Technology is not quite there, but headed in the right direction.
By Chris Gillis
Could the U.S. trucking industry's hundreds of thousands of trailers be used as platforms for solar electric-generating panels?
That's what industrial designer and solar power specialist Jason Hill recently pondered.
'It comes down to how do we make an even bigger dent in our energy consumption?' Hill said in a recent interview. 'Using the space on top of a truck trailer for solar panels appears to be a huge opportunity for this.'
Hill, who operates Long Beach, Calif.-based design studio Eleven (designby11.com), has designed and overseen construction of solar-powered cars and tour boats. For him, truck trailers appear to be the next logical extension for this promising renewable energy power source.
'Solar technology is getting cheaper and more efficient,' Hill said. 'It makes sense to take it to the next level, which is moving goods.'
Many warehouse operators in recent years already use solar arrays, or sets of photovoltaic panels, on their rooftops to generate electric power. For example, FedEx has set up several multimegawatt solar power systems at its facilities in California.
Even open property surrounding warehouses is fertile ground for erecting solar panels. In late September, Staples and SunEdison unveiled a 1.5 megawatt ground installation at the office supply company's distribution center in Hagerstown, Md. The system consists of more than 11,000 solar panels and will generate about 2 million kilowatt hours of energy a year and more than 37 million kilowatt hours over the next 20 years.
Hill believes truck trailers equipped with solar panels have the potential to generate electricity both during movement and at rest. The average 53-foot trailer could easily provide enough space for a 5 kilowatt panel, he said.
Power generation while a trailer's in motion, especially those with refrigeration units, could use the electricity from the panels as supplemental power instead of exclusively relying on the refrigeration unit's diesel engine. When the solar-equipped trailers are stationary they could feed excess power back into the terminal's electric system, Hill explained.
Solar panels used for powering refrigerated tractor trailers have been undergoing tests in Europe for more than a decade. According to a Sandia National Laboratories study on the feasibility of solar powered refrigeration for transport applications, the first commercial use of this technology was deployed in 1997 when solar panels were mounted on the roof of a trailer used to charge batteries that powered a refrigeration system. The application was for the delivery of food products by a supermarket chain.
Yet today, solar panel technology, both from a cost and component standpoint, is not quite ready for the rigors of the trucking world, industry experts say.
Sandia's study concluded in 2001: 'The payback analysis indicated that at present time, the economic justification for wide spread use of solar is moderate, but not compelling. However, as the price of diesel fuel increases and the price of solar modules and vacuum panels decreases, the economic case will improve. These are expected trends. In addition, any new regulations impacting diesel emissions will likely favor solar.'
Nathan Armstrong, president of Calgary, Canada-based engineering firm Motive Industries, said installing solar panels on truck trailers would require an intricate and expensive mount system. If the panels are the rigid glass type, they must also endure trailer-flexing and stand up to all sorts of weather and traffic conditions.
'There are definitely issues of robustness of the units,' said Tom Kampf, trailer and rail product manager for North America at Thermo King Corp., based in Minneapolis. 'We have yet to find solar units built for the rigors of over-the-road transport.'
Armstrong said a 5 kilowatt panel would cost $35,000 to $45,000 and wouldn't generate the level of power required for a truck reefer unit.
Dave Augustine, engineer in charge of new technology at Thermo King's Climate Solutions, estimated a solar panel-covered trailer roof would only generate about one-third of the power required for a reefer unit. On cloudy days and nights, the solar panels are in effect useless, he said.
The additional weight of current solar panels to the trailers would require trucking companies to burn more fuel in transit and could raise the level of maintenance for the trailer fleet, said Dave Kiefer, director of marketing and product management for Carrier Transicold in Athens, Ga.
In recent years, Thermo King and Carrier, the largest providers of truck cab and trailer temperature-controlled systems in North America, have introduced reefer units that rely on electricity rather than exclusively on diesel engines for power. These new systems are designed to reduce both particulate and noise pollution often associated with older mechanical reefer units. In addition, they help meet increased shipper demands to reduce transportation-related carbon footprints and comply with environmental regulations.
Carrier, for instance, continues to enhance its all-electric Vector reefer units, which it first introduced to the freight transportation market in 2006. The new Vector 6500 obtains its power from the refrigeration unit's onboard 23 kilowatt electric generator, Kiefer said.
Electric reefer units offer some potential for connection to solar power. The Vector 6500, for example, can be equipped for electric standby, allowing it to be plugged into grid power when parked. One of Carrier's customers, a California microbrewery, uses solar power from its building to keep its Vector 6500-equipped 53-foot trailer running while parked.
Thermo King's TriPac supplies power to the truck driver's onboard living quarters while the diesel engine is off. The batteries for this cab system may be charged by an 8-by-16 inch mounted solar panel, Kampf said.
'Because we're done with the days of cheap fuel, we're waking up to these types of alternatives,' Kiefer said.
'I see a possibility to use both fixed (at station) and mobile (on trailers) solar,' Hill said. 'The mix of this energy would be used to charge a battery pack for the refrigerated part, and be changed with a fresh one (if needed) at the stopover. That way you are using the panels on the trailer to top off and keep the battery pack running well, and using the fixed panels to fill batteries that power the cooling part.'
Both Thermo King and Carrier haven't dismissed solar as a future electric power source for their reefer units.
'It will probably happen someday,' Kampf said. 'Right now, we just don't have widespread integration of solar systems.'
'Solar is definitely headed in the right direction,' Kiefer said. 'Over the years, the solar industry has refined its manufacturing to make the technology less expensive and generate more output.'
Kiefer noted that the cost per solar cell is now about $3 a watt, compared to about $7 more than a decade ago. He said the price needs to get to about a $1 per watt before the technology is considered a cost-viable energy option for the transportation industry and that's at least several years away.
Harry Zervos, technical analyst for IDTechEx, recently wrote, 'We need to progress from heavy, rigid structures, that are expensive to ship and install, to conformal, thin, lightweight photovoltaics.' While this technology has started to appear on the market, Zervos said it's still only one-tenth efficient and much more expensive than conventional crystalline solar cells.
The European transportation sector, which has for years experienced significantly high diesel prices and tough environmental controls, actively experiments with trailer roof-mounted solar power systems.
At the September IAA Commercial Vehicles show in Hannover, Germany, Fahrzeugwerk Bernard Krone GmbH presented a trailer covered with flexible solar modules made by Solarion AG and included a Carrier Vector 1550 reefer unit. The 30 solar modules, which are made of copper, indium, gallium and diselenide, have an efficiency of 10 percent and can deliver a peak power of 3 kilowatts. According to Solarion, the modules can save about 1,000 liters of diesel fuel a year.
Frank Albers, marketing director for Fahrzeugwerk Bernard Krone, said the thin modules are lightweight, and can be easily installed.
'We always strive for a better refrigerating efficiency,' Albers said. 'We achieve this with better insulation but also through the use of renewable energy in the refrigerating units.'