The solar trailer

Renewable energy is en vogue. Dominating electricity investment in Europe, the US and the world, it is quickly becoming the new norm and inspiring engineers at all levels to leverage it more effectively. The most prominent renewable energy source still is the sun: According to the International Energy Agency, some 27 per cent of global electricity will be solar-powered by 2050 – the vast majority of it harvested stationary.

To make solar power available on the go, the automotive industry has been working frantically over the last half decade or so, hoping for technology to advance so it would become more lightweight and commercially viable. But a fluctuating diesel price and technical issues have been holding up progress, prompting potential adopters to wonder whether or not ‘going solar’ can provide a reasonable Return on Investment – especially in a commercial transport context.

To date, little success has been found from attempts to power entire trucks with roof-mounted solar panels, such as the concept vehicle developed by Japanese electronics company Sanyo. Presented at the Eco Products 2009 International Exhibition in Tokyo, the truck required 18 hours of charge for just 130 km of travel – not quite enough for an industry where the trucks are known to cover ten times that distance on a daily basis.

Instead, many a company has set its sights on the more achievable goal of using solar to power the batteries for smaller components such as refrigeration units, mobile barge pumps, tail lifts and truck cab comfort systems – with reasonable success. German company Solarion, for example, put together a solar powered system with trailer OEM Krone in 2010, and in the US, trailer refrigeration specialists Carrier Transicold and Thermo King have both released Photovoltaic (PV) assisted systems in the past. However, these systems can only do part of the job for the fridge units, which still require a fuel tank to run.

Now, Dutch company Twan Heetkamp Trailers (THT) is about to set a new standard. The brand’s ‘New Cool’ model is capable of chilling a whole box van with an electrical engine powered entirely by environmental sources such as solar. Prompted by changes in emissions regulations and the call for quieter vehicles in the Netherlands, the first New Cool trailer hit the streets in January this year – indicating that mobile solar energy may just be ready for its breakthrough.

Behind the scenes, however, the technology has been a long time in the making. UK supermarket chain Sainsbury’s already tested what is believed to be the first solar-assisted trailer refrigeration unit before the turn of the century. The system required a myriad of solar panels lining the entire roof of the trailer with a staggering payback period of 18 years – factoring in both the initial price of the solar panels and on-going maintenance costs.

On top of that, a 2001 feasibility report found that the “extra cost of insurance” was the largest single operating expense of the solar powered system, as the higher value of the trailer caused the insurance premium to go up. At the time, that was enough for industry to forget about solar again, and the technology returned to the development stage.

In 2009, researchers on the other side of the world at the Australian National University in Canberra investigated the viability of solar power in Australia – a country with a significantly higher ‘insolation average’ than the UK, where the Sainsbury trial was carried out. It was thought that the stronger and more consistent sun in the country had the potential to provide more energy and thus offset more of the cost.

The results were positive, finding that solar power was capable of displacing 85 per cent of the diesel used to refrigerate the test trailer down to -18°. However, the price of diesel in Australia at the time of the research was relatively low, so when the savings were compared to up-front costs, solar still came out second.

But, it was enough to inspire THT to have another go at developing a solar-powered truck and trailer combination. Now using more advanced PV-assisted systems, the Dutch company was able to solve a plethora of issues from the get-go. For example, trailers have been observed to undulate when travelling at highway speed, with the bending roofs creating real problems for solar panels that are mounted flush to the trailer roof. New technology panels are now able to offset that movement, enabling THT to create a more flexible ‘power plant’ on the back of a rig.

One company that specialises in the design of flexible solar panels is North American-based Go Power. Joseph Aschenbener, General Manager for Go Power distributor, Cummins Crosspoint, explains that modern-day panels are able to flex with the roof of the trailer, curving up to 30 degrees. “Although thin – only 3mm thick – they are incredibly durable, and have no problem handling extreme heat or cold and rain,” he says.

As such, the required flexibility was taken into consideration by THT during the development process, supported by the Netherlands Technical Road Transport Association (TRTA), axle specialist Valx and TRS cooling systems. The result is a system that doesn’t require a fuel tank at all, shucking 150kg and saving around 30 litres of fuel per trailer per day while completely eliminating CO2 and fine dust emissions. According to THT, all data has been confirmed during a lengthy road test with a Dutch supermarket chain.

To store energy, the fuel tank has been replaced with a battery that is charged by four solar panels working in tandem with a Valx Energy Axle. Revealed at the 2012 IAA Commercial Vehicles show in Hanover, the Valx Energy Axle recovers energy while braking, feeding additional power into the system.

During the first test cycle, the system worked so well that THT was awarded the 2014 Innovation Award in the ‘Environment’ category at the IAA Commercial Vehicles Show in Germany. What’s more, the New Cool was also named as a finalist for Dutch bank Rabobank’s Herman Wijffels Prize for sustainable innovation. But there is more
work to be done.

In a recent statement, THT revealed that while it only takes about a week to convert a trailer to a New Cool spec, the ROI timeframe is still around seven years – significantly less than in the past, but not quite enough for many commercial applications in mainland Europe. As a result, THT is trying to reduce the payback period from seven to five years by halving the number of solar panels to two. Until then, the New Cool trailers will likely be offered as rentals only.

But there is hope their time will come soon. In a breakthrough that could pave the way for volume-production, researchers in Australia have found a way to increase the efficiency of solar panels to gain more electric charge in the same amount of time. In January, a team from the University of New South Wales (UNSW) successfully converted over 40 per cent of the sunlight hitting a solar panel into energy, effectively doubling the performance of a standard unit.

“This is the highest efficiency ever reported for sunlight conversion into electricity,” says Professor Martin Green, UNSW Scientia Professor and Director of the Australian Centre for Advanced Photovoltaics (ACAP). The research, funded by the Australian Renewable Energy Agency (ARENA), set a new world record in solar energy efficiency that could eventually translate into fewer required panels for trailers like the New Cool. And it gave OEMs like THT new hope that improved solar technologies are underway that will finally help keep the costs of mobile applications in check. So, maybe those solar powered trucks aren’t too far off after all.

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