Research on Low-Cost Adaptation Solutions for DC Shore Power Systems for Small Inland Vessels

I. Background and Requirements: The Urgency of Green Transformation in Inland Shipping

As a vital component of the transportation system, inland shipping plays a critical role in the transport of bulk cargo. However, during port stays, traditional inland vessels universally rely on diesel auxiliary generators for power. This practice not only generates significant carbon emissions but also results in noise pollution and fuel consumption (averaging 50–150 liters per day). In this context, shore power technology has become a core method for emission reduction in shipping. By utilizing port power supply systems to replace onboard generators, "zero emissions and low noise" can be achieved during port stays.

Compared to ocean-going vessels, small inland vessels (tonnage ≤ 500 tons) have distinct characteristics: they are numerous (accounting for over 60% of total inland vessels), operate on fixed routes, have short port stays (averaging 4–8 hours daily), and have relatively simple power requirements (mainly for lighting, communication, and living equipment, with power demands mostly between 5–30 kW). However, existing shore power facilities are primarily designed for large vessels, leading to issues such as non-uniform interfaces, high retrofit costs (over 100,000 yuan per vessel), and insufficient adaptability. Consequently, the penetration rate of shore power for small vessels is less than 5%. Therefore, developing a low-cost, easily deployable DC shore power adaptation solution is of great significance for promoting the green transformation of inland shipping.

II. Existing Pain Points: Core Obstacles to Shore Power Adaptation for Small Vessels

The promotion of shore power for small inland vessels faces three core issues:

1. Non-uniform Interface and Voltage Standards
Port shore power facilities mostly adopt AC 380V or high-voltage DC (e.g., 600V) standards. In contrast, the original power systems of small vessels are mostly low-voltage DC (24V/48V) or low-power AC (220V). This mismatch requires additional voltage conversion equipment, increasing retrofit costs.

2. Mismatch Between Retrofit Cost and Operational Benefits
Small vessels operate on thin profit margins. Traditional shore power retrofits involve replacing cables, installing chargers, and upgrading distribution systems. The initial investment per vessel exceeds 50,000 yuan, and the payback period often exceeds 3 years, making it difficult to motivate shipowners to retrofit.

3. Insufficient Port-Vessel Coordination
The coverage of shore power facilities in some inland ports is low (especially in small and medium-sized ports, where it is less than 20%). Furthermore, the lack of a unified power supply dispatch mechanism means vessels may face situations where "there is a vessel but no power" or "there is power but it is incompatible."

III. Low-Cost Adaptation Solution Design: Focusing on "Simplification, Reuse, and Standardization"

To address these pain points, this paper proposes a low-cost DC shore power adaptation solution based on "Interface Standardization + Modular Retrofit + Existing Equipment Reuse." The core objective is to control the retrofit cost per vessel within 20,000 yuan and shorten the payback period to less than 1.5 years.

• Interface Standardization: Unifying Low-Voltage DC Interfaces
  A 220V DC standard interface is adopted as the universal solution:

1. Basis for Voltage Selection: 220V DC balances safety (below the 380V AC safety threshold) with transmission efficiency (line loss is reduced by more than 60% compared to 24V/48V), meeting the 5–30 kW power demands of small vessels.

2. Interface Specifications: Referencing the China Classification Society's "Technical Requirements for Inland Vessel Shore Power Systems," interface dimensions and pin definitions (e.g., 3-core: positive, negative, signal feedback) are unified to ensure plug-and-play functionality for both port and vessel ends.

• Modular Retrofit: Configuring Core Components as Needed
  The shore power adaptation system is broken down into three independent modules, allowing shipowners to purchase flexibly based on their power needs, avoiding "one-size-fits-all" over-investment:

1. Power Conversion Module: Uses industrial-grade DC/DC converters (Input 220V DC, Output 24V/48V, Power 5–15 kW). Costs are controlled between 3,000–8,000 yuan (50% lower than customized equipment).

2. Energy Management Module: Simplifies complex traditional control systems by using low-cost PLCs (Programmable Logic Controllers) for basic charge/discharge management (e.g., overvoltage/overcurrent protection, battery status monitoring), costing approximately 1,500 yuan.

3. Interface and Cable Module: Selects waterproof industrial plugs (IP67 rating) and flame-retardant cables (cross-section 6–10 mm²) compatible with port standard interfaces, costing approximately 2,000 yuan.

• Existing Equipment Reuse: Reducing Retrofit Costs
  Fully utilize the vessel's original power equipment to minimize new investment:

1. Battery System Reuse: Small vessels are generally equipped with 24V/48V lead-acid batteries (capacity 200–500 Ah), which can be directly used as energy storage buffer units for shore power supply, avoiding the need to purchase additional storage batteries.

2. Distribution System Retrofit: Only requires adding a DC circuit breaker (costing approximately 500 yuan) to the original distribution box to switch between shore power and the onboard generator, eliminating the need to replace the entire distribution wiring.

IV. Key Technologies and Implementation Points

• Simplified Energy Management Strategy
  Complex algorithms are unnecessary; basic charge/discharge management is achieved through "Voltage Threshold Control":

1. When the vessel's battery voltage drops below 22V (24V system) or 44V (48V system), shore power charging automatically starts.

2. When voltage reaches 28V (24V system) or 56V (48V system), charging stops to prevent overcharging.

3. Overcurrent protection (threshold 100A) and short-circuit protection (response time < 0.1s) are configured to ensure electrical safety.

• Low-Cost Port-Side Retrofit
  For small and medium-sized ports, a "Distributed DC Power Supply Pile" solution is proposed:

1. Photovoltaic + Storage is used to supplement grid power (especially in remote ports), reducing dependence on grid capacity.

2. Each supply pile is configured with 2 units of 220V DC output (15 kW per unit), with costs controlled within 15,000 yuan (only 1/3 the cost of traditional AC shore power piles).

• Policy and Standard Coordination
  Promote local maritime authorities to issue supporting policies:

1. Provide one-time subsidies for retrofitting vessels (e.g., 3,000–5,000 yuan per vessel).

2. Mandate that newly built small vessels reserve shore power interfaces to reduce future retrofit costs.

V. Application Cases and Benefit Analysis

Taking a 500-ton bulk carrier in the middle and lower reaches of the Yangtze River as an example, after retrofitting with this solution:

· Retrofit Cost: Power conversion module (6,000 yuan) + Energy management module (1,500 yuan) + Interface cables (2,000 yuan) + Distribution retrofit (500 yuan) = Total 10,000 yuan, which is 60% lower than traditional solutions.

· Operational Benefits: Average daily port electricity usage is 100 kWh. With shore power electricity prices at 0.6 yuan/kWh (diesel generation costs are about 3 yuan/kWh), daily savings are 240 yuan. With approximately 150 port days per year, annual savings amount to 36,000 yuan, resulting in a payback period of only 0.3 years.

· Environmental Benefits: Annual diesel consumption is reduced by approximately 7.5 tons, corresponding to a reduction of 20 tons of CO₂ emissions and 0.15 tons of NOx emissions.

VI. Conclusion

The low-cost adaptation solution for DC shore power for small inland vessels, through the three core strategies of "Interface Standardization, Modular Retrofit, and Existing Equipment Reuse," can significantly reduce retrofit costs (≤ 20,000 yuan per vessel) and shorten the payback period (≤ 1.5 years), providing a feasible path for the green transformation of inland shipping. In the future, it is necessary to further promote standard coordination between ports and vessels, policy support, and technological iteration to accelerate the large-scale application of the solution and help achieve the sustainable development of inland shipping under the "Dual Carbon" goals.

Unified interface standards; the development of plug-and-play power modules and standardized wiring harnesses compresses the retrofit time per vessel from 3 days to 8 hours; innovative "shore power - vessel original distribution system" seamless switching solutions achieve an equipment reuse rate of over 70%, further reducing hardware investment.

For a 500-ton freight vessel, the total investment is only 18,000 yuan, the retrofit cost can be recovered in 14 months, and annual carbon dioxide emissions are reduced by more than 15 tons.

lcxpower.com will collaborate with industry associations to promote "Vessel-Port-Power" standard coordination and develop "Shore Power + Photovoltaic" complementary solutions. If your fleet or port faces issues such as high shore power retrofit costs and long payback periods, lcxpower.com will provide full-chain services to help inland shipping move towards a "Zero-Carbon, Efficient, and Sustainable" future.