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The Final Design

Sizing the System The Structure The PV panels Field Wiring Tilt Angle



Site Information

Latitude:  33.343 deg. N
Longitude:  117.233 deg. W
Winter solstice noon elevation:  33.22 deg.
Summer solstice noon elevation:  80.1 deg.
Slope of bank: approximately 20 deg.
Annual average capacity factor:  0.21

And here is the site. The array will be oriented 0.57 degrees west of true south in order to best fit the support posts to equal elevations along the bank.
The final design of the photovoltaic generating plant is a semi-fixed array with adjustable elevation. The support structure is made of galvanized pipe and 12 gauge galvanized steel channel struts.

The Final Design

There are 18 bays of the structure, each with an axle that supports a frame of four PV panels. The frame in each bay is center mounted on a length of 2" pipe, which has been placed over the horizontal "axle" of 1-1/2" pipe. The 2" pipe can roll around the concentric 1-1/2" pipe allowing easy adjustment of the array's elevation angle.

Front View Drawing
PDF copy
The elevation angle is adjusted by loosening the pipe straps on the elevation braces and rotating the support frames. The pipe straps, when loosened, can slide along the length of the braces. The drawing shows solar elevation angles at noon for a specific day of each month at this latitude. This information helps when making declination adjustments.

Side View Drawing
PDF copy
Application for the building permit, and also for the net metering and interconnect agreement with San Diego Gas and Electric, required a one-line electrical drawing of the system.

The string of four panels in each bay are series-wired with extra flexible #6 conductors that carry a UL RHW-2 designation. I investigated a variety of wire types before making the final selection.

One Line Drawing
PDF copy
The San Diego county building department recently offered a one-day seminar for  their enforcement officials (inspectors) in which they were trained to inspect photovoltaic installations. I quietly strolled into this seminar, fully expecting to be thrown out. But no one objected and I received my best training regarding application of the National Electric Code to PV systems.

One segment of the seminar focused on clues that identify the system builder as "untrained and inexperienced". Most of these clues are blatant violations to the NEC, such as use of incorrect wire types, inadequate wire sizing, or improper grounding. This inspired me to prepare a checklist that I presented at inspection time. It served two purposes; to show the inspector that calculations were properly done, and to promote the illusion that I was a trained and experienced PV system builder. I think it worked!  The inspector approved the system and took the checklist, asking if he could use it to develop an official checklist for inspecting PV systems.

Inspection Checklist
PDF copy of my checklist.
PDF copy of blank checklist.
MS Word copy of blank checklist.