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Solar electric power for boats
Interactive guide to help you find the optimal solar solution
for your boat and needs!

(click on one)
What size of installation do I need?
Where should I install the panels?
What type of panel should I choose?

This interactive guide is protected under U.S., EU and other international copyright laws and may not be reproduced or used outside our web site without the explicit permission of Aurinco. The answers provided are only for guidance, we cannot guarantee the performance of an individual installation.

What size of installation do I need ?
Tell us what use you have in mind for your solar power by clicking on a choice below:
I want to keep batteries topped off while not using the boat
What equipment will remain connected, click on one below:
I only need to compensate for battery autodischarge
Select battery type below (and don't forget to keep the batteries clean to avoid stray current between terminals) :
Conventional lead acid batteries:

Estimate 5W of solar panel power for each 60Ah of battery capacity assuming that the solar panel receives some direct sunlight at least 6 hours per week. The use of a charge controller is optional if battery capacity is higher than 30Ah for each 5W of panel power.

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Sealed gel or AGM batteries:

Estimate 5W of solar panel power for each 120Ah of battery capacity assuming that the solar panel receives some direct sunlight at least 6 hours per week. The use of a charge controller is necessary to protect the battery.

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Small 18W panel for topping up batteries

I have a bilge pump and/or some small (<0.1A) permanent loads
My boat is a:
Up to 20 ft (6m) vessel with selfdraining deck and cockpit.

A rough estimate is a 10W solar panel for the first 80Ah of battery capacity assuming that the solar panel receives some direct sunlight at least 6 hours per week. Add 5W for each additional 60Ah of conventional battery capacity or 120Ah of sealed gel/AGM battery capacity. A charge controller is recommended (necessary for gel-AGM batteries).

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20-40 ft (6-12m) vessel with selfdraining deck and cockpit.

A rough estimate is a 20W solar panel for the first 120Ah of battery capacity assuming that the solar panel receives some direct sunlight at least 6 hours per week. Add 5W for each additional 60Ah of conventional battery capacity or 120Ah of sealed gel/AGM battery capacity. A charge controller is recommended (necessary for gel-AGM batteries).

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Larger vessel or vessel without selfdraining deck and cockpit

Contact us with details of your boat, equipment left connected, how long it is moored between uses, as well as your location and type of climate for an estimate.

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I want to keep a refrigerator or other higher energy equipment running
You have a:
Recent compressor driven low energy fridge

In most climates we would recommend at least 80W of solar panel power if the fridge is going to be on permanently. You also need a dual battery system with at least 120Ah on the household side. If it rains all the time? Most modern fridges are equiped with an automatic cut-off to protect the battery if voltage becomes too low. But don't store real caviar or other expensive perishables if you're away for long!
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Older fridge, electric coolbox with Peltier elements or other high power equipment

Contact us with details of your boat, equipment left connected, how long it is moored between uses, as well as your location and type of climate for an estimate.

I want to avoid starting up the engine while at anchor or under sails for 1-2 days
Tell us what equipment you will be running:
Electronics for navigation, radio, lights for a few hours, other low power equipment

We would think a 20W panel would do for most boats up to 20 ft (6m). Maybe 30-40W for a boat up to 40 ft (12m). Battery capacity should be at least 80 Ah, higher for larger boats. This provided there are some sunny spells. If it just keeps pouring down, OK, you may have to start that engine! For piece of mind, install a battery monitor.

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As to the left but adding a top loaded compressor refrigerator and/or a TV

We would say at least 40W for a smaller vessel for a day in the sun without engine power. For a larger boat, count on 60-100W, maybe more if the fridge is large and loaded from the side. Minimum 120Ah battery capacity. Again, if the skies are leaden and the fridge cuts out you may have to start the engine.

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More extensive list of equipment or high power items

Don't count on solar power for supplying current to stoves, space or water heaters, air conditioning or similar energy hogs. You will run out of mounting space, if not money. Install as much capacity as you can find space for and afford and be satisfied that the planet will be greener because you don't have to turn on the engine quite as often as before!

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I need to keep my equipment running for extended periods without engine or land power
Ok, you are probably planning an ocean crossing or a long leg in a sailing boat. Or perhaps you are just tired of using fossil fuels or being connected to the grid.

First, let's restate that you cannot count on solar or wind power for supplying current to stoves, space or water heaters, air conditioning or similar energy hogs. For this you will still have to resort to liquid fuel or gas, although you could use a solar stove on a calm sunny day in the tropics. The key is to reduce such use to a minimum and invest in energy efficient appliances. The same applies to electric equipment. You may have to be satisfied with canned dinners rather than to rely on a big fridge or freezer. Figure out what is really essential, then make a list of these items. Find out how many watts each uses or if the current use is given in amps, multiply the amps by your system voltage to get watts (e.g. 1A x 12V = 12W). Then multiply this number by the time in hours per day you use the equipment to get your daily consumption in watt-hours (Wh). For instance, a 45W fridge with a compressor which runs 1/3 of the time 24 hours a day uses 45W/3x24h = 360Wh. A 12V 10A bilge pump which runs 6 minutes a day uses 12Vx10A=120Wx6/60h = 12Wh. Add the power use for all your equipment to find out the total Wh you need per day.

Typically a well placed solar panel produces an average 5 hours at its rated power per day. Be more pessimistic if you sail in a foul weather area or in winter, more optimistic if you plan to be in the sunny tropics. With an average of 5 hours of full sunshine a 120W solar installation produces 120Wx5h = 600Wh per day. So you dimension your installation accordingly, but available space is often a limiting factor.

You also need to convert the total Wh your equipment consumes in a day into amp-hours (Ah, divide Wh by 12 for a 12V battery system) to make sure you have enough capacity in your batteries for the number of consecutive days you can expect to encounter with little or no sunshine.

Please feel free to contact us for further advice or explanations.

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© Aurinco 2009-2011

Last update 31OCT2014

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