Solar Panel Questions

[a64pilot]

I find electrical power is a lot like money.
First I’ve heard of having too much of either, but don’t really believe it.
Second, you will spend what you have, both in power and money. Having just enough panels to barely get by will mean your always watching consumption, just like a money budget, having more than you need means you won’t worry about how much you spend, or use.
Fit as many panels as will fit or you can afford, as long as you can live with the appearance, some can’t which is understandable.
For those you can spend more $$ and hide them like Ken did with his flexible panels on his Bimini.

[Oceanride007]

I would think you already should have numbers to calculate how much solar you need.
If you need to get a SS frame made up, with your best estimate size your Frame for room for say 25% extra (whatever to make the arithmetic to work out), 125Watt is already to big to handle in case of windy weather (You may need to get them down alone) allow easy fastenings.

I use 2.77A average at night, 3.62A average per day. I monitor the capacity and battery voltage each morning. On a bad day I reckon I can still get half power from my panels, plan on 2 bad days in a row. Have you still got 60% SOC by the morning of 3rd day.

How much extra power do you require sailing, have you got enough to drive your AP all day. Mine averages extra 4amps. What about sailing at night (night time is much longer due to low incident light late afternoon or early morning) allow ~17 hours without solar (Day time solar use is more effecient due to battery inefficiency.

Bad planning would be a disaster, order your frame only when you have ducks in a row. A friend just payed $5000 for his bells and whistles model. Allow for Wind Gen mount. Stbd side for Southern Hemisphere, Port for the North or make it swichable (due to Trade winds and shadow.) Lots of ifs, buts, compromise, get your ducks in a row.

Despite being well prepared I underestimated and now dealing with 2 different panel sizes, its OK I have extra room.

[Kenomac]

Originally Posted by Kenomac

The OP has a generator, he doesn't need 1000-2000W of solar on a 47ft boat.....
He doesn't need to spend money to build a floating a solar farm when he already owns a generator..

Diesel fuel run through the generator already owned by the OP for an hour or so every few days is far cheaper than adding any more solar than 400-500W. Unless the guy likes to have his jumbo-sized deep freezer turned on full-time at minus 20 degrees C... 400-500W of solar is all he needs.

[daletournier]

If I had a built in generator then I believe Ken's suggestion is the best way. No need for more panels unless you don't want to run the generator.

Without a generator more solar is better, you don't get full sun everyday, this is where power budgets fail, the variables.

I have 480w, if there is sun they easily meet my energy needs. On days like today the Honda needs to come out.

I'll be adding more panels as I would prefer to use the Honda as little as possible.

In saying the above no one complains about to much solar!

[UFO]

Originally Posted by travellerw

Hmm we get "rated output" (actually more) at noon

That's my point - At Noon Height of summer for an hour - You can't base any output solely on rated wattage - That's in optimum conditions - Angle of sun, temperature, time of day, cloud cover etc will have an effect. Also I would be very suspect on anything long term for output with the cheaper Chinese panels - In some instances you do get what you pay for - I have dealt with Chinese manufacturing for a decade (not Solar) and know that Quality Control for most manufactures is very poor - There not just cheap because of Cheap labor, its also cheap components and manufacturing processes.

[GordMay]

Greetings and welcome aboard the CF, Gregoire.

[travellerw]

Originally Posted by UFO

That's my point - At Noon Height of summer for an hour - You can't base any output solely on rated wattage - That's in optimum conditions - Angle of sun, temperature, time of day, cloud cover etc will have an effect. Also I would be very suspect on anything long term for output with the cheaper Chinese panels - In some instances you do get what you pay for - I have dealt with Chinese manufacturing for a decade (not Solar) and know that Quality Control for most manufactures is very poor - There not just cheap because of Cheap labor, its also cheap components and manufacturing processes.

All panels are rated like that "optimal conditions".. Even the highest end ones.

My experience disagrees with your view. Our panels will produce over thier rated wattage at any time of the year. The reason I said noon is because our panels do not tilt. No panel will produce its rated output if its not at the optimal angle. Where we cruise, that optimum angle happens at noon.

As to longevity.. Ours are 24 months old and still over producing. We know other cruisers who's Chinese panels are 5 years old and still producing thier rated wattage.

Personally I don't see the value in spending more unless I'm going for the highest efficiency (to save space). So far, 24 months of living aboard and cruising I'm happy with the panels I have.

[Suijin]

Originally Posted by gregoire.poirie

I need to correct that we only want to use the 8.5w generator as a backup only, and depend on solar when cruising or even out on a mooring. Goal is to outfit her for long passages and extended time off shore power.

I agree with Ken that loading up on solar when you do have a generator for bulk charging may not be an economical (or aesthetically pleasing) path to take.

That said, you've not told us what your battery bank looks like. I mentioned that as a general rule you want more watts than you have amp hours. If you have AGM batteries, you're going to want to get them to float at least a few times a month. The more often you can get them to float the longer they will last. A compromise might be to just run the generator once a week or every 10 days to get them to float.

You CAN in fact have too much solar. If you don't have the capacity to store it, and aren't using the excess routinely for a water maker or other appliances, it's just money down the drain.

So you want to have enough amp hours to meet your usage requirements (>200% of your average daily draw). If you don't know what this draw is then you can't evaluate whether you have enough storage, and so can't design a solar system that will meet your needs.

[valhalla360]

Do an energy audit and then consider if you want to up-size a bit. Just going big for no reason can be a waste of money.

But don't just consider the solar panels. You need Battery Bank info, number of days between generator/shore power top up.

Since you have a generator already, run the numbers on using it periodically to top up rather than putting in a larger system. You need to exercise the generator periodically anyway, so if you run it for an hour once or twice a week, it may cost you very little in fuel while saving the generator long term all while allowing a smaller solar array.

[sailorboy1]

Originally Posted by gregoire.poirie

We are looking to add solar panels on our live aboard, 47" Beneteau sailboat and wondered if a good target is getting 400w in 4 panels. Since we have most of modern conveniences, we want to offload expenses when on shore power and want to use the gen for backup to keeping dry battery bank fully charged when cruising.

Suggestions?

By now you know the answers are - it depends. But I will just say the answer is yes 400W will do you fine. I have 290W and keep fighting the urge to add more as the cost of the solar doesn't really justify it. I reviewed my logs for the past year and found that I rarely ran the generator to just charge the batteries. I ran my generator for something else and charged the batteries at the same time. So since more solar doesn't really end up with less need to run the generator and the generator is already paid for and installed, by pay for more solar.

Btw - in order to really give my answer meaning you would need to know my normal power usage. So on my boat the normal daily use at anchor is around 150-175AH

[Eder]

I have 400w of flex panels velcro'd to my bimini top as well as a 6kw gen. No sense making your sailboat look like it came from the Mad Max movie if you already have a diesel gen.

We run the gen in the morning for a bit while running coffee makers,toasters,electric cooktop,watermaker etc.

Rest of the day the solar does its job keeping the 2 freezers running as well as all my instruments including 2 chartplotters,radar,auto pilot,various other electronics.

I do have a 260gal fuel tank so running the gen is pretty much unnoticeable,not sure the size your boat has.

[a64pilot]

Originally Posted by Suijin

You CAN in fact have too much solar. If you don't have the capacity to store it, and aren't using the excess routinely for a water maker or other appliances, it's just money down the drain.

I’d say what “too” much Solar gives you is not so much more max output as often your batteries can’t accept the max anyway, but it gives you more usable Solar hours in a day.
It’s not from a lack of Solar capacity that has me running the generator in the morning, it’s from not having enough useable hours of output.
I have an AGM bank and can tell you in my opinion, it may not be the best chemistry for a cruising Boat, cause you really do need to get to fully charged often, not float, fully charged, cause if you rely on your charger to go to float to determine full charge, almost always your not getting there.
The exception of course is a programmable Charger that you can program an amperage to determine when to trip to float.
However it’s been my observation so far that if you actually using the Boat and it’s electrical system, your better off to program the charger so that it never trips to float, your not going to overcharge your bank.
A boat sitting on a mooring unoccupied is different of course, with nothing but an anchor light on, you can overcharge a bank.