electricity Price
  •  Available Incentives

Ideally you have a large south facing roof, pitched at your latitude in the northern hemisphere, and it is shade-free year round. If you’re home or property has passed the orientation, tilt, and shade tests you can begin looking at a few other factors to help decide on the right solar system.

How old is your roof and what type of a roof is it? Will you need to replace your roof in the near future or did you recently get a new roof? Installing a solar system at the same time as you replace your roof is a great idea so that they can have similar warranty lives. If you are going to need a new roof in the near future, you may want to wait to do the solar install at the same time, but if you recently got a new roof within the past 5 years this will probably not be a concern for you.

The solar installation on your home will be connected to your electric service panel and will back-feed your current electrical service. It is important that there is room on your panel board to place a 2-pole breaker for the solar system. In addition to the physical space your electrical service also needs to have the electrical capacity to take on the power produced from the solar system. A solar professional will be able to determine all of this for you and should also be able to fill out any paperwork required by your utility for interconnection.

The financial analysis of your solar investment is a very helpful tool that can assist you in your decision making process. When looking at the numbers you will take into consideration the price you currently pay for electricity, the price of the solar system, the expected production of the solar system, and any available incentives for a solar installation in your area. All of these factors are important but as long as you work with an experienced solar installer an ROI analysis should be provided for you.

Bill Ehrlich is a Mosaic blog contributor who works in the electrical industry. After graduating from Notre Dame with a degree in Finance he worked on a cattle ranch in Wyoming and then taught English in China. Returning home to the States he worked at Inovateus Solar, a solar integrator in South Bend, Indiana. Originally from Minnesota, he is currently getting his hands dirty doing electrical construction in the city of Chicago. Outside of work Bill enjoys investing, solar power, and most of all, investing in solar power!




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