Solar Site Survey

A thorough solar site survey is the first step you should take to ensure you will get the best performance from your new solar power system. If your proposed site is not suitable for installing PV panels, or if your system is not properly positioned during installation, you will not generate the electrical output hoped for. Below, we'll look at how to determine your site's potential for generating solar energy.


Solar Site Survey Checklist

Solar Site Survey ChecklistSolar Site Survey Checklist to Find the Best Location
(Source: ©catalby/Depositphotos.com)

Why a checklist? Because you will need to choose the BEST location for your PV panels. They must be positioned where they will receive the most direct sunlight. A south facing location is always best for getting the most amount of sunlight. That location may be the roof of your house or some clear, open space on the ground that offers an unobstructed view of the sun throughout the day, throughout the seasons.

However, before deciding on a final location, we need to examine several key requirements:

  • Local Planning

  • Solar Insolation

  • Shading

  • Orientation and Tilt

Complete your solar site survey with an open mind and take time to be thorough. You might be surprised at the results.

Local Planning Requirements for Solar

As the first step to evaluating your site, check into the local building codes, zoning ordinances, and possible subdivision covenants that might apply to your property. Most townships and municipalities have set policies governing the installation of residential solar power systems.

Aside from needing a building permit, you must comply with all existing building procedures. A visit to your local municipal building department could save you needless headaches later. Some issues that homeowners have encountered include:

  • Exceeding area and height restrictions on a ground mount system.

  • PV panels reflecting glare onto nearby buildings.

  • Ground mount system located in the font yard.

  • Rear yard access prevented by side yard obstruction.

  • Solar power system situated too near street and lot boundaries.

  • PV panels located on front slope of a roof that's visible from the street.

  • Solar array exceeds the roof load.

  • Lack of proper building permits.

  • Improper electrical wiring procedures.

Solar Insolation

Your geographic location can have a huge effect on the efficiency of your solar panels. Knowing the solar "insolation" value for your property will enable you to estimate the size and output of the PV panel array you'll need to meet the electrical needs of your family.

Insolation (short for "incoming solar radiation," also known as "solar irradiance") refers to the amount of solar radiation (heating) that hits the earth at any given geographical location.

It's an important concept in relation to solar panels because each solar electric installation is at a unique location on the planet's surface and receives a particular amount of sunlight that effects how much electric power it will be able to produce.

Think of it this way:

A solar array located in Juneau, Alaska will receive a different amount of sunlight than a solar array located in Denver, Colorado no matter whether it's June 31st or December 31st. This is caused by the angle of the sunlight reaching the earth at different geographical locations (latitudes) on the planet.

The insolation your PV system will receive will be a factor in determining the size (and the resulting cost) of the solar electric system you'll need to install in order to meet your desired energy needs.

But don't worry, you won't need to figure out your project's insolation value by yourself. Your government provides helpful maps that will quickly give you the insolation number that you need to plug into your calculations.

To find insolation values for the United States, use the maps provided by the National Renewable Energy Laboratory (NREL):

http://www.nrel.gov/gis/solar.html

To find insolation values for Canada, use the maps provided by EcoSmart™ that are based on monthly data from Natural Resources Canada (NRCan):

https://ecosmartsun.com/canadian-solar-maps-province/


To find insolation values for locations in other countries, search online for the words "solar maps," "insolation maps," or "solar radiation maps" plus the name of the country you are interested in researching.

Solar maps typically provide monthly average, daily global insolation (kWh/m2/Day) data. The insolation value to use in your calculations represents the solar energy available to a flat plate collector, such as a solar panel, oriented to true south at an angle from horizontal equal to the latitude of the collector location.

For example, by comparing the insolation table values to Denver's approximate location on the insolation map (see below), we can determine that Denver's average daily insolation value in December is about 4.0.

Solar Insolation ValueDetermining the Solar Insolation Value for Denver, Colorado
(Source: ©Don Bell)

Look for the PV Solar Radiation Static Maps that show "monthly" averages; that's because using a yearly (annual) average will give you incorrect values for the summer and winter extreme temperatures.

Always use the monthly average with the "minimum" insolation value, which is December's average for Canada and the United States. That way your estimate will be based on the "least" amount of the sun's energy available for your location, and your solar electricity system will be able to handle your family's energy needs even when the sun's energy is at its weakest.

Solar Window and Shading

Once you know your area's solar insolation value, you will want to find the best location on your property for your solar panels. You may be considering a rooftop installation or a ground mount system in your yard, but you cannot afford to decide until you perform a shading assessment. You must choose the location that has the least overall shade!

Shading can have the biggest effect on the performance of your solar power system. Shadows cast by trees, embankments, flag poles, and buildings vary in length and direction throughout the daylight hours, and from season to season. The longest shadows will occur in the winter months when the sun has a lower path in the sky.

You must conduct a physical site inspection, preferably with a Solar Pathfinder. Track the shade impacts monthly and to be absolutely sure, track the four corner locations of your proposed PV array to determine the average amount of sunlight falling on the entire array. You wouldn't want part of your array left in the shade and under performing.

Professional Solar Site Survey Tools

Professional installers use solar site survey tools such as the Solar Pathfinder and the Solmetric SunEye to determine the most efficient location for a PV array by analyzing the "solar window" — the average amount of sunlight falling on the site during hours of daylight.

Solar PathfinderSolar Pathfinder for Analyzing the Solar Window
(Source: ©Don Bell)

For example, the Solar Pathfinder features a built-in compass and level, so it can be properly aligned to the true south. By using a highly reflective transparent dome to mirror the surrounding area, all structures, trees, and other obstructions causing shade appear as a visible reflection on the dome.

The horizon outline that's reflected on the dome can easily be traced on a sun path diagram beneath the dome for study later, or it can be photographed for a detailed solar analysis online.

Watch the following YouTube video, as homeowner demonstrates how to use a Solar Pathfinder to identify the best location to install of a solar power system.


Common Solar Site Survey Methods

Less costly solar site survey tools are readily available online as apps for smart phones and tablets. While not as accurate as the professional tools, they can indicate where a potential solar window is likely to be found. Simply use the words "sun path" or "solar orientation" to search for mobile apps.

Sun PathSun Path on August 28 at 2:17 PM
(Source: ©Don Bell)

You can also use simple observation to confirm your solar site survey. Visit your potential site in the early morning, noon, and late afternoon once each month throughout the year, and watch where the shadows fall. Photographs can prove helpful for analysis later, as you consider the location that sees the most direct sunlight for your solar project.

Solar Site Survey ObservationsObservation of Shaded Areas for Solar Site Survey
(Source: ©Don Bell)

For example, the above photo was taken on September 9th at 2:30 PM. Note the heavy dew remaining within the shaded area, whereas the northern half of the field is now dry thanks to the warming rays of the sun. Therefore, a solar array installed in front of the stand of cedars has the potential to perform well.

Orientation and Tilt

Now that you've decided on the best location for your panels, they need to be installed at the optimum "azimuth" and "tilt" to produce the best results.

Azimuth refers to the orientation of the panels, the degree of southerly direction they face, whereas tilt refers to the angle of their surfaces in relation to the sun, 90 degrees being optimal. These measurements can be determined by using simple tools that are readily available to homeowners.

Azimuth

An array's orientation is best referenced to true south. Depending on your geographic location, you cannot always depend on a compass needle to point to true south. You need to consider the "magnetic declination," the angle between magnetic north/south and true north/south.

Visit the National Centers for Environmental Information (NOAA) site for an online Magnetic Field Calculator. To use the tool, simply look up your country and your nearest major city to discover your latitude and longitude. The calculator will enter those values and give your estimated magnetic declination.

Magnetic DeclinatonMagnetic Declination for Toronto
(Source: Don Bell)

By using a simple compass and knowing your local magnetic declination, you can determine the orientation of your roof or yard to true south and the sun's path. Obviously, most house roofs in North America do not face true south, but as long as yours lies within 30° to 40° of true south, it will still offer good potential for generating solar energy.

Tilt

Most rooftop solar installations are mounted directly on the surface of the existing roof to minimize the hazard of wind load and the homeowner's concern for appearance. Therefore, the fixed pitch of the roof will determine the array tilt.

Clinometer Roof Pitch Measurement19° Roof Pitch Measured by Clinometer App
(Source: ©Don Bell)
Degree of Roof Pitch19° of Roof Pitch

The degree of pitch can easily be measured using your tablet or smart phone and a "clinometer app" that measures slopes. Simply lay your mobile device on the roof and read the degree of pitch. The slope measurement obtained will be accurate enough for your purposes.

The optimal tilt is often not critical for most homeowners. Having your photovoltaic panels flush mounted on an existing roof that's facing true south will bring them close to their optimal annual output. As an added benefit, the leaves, ice, and snow tends to slide off.

Significant money can be spent on making a rooftop array adjustable for tilt, but such costs are unlikely to be reclaimed by the negligible increase in output. Extra money is best invested on installing additional panels.

For ground mounted systems, the rack can be fixed or made adjustable for the optimum tilt. Since the path of the sun is lower in the winter months and higher in the summer months, manually adjusting the tilt twice a year can offer a notable boost in energy output.

Seasonal Track of SunSeasonal Tracking of the Sun, Peterborough, Ontario, Canada
(Source: ©Don Bell)

Visit the Optimum Tilt of Solar Panels site for orientation information and tilt reference tables to help you to determine the best angle from horizontal to tilt your solar panels given your latitude. You will find this information quite helpful for your solar site survey.

Choosing the Solar Site Location

Solar Site LocationSite Location for Ground Mount Solar Power System
(Source: ©meodif/Depositphotos.com)

As outlined above, where you install your solar panels requires careful consideration. They need to be positioned on the side of the property that receives the most sunlight year-round. For North America's northern climate, this means the panels should be installed on the south-facing side of your house or yard. Similarly, the north-facing side of the house should be considered for homes located in southern climates.

Most residential solar PV systems tend to be installed on the roof to provide the most shade-free exposure to the sun. Roof installations are often essential in built-up areas where smaller yards are the norm and access to the open sky is often obstructed. However, if your roof isn't southerly facing, this might not be the best location for your panels. If you have an adequate sized yard, it might provide the better option.

The key is in making sure you face the PV array for optimum sunlight, the best solar window possible. This will ensure it collects as much of the sun's radiant energy as it can and work as efficiently as possible. To be clear, solar panels work best when they have an unobstructed view of the sun and are pointed directly at it.

The solar energy your panels collect is directly related to their position (orientation) and angle (tilt) to the sun. Ideally, a pole mounted solar tracker system with its rotating mounts will allow your panels to follow the daily path of the sun from horizon to horizon so that sunlight always shines on the face of the panels.

Many homeowners choose the less costly option by installing PV panels on the ground, either mounted on a raised pad or elevated on a sturdy support structure. These panels are fixed in the "optimal" tilt and azimuth to gather the most potential energy, or they can be made so the tilt can be adjusted manually, depending on the season of the year.

Everything depends on the solar panels gathering the maximum sunlight that's available. Thanks to recent advances made in solar cell efficiency and a careful solar site survey, PV systems are more efficient today than ever before.

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