Solar and Wind Power for Boats

Hotwire specializes in solar and wind power alternative energy for boats.  We can recommend options for charging batteries.

How do you use your boat?

Boat kept in a marina (or on a trailer at home) with shore power and a battery charger…

If you want to be able to maintain battery power while out for a weekend, the best solution is to add another battery and, over a day or so, let it partially discharge. Then when you return to the dock, the battery will have a chance to recharge. No need for solar or wind.

Occasional use of a boat stored on a trailer or a mooring where there’s no electrical access…

If you’re using a flooded, deep cycle battery, it will self-discharge over time, more rapidly than gell or AGM batteries. A small solar module provides what is called a trickle charge so that the battery is fully charged when you need it. A small, inexpensive solar module (panel) is all that is needed to keep the battery from discharging and prematurely failing. To determine the size module needed, look on your battery label to find the amp-hour capacity (NOT the cold cranking amps). The battery can tolerate up to 2% charge over that with no problem without a charge controller if the battery is flooded (wet, the kind you can add water to). Multiply the amp hour capacity by 1.2% to determine the maximum number of amps you’ll need for trickle charge and then refer to our output column on the solar module page to identify which module comes close to your calculation without exceeding it. This will be sufficient to maintain your battery without overcharging it and without the need for a charge controller. We have a 5 watt panel that will work for most boats with a single battery -only $18. This is a mono-crystal panel, made in China, see: You’ll need to attach wires and alligator clips or a cigarette lighter plug, or call, and I can do that for you.

If you’re using AGM or gel batteries, they’ll hold a charge very well and trickle charge is less likely to be needed. You’re less likely to need a solar module. If you decide to purchase one, these battery types are more sensitive to overcharge and would be more likely to need a charge controller.

For a boat on a mooring with an anchor light, the best solution involves an LED anchor fixture or bulb replacement (see our anchor light options), so that a smaller solar module can be used.

If you’re unsure of your calculations or your choices, please contact us for assistance. We’ll be happy to help you.

Weekend use with the battery discharged when you return…

You’ll need more than a trickle charge. You want to recharge. You’ll need a larger solar module for a larger output, and you’ll need a charge controller to prevent overcharge. However many amp-hours you’ve removed from your battery (or battery bank), you’ll need to replace those amp-hours for healthy battery maintenance and for a reliable charge when you’re ready to take the boat out next time. To determine the size of the solar modules, you’ll need to calculate the amp-hours used on the weekend, then size the array so that the batteries get topped off before the next weekend. Contact us for help with the calculation.

Cruise for a week or two, or a month or two…

You’ll be using your engine sometimes, and a good high output alternator can charge your batteries better than the alternator that likely came with the boat. Please see our alternator page. Solar power works anywhere that the sun shines. You can install a small solar array and be recharging your batteries silently during daylight hours. Figure out where you can put one or more solar modules where they’ll be unlikely to be shadowed most of the time. Measure the space available to see what you can fit into that location. Figure out how many amps the system will be capable of producing, and select a charge controller that has a large enough amp capacity for your array. Consult a wiring chart to determine what size wire you’ll need to use in order to get the best benefit from your investment in solar. Or contact us for assistance with these decisions. We can talk you through it, helping you with the details and suggesting the most effective products for your situation.

Live aboard, heading for the trade winds (Bahamas or Caribbean or beyond — HOORAY!)

If you’re headed for wind territory, a wind generator can be more cost-effective than solar, but we recommend a hybrid system (wind & solar together) for the “insurance” of being able to charge regardless of weather conditions. The KISS High Output is the wind generator of choice for a great many cruising sailors because of its quiet running, high power output and simple design. It takes up a smaller “footprint” than the number of solar modules needed for its equivalent output. If you have a mizzen mast, that’s a great place for a KISS, high where the wind is good. If you don’t have a mizzen mast and you’re going to the Caribbean, plan to install your wind generator on a tower on the port side of the stern. Think about it: winds from the east (bow pointing east), sun south of you most of the year, solar on the stern and/or starboard side, wind generator on the port side where it’s less likely to shadow your solar. Make sense? So you have great winds (10-15 knots in the summer, 15-25 knots in the winter), great wind power for those windy days and supplemented by your solar array, and the solar constant on those rare days when the wind doesn’t blow. Makes GOOD sense!

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