Comparison of Three Regenerative Energy Recovery Solutions for Port Cranes: Grid Feedback, Braking Resistor, and Supercapacitor Energy Storage

Port shore cranes and container gantry cranes are typical heavy-duty potential energy equipment. During operation, heavy-load lowering, mechanical deceleration and braking docking continuously generate substantial regenerative electric energy. For such regenerative power, the industry mainly adopts three processing solutions: traditional braking resistor energy dissipation, grid power feedback, and supercapacitor closed-loop energy storage recovery. These solutions differ greatly in energy-saving efficiency, renovation cost, operation and maintenance pressure, grid adaptability and working condition compatibility, which directly determine the energy consumption level, operational cost and grid operation stability of port equipment. Combined with the high-frequency start-stop, heavy-load fluctuation and complex outdoor working conditions of ports, this paper comprehensively compares the advantages, disadvantages and applicable scenarios of the three solutions, providing accurate technical references for the selection of port energy-saving renovation.

I. Core Working Principles of the Three Solutions

1. Braking Resistor Energy Dissipation Solution (Traditional Standard Configuration)

As the most basic and original energy processing method for port cranes, this solution requires no complex electrical control renovation. The regenerative electric energy generated by equipment deceleration, braking and weight lowering is directly connected to braking resistors and completely dissipated into heat energy. It consumes redundant bus power and stabilizes inverter voltage to ensure normal equipment braking. With no energy recovery or secondary utilization throughout the process, it only serves as a passive energy-consuming method for equipment safety braking.

2. Grid Energy Feedback Solution (Grid-Connected Feedback Type)

By installing feedback units and active inverter devices, the DC regenerative power generated by cranes is converted into high-quality AC power with the same frequency and phase as the grid, which is reversely transmitted to the public port grid for synchronous use by other on-site equipment, realizing grid-connected reuse of regenerative energy. Adhering to the core logic of "on-site generation and universal grid-connected reuse", it achieves no thermal energy loss and belongs to an open energy recovery solution.

3. Supercapacitor Energy Storage Recovery Solution (Local Closed-Loop Energy Storage Type)

Relying on the supercapacitor’s characteristics of high power, fast response and resistance to high-frequency cycles, and matched with a bidirectional DC/DC conversion system, a local closed-loop energy system for equipment is constructed. The regenerative energy generated by crane lowering and braking is quickly stored in the supercapacitor module; when the equipment requires peak power for lifting, climbing and starting, the capacitor instantly releases energy to supply power together with the grid. The regenerative energy realizes local storage, local reuse and closed-loop circulation, with no grid connection, no energy waste and no thermal loss.

II. Comprehensive Multi-Dimensional Comparison of Advantages and Disadvantages

1. Energy Saving and Energy Utilization Efficiency

Braking Resistor Solution: Zero energy-saving rate with 100% of regenerative energy lost as heat. It not only wastes electric power, but also raises the ambient temperature of the machine room, increasing additional energy consumption for on-site heat dissipation and air conditioning cooling, which is an extensive energy-consuming mode.

Grid Feedback Solution: It achieves 20%–30% energy-saving reuse, and the regenerative energy is connected to the grid for other factory equipment without thermal waste. However, it causes grid-connected harmonics and power quality loss. In addition, the large fluctuation of port load leads to the failure of partial feedback energy consumption, resulting in low actual effective utilization rate and difficult power metering and income accounting.

Supercapacitor Energy Storage Solution: The energy recovery utilization rate exceeds 90%, with a comprehensive energy-saving rate of 20%–40%. All regenerative energy is reused in a local closed loop without grid-connected loss or harmonic waste. It accurately matches the peak power demand of cranes, featuring far higher energy utilization efficiency than the other two solutions, as well as stable and accurately measurable energy-saving effects.

2. Grid Impact and Power Supply Stability

Braking Resistor Solution: It causes no grid-connected fluctuation or grid interference, but cannot solve the instantaneous peak power impact during crane lifting. The grid peak-valley difference is large, the transformer operates under long-term pressure, and the grid load remains high.

Grid Feedback Solution: Grid connection of regenerative energy easily generates harmonics and slight voltage disturbances, affecting grid stability and power quality. It imposes high requirements on the voltage stabilization capacity of the port grid; excessive grid fluctuations may lead to inverter failure and grid-connected faults, making it incompatible with old port grids.

Supercapacitor Energy Storage Solution: It completely isolates regenerative energy from the public grid with no harmonics or grid interference. Meanwhile, it realizes peak shaving and valley filling, compensates peak power during lifting, suppresses instantaneous grid impact, effectively reduces transformer load, and greatly improves the overall stability of the port grid.

3. Equipment Operation, Maintenance and Service Life

Braking Resistor Solution: Resistors work under long-term high temperature, prone to aging and burnout, requiring frequent replacement, circuit inspection and heat dissipation equipment cleaning, with high maintenance frequency and labor cost. The long-term high-temperature environment accelerates the insulation aging of electric control cabinets and cables, resulting in high equipment failure rate and shortened overall service life.

Grid Feedback Solution: The inverter equipment has a complex structure and precision components, which are prone to faults under long-term harmonic conditions and require high-level maintenance technology. Although it causes no high-temperature loss, it cannot alleviate the load impact of peak working conditions on the whole equipment, with no obvious improvement in equipment aging speed.

Supercapacitor Energy Storage Solution: With no heat loss or high-frequency aging components, supercapacitors support millions of high-frequency cycles and adapt to high-frequency start-stop working conditions of ports. It greatly reduces the loss of braking resistors and electric control equipment, lowers the overall failure rate, minimizes operation and maintenance pressure, and effectively extends the service life of lifting equipment.

4. Renovation Cost and Implementation Difficulty

Braking Resistor Solution: It has extremely low initial procurement cost, simple installation and no complex electrical renovation, serving as a low-cost temporary adaptation solution. However, its long-term energy consumption and maintenance costs are extremely high, resulting in poor comprehensive economy.

Grid Feedback Solution: It requires the installation of high-precision feedback inverter units and power filtering devices with complex renovation and construction procedures. In addition, it needs grid acceptance and compliance grid connection with cumbersome approval processes, featuring high renovation cost and poor adaptability for old ports.

Supercapacitor Energy Storage Solution: Adopting modular parallel renovation, it requires no modification to the original equipment structure and control logic, with short construction period and low downtime loss. It has moderate initial equipment investment, no subsequent consumable replacement or high-frequency maintenance cost, and the lowest long-term comprehensive renovation cost.

5. Working Condition Adaptability and Environmental Resistance

Braking Resistor Solution: It adapts to all port working conditions and grid environments with no compatibility restrictions, but only meets basic braking demands with no energy-saving and efficiency-increasing value, featuring single adaptability and backward functions.

Grid Feedback Solution: It has extremely high requirements for grid quality, only applicable to newly built standardized ports with stable grids and complete supporting facilities. It cannot adapt to old lines and complex outdoor working conditions with large grid fluctuations, resulting in weak environmental adaptability.

Supercapacitor Energy Storage Solution: With a wide temperature range, salt spray resistance and impact resistance, it perfectly adapts to harsh outdoor port environments with high temperature, high humidity, dust and salt spray corrosion. It is not affected by grid fluctuations, universally applicable to new and old ports and various shore cranes and gantry cranes, with the strongest working condition compatibility.

III. Core Parameter Comparison Table of the Three Solutions

IV. Applicable Scenarios and Selection Summary of Each Solution

1. Braking Resistor Solution: It is only suitable for old simple ports with extremely low budgets, temporary transition demands and no energy-saving requirements. With no energy-saving benefits, high maintenance costs and potential safety hazards, it fails to conform to the green and low-carbon port renovation trend and is a phased-out backward solution.

2. Grid Feedback Solution: It is applicable to newly built standardized ports with complete grid supporting facilities, stable voltage, qualified grid connection and sufficient load. It delivers medium energy-saving effects, but features high grid connection thresholds, high power quality risks and unstable returns, making it difficult to adapt to the renovation of old ports.

3. Supercapacitor Energy Storage Solution: It adapts to most new and old port shore cranes and gantry cranes, serving as the optimal solution for current port energy-saving renovation. It integrates multiple advantages of high energy-saving rate, zero grid interference, low maintenance, long service life and strong working condition adaptability. Independent of grid conditions, it realizes local closed-loop energy circulation, achieving cost reduction and efficiency improvement while supporting the green low-carbon compliance upgrading of ports.

V. Conclusion

With the upgrading trend of smart and green low-carbon ports, extensive resistor energy dissipation and restricted grid feedback solutions can no longer meet the long-term demands of ports for cost reduction, quality improvement and compliance. Featuring comprehensive performance advantages, the supercapacitor regenerative energy recovery solution has become the mainstream trend of energy-saving renovation for port lifting equipment. Tailored for the high-frequency start-stop and heavy-load potential energy release working conditions of port machinery, Tsingyane Electronics’ port supercapacitor energy storage and recovery system efficiently recycles regenerative energy, suppresses grid impact and reduces maintenance costs, providing low-cost, high-benefit and zero-risk integrated energy-saving and carbon reduction solutions for various ports.