Refrigerated containers, otherwise known as reefers, are specialized containers that keep their insides cool and insulated to store perishable items such as food and medicine. They account for a huge portion, 20-45%, of the total energy that is used at ports.[1]Iris, Çagatay, and J. Lam. “A Review of Energy Efficiency in Ports: Operational Strategies, Technologies and Energy Management Systems.” Renewable and Sustainable Energy Reviews, 2019. … Continue reading Accordingly, depending on the type of reefer the ports choose to use, reefer emissions can be very high—at the Port of Boston, which has 400 diesel reefers, total reefer emissions reach 9.76 tons of particulate matter a year and 11,732 tons of carbon dioxide a year.[2]“Electric Refrigerated Container Racks: Technical Analysis.” Electric Power Research Institute (EPRI), December 2010. … Continue reading For comparison, the entire transportation sector of Boston emits 418,760 tons of carbon dioxide a year from diesel.[3]“Boston’s Carbon Emissions | Boston.Gov,” October 5, 2021. https://www.boston.gov/departments/environment/bostons-carbon-emissions. However, electric reefers also exist and are in widespread use, in which case their indirect emissions depend on the port’s energy grid.
Reefers are generally stored at ports for about 3 days on their way out of the port, and about 24 hours on their way into the port. Traditionally, reefers are stored in “wheeled storage”, which means each reefer is given its individual plot of land and outlet and directly wheeled to and from the quay; however, a less land-intensive way of storing reefers is “rack storage”, which connects 22-26 reefers in the same rack to the same outlet.[4]“Electric Refrigerated Container Racks: Technical Analysis.” Electric Power Research Institute (EPRI), December 2010. … Continue reading Both kinds of storage are in widespread use today; the cost-benefit analysis is thus performed for both wheeled storage and rack storage.
One way to cut down on reefers’ energy consumption and emissions while they are stored at ports is by installing solar roofs over them. This has a twofold benefit: solar panels help generate energy and the existence of a cover over the reefers decreases the amount of energy needed to maintain an appropriate internal temperature, by approximately 9% over the course of a day.[5]Budiyanto, Muhammad Arif, and Takeshi Shinoda. “Energy Efficiency on the Reefer Container Storage Yard; an Analysis of Thermal Performance of Installation Roof Shade.” The 6th International … Continue reading In addition, ports still using diesel reefers should switch to electric reefers to cut down both on emissions and on overall cost.
Solar roofs should be installed over reefer storage yards to allow reefers to move in and out of them, in contrast to the idea of installing solar panels directly on the top surfaces of reefers so that they can always draw from solar power as long as they are in the sun. Installing solar roofs instead means that reefers cannot draw from solar power in transit, but it allows reefers in storage yards to take advantage of the energy savings of shade and solar power at the same time. Furthermore, it will be easier and cheaper to maintain a large solar array in one port than to maintain individual reefers’ solar panels through all the wear and tear of the shipping process.
From the analysis below, implementing solar panels achieves breakeven in 9 years if electric reefers are already installed, and between 7-10 years if the port starts with diesel reefers and buys new electric reefers. Not only would solar roofs provide a significant amount of the energy needed by reefers, they would be able to provide security in the event of a grid malfunction during high-traffic times of day, as they provide a baseline amount of energy that could keep reefers cool enough for the goods inside to keep temporarily.
| Wheeled storage | Rack storage | |
| Land usage per reefer | 400 ft2 | 80 ft2 |
| Capital cost of reefer installation, per reefer | $21,250 | $24,000–$30,000 |
| Peak solar power output | 7.7 W/ft2 | 7.7 W/ft2 |
| Reefer power usage in maintenance mode (95% of operation time) | 3000 W | 3000 W |
| Reefer power usage in pulldown mode (5% of operation time) | 15,000 W | 15,000 W |
| Power saved purely from roof shade, per reefer | 270 W | 270 W |
| Power produced by solar panels | 3080 W | 616 W |
| Annual cost of fuel for diesel reefer | $4123 | $4123 |
| Annual cost of fuel for electric reefer | $927 | $927 |
| Annual fuel savings compared to diesel, after converting to electric + solar roofing installation | $3987 | $3355 |
| Annual fuel savings compared to electric, after solar roofing installation | $791 | $159 |
| Cost to install solar panels in Boston, per reefer | $7104 | $1420 |
| Time for breakeven from diesel reefer | 7.1 years | 7.6–9.4 years |
| Time for breakeven from electric reefer | 9 years | 9 years |
References
