A Well Balanced System

You’ve made the decision to reduce your fossil fuel use while sailing. Great news; it’s not as daunting as it seems. The electric propulsion system is straightforward with only a few components and even fewer moving parts. You will want to build a system that can recharge and use the energy onboard to meet your motoring needs. There’s a balance between having energy to use and how quickly that energy can be recharged. From personal experience, the 33 kWh propulsion bank has been nice, but I’ve only drained it down to 8% once in the past year of use. This is due to the solar array, and the fact that getting becalmed for days on end doesn’t happen that often. To charge your system, you’ll want to use the latest battery tech, which is our LiFePO4 batteries. This chemistry accepts charge very easily with a charge efficiency of 98%. There is so little resistance in the cells of the battery that you don’t waste hours of charge time to get past the last stages of charge, like you would with a flooded lead-acid or AGM battery. Additionally, these LiFePO4 batteries have no memory, which means they can be charged and left at any state of charge you choose without them eventually adapting that state of charge as the new full charge. Lastly, this battery chemistry can be discharged down to 10% safely without damage, which unlike FLA or AGM, you should only drain down to 80% before recharging through the charge cycles and back to float. Crazy to think the antiquated battery chemistry only allows 20% of the advertised energy to be used.

Now that you have a battery bank that can handle the deep discharges and quick recharges of a propulsion system, how do you charge it? With renewables, the quietest and lowest maintenance is via solar panels. We have a great relationship with Maxeon, who makes high-voltage, high-efficiency solar panels. To charge the 48V bank, you’ll need 5V above system voltage, which can be 62V, which is why Maxeon's 76V panel works so well. This high voltage also allows earlier charge times by turning on the MPPT earlier in the morning. The 470W panels we’ve tested have overproduced in every environment. We are seeing 2-3 kWh per panel consistently. The beautiful thing about the solar electric motor combo with a fast charging battery chemistry is you can motor while using only the sun. The amp offset allows you to reduce the overall amp draw or completely cancel out the motor amp usage.

When solar isn’t the optimal choice for your location, a wind generator can be used. These produce power at higher wind speeds. This means while sailing downwind, the efficiency will be lower with a slower apparent wind, but if at anchor and it’s blowing, you’ll be charging overnight when a solar-only boat will be sitting idle. It’s a balance. The other route which shouldn’t be discarded is a generator. There’s nothing wrong with reducing your fuel burn and not eliminating it completely. A diesel genset will use a much lower fuel rate than your existing main diesel engine. A 2-cylinder diesel will only use .26 gal/hr per hour and can produce 70-120 amps to your batteries. When this system is designed correctly, you can have a diesel hybrid configuration which would allow you a 5-knot boat speed or slightly higher while only burning .26 gal/hr compared to the 1 gal/hour a main diesel would use. Having less emissions impact is the goal here. You don’t have to be a purist and never use fossil fuels again. Just try to use less while using a product that requires less maintenance. The reward is more time sailing!