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How to install solar panels on the roof of your home

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A New York solar pro walks through the process of designing and installing a rooftop solar system in a historic district

All photos courtesy Brooklyn SolarWorks

The roof: A sunny, flat expanse topping a two-story limestone townhouse on Maple Street in the Lefferts Manor Historic District in Brooklyn. The home was built in 1909, but its current owner wanted to bring the building’s energy system into the 21st century.

The bid: The building’s owner teamed up with eight other homeowners in the neighborhood, brought together by pro-solar nonprofit Here Comes Solar. The group asked for bids to outfit all their homes with solar panel systems and were able to get a base price of $5.50 per watt from the winning bidder, Brooklyn SolarWorks.

The math: After winning the bid, Brooklyn SolarWorks looked at the energy bill for the home on Maple Street to determine how much power a panel system would need to produce to both meet the home’s requirements and make financial sense for the homeowner.


"We calculated how many kilowatt hours the solar system would produce and multiplied that number by the rate he’s paying the energy company. That gives us a savings number," explained T.R. Ludwig, co-founder of Brooklyn SolarWorks. The proposed solar panel system on Maple Street would produce 6,804 kilowatt hours a year with a monthly savings of roughly $153.

The plan: Based on that number and the roof’s features (skylights, chimney, pipes) Brooklyn SolarWorks designed an efficient layout using 18 LG315 panels angled to the south and a wiring path running down the back of the building to the electric service panel in the basement.

The Maple Street roof pre-installation

The money: The total cost of installing a the system on the Maple Street home was $33,226. However, Brooklyn SolarWorks found a number of state and federal incentives that reduced the amount paid by the Maple Street client to just $3,947.

"To be fair, [the homeowner] was in a sweet situation where the stack of eligible incentives covered 95 percent of his total costs," said Ludwig. The incentives included a $3,400 state rebate for solar panels, a federal income tax credit covering 30 percent of the system cost, a $5,000 state tax credit, a historic preservation tax credit, and a New York City property tax abatement.

Ludwig admitted that such a high subsidy was unique, but added that the average incentives for a New York City installation will still typically cover 70 to 75 percent of a system's cost.

A digital mockup of the solar panel system

The paperwork: All New York City solar panel installations require a permit from the Department of Buildings. However, this home’s design, location, and landmark status meant that Brooklyn SolarWorks was required to jump over a few extra hurdles.

They had to submit their plans to the fire department for approval to infringe on the roof’s existing fire path, and demonstrate to the Landmarks Preservation Commission that the solar panels would not be visible from the street or the backyards of neighboring homes.

The timeline:

Once Brooklyn SolarWorks won the group bid, they visited the home and performed a site survey where Ludwig and his team spent roughly an hour measuring the roof and taking dozens of pictures to help their system designer lay out the panel and wiring plan. They also examined the basement-level electrical service panel to see if it needed to be replaced. It didn’t.

Then they kicked off the landmarks paperwork with a second hour-long visit to the home. Using long painted sticks, the team made sure any solar panels wouldn’t be visible from various vantage points around the home, and documented this fact with more photos.

The system designer planned an efficient layout for the panels and wiring, creating a digital model of the installation. Then Brooklyn SolarWorks presented this plan to the homeowner and explained the benefits, cost, and available rebates and incentives. The client said yes to their proposal and signed an agreement in addition to other paperwork for the landmarks approval process, Department of Buildings permit, and an "interconnection application" with the homeowner’s current energy provider, ConEd.

Brooklyn SolarWorks

Brooklyn SolarWorks submitted plans to ConEd showing how big the solar panel system would be and how much energy it would produce. They also had to submit the plans to NYSERDA, the state agency that issues rebates for solar systems. Then it was a waiting game for approvals from the FDNY, Landmarks, NYSERDA, ConEd, and finally, the Department of Buildings.

Once those came through, Brooklyn SolarWorks coordinated with the homeowner for a day to begin installing the system and ordered the equipment from a solar panel distributor. The company also arranged to have a hoist to get the panels up onto the roof.

The actual install only took two and a half days. The first day was taken up with getting all the attachments and pipe structures onto the roof, laid out, and attached to rafters. At the same time, the electrical crew began running conduit pipe from the basement up to the roof.

The second day involved attaching the solar rail to the pipes and bolting the panels to the solar rails. The electrical team installed the system’s inverter in the basement and ran the conduit through a channel cut in the basement’s sheetrock.

Once the inverter was hung and the panels in place, the team wired the system together. Each panel is wired in sequence to a junction box on the roof. Wires from the junction box run through the conduit on the back of the house down to the basement inverter.

The inverter’s feed was then "hot tapped" into the place where the energy company’s main cable connects to the service panel. The system is wired in a way that if the home needs power it will draw first from the solar system, and then the energy company if necessary. If the home doesn’t need power, the solar system feeds electricity out through the main to be used by other homes.

Once the system was entirely up and running, Brooklyn SolarWorks alerted ConEd so they could swap out the home’s old electric meter with a Net Meter that would track the flow of electricity both in and out.

"It’s designed so ConEd can tell whether there are kilowatt hours being consumed by the homeowner or if there’s energy exported out into the grid," explained Ludwig. "When that happens, energy flows out through meter, and the client gets a credit for the exported energy."

Once the new meter was in place, the entire solar panel setup had to get the thumbs-up from the Landmarks Preservation Commission, which entailed submitting more photographs and, in this case, bringing preservationists to the neighborhood to see the system for themselves.

Then Brooklyn SolarWorks scheduled an electrical inspection, and at first, the inspector failed the home. Brooklyn SolarWorks had swapped out a newer model inverter for the older one specified in the plans, so the company had to re-file all of their paperwork showing the model number of the new inverter before a new inspector came out and signed off on the home.

After that, it was time for the official Department of Buildings inspection, which the home passed. Receiving the DOB’s letter of completion also triggered activation of the final tax incentives for the project.

A view of the home monitoring system

But Brooklyn SolarWorks wasn’t quite done yet. They went back to the home one last time and installed an easy-to-read energy monitoring system for the owner to see just how much power the home is using and how much the panels are producing.

From winning the group bid through the paperwork, panel installation, and final inspection took eight months. "This was a fairly long one because of the electrical filing," admitted Ludwig. "More typical would be five or six months for a landmarked project. If it’s not landmarked, it can be as fast as six weeks."