It's payback time

It's been four years since a grid-connected photovoltatic system was installed for the Buffalo office, so it's time for a review.


Courtesy: Cannon DesignIt's been four years since a grid-connected photovoltaic (PV) system was installed for the Buffalo office, so it's time for a review—was this project a worthy exercise?

A local company, Solar Liberty, installed a 23.1-kW system consisting of 120 flat-roof solar panels in July 2009, pitching them at a 10-degree angle toward the sun to improve energy production. The system predicted a 439-ton carbon footprint reduction over its lifetime. This system was installed at the peak of NYSERDA's incentive program for PV systems, with an incentive of approximately $4/Watt.

Courtesy: Cannon DesignThe system has generally met the modeled energy production estimates, which assumed ideal conditions. The system was modeled to produce 25,640 kWh per year, while the actual production has been only 2% less than the modeled estimate.

What about the cost and the payback?

We wouldn't have taken on this project without the benefit of local utility incentives and federal tax rebates. The "list" price of the project was $170,000, but after counting incentives, rebates and accelerated depreciation of our asset (a tax strategy), we will have made $13,000 by installing the system, and that's before we produced a single kilowatt!

The system's ROI was recorded between the third and fourth years of installation, creating a positive generation of cash flow. So after all initial costs, the system has already paid for itself.

Courtesy: Cannon DesignElectrical energy rates have gone down significantly since the system was installed, counter to our initial assumptions in 2009. The graph to the right is an estimate from our 2009 system proposal indicating increasing energy costs.

Another interesting fact is a 23.1-kW system doesn't actually produce 23.1 kW for the building. There are losses in the electrical distribution and conversion from dc to ac that do not allow for the full output of the panels to be realized. The typical peak output is between 20 and 21 kW.

Other factors that impact the Buffalo office's energy reduction

Courtesy: Cannon DesignThis chart (right) shows the office's demand (metered peak kW) and the actual cost (blended cost per kWh). No data was recorded in 2009 because of the office renovation.

It would be misleading to say that the PV panels were the only contributing factor to the office's overall energy reduction. Other contributing factors include the building-wide renovation in 2009 that replaced several outdated systems, the physical removal of network servers to an offsite location, as well as replacement of lighting systems. The system has also operated for four years without a day of downtime or maintenance.

Buffalo? An ideal location for solar panels?

I've been asked about the impact of snow and the production of electricity. The vast majority of electricity production occurs in the summer, when the days are longer and the sun angle is higher. Winter electricity production is limited, so there is less worry about the impact of snow. Another interesting fact is that hotter is not better. The panels actually de-rate at higher temperatures, so the peak electricity production is best under sunny and cool conditions.

Practicing what we preach

Courtesy: Cannon DesignThe following are some highlights from current PV renewable energy system projects that Cannon Design has been recently involved with. The State University of New York at Oswego, Science, Engineering and Technology Building, was designed with a 36-kW rooftop PV installation. The PV system is in the final stages of construction which will be operational in mid-summer 2013. Also at the SUNY Oswego campus, the Rice Creek Field Station, a science and nature observatory building, was designed with a 36-kW rooftop PV installation. This system has been installed and is currently being commissioned.

On the SUNY Old Westbury campus in Westbury, N.Y., a multi-phase library renovation project was combined with a 40-kW rooftop PV installation. This system has been designed and is expected to be installed in the second phase of the renovation project. The SUNY campus's wanted to highlight these PV installations as "science on display" with the use of an interactive energy kiosk at the building's entry. This leading by example approach will be affective in promoting green initiatives to their students and staff for years to come.

For the Oak Ridge National Laboratory (right), south-angled PV panels alternate with north-facing clerestories in a sawtooth configuration that elegantly combines electricity generation with natural illumination of interiors.

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