Site Assessment for Solar Water Heating Systems

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Proper planning is important to maximize system performance.
Ideally, solar thermal collectors should be positioned to get full sun between 9 a.m. and 3 p.m. solar time. Proper planning is important to maximize system performance.
Street-level view
Street-level views can assist with identifying site-specific characteristics, such as roof type and roof slope, and potential shading issues.
Aerial photo
Aerial photos from online maps can also be used to spot potential shading issues. In addition, they can help the assessor determine the building’s orientation.
Solmetric’s free online Roof Azimuth Tool
Solmetric’s free online Roof Azimuth Tool can calculate a roof’s orientation angle with two clicks of a mouse.
Fitting additional solar equipment into an existing utility room
Fitting additional solar equipment into an existing utility room can be a challenge and may affect system design.
replace damaged or old roofing
Since an SWH system is designed to function for at least 20 years, it may be best to replace damaged or old roofing material prior to the system’s installation.
Solmetric’s iPV app
Solmetric’s iPV app offers a sample shade analysis for a site in San Francisco showing a 20% annual loss due to shade.
Solmetric’s iPV app
Solmetric’s iPV app allows users to trace obstructions on-screen to determine the site’s effective skyline.
Solmetric’s SunEye
Solmetric’s SunEye is a digital interface that provides detailed information about a site’s solar access.
Example SunEye Site Data
Solmetric’s SunEye is a digital interface that provides detailed information about a site’s solar access, expressing it as a monthly, biannual, and annual percentage.
The Solar Pathfinder’s Sun Trace Wizard
The Solar Pathfinder’s Sun Trace Wizard allows users to trace the shadows of obstructions from a digital photo, and then calculates monthly solar access.
The Solar Pathfinder solar assessment tool
The Solar Pathfinder solar assessment tool can be used manually (users trace the outline of obstructions reflected on the plastic dome onto the black sun path diagram) or an image can be imported into software for automated calculations.
Proper planning is important to maximize system performance.
Street-level view
Aerial photo
Solmetric’s free online Roof Azimuth Tool
Fitting additional solar equipment into an existing utility room
replace damaged or old roofing
Solmetric’s iPV app
Solmetric’s iPV app
Solmetric’s SunEye
Example SunEye Site Data
The Solar Pathfinder’s Sun Trace Wizard
The Solar Pathfinder solar assessment tool

Without a proper site assessment, you may be putting your solar thermal system at risk for poor performance.

It is a fairly common occurrence for a solar professional to hear from a potential client, “We get tons of sun,” or “Our roof faces due south,” and then discover that the site is not nearly as ideal as the homeowner’s optimistic assessment.

Several years ago, a general contractor contacted me about a project that was nearing completion. His company had gutted a home and was finishing the retrofit designed by a local architect. Our meeting contained a bit of immediacy on his part. I then proceeded to make a decision that betrayed every lick of common sense I had—I committed to the job, site unseen.

I ordered the equipment specified in the design plans and planned two days at the end of July to complete the job. After a stop at the supply house and a long drive, my crew and I arrived at the job site around 10 a.m. As soon as I stepped out of the truck, I began to regret taking the job.

I peered up at the south-facing roof—and noticed nothing but shadows. Several 70-foot-tall trees were shading the roof. To make matters worse, the trees were on the neighbors’ property.

Initial Info Gathering

Given that solar water heating (SWH) collectors provide heat for domestic hot water and sometimes for space heating, it is vital that they are appropriately positioned. And part of that is assessing any shading impacts that might occur during the service life of the system.

A thorough site assessment helps identify any site deficiencies, such as a sagging roof or plumbing code violations, and is used to determine how to integrate the SWH system with existing water heating appliances. Homeowners putting in their own system can observe the site over long periods. A solar professional typically has less than an hour to get it right.

A solar heating system site assessment typically begins long before an installer or salesperson sets foot at a prospective job site. This process begins during the first communication, when a solar professional asks for information:

What type of project is the customer considering? It is important to determine whether the system is for heating domestic water, supplementing the customer’s space-heating system, or heating a swimming pool.

What are the primary reasons for this project? Customers inquire about SWH systems for a variety of reasons. Perhaps they want to reduce their energy costs, gain greater energy independence, or reduce their household’s carbon emissions. Professionals assess these motivations to determine the best approach to take with their prospective clients.

Where is the prospective site? Determining the exact location of the site helps a solar professional make preliminary assessments on particular design challenges, such as nearby obstructions that may cause shading.

Is there shading that might affect siting or require tree removal? It is good to have a discussion about the impacts of or possible remedies for trees or adjacent buildings that will have a significant impact on system performance. At times, this can be a deal-breaker.

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