PV Pergola: Page 3 of 3


Inside this Article

Pergola-Mounted Solar Electric Array
PV Rack Rails Installed Atop Pergola
Once the structure was completed, the PV rack rails were installed.
Taylor Batteryless Grid-Tied PV Pergola System
Kaco Inverter
This Kaco inverter has the required input voltage, closely matches the array size, and can work with positive-ground SunPower modules.
Transducers at the main breaker box.
The TED monitoring system uses input from transducers clamped around the cables at the main breaker box.
Solar Pergola Installation
Once the rails were up, the modules were mounted in a landscape configuration.
Solar Pergola Installation
The city’s planning department allowed the PV pergola by terming it a “garden structure.”
Pergola-Mounted Solar Electric Array
PV Rack Rails Installed Atop Pergola
Taylor Batteryless Grid-Tied PV Pergola System
Kaco Inverter
Transducers at the main breaker box.
Solar Pergola Installation
Solar Pergola Installation


The system’s performance met my software estimates fairly closely. Before installing, I modeled system performance using the National Renewable Energy Laboratory’s (NREL) Solar Advisor Model (SAM) software. Unlike NREL’s PVWatts or other web-based calculators, SAM can perform a more detailed analysis using specific system components and historical irradiance data from near my home. This software is not easy for the layperson to use, but if you are willing to learn, it is not insurmountable.

I took SAM’s output, applied the monthly shading estimate from the Solmetric app, and then compared that to the actual performance. Our system’s yearly generation was about 2% less than SAM predicted, which I consider quite close. Month-to-month variations from the estimate have ranged from -39% to +19%. Any number of factors could explain the variation—dirty panels, snow cover, winter pollution, wiring losses, solar radiation different from the average, etc. But from May to August 2011, I had four straight months of negative meter readings, essentially turning the meter clock backward—a satisfying feeling. 


Other than the city permitting process, the design and installation went smoothly. Because of my solar experience and the unique design and location, I took on a burden that the average homeowner shouldn’t need to—the installer normally will design the system, apply for the permits, handle the interconnection application and incentive paperwork, get utility interconnection approval, and perhaps even set up the data monitoring system. Just remember that the lowest bid usually won’t give you the best service. Make sure you clearly discuss what is and isn’t included in the package price with your proposed installer.


Mike Taylor is the research director for the Solar Electric Power Association (www.solarelectricpower.org) in Washington, D.C. A thermal energy audit and retrofit, with solar space or water heating, is his next personal energy challenge.

Alpenglow Solar • www.alpenglowsolar.com • PV installer

Solar Advisor Model (SAM) • www.nrel.gov/analysis/sam • Performance estimator

Solmetric iPV • www.solmetric.com • Shading analysis iPhone app

SolarAnywhere • www.solaranywhere.com • Satellite irradiance data

Database of State Incentives for Renewables and Efficiency • www.dsireusa.org • RE incentives

System Components:

Kaco New Energy • www.kaco-newenergy.com • Inverter

SunPower • www.sunpowercorp.com • PV modules

The Energy Detective • www.theenergydetective.com • Monitoring

Unirac • www.unirac.com • Rack


Comments (2)

johnd02's picture

Sounds like most of your cost was in the aesthetics.

I am surprised the building department passed the structure without soil geotech and structural engineering. Here in Rancho Cordova Ca I have been going back and forth since July trying to get a building permit for what started as a 4 panel ground mount system in my backyard. It could have been done a long time ago if I would have hired an engineer to design it. I should have at least gotten some estimates but my feeling was paying for engineering would cut the ROI and killed the project. The last set of plans were done with IronRidge ground mount design assistant and submitted 12/14/2015. I got the plans back 1/15/2016 with a note that starts with "The packet provided as engineering for the project is not adequate and ends with I need a Ca. licensed engineer or architect to provide the correct specifications. Included their stamp and signature on the specs.

The main hold up now is wind exposure class at 100 mile per hour 3 second gusts.
IronRidge says I should ask my building department if I live in a Urban area. If you then the wind exposure is B and the program will use the B values to do the calculations for maximum East West pier spacing.

SolarKismet's picture

Update: 1/1/16: In 2015 we used 4,440 kWh of electricity and our solar panels generated 3,317 kWh of solar electricity, making us about 75% solar for the year from 9 panels (2.1 kW).

Our consumption includes an electric hot tub and as of Oct 2015 a plug-in hybrid car (we don't really use AC and have a natural gas water heater). The average area home uses 5,644 kWh/yr.

The panels and/or the solar resource continues to be 2-7% above my original modeled estimates for how much solar we would make each year.

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