Residential Solar Site Measurements: Page 7 of 7

New Developments

Beyond initial performance verification at the time of commissioning, ongoing performance monitoring is becoming more important industrywide, especially when residential leases and performance guarantees are in play. “Performance guarantees are becoming the norm, but they create a problem. In the past, a program would verify the performance expectation only one time after construction,” states Kevin Wright, managing director of United Management and Consulting. “Under the new model with a PPA , performance is constantly evaluated,” he adds. “In the end, this means system design and accurate site analysis are much more critical. Installation companies are married to the project for life.” Clean Power Finance’s Myers echoes Wright’s comments: “Project underwriters are the new driver of best practices for financed systems and are accountable for maintaining prolonged system performance for the lifetime of the contract.”

To allow repetition of an on-site shade measurement years later, most likely by a different operator, it is critical to identify the precise physical location on the roof where each measurement was taken, since the solar access is different at different locations. Limitations of instrumentation accuracy and on-site measurement accuracy can both contribute to uncertainty in shade measurements. Dedicated shade measurement tools like the Solmetric SunEye are factory calibrated for precise operation of the camera and lens, as well as the compass and tilt sensors. The angle accuracy after calibration is typically less than 1° azimuth and 1° elevation. To facilitate accurate positioning of the shade profile skylines, the Solmetric SunEye measurement locations can be pinpointed on an aerial ortho image with the recent addition of a skyline-mapping feature, as illustrated in Figure 9. These measurements can be stored securely online and then used as a reference for future shade measurement comparisons.

Other Trends to Watch

In addition to the tools and techniques I have discussed, other trends and developments are having an impact on the industry and will continue to do so in the coming years. Tablet computers and smartphones are becoming more capable and affordable, allowing users to automate and simplify many tasks on-site, including data gathering, proposals, audits, inspections and other functions. Data collected on-site, including shade measurements and performance verification data, will increasingly be securely stored online in the cloud, allowing streamlined access by the appropriate stakeholders. The solar industry will likely continue to benefit from business models and tools that have been developed in the more time-tested construction market.

Due in part to the increased availability and sophistication of financing options, the residential solar market is expanding rapidly. With this expansion comes more focus on system performance and on costs at every point in the system life cycle. Powerful web-based tools are enabling remote preliminary evaluations of solar sites and, coupled with accurate on-site measurement tools, are giving installers the ability to find the right balance between cost, time, risk and ROI. Whether on-site, online or both, measurement tools and techniques are evolving at a rapid pace to help meet the needs of a dynamic industry.


Peter Hoberg / Solmetric / Sebastopol, CA /


Aerialogics / 877.623.7425 /

Bing Maps /

Bright Harvest Solar / 510.863.4786 /

Clean Power Finance / 866.525.2123 /

EagleView Technologies / 866.659.8439 /

Google Earth /

Google SketchUp /

Google Street View /

NREL (In My Backyard software) / 303.275.3000 /

Pictometry / 888.771.9714 /

Precigeo / 888.577.3244 /

Skelion /

SolarNexus / 510.842.7875 /

Solar Pathfinder / 317.501.2529 /

SolarTech /

Solmetric / 877.263.5026 /

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