Electric outboard motors are an option for boat propulsion. Most electric outboard motors have 0.5 to 4 KW DC electric motors, operated at 12 to 60 volts DC. These systems have the propeller fixed directly to the motor which is mounted in the lower unit under water - see trolling motor. This setup limits the power output. Recently developed outboard motors are powered with an AC or DC electric motor in the power head like a conventional petrol engine. With this setup a motor can produce 10 KW output or more and is able to replace a petrol engine of 4-8 HP.
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The advantage of electric boat propulsion systems are the low maintenance costs, the limited noise and emission free operation. The disadvantage is the limited range due to the wieght and size of the batteries. lead acid batteries have high weight (38 watt hours / kilogram) and limited capacity when quickly discharged (60% at 1 hour). Newer battery technologies like lithium systems (e.g. LiFePO4 or Lithium polymer) offer up to seven times the performance of a lead acid battery but they are very expensive. Charging the batteries with a photovoltaic solar system can make the system independent of any external energy source. For longer trips, the system can have a range extending gasoline or diesel generator which recharges the batteries.
Electric outboatd motors cost two to three times the cost of a four stroke petrol engine, but operation costs are lower. A 2 horsepower electric outboard motor including a lead acid battery can be purchased from USD 750.00 (2010) which is already competitive to a 2.5 HP petrol engine.[1]