Energy efficiency of a hybrid cable yarding system: A case study in the North-Eastern Italian Alps under real working conditions

Abstract

In order to reduce greenhouse gas emissions, low emission or zero-emission technologies have been applied to light and heavyduty vehicles by adopting electric propulsion systems and battery energy storage. Hybrid cable yarders and electrical slack-pulling carriages could represent an opportunity to increase the energy efficiency of forestry operations leading to lower impact timber harvesting and economic savings thanks to reduced fuel consumption. However, given the limited experience with hybrid-electric systems applied to cable yarding operations, these assumptions remain uncertain. This study assessed an uphill cable yarding operation using a hybrid cable yarder and an active slack-pulling electric power carriage over thirty working days. A total of 915 work cycles on four different cable lines were analysed. Longterm monitoring using Can-BUS data and direct field observations were used to evaluate the total energy efficiency, total energy efficiency (%), and fuel consumption per unit of timber extracted (L/m3). The use of the electric-hybrid system with a 700 V supercapacitor to store the recovered energy made it possible to reduce the running time of the engine by about 38% of the total working time. However, only 35% to 41% of the Diesel-based mechanical energy was consumed by the mainline and haulback winches. Indeed, the remaining energy was consumed by the other winches of the cable line system (skyline, strawline winches and carriage recharging or breaking during outhaul) or dissipated by the system (e.g., by the haulback blocks). With reference to all work cycles, the highest net energy consumption occurred during the inhaulunload work element with a maximum of 1.15 kWh, consuming 70% of total net energy consumption to complete a work cycle. In contrast, lower energy consumption was recorded for lateral skid and outhaul, recording a maximum of 23% and 32% of the total net energy consumption, respectively. The estimated recovered energy, on average between the four cable lines, was 2.56 kWh. Therefore, the reduced fuel need was assessed to be approximately 730 L of fuel in the 212.5 PMH15 of observation, for a total emissions reduction of 1907 kg CO2 eq, 2.08 kg CO2 eq for each work cycle.

On the Design of Hybrid Tower Yarder Drivetrains: A Case Study

“…Considering this result, the maximum power of the drums given in Table 1 is in the range of what could be achieved with an average-sized dedicated engine. The values chosen for NEC and EC appear reasonable considering data in Table 5 and the discussion around the publication by Cadei [23], noting that the extraction distance may be significantly longer and the skyline may be steeper than in the example setups above. Finally, durations and speeds of the hauling out and hauling in subtasks are chosen to be reasonably large and congruent with an extraction distance of 750 m. The remaining time periods (t 2 , t 3 , t 6 -t 8 ) are chosen to be fairly short to create a worst-case scenario.…”

“…Based on the authors' experience, this type of control strategy is the norm within this industry. The study of a hybrid TY by Cadei [23] presented similar transport data as given in Table 3, with a special focus on power, energy, and fuel need of the individual transport cycles. The hybrid TY is of lower power and the average load per cycle is smaller than for the setups of Table 3.…”

“…Table 5. Statistical transport data and energy consumption of the hybrid TY in various uphill configurations making use of both the haulback and mainline drums [23].…”

“…While the hybrid TY consumed 0.25 L m 3 − 0.32 L m 3 of transported timber on a 62.2 m extraction distance in closed-loop uphill configuration, the conventional TY study reported 1.27 L m 3 at a similar yarding distance. From [23,30] it can be further found that the consumption more than doubles with a four-times-longer extraction distance.…”

“…A hybrid TY (K507e-H) and a hybrid SDSK (HULK 4.0), as shown in Figure 1, are expected to be introduced to the market in 2022 by Koller Forsttechnik [20] and Leitalpin [21], respectively. While no works or studies have yet been published on electrified SDSKs, Leitner [22] and Cadei [23] performed comparisons between conventional and hybridized TY drivetrains based on theoretical and practical evaluation studies, respectively. The study by Cadei revealed that the K507e-H, first presented at the exhibition Austrofoma 2015 in Austria [18], comprises a series hybrid concept.…”