How Many Watts of Solar?

[Mike OReilly]

Guess it depends on where you cruise NH. Even though I have modest power needs, 200 watts would be inadequate. But I cruise more northern latitudes (~50 degrees north).

My main point is that for most modest monohulls, the main limiting factor will be solar panel space. So a simple answer is to maximize your panel installation (within reason, of course). Beside, I’ve never heard any cruise complain that they had too much solar generating capacity.

[AndyEss]

Originally Posted by Mike OReilly

Guess it depends on where you cruise NH. Even though I have modest power needs, 200 watts would be inadequate. But I cruise more northern latitudes (~50 degrees north).

My main point is that for most modest monohulls, the main limiting factor will be solar panel space. So a simple answer is to maximize your panel installation (within reason, of course). Beside, I’ve never heard any cruise complain that they had too much solar generating capacity.

Space for panels is the limiting factor in my estimation, as long as you don't go to the big buck "marine" panels. If you go $$, budget of course, figures far more prominently.

Right now I have 580 watts of solar installed, in 8 panels, wired in parallel in two charging circuits, with two separate MPPT controllers. I have 300 amp-hrs of LiFePo. I spend nearly all my time at anchor, so orientation of the panels is up to wind and tide. La Paz is 24 degrees north, so we have a not insignificant variation in seasonal insolation.

Because of my canoe stern, windvane and already installed wind turbine/light pole to starboard and a radar pole/outboard crane to port, I can't/won't build a stern arch.

Because of unavoidable shading of rigging and my boom, shading is significant (again, I swing at anchor, I'm not in a marina tied to a dock the vast majority of the time) so other than at high noon, I often have only half of the power capacity of the 580 watts installed - i.e. 290 watts available.
Power boats and land installations are different from sailboats. Shading is unavoidable in many situations.
My solution is to install as much solar as I have real estate for, consistent with esthetics and safety.
I am going to install one more 120 watt panel on top of my bimini, which should only be partially shaded by the boom during only certain boat orientations, for a total of 700 watts.
Figure on many sailboats with no stern arch (clear of the boom), you will very often loose 1/2 of your installed solar power capacity due to shading from your boom and other rigging.

[thomm225]

Originally Posted by KP44

Two 235 amp hour 6 volt batteries in series equals one 235 amp hour 12 volt battery.
I have 8 of them. Which gives us four time 235 amp hours. (Not 8 times.)

About 900 amp hours is very good if you have the space for 8 batteries.
I also carry two starting batteries (in parallel) that never do anything except run the engine.

I may have spoken too soon. My two 12 volt 80 ah batteries in parallel may be enough

I just unhooked one panel and am now just using my 65 watt panel to the Victron MPPT Controller. I have three other panels totaling 90 watts if I need them. I'll hook them to the pwm controller when I anchor if power is low

I don't need any battery power for the engine.

The main draw is the lights which I rarely have on. Anchor light is a battery powered LED Lantern

[john61ct]

Originally Posted by AndyEss

My solution is to install as much solar as I have real estate for, consistent with aesthetics and safety.

Precisely.

And sailing performance, seen plenty of installs with crazy windage.

But that usually far past the point they've ruined the beauty of their boat.

Which of course is none of my business.

But for my setup I plan for the goal of whatever solar I do put in, to just reduce ICE runtime, so I'm not sacrificing those other factors too much.

[EmeraldCoastSailor]

On my 34' the strategy was to start with 220w on the bimini with a Victron sized to that. Too soon to tell how close it will come to meeting my needs but my plan is to add another 100w with another small controller if my consumption leads me to running engine at anchor excessively. I don't have a lot of room for panels.

[Lagniappe]

You are getting a lot of good advice from folks many of whom have a lot of experience with what works and what doesn't on their boats. As someone who has been cruising full time for almost 6 years on a 37' Pacific Seacraft I have struggled with getting the right balance of solar and wind power for my needs.

I would suggest you make a phone call to folks who put together these systems for a living. Contrary to popular belief the good folks will not try to sell you a lot more then you need. I suggest contacting Gretchen at Coastal Climate Control in Annapolis (301) 352-5738 or eMarine Systems in Florida at (954) 581-2505.

When making this type of investment in panels, controllers and installation it pays to at least talk to the experts.

[Sidney777]

Microwave?
Most likely not. Huge inverter & number of batteries needed

[Happ]

The first response was correct. You need to start with an energy audit. This will take into account what kind of lights you are using? LED? Are you anchoring thus using an anchor light? How much draw is your laptop using or can you just charge the battery when you need to? How big is the microwave? Once the energy audit is done know you will know much power you are going to use. Then think about what kind and how many batteries you need. For instance AGM batteries discharge to a lower level then others. Once this is done it’s simple to know how much solar you need.

When I built my electrical system from scratch I discovered batterystuff.com. They are a great resource as they have much of the calculations online. Just fill in the blanks. They also sell everything you need. You can also call them as they have very knowledgeable people. As an internet company their prices are great.

I am a customer and not affiliated with them.

[dancor01]

Originally Posted by Razoo

How many watts of solar is need for a 34'-38' sailboat? I'm trying to figure out what I need to run lights, laptop, micro wave etc.


Thanks.

400 in summer, 800 in winter. Battery banks betweem 800 and 1000 amps.

[john007]

I have a Beneteau 375 with two 100 amp hour batteries for the domestic supply. I have over the past three years had satisfaction with 400 watts of power. The boat is marina based in the south of France. Leaving the fridge on overnight does not cause a problem, the battery recovering an overnight loss, down to 80 % back to 100 % within the hour

[newhaul]

Originally Posted by john007

I have a Beneteau 375 with two 100 amp hour batteries for the domestic supply. I have over the past three years had satisfaction with 400 watts of power. The boat is marina based in the south of France. Leaving the fridge on overnight does not cause a problem, the battery recovering an overnight loss, down to 80 % back to 100 % within the hour

that doesn't sound possible to be fully recharged from 8o% what are your charging sources

[john007]

No complicated mathematics. Practical observations. Regularly the loss will be evident on my battery meter showing the figures I have stated. Indicating that the panels are working. If that recovery rate does not occur I look for the reason.

[Captain Bill]

Originally Posted by john007

I have a Beneteau 375 with two 100 amp hour batteries for the domestic supply. I have over the past three years had satisfaction with 400 watts of power. The boat is marina based in the south of France. Leaving the fridge on overnight does not cause a problem, the battery recovering an overnight loss, down to 80 % back to 100 % within the hour

Within the hour? Which hour are you talking about? You claim you are down 40 amp hours overnight. 400 watts of panels are not capable of producing 40 amp/hrs of power in any one hour period even with the sun directly overhead and that is never going to happen in the south of France. The maximum you can produce is 33 amp/hrs and even then charging is not 100% efficient. If you were claiming to have 40 amp/hrs by noon I might buy it, but within an hour?

[Razoo]

Originally Posted by Sidney777

Microwave?
Most likely not. Huge inverter & number of batteries needed

Yup! I threw the microwave to the fishes so to speak. I figured out the amount of times I would use it and I came up with maybe 10 times a year. Useless extra weight.

[john61ct]

Originally Posted by Sidney777

Microwave?

Most likely not. Huge inverter & number of batteries needed

Actually microwave used only an avg few minutes per day does not consume many Ah.

Yes a matching inverter is needed.

And personally I think silly on a small boat, but plenty do it, even in vans too.