Reefer Solar Panels Help Save More Diesel Than You Might Think

Posted on 12/06/2022 at 08:00 by Kelly Junge


Reefer Solar Panels Help Save More Diesel Than You Might Think Title Graphic

Refrigerated transportation is a big business. Before finding a home in your local grocery store, the cold items originated from across the United States. These goods are kept at the proper temperature using transportation refrigeration units (TRUs) which allow for bulk transport but have a measurable effect on the amount of diesel a vehicle consumes. 


You might think you'd need a sizable solar panel to affect diesel consumption, but a small, cost-effective solar panel has a significant impact.


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A nationwide refrigeration fleet recently completed an extensive two-million-gallon study looking at the effect of reefer solar panels. The fleet worked with Carrier Vector hybrid reefers across all of their equipment. 


The test used a Differential Fuel Meter1 (DFM) mounted to each reefer's fuel lines and monitored data via telematics. Diesel usage data was taken along with the solar status of each reefer. The study took place over an entire year with warm and cold months, and the transported product was kept at either 0°F or -5°F.


The early results were promising, leading the fleet to add more and more solar throughout the study. A single reefer could have diesel data with and without a solar panel, depending on when the installation occurred.


The final result of the study was a 0.09 gallon/hour diesel savings with the addition of a 20-30W solar panel. In addition, it was found that the diesel savings were more significant in the colder months (starting a cold diesel engine to charge a low-voltage battery can be inefficient).


The diesel energy savings occurred when the solar panel offset alternator/battery charger demand. Carrier Vectors use battery chargers powered by a generator instead of an alternator. In fact, throughout the study, an alternator failure message from the reefers had to be ignored. The reefer gave this error because it monitors the amount of current coming from the alternator/battery charger to the battery. Thus the reefer assumed, since no current was flowing from the alternator/battery charger to the battery, that the alternator had failed. While in reality, the battery was kept at a high enough voltage by the solar panel, the alternator/battery charger never received the command to supply current.


These diesel savings result in reefer solar panels paying for themselves in a couple of months. Every 24 hours, your reefer runs with a solar panel you can save over two gallons of diesel. For example, if diesel is $5/gallon, you can calculate your projected savings using the formula below.


 Diesel Savings Formula


Additional Solar Test To Come


Does a 110W solar panel on the tractor fairing save diesel in a similar method? 


Energy conservation suggests that “if” a solar panel supplies energy to the battery, the alternator won’t need to provide as much power, thus saving fuel. That “if” is very important. Typical solar panels have a low cut-off voltage (14.1V to 14.5V) to protect a wide range of battery chemistries. 


Standard truck alternators can push battery voltages up to 14.6-15.1V, effectively shutting off the solar input. If there were alternator-matched solar panels that didn’t shut off, then diesel savings should appear.


Contact us for more information about the studies, solar panels, or differential fuel meters.


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Categories: Transportation