How Much Solar?

The question that everyone that is going for extended cruising/voyaging asked at some point in their planning. How much is enough? You can never really have too much, but not having enough can be a real pain. Below is a screen shot of a spreadsheet I created to help me find a good balance.

Solar panel calculation spreadsheet.

There is probably too much information calculated, but I didn’t know what I didn’t know when I created it, so I added in everything I could think of. The most important calculations include total amp hours used and total amp-hours produced. The amp hours produced is calculated based on the total output of the panels multiplied by the average number of hours a day that are considered productive for solar panels for my area. If you do an online search for expected output for your solar panels, you should come up with charts that will show you how many hours are productive for your area.

Our plan was to have around 600 watts total, but we found a good deal on 285-watt panels, so two of those, along with what we now have, comes to 770 watts total. We bought one 285 watt panel so far and will buy the second in a week or so. We will have to buy a new MPPT charge controller, but for now, our current one is handling the load. How much you need is very dependent on your power needs. Your boat will more than likely not have the same equipment as ours, so your calculations will vary.

Let me know if any of you want a copy of my spreadsheet and I will email it to you. Shoot me an email at and I will be happy to respond!

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About Captain Tom

Over 10 years sailing and over 3500 miles under our keel. Was an engineer (EE) for over 30 years, then after moving into management, decided that the corporate world was no longer for me. Ran my wife's law office for 15 years and recently retired. Now we live aboard and sail the California coast, soon to leave for the Sea of Cortez.
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