Site Assessment for Solar Hot Water Heating Systems

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

This piece originally appeared in Home Power Magazine | Vaughan Woodruff, 2/2014

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.

How will the building’s orientation and architecture impact collector placement? Some buildings are perfectly situated for a roof-mounted collector array. Others may require a wall- or ground-mounted array. These approaches may affect system cost and performance.

How is the water currently heated? Almost all SWH systems are integrated with water heaters powered by electricity, propane, natural gas, or oil. The type of auxiliary heat used with the SWH system will have a significant impact on the type of tank that is appropriate.

How many people live at the home? Since the production of a SWH system is dependent upon household hot water consumption, it is important to gauge whether the household uses enough hot water to justify the expense.

How much money is currently being spent for water heating? Throughout its history, the solar industry has been driven by competing energy costs. If a system has the potential to save its owner a bunch of money, this is a huge benefit. By determining the costs of water heating, a professional can also more precisely estimate the average hot water use for the household.

Some prospective clients have done their homework, identified the system type that best fits their desires, and have a good sense of the system costs. Others might simply be interested in “going green,” becoming more self-sufficient, or reducing their energy costs. In all cases, the professional should visit the site to verify the conditions before proceeding. If any homeowner interested in self-install has doubts, they would be wise to hire a pro to perform an initial assessment.

Powerful online tools are huge assets to the solar professional during this preliminary phase. Aerial maps and satellite photos from common online providers allow remote site observation. The building’s orientation, large trees or other obstructions that might cause shading, and roof space that might be appropriate can be identified. Street-level and isometric views provide greater detail for gathering as much information as is practical before visiting the site.

A site assessor can use these tools to observe barriers for installation. Had I checked remotely on the project mentioned earlier, I would have seen that the neighboring trees were a significant problem and been able to address this issue during the planning process, instead of after arriving on-site.

On-Site Assessment

Key details must be confirmed before selecting equipment and determining the system design. Some of these include:

How will the system be integrated with the existing heating system? The type of heating fuel is critical, as it affects tank selection and controls. If the existing heater is old or inefficient, it may make sense to replace it.

Will the SWH system also provide space heating? A system that provides space heating also increases complexity. Information is needed about the type of distribution (i.e., baseboard, radiant tubing, ducts, etc.), the efficiency of the building envelope, and the configuration of the current heating system.

Where will the equipment be located? The collector location can often be approximated without a site visit. Details such as the location of storage tanks, controls, piping, expansion tanks, and other components often require a site visit.

Will the storage tank fit? It is important to verify that a preferred tank will actually fit. In addition to checking that there is sufficient clearance, door widths are checked to ensure the tank can be maneuvered into place.

Will changes to existing systems be required? Existing plumbing or electrical code violations should be addressed before the new system is installed.

Are there any red flags? Some issues don’t lend themselves to remote observation. For instance, is the roof sound enough to hold a system for 25 to 30 years? Are there major code violations or safety concerns with the existing water heating system? Will there be significant extra costs due to the need for electrical upgrades or complicated piping runs?

Shading Assessment Tools

Another key detail that can be observed during a site visit is the impact of shading. A shading assessment may be required for local incentives such as state tax credits or utility rebates.

Handheld digital devices and smartphones can use apps such as Solmetric’s iPV (for iPhone; $39.99) and Comoving Magnetic’s Solar Shading (for Android; $16) to measure the amount of shading at a site. They can provide a reasonable shade profile for homeowners who don’t need a professional shading assessment tool for a single installation.

When I went out to the tree-shaded site mentioned above, all I had with me was iPV. After using it for a few minutes on the roof, I returned to the ground with a shading profile of the site. For 80% of the year, the roof received no sun. The architect arrived, and I attempted to tactfully address the situation. After introductions and a couple of clarifying questions about why I had requested her presence, I explained that the trees on the neighbor’s property were going to be an issue.

I discussed sun angles and the performance of shaded collectors while trying to restrain my inner-Mainer, who occasionally defaults to an unhealthy dose of sarcasm. The architect was initially skeptical of my assessment, until I pulled the iPhone out of my pocket and showed her the results.

Designed primarily for assessing PV sites, the Solmetric SunEye 210 ($1,995) is a handheld device that includes a fish-eye camera and a touch screen for operation. The site assessor can input information about the project, such as the collector’s tilt and azimuth and the site’s coordinates. Once this information is entered, the touch screen displays a view through the fish-eye lens, a digital compass, and a digital level. While the SunEye is level and oriented to true south, the operator captures the fish-eye image. The device then compiles the data, overlaying a silhouette of the obstructions on a diagram that illustrates the sun’s position in the sky throughout the year.

From this, the SunEye calculates the percentage of available solar radiation at the site during each month and over the course of the year. The calculations are presented almost instantaneously and can help an installer make decisions on the fly. For instance, the site assessor can modify the graphic by erasing trees to determine how tree removal would affect shading. Solmetric offers PV Designer software that syncs with the SunEye data to aid in solar-electric system design, but does not offer a comparable program for SWH systems. Instead, the data must be entered into separate solar heating modeling software, such as RETScreen, F-Chart, T-Sol, Polysun, or the Solar Pathfinder Assistant (SPA; see below).

The Solar Pathfinder (starting at $260) is a simpler device consisting of a plastic dome that overlays a sun-path template appropriate for the site. Once the device is leveled and oriented true south, the reflection of objects on the dome can be traced on the template with a grease pencil. Alternately, the Pathfinder can be aligned with magnetic south, and a photo of the reflection can be imported into the SPA modeling software. The software will automatically account for the site’s magnetic declination.

At the site, the assessor can manually calculate the shade derating each month by counting the shaded numbers on the template. Each sun-path on the template shows a number for each half-hour increment of the day. The numbers are the percentage of the day’s total solar radiation occurring during that half-hour window. During the middle of the day, when solar radiation passes through less atmosphere, it is more intense and the percentages are higher. In the early morning and late afternoon, the percentages are much smaller. The procedure is less precise and more arduous than with the SunEye, but gives the site assessor a fairly solid idea of the site’s potential.

Many solar professionals will qualitatively observe the reflections on the diagrams of the Solar Pathfinder to compare the shading at various locations around the same site. For accurate assessment, the site assessor will take a digital photo and import it into the Solar Pathfinder Thermal Assistant Software ($189), which allows users to input various details about the proposed system (number of collectors, collector model, collector tilt and azimuth, size of storage tank, etc.) and the hot water use in the home (i.e., average daily hot water use, delivery temperature) to estimate the system’s monthly and annual production.

Many states’ incentive programs require the use of the Solar Pathfinder or SunEye to verify that a project is properly situated and worthy of funding. Most solar heating professionals use one of these two tools for meeting these requirements and for quantifying the benefit of an SWH system.

Thinking Like a Pro

As you plan, you can take an approach similar to the pros. Start by using aerial maps and other online tools to get an idea of the site’s overall suitability. If you want more accuracy, consider investing in a solar siting tool. (Local organizations may have the shade-assessment tools available for the public to borrow or rent.)

If you are planning to install the system yourself and have limited knowledge of SWH, you will do well to use an engineered system that has received OG-300 Certification through the Solar Rating & Certification Corporation (SRCC) or the International Association of Plumbing and Mechanical Officials (IAPMO).

These systems have been reviewed and approved by a third party in accordance with national standards and are required to have thorough installation and operation manuals, alleviating some of the challenges that arise with installing and also integrating a new SWH system with your existing water heating system. Specifications for system equipment are included, which will help you determine where this equipment can be placed—or whether it will fit at all.

Finally, you could use the shading assessment to estimate the system output. You could make an investment in a Solar Pathfinder and Solar Pathfinder Thermal Assistant software, purchase another solar heating modeling software, or use free resources for estimating system performance (see “Methods“, in HP157).

These approaches are valuable for solar professionals, whose success depends upon providing productive systems for their clients and minimizing trips to the job site. For do-it-yourself projects, these approaches help prevent very unpleasant surprises and maximize the production of a solar heating system.

Vaughan Woodruff | Home Power Magazine, 2014

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