Introduction. How to Define an Array. Technical Bulletin 0012

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1 Technical Bulletin 0012 January 2014 Technical Bulletin 0012: Arrays and Shade Measurement Author: Chris Sommerfeld - Field Operations Manager This technical bulletin defines arrays and how to measure shade per array to ensure accurate performance estimates. Introduction One of the critical inputs to accurate PV performance modeling is shade. Sunrun Partners are responsible for quantifying shade per array using the Solmetric Suneye shade measurement tool on every project. Shade measurements are ultimately used in the Sunrun Proposal Tool to calculate annual energy production and the customer s performance guarantee is based on this output. Accurate shade measurements are required for accurate energy modeling and ultimately customer satisfaction, delivering the energy that the partner and Sunrun guarantee to the customer. How to Define an Array Table of Contents How to Define an Array Example: 1 Array Example: 2 Arrays Example: 3 Arrays Example: 4 Arrays Solmetric Suneye Guide Example: Array with a perimeter side longer than 20 Example: Array(s) with nearby shading obstructions Example: Deciduous Trees Example: Erroneous Shade The Sunrun definition of an array is: A group of solar modules that share the same tilt and azimuth and are physically contiguous with one another. Arrays are not defined electrically by individual DC series strings of modules or AC branch circuits. Arrays are furthermore not defined by the inverters that they are electrically connected to. Arrays are purely defined by the physical proximately of modules to one another and the structure they are connected to.

2 Example: 1 Array Example: 1 Array All modules are tilted at 18 degrees with an azimuth of 180 degrees. This layout has 1 array of modules. Example: 2 Arrays Example: 2 Arrays All modules are tilted at 18 degrees with an azimuth of 180 degrees but there are two separate groups of 5 modules, separated by physical space and/or obstructions. This layout has 2 arrays of modules. 2

3 Example: 3 Arrays Example: 3 Arrays Arrays 1 and 2 have already been defined in the previous example. Array 3 has 5 modules with a tilt of 18 degrees and an azimuth of 270 degrees. This layout has 3 arrays of modules. 3

4 Example: 4 Arrays Example: 4 Arrays Arrays 1, 2, and 3 have been defined in the previous examples. Array 4 has 3 modules with a tilt of 18 degrees and an azimuth of 270 degrees. Note that array 4 may or may not be electrically connected in series to array 3, but this does not play a role in the definition of an array. This layout has 4 arrays of modules. 4

5 Guide to the Solmetric Suneye Tool Sunrun relies on the Solmetric Suneye Shade Measurement tool to quantify shade per array. Like all components, the manufacturer s instructions should be followed to ensure accurate use of this tool. Critical steps to using the tool include, but are not limited to: Inputting the correct longitude, latitude, tilt, and azimuth for the proposed array Measuring shade at the proposed height of the array (4-6 above the roof surface in most cases) Verifying and editing the obstructions automatically identified by the tool Taking shade measurements at every corner of each array with a maximum of 20 between any perimeter measurements. If there is a nearby shading obstruction (vent, chimney, or tree branch) within 20ft of the array, an additional measurement should be taken at that point. Examples shown below. 5

6 Example: Array with Perimeter Side Longer than Array 1 would require 6 measurement points, each of the 4 corners and 2 additional points at the mid-span of the 27 sides of the array. Example: Array(s) with Nearby Shading Obstructions Arrays 1 and 2 would both require 7 shade measurement points, each of the corners and an additional measurement for the nearby chimney shading obstruction. Note that in this example, an additional measurement was not required for the vent because its low height does not cast a shadow on the arrays. 6

7 Example: Deciduous Trees A severe example of inaccurate obstruction detection is Suneye measurements taken in winter months when deciduous trees have no leaves. The skyline on the left was taken during the winter and the skyline on the right was taken at the same point during the summer. The technician should have edited the original skyline (following Solmetric instructions) to account for summer month shading when the trees branches are filled with leaves. Below each image, you can see the significant difference in performance. Example: Erroneous Shade In this case, the Suneye has clearly picked up blank sky as an obstruction during the morning hours of every month. The technician can correct this through either editing the photo or changing the device s settings. 7

8 Required Shade Report Documentation All arrays should be labeled on plan sets submitted to Sunrun following the array definitions outlined in this document. Shade reports should be taken per array per Solmetric s published best practice guidelines outlined in this document. Each shade report must be named to match the naming convention used on the plan set. For example, if the plan set shows arrays named Array 1 and Array 2 the corresponding Suneye PDF reports submitted to Sunrun should be named Array 1 and Array 2. Resources All technicians who use the Solmetric Suneye should be properly trained in its use. Critical instructional documents can be found on the Solmetric website, including: Best Practices for Suneye 210 Shade Measurements Sometric Suneye 210 User s Guide Solmetric offers a comprehensive, self-paced, 4-hour online training course. This is an excellent resource and should be required for anyone who uses the Suneye tool on a regular basis. When you register using the link below, you may use the Sunrun discount code to enjoy a $30 discount per registration. Solmetric Certified Shade Analysis Training Sunrun Discount Code: sunrunpartner 8