| Sustainable Electric Power on Land and at Sea
Electric propulsion of sail and power boats offers the same clean energy advantages as extended range electric cars. Until now there have been few solutions available to the boatbuilder to install a hybrid system with the same ease as conventional diesel power. Hybrid Propulsion Corporation closes this gap with standard components for assembling hybrid systems for boats ranging from 10-ton catamarans to 100-ton trawlers and schooners.
Battery powered electric propulsion is silent and clean. It provides instantaneous thrust or braking. It minimizes prop drag and provides efficient, quiet motorsailing. When under sail, excess wind power is harvested to re-charge the battery banks.
Hybrid Propulsion builds systems optimized for boats and other applications requiring between 20 and 400 horsepower and which use either LiFePO4 (lithium) batteries or AGM batteries for battery operation. Battery Management is crucial in these systems and Hybrid Propulsion components are optimized for large battery banks at the high voltages required at these power levels.
Even small electric motors are efficient for low speed maneuvering because of their instant starting and high torque. For long distances at high speed, a boat needs the same total power whether it's powered by a conventional diesel or electric motor. If the vessel requires a 100 horsepower diesel engine to reach displacement hull speed, then it will also require 100hp (75kW) when using an electric motor in the same conditions. However, at low speeds, even a small electric motor can provide much greater acceleration, and improved braking with far greater control.
Hybrid Propulsion combines the best of both worlds. Diesel use is optimized because the generator only operates periodically to top off the batteries and only at its most fuel efficient loading. For long distance at higher power, the battery bank can be bypassed completely. Then the vessel operates in a diesel electric drive mode similar to nearly all modern ships.
The battery bank in a hybrid electric boat needs to have a high enough amp-hour rating to handle the continuous power you'll need for the motors, The amp-hours required are at least two to three times the highest current needed by the motor. The voltage of the battery bank should be sized to keep the maximum current under about 300A. For a 100kW propulsion system, this will be about 330 volts, provided in at least a 300AHr battery bank. When current exceeds 300A or voltage exceeds 600 volts, components and wire become large and very expensive. Above 200kW, it's usually more cost effective to provide a redundant system with either twin screws, two motors on a common drive shaft, or an electric motor on the same shaft (with a clutch) with a conventional diesel.
Hybrid Propulsion's power systems are tailored for banks of large LiFePO4 3.4 volt cells, and can support and balance cells up to 2000 AHr each. For a 100kW power train, the cost of 100 300AHr cells and battery management electronics is approximately $36,000. An equivalent high quality AGM battery bank would has a nearly identical cost but only provides half of the power per charge cycle and only last about 1/10 as many charge cycles before needing replacement. A properly managed LiFePO4 battery pack will last 3,000 to 10,000 recharge cycles.
Imbalance of batteries is the leading source of battery damage, shortened lifespan, and even fires in large, high voltage battery banks. Hybrid Propulsion battery management maintains a history of each cell over time and tailors the balancing to the needs of each cell.
Redundant safety systems instantly disconnect all power over 48 volts between batteries and to all loads in the boat in the event of an electrical fault or any wiring compromise. All high voltage cables are sheathed in an insulated bronze armor with electronic monitoring sensitive enough to recognize microvolt level disturbances even when a cable is simply bent or compressed.
Standard disconnect module safely couple each power source and load to the high voltage DC bus. The modules are simply bolted together side to side with tinned copper bars between. Each module has a status display, voltage and current monitoring, and disconnects on both the positive and negative terminals. Each also includes soft-charge electronics to deal with the dangers of high voltage arcing, and to pre-charge capacitive loads.
A typical propulsion system in the 35 to 150 kW range can be expected to cost around $1 per watt. For example, a 130 horsepower propulsion system including 100 kWHr of LiFePO4 battery storage, 75kW AC generator, 100kW permanent magnet motor with drive and gearbox, and all Hybrid Propulsion battery management, and system control components, will cost under $100,000. Small electric-only propulsion systems with LiFePO4 battery bank and charger, are available for under $20,000.