REI Saves Big with Solar

May 5, 2009

A national outdoor retail co-op cuts costs and energy with photovoltaic systems

The new energy strategy at Recreational Equipment Inc. (REI), the Seattle-based national outdoor retail cooperative, is very straightforward: Conserve first and, wherever possible and whenever economical, produce as much energy on-site with photovoltaics (PV) as possible. It’s a good philosophy to pass on to your clients.

REI was looking for a new way to improve its energy baseline after implementing a wide range of energy-conservation strategies at its existing stores. So, the hunt for viable on-site power generation began. “On a commercial retail building, a 100-foot windmill isn’t necessarily realistic,” notes Sharon Im-Lee, energy manager at REI, Seattle. Geothermal was considered, but retrofitting proved difficult. Solar wasn’t only the logical choice, but the maintenance also seemed reasonable, and the systems’ long life was equally appealing. When incentives made the projects economically feasible, REI jumped at the opportunity.

In 2008, REI installed solar panels on 11 of its 105 U.S. stores. Combined, REI’s installations equal more than 4 acres of solar panels. “It really has made a significant impact on our overall energy strategy,” says Im-Lee.

Solar Energy FAQs

Architechweb.com asked Brian Bruggeman, principal at Boulder, CO-based Echelon Energy LLC, to answer some questions about solar applications.

Q: What is the difference between solar thermal energy and photovoltaics?
A: For commercial buildings, there are two main types of solar energy systems: solar thermal and solar electric (or photovoltaics [PV]). Solar thermal systems primarily offset building gas usage, while PV systems primarily offset building electrical usage.

Solar thermal systems use solar collectors that heat a water/glycol mixture. This liquid is then run through heat exchangers to heat domestic hot water, fan coils, baseboard heaters, or radiant heat. PV systems use solar modules that produce a DC current; this current is then run through an inverter that converts DC to AC. The AC power is then used to offset electrical usage.

Q: Does it help to build a building with PV in mind vs. retrofitting?
A: Designing PV into the building from the start will always be more cost effective than trying to retrofit later. Even if the modules aren’t installed during construction, having the conduits in place will save a significant amount of time when the system is installed in the future. PV can always be retrofitted in at a later point, but conduit routing can be complicated, and special care needs to be taken for roof penetrations.

Q: How much power do PV systems provide?
A: Typical PV systems will produce about 12 watts per square foot of roof area, while solar thermal systems will produce about 60 watts per square foot, or 215 BTUs per square foot per hour.

Daily power production varies based on local climate conditions, solar insolation, and the angle and azimuth of the panels. (Solar insolation is the amount of solar energy available in average sun-hours per day. This varies from about 3.5 sun-hours per day in the Pacific Northwest to 5.5 sun-hours per day in the Southwest. The East Coast is around 4.5 sun-hours per day; therefore, in the Southwest, PV will produce about 66 watt-hours per square foot per day [12W X 5.5 hours].)

The company enlisted help from a large team: Everyone from facility managers to architects to structural and solar electric design engineers weighed in. (Architects were called upon for input due to their familiarity with the buildings being outfitted with solar panels.)

The Feasibility Study
Working with Blue Oak Energy, based in Davis, CA, REI surveyed its stores and evaluated the feasibility of solar installations. This study took nearly a year to complete, with more than 80 stores considered. Some factors that the team – including architects – had to think about:

Structural integrity and the condition of the roof. Due to limited roof space, REI opted for solar panels vs. a lightweight, thin-film solar system. Because of this decision, every building had to be assessed for its ability to hold the additional weight on the roof. “Retail buildings aren’t built like Fort Knox, so a structural assessment is super important,” says Im-Lee.

The condition of the roof was also scrutinized. According to Amy Hoagberg, vice president of project management at Blue Oak Energy, “Potential sites should have a relatively new roof to ensure that roof lifetime and solar-array lifetime (20-25 years) are concurrent.” Of the 11 REI stores with solar panels, three received new roof systems as part of the projects.

Local solar radiation. Blue Oak Energy helped REI assess which stores received enough sun to justify the investment in solar power. “We have a good understanding of historical weather patterns and can predict, with a high degree of accuracy, how much energy will be created over time,” adds Hoagberg.

Local electric rates. Stores with especially high electricity costs quickly became candidates for a solar panel installation – they would benefit most from even a small amount of on-site power generation. “Here in Seattle, our electricity costs are only 5 to 6 cents per kilowatt-hour; in California, we’re seeing upwards of 17 to 20 cents per kilowatt-hour, so what you’re offsetting is dramatically more in California,” says Im-Lee.

State and local solar incentives. REI decided to purchase the solar arrays outright, making state and local incentives and tax credits a deciding factor in which stores to install the panels. Im-Lee explains: “Oregon has a 50-percent state tax credit on top of the 30-percent federal tax credit. So, if you’re a retailer that has a tax appetite, it makes a lot of sense.”

Commitment to the location and store ownership. Not all of the 11 stores outfitted with solar panels are owned by REI, so support from landlords was essential. During the feasibility study, the amount of years remaining on leases was considered, as well as how committed the company was to having a store at that location long term. REI didn’t want to purchase a 20-year solar array for a store it might vacate in 5 years.

“Solar radiation, electric rates, and local incentives allowed us to rank stores by economic feasibility. Rooftop and ownership details allowed us to determine physical and logistical feasibility,” explains Blue Oak Energy’s Hoagberg. With the study completed, the 11 stores were selected – seven in California (Arcadia, Folsom, Sacramento, San Carlos, San Diego, San Francisco, and Santa Rosa), three in Oregon (Clackamas, Hillsboro, and Tualatin), and one in Texas (the company’s second prototype store in Round Rock).

The Solar Panels
“The photovoltaic arrays on REI’s rooftops convert sunlight to power and directly backfeed each store’s electrical switchgear (breaker panel). The store’s electricity-consuming devices, such as HVAC units, lights, computers, etc., use power supplied by the PV system first, and draw additional needed power from the utility company. This is all done seamlessly through the PV system’s intelligent electronics,” explains Hoagberg. The sunlight is converted to direct current (DC) power and, at the inverter, converted again into alternating current (AC) power.

At nearly all of the 11 stores, the stationary (or fixed-tilt) arrays are adhered to the building structure as opposed to ballasting, which weighs the system down. Because of this, it was especially important that all roof penetrations were sealed properly and that the roof-system warranty wasn’t voided.

The amount of power generated by the panels is significant. “It ranges anywhere from 7 to 45 percent of a particular store’s energy use. In Oregon, the systems are much smaller, and so the range there is from 7 to 17 percent. In California, the range is from 19 to 45 percent of that store’s energy use,” says Im-Lee. In total, the solar arrays at REI’s 11 sites are generating 1.1 million kilowatt-hours of electricity annually.

The Future of Solar at REI
The positive experience that REI has had with these installations has encouraged it to add photovoltaic panels to other stores in the future. New stores are now being designed to accommodate future solar panel installations. “We actually increased the building load requirement that we hand to landlords and developers when we’re building a site so that we can be prepared to put solar on them in the future,” she explains. Not only does this affect the building structure, but it also affects placement of rooftop HVAC units and skylights. Making new stores more solar friendly is a testament to just how successful the current applications have been.

Jana J. Madsen is a Cedar Rapids, IA-based freelance writer with nine years of experience in writing about the commercial buildings industry.

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