Power...

[Member 131497]

Hi guys... So is it the norm or the accepted mantra 100 watts solar panel?
Its a small 24 Bristol, and not all the appliances are gonna be on at the same time(2 battery banks)... What says you?

 

[JohnShannon]

You need to make a budget. What loads do you have? Ice box or fridge? LED lighting? Autopilot, Radar, or just Mk1 eyeballs?
What is your intended use?

 

[Bob J.]

FWIW, One guy I know has a 50 watt panel & it keeps his battery charged. He runs a simple boat, depthfinder, knot meter, not much else.

Another has a 100 watt panel. He runs a MFD at the helm & has refrigeration. He has all the power he needs.

 

[Charlie Jones s/v Tehani]

I lived aboard and cruised for 2 1/2 years with a 32 watt panel. had to go into a marina once to plug in due to extended clouds (days and days) . It's now reached the end of it's time and I'll replace with at least a 50 watt, but 100 would be better.

BUT be aware I'm a kind of luddite No A/C, no 110 aboard

 

[Benny17441]

The rating of solar panels is given as an average over a number of days, to diminish the effect of cloudy days. The average number of cloudy days in your specific area should give you an expectation of anticipated performance. Is that Ruskin, FL, you should be fine? Remember it is not the size of the boat but the power consumption habits of its Master.

 

[dlochner]

As others have said, it is necessary to know how much power is being used on a typical day and what other sources of power you have, engine, shore power.

Nigel Calder now suggests daily panel output of a high quality monocrystalline panel will be 3 times the rated output. Assuming the OPs panel is a high quality monocrystalline panel and uses an efficient MMPT controller, then the estimated out put will be 300 watts or 25 amp hours per day in good weather. A less efficient controller or a polycrystalline panel will see lower out put.

It is also important to remember it is not a 1:1 ratio when charging the batteries. If 10 amp hours are drawn out, it will take more than 10 amp hours to recharge the battery.

 

[capta]

We've had solar for about 8 years.
Do not count on the panel's listed rating to have anything to do with it's actual output except on a cloudless sunny day (& no shadows on the panel) around noon. There will be plenty of days when you will not get near the 100 watts at any time of the day. Count on an average of between 20 and 35% actual output over the long run, unless you are sailing in a desert or somewhere else very sunny and unusually cloudless.
Planning your solar array is just plain math. You must figure how much electricity you will use, in watts or amps, then how much solar power you will need to stay ahead of your needs. Remember, once you have free power, it's awful easy to add more devices, so perhaps plan for 10 to 20% more consumption than you currently are considering.

 

[Hello Below]

Nigel Calder now suggests daily panel output of a high quality monocrystalline panel will be 3 times the rated output.

I certainly was not aware of this. If this is the case, I may need a new charge controller as my Victron controller seems to be sadly undersized. Dave, do you have a reference/link for this.
Thanks

 

[dlochner]

I certainly was not aware of this. If this is the case, I may need a new charge controller as my Victron controller seems to be sadly undersized. Dave, do you have a reference/link for this.
Thanks

Calder wrote an article on Solar panels for the December/January Professional Boatbuilder magazine, page 45-46. (Sorry don't have an online or electronic reference.)

Over the years, I have steadily amended my calculation for the anticipated daily output of a solar panel. Today, given quality monocrystalline cells in a quality panel, I assume I will see the equivalent of three hours' worth of output at the panel's full rated capacity, i.e., a 100-watt panel will deliver 3 x 100 watt-hours = 300Wh a day (which, at 12v translates to 25 amp-hours). The crude calculation seems to work reasonably well in the summertime regardless of latitude, and in the tropics year round.

The controller should be sized for the panel's out put at any given moment, not the total output for the day. The Victron 75/15 would be more than adequate for a 100 watt panel. I use one for each of my 150 watt panels.

 

[Hello Below]

Total

The controller should be sized for the panel's out put at any given moment, not the total output for the day.

Totally agree. I missed the daily output part. Thanks for the clarification.

 

[finding41]

Go bigger than you think you will need. Also with the controller. You will probably want to up the # of W and panels someday.
MPPT controller is best for getting all the power out of the panel.
I had 2 100w flexible panels and a 30A PWM controller. I only run lights, radio, and charge devices (3 phones, 1 tablet and camera) and thought the setup was lacking.
Ive upgraded to a single 230w panel on an arch and a 30a MPPT controller. Now I don't worry about cloudy days. It seems to keep up.

The arch is great for drying towels too.