Finally Walking My Solar Talk: Page 4 of 4


Inside this Article

Author drilling a hole to attach the PV array
Dave Strenski prepares to attach the rooftop PV array.
The home and PV array
Even with some reduction in efficiency, “non-optimal” array orientations, like on this west-facing roof, can pencil out financially.
Array visible from the street
Even though the PV system on the west-facing roof is visible from the street, the system was approved by the Historic District Commission.
Installing the PV modules
Homeowner and volunteer labor helped reduce installation costs. After rebates and projected production incentives, the calculated cost was about $1.16 per installed watt.
Photo of PV array
This west-facing array provides about 75% of the production of a similarly sized array that would be oriented to true south.
Enphase M250 inverters were installed on SolarWorld rails attached to Quick Mount PV flashed feet.
The load center
The Enphase Envoy production meter, which lives near the service panel, communicates to the Enlighten Web interface.
Screen shot of PV system web interface
The Enphase Enlighten Web interface allows real-time and cumulative tracking of individual module and whole-array performance.
Strenski family photo
The author and his family in front of the PV production meter.
Author drilling a hole to attach the PV array
The home and PV array
Array visible from the street
Installing the PV modules
Photo of PV array
The load center
Screen shot of PV system web interface
Strenski family photo

As a nine-year volunteer for SolarYpsi, a grassroots solar advocacy organization, I’ve helped design and install about a dozen grid-tied solar-electric systems in Ypsilanti, Michigan. Ironically, until recently, my own home’s rooftop had remained without photovoltaic (PV) modules.

I often dreamed of solar power for our family’s home, but the high initial system cost, the  home’s orientation, and its location in the historic district seemed like high hurdles. The front of our 122-year-old Victorian home’s gable end faces south with three large maple trees shading it, and its roofs face east and west. The backyard is filled with trees and a garden, so a ground- or pole-mounted system was not an option.

Then there was the cost of the system itself. In SolarYpsi’s early years, PV systems cost $7 to $11 per installed watt—and that was with using an all-volunteer labor force. My interest was renewed after I calculated the installation cost for our latest PV project at the Ypsilanti Food Cooperative. Using volunteer labor and $0.78-per-watt Evergreen PV modules from a bankruptcy sale, SolarYpsi was able to install the system for $3 per watt. This was the first time PV power seemed it might be affordable for non-ideal orientations or locations. More surprising was that the $0.78 per watt was not an anomaly. Later that summer, closeout UniSolar modules were available for $0.50 per watt after the company’s bankruptcy. That motivated me to start searching the Internet regularly, and I soon discovered that $1-per-watt PV modules were becoming common.

Three occurrences inspired me to revisit the idea of putting a PV system on our house. Our retired neighbor, Larry, was installing a PV system at his house, and he was able to self-install his system for less than $2 per watt (before incentives). He took a creative approach to the mount, purchasing aluminum channel for the rails at a scrapyard for a fraction of the cost of new rails. He also saved some money by fabricating his own top clamps and roof mounts. Note that creating custom racks can save some money upfront, but the responsibility of making sure all of the appropriate engineering calculations have been considered and  implemented  falls on the system owner (see Web Extras for an article on racking options for roof-mounted PV systems).

Then, a new PV installation company, Sade Power, established itself in southeast Michigan and was advertising batteryless grid-tied PV installations for $2.50 per watt. Another local solar contractor—AJ Leo—was also installing systems for about $3 per watt using Michigan-made PV modules and inverters.

I was aiming for a gross price of $2.50 per watt. This would be reduced 30%, since we could take advantage of the federal tax credit. Our local utility company, DTE Energy, also was sponsoring a solar incentive program, offering an upfront rebate of $0.20 per installed watt and a production-based incentive of $0.03 per kWh generated for the next 15 years. This would make the final installed cost less than $1.50 per watt.

The final motivation came from a Home Power article that discussed non-optimal array orientation and system performance (see Web Extras). I had assumed that east- and west-facing arrays would generate only about 50% of the energy of south-facing arrays and were not cost-effective. However, the article reported that these orientations could provide up to 80% of the energy generated by a south-facing array. I decided to take another look at our home’s solar prospects.

Designing the System

My main goal was to maximize the power that the array could generate on the west-facing roof with Michigan-made Sonali Solar 250-watt modules. I sketched out both landscape and portrait layouts to determine what would yield the best use of space and highest production.

Our utility provides its customers with the past three years of their electricity use data, and I was able to download it for our home. Our average monthly use was 450 kWh, or about 5,400 kWh per year. Once I’d calculated this amount, I used PVWatts to find our site’s average number of sun-hours. A west-facing PV array tilted to 45° would receive an average of 3.18 daily sun-hours. Applying an overall grid-tied system efficiency of 75% (to account for shading, inverter inefficiency, and wire losses) would mean we’d need a 6.6 kW PV system to zero out our electricity bill on an annual basis. However, the roof space limited the array size to 4.5 kW.

Once we’d decided on the system’s size, we needed to convince the local Ypsilanti Historic District Commission that putting PV modules on our home would not destroy its historic aspects. The commission had already approved several municipal solar projects, but this was the first time a residence would have PV modules visible from the street. They mulled it over and finally ruled that historic preservation and renewable energy systems could coexist. Their biggest concern was making sure that the PV modules were “removable,” and that the array wouldn’t cover or damage any unique architectural features of the building. They liked the proposed design since it covered the entire roof face and not just part of the roof—they felt it blended into the roofline better. (In Ypsilanti, there are no fire setbacks required by local fire or building codes, so having an edge-to-edge PV array is permitted.)

The Sonali Solar 250 W modules were available for $0.95 per watt. I wanted to use a Renovo string inverter (also Michigan-made) with them, but a few trees and a power pole created some shade, making microinverters a better choice, since shade on one module won’t sabotage the power output of the entire string in a microinverter-based system. After researching different microinverters and accounting for the costs of specialized cables, mounting hardware, terminators, and a communication gateway, I opted for Enphase M250 microinverters. Initially, I thought that all 18 inverters could be placed on the same cable, but this exceeded the limit for a 20-amp, 240 VAC circuit. Thus, an additional cable, terminator, and combiner box was required to protect each string of nine inverters with a 20 A, two-pole circuit breaker. In fact, with all of the “hidden” costs, the inverters, communication, and AC power transmission constituted the largest part of the final installation costs.

With my full-time job as a computer applications analyst, I didn’t have a lot of free time to design and build a rack. So I contacted a local solar contractor, SUR Energy, to order the balance-of-system components: an AC disconnect, combiner box, Quick Mount PV’s Classic Comp mounts, SolarWorld Sunfix Plus rails, and the Enphase microinverters. It was the classic trade-off of available time versus money.

One interesting aspect of the installation was how quickly the parts could be delivered and installed. The final decision to do the installation was made in September 2013; by October I had all the parts. The installation was completed during two weekends in November with assistance from three of my neighbors who were excited to help and learn about solar-electric systems. The coming cold weather also motivated us to finish the installation quickly. Getting the system online before the end of the year also meant that I could collect the 30% federal tax credit for the 2013 tax year.

Since there were contractors installing PV systems for $2.50 per watt, I set that as my budget’s upper limit. I hoped to come close to my neighbor’s installation cost of just under $2 per watt, but the microinverters bumped up costs slightly. The final gross cost was $2.43 per watt, using volunteer labor. With the 30% federal tax credit and our local utility company’s incentives (an upfront rebate and production-based incentives), the net cost was $1.16 per watt. Depending on its production, the system should pay for itself in eight to nine years—assuming a fixed price for electricity of $0.17 per kWh. Not a bad investment for something that has a 25-year warranty.

Unexpected Lessons

There are some advantages to DIY installation, but it can also come with some caveats—especially if you’re working on a second-story, steep roof. You need to feel comfortable climbing on high roofs and being roped in. For me, this was the fun part of the project. On the 12:12 roof, a good ladder with a stabilizer bar was a must. For safety, we also used a fall-protection system (see Web Extras for a roof safety sidebar in “PV Rack Strategies”). Having extra parts like nuts and bolts while up on the roof was a must, saving trips down and up the ladder when they slip from your hands and roll off the roof.

The stressful parts of the project were making sure I had dotted my i’s and crossed my t’s when it came to understanding all of the electrical and structural codes that applied. A big pitfall would have been to have the system fully installed and then find out from the electrical inspector that I had not grounded everything properly—and have to redo the whole project to fix the error. But worse would have been to have unknowingly used wire that was undersized for the project and then have to rewire the whole system. For my installation, the building inspector insisted on having structural drawings to prove the roof could handle the system’s weight. The roof had only one layer of existing shingles and 2-by-12 rafters on 16-inch centers. The PV modules’ combined weight was similar to another course of asphalt shingles, and he agreed that the roof could accommodate the system.

One design aspect we wrestled with was how to space the module rows. Although the gap between the modules in a single row is fixed by the top clamps (about 3/4 of an inch), the gap between the rows can be whatever you want. For shedding snow, a small gap (less than 1 inch) helps the rows act as one continuous slippery surface, letting snow slide off in one sheet. While a larger gap (several inches) might aid in summer cooling, in the winter, snow on the upper module can slide into the gap, creating a small snow dam. In the end, practicality won out—a gap of 12 inches was chosen because it gave us more room to stand on the steep roof while we installed the modules and microinverters.

PV Power

The M250 microinverters’ monitoring software shows how much power each module is producing. This winter, it was interesting to see which modules shed their snow the quickest to start producing power. The system is performing close to my expectations, although the array receives more shade than I anticipated, which results in lower production in some months compared to the original PVWatts estimates (see “PVWatts Estimates vs. Actual Production” table).

Besides the system’s clean energy and lower utility bills, the next-best part of the installation has been people visiting our house who don’t even notice the modules on the roof. It’s amazing how quickly the solar modules have blended into the neighborhood’s landscape.

Web Extras

“PV Array Output at Various Tilts & Orientation” by Justine Sanchez in

“The Right Fit” by Jeff Tobe in

“PV Rack Strategies” by Greg McPheeters & Tim Vaughan in

Strenski PV array time-lapse video •

Comments (4)

doug stecklein's picture

I just completed a diy solar installation as well. I live in Kansas so no incentives besides the 30% federal credit. ( 21) 270watt panels with m250 micros, facing due East. The installation cost $2.40/watt. $1.68/watt after the tax credit. It's been running for two months. It has so far produced 1.2 MWh's of electricity and is 6% ahead of PV Watts projections.
I am as tight as they get with money and I could see that this was an investment worth making.
Get ready for the residential solar revolution!

Dave Strenski's picture

If anyone is interested in the "talk" part of the article, here is a video that Google made about SolarYpsi.

Dave Strenski New Energy for Detroit

And here is a TEDx talk about solar power I gave about a year ago.

Understanding Solar Power in Ypsilanti: Dave Strenski at TEDxEMU

Marc Fontana's picture

Thanks for sharing details about your DYI PV installation project. I love the hand powered drill !

I am curious about your selection of the Enphase M250 micro-inverter - The micro-inverters make sense for your shaded location, but I wonder why you did not select the less costly Enphase M215 model ? The M215 can produce up to 225 Watts and would still maximize your energy production with the Sonali SS-250 modules which have a PTC rating of 213.4 Watts. There's not a huge difference in price (the M215 is ~ $20-30 less) but it adds up. The newer M215's have same integrated ground and monitoring capability as the M250.

Dave Strenski's picture

I went with the M250 because of the integrated ground. I didn't know the newer M215 have the same integrated ground. Another pit fall of a DIY project.

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