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Solar Power Heats up Design Challenge for BigBelly Trash Compactor
Self-contained unit posed design challenges around parts and materials selection to accommodate low-energy consumption
Beth Stackpole, Contributing Editor -- Design News, October 8, 2008
It's an unsightly spectacle that's all-too familiar – trash bins overflowing with rubbish, littering the landscape from city streets to local beaches with mountains of plastic bottles, newspapers, Styrofoam take-out containers and everything in between.
Yet amid the mounting piles of garbage, a group of engineers saw opportunity. After learning that garbage trucks are one of the most costly vehicles to operate – they consume over 1 billion gallons of diesel fuel each year in the United States alone and limp along getting an average of 2.8 miles to the gallon – the team formed a company in 2003 to take on the growing waste management problem and design a new kind of trash receptacle.
BigBelly Solar had a few very specific design goals: The trash compactor had to be around the size of a normal receptacle so it could easily fit street-side; the unit had to process larger quantities of trash to reduce the frequency of garbage pickup, and it had to be standalone so it could derive power from an alternative energy source. Wind was quickly ruled out because the energy source wasn't constant and it was too dangerous to have wind turbines lined up across city streets.
"When you're aiming for the street corner, there are a lot of limitations as to what you can use for power," says Jeff Satwicz, BigBelly product manager and one of the original engineers behind the company. "In order to run an electrical line to a standard outlet, you're talking about thousands of dollars of investment for each location just to provide power there. (As a result), the whole value proposition of cost savings around not collecting trash goes out the window because you're paying so much to install the unit."
None of that was the case with solar power. While there were no major breakthroughs in solar panel technology that led to BigBelly Solar's decision, the timing pointed to solar energy as the natural path to choose. Other solar, so-called off-grid applications were being introduced, including solar-powered parking meters and solar-powered traffic signals, which underscored the effectiveness of this power source for BigBelly's trash compactor application.
"Solar applications are becoming more acceptable everyday technology," Satwicz says. "There are solar panels on calculators and walkway lights – it's something people are starting to see more and more on things other than rooftops."
Back to the Drawing Board
While the timing was right, BigBelly's original design concept – a simple refashioning of an existing trash compactor into a solar unit – was not. Existing trash compactor designs zeroed in on cost efficiencies or ruggedness, but none took into account energy consumption, which was so critical to the solar-powered design. Because BigBelly was committed to delivering the compactor as a smaller, self-contained unit, it needed to rethink the design for a fresh approach that demanded less energy. "If we didn't take steps to minimize energy consumption, the whole idea of a solar-powered trash compactor would be a total failure," Satwicz says. "The size of the panel we'd need to power the system would be the size of a wall and that would defeat the whole purpose of having one self-contained unit."
Armed with 3-D CAD and simulation tools from SolidWorks, the BigBelly engineering team went back to the drawing board to rethink its design in a way that would best leverage solar power. Drawing inspiration from the simplicity of a bicycle chain, the BigBelly team created a drive chain mechanism to propel the compaction system, which in turn uses no hydraulic fluids and consumes minimal energy. As a result, the BigBelly trash compactor is powered by a 30W solar panel, which measures 18 inches by 22 inches – just the right footprint to accommodate the design goal of creating a self-powered, self-contained unit.
The next step was to optimize every component choice and all materials for efficient energy consumption. The BigBelly receptacle features a monitoring system comprised of a microprocessor, circuit board and infrared emitter and sensor, which determines when the trash needs to be compacted and collected. The design also calls for a multicrystalline solar photovoltaic module used to collect the sun's energy for subsequent storage in a 12V battery. That's where the chain mechanism and gear motor kick in. They leverage the stored energy and transform it into compaction power, Satwicz says.
The choice of materials was also a major design challenge. When the price of steel went up early in the design process, the BigBelly team and its outsourced partners embarked on a major effort to remodel the early prototype to reduce the amount of steel parts, both to make the unit more price competitive and in keeping with an eco-design focus. Using SolidWorks' sheet metal features and the finite element analysis features of COSMOSxpress, the BigBelly unit was rearchitected with 30 percent fewer steel parts, Satwicz says.
Other materials choices included a Lexan polycarbonate cover to protect the solar panels on the top of the trash barrel. While the polycarbonate blocks out minimal amounts of the solar radiation, it was a better design tradeoff than leaving the panels exposed to the elements, according to Satwicz.
SolidWorks' eDrawings email-enabled viewing and communications tool also played a key role in the on-going development effort. Using eDrawings, the BigBelly team was able to send 2-D drawings and 3-D models back and forth with both its outsourced design and manufacturing partners, a process which kept everyone on the same page and speaking the same language when it came to the product's evolving design.
The ability to send lightweight 3-D models back and forth with the eDrawings tool really helped BigBelly and its manufacturing partner, Mack Molding Co. meet the company's tight production and launch deadlines, according to Chris Glaski, sheet metal manufacturing engineer at Mack. Rather than the time-consuming process of sending memory-intensive CAD files over the Internet, the teams were able to share smaller eDrawings files in a timely fashion, which aided in identifying and modifying potential areas of interference. That was especially the case with some of the initial sheet metal designs, which proved not to work properly with Mack's press break tooling. "It's one thing to design a sheet metal assembly in SolidWorks; it's another thing to manufacture it," Glaski says.
Today, there are over 1,700 BigBelly solar trash compactors spread across the U.S. and the world, including a couple of high-profile units at Boston's Fenway Park and the Portland Oregon Zoo. At 300 lb and about the same height and width of an average receptacle, BigBelly compresses the equivalent of five trash cans into a single receptacle, which helps companies and municipalities avoid four out of five garbage collection trips, on average, Satwicz says.
The newest iteration of BigBelly launched last year and the company is planning new designs, including a dumpster-sized system and adding new technology that communicates information wirelessly back and forth between the unit and its owner. In this way, customers can get a sense of when a BigBelly unit is full and arrange trash pickup accordingly.
All of these innovations wouldn't be possible without 3-D models driving the iterative process. Says Satwicz: "Given that we're a mature product now, if we didn't have CAD to try out new ideas and see how they fit with our robust design, we wouldn't be able to make any changes."
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Solar Power Heats up Design Challenge for BigBelly Trash Compactor
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