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Go Back   SailNet Community > General Interest Forums > Gear & Maintenance
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  #11  
Old 03-27-2008
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Chuck...you will be lucky to get 30.
Forget what you are seeing on amps and voltage...take your watts and divide by 3 and that is what you will average per day IF they are unshaded. When you tilt them to the elevation of the sun, that helps but it is on the order of 10% unless you are constantly adjusting.
You need a link to really track it since volts and amps will constantly vary.
If you see 14.5 V then you can only be seeing 5.6 amps maximum (with no loss in the controller) so you would need to see 7 hours of FULL unubstructed overhead equivilent sun to get to 40. You won't...I had fixed 160 watt panels and was lucky to average 40amphrs/day in the Bahamas.

Your AGM's can take more maximum current than flooded...but this has ZERO implications in this situation as you are only capable of generating 5% or so of a group 31 capacity with the panel. It is only an issue with a high output charger or alternator in terms of how fast you can charge them.

BTW...your panel output is probably in the 17.5V range and it is reduced to 14.5 by your regulator whenever your panel is in full sunlight. I take it you are not running refrigeration so maybe 30amphours a day is sufficient for you.
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Old 03-28-2008
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Yeah, no refridge - it's a propane powered Dometic, draws .5amps for the fan if it's needed (1/4 of the time or so).
I've seen 5 amps going in according to my XBM monitor, last time I was looking was when Xort visited - it was a bright chilly day, around 1pm - I forget the exact number but it was about 5amps or higher at 14. something V and the batteries were at 99.9%

I'm going to have to put the PC link on line so I can chart usage, estimating can get me in trouble if I don't track all the pieces and parts. One thing I'm not going to do anytime soon is add a bunch of battery capacity - it simply weighs too much for my boat.

My self stated goal is 3 days on the hook with no motor to top off. If my draw per day is 60, and the panels give me back 30 that's 90 ah for a three day weekend. So long as I start near 100% that's sufficient. If I add a honda 2000 to the mix in order to run my air conditioner it's all gravy from there.

Most of my daily draw on the hook is iPod/Radio playing or recharging, night time is a couple ah of lights, a little water pump action and of course the anchor light if not 'sharing' someones at a raft up.
The few times I've had an opportunity and remembered to check (only had the boat one season) - the motoring involved to go up creek and drop anchor has topped off my charge to 99% - my chartplotter, raymarine instruments etc. don't draw much, auto sits at idle mostly because the boat tracks good. The observed draw is under 2 amps while sailing (and autopilot actively turning the boat ) with everything on, I realize that means I'm really using the panels output and 2 more amps because the XBM is only showing the cumulative effect on the batteries.

We seldom go more than 5 hours of sailing to get where we are going. I figure 20 minutes of motor for anchoring at 1500 to 2000 rpm puts maybe 10 ah back to the battery (55amp stock alternator) if I'm lucky. It seems to work out to a net zero, full battery on anchor drop.
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Makes sense to me Chuck.
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You sure that's not a Tayana 58 you got there Cam?
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Old 03-28-2008
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Quote:
Originally Posted by camaraderie View Post
Chuck...you will be lucky to get 30.
Forget what you are seeing on amps and voltage...take your watts and divide by 3 and that is what you will average per day IF they are unshaded. When you tilt them to the elevation of the sun, that helps but it is on the order of 10% unless you are constantly adjusting.
You need a link to really track it since volts and amps will constantly vary.
If you see 14.5 V then you can only be seeing 5.6 amps maximum (with no loss in the controller) so you would need to see 7 hours of FULL unubstructed overhead equivilent sun to get to 40. You won't...I had fixed 160 watt panels and was lucky to average 40amphrs/day in the Bahamas.

Your AGM's can take more maximum current than flooded...but this has ZERO implications in this situation as you are only capable of generating 5% or so of a group 31 capacity with the panel. It is only an issue with a high output charger or alternator in terms of how fast you can charge them.

BTW...your panel output is probably in the 17.5V range and it is reduced to 14.5 by your regulator whenever your panel is in full sunlight. I take it you are not running refrigeration so maybe 30amphours a day is sufficient for you.
Doesn't the output also vary with temperature. I get much more out of my panel than your figures would indicate. I understand that solar panels lose efficiency when they heat up and, contrary to what most people think, hot sunny days are not as productive as cool sunny days. Here in the PNW I get about 3 amps per hour out of a 48 watt panel for about 8 - 10 hours a day.
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Old 03-28-2008
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Output does vary with temperature...it reduces as things get hot. You will not get MORE than 48 watts out of a 48 watt panel. Indeed...the ratings used to establish a 48watt output include DIRECTLY overhead sun and a 5000ft. above sea level elevation and 70 degrees...which is why the state of California ratings are always less than mfr. ratings. (They rate at sea level and a 45 degree angle). So...there is NO chance that you will get more than mfr. rated power inthe real world.

While it may be comforting to THINK you are getting 3 amps for 10 hours on a 48watt panel....at 50 degrees latitude...you most certainly are not. At full output (direct overhead sun and no clouds or shadows) your panels can put out 3.6 amps at 13.3 V (minimum charging voltage)...on a discharged battery needing a 14.5V charge you can put in a maximum 3.3 amps.
Since 10 hours of USABLE (low horizon angles produce nothing worth mentioning) sunlight is the max and 45 degrees off axis is the AVERAGE sunlight angle...the most you can expect on a bright sunny day is half of the maximum outputs listed above...or 5 hour worth of 3.3-3.6 amps depending on battery state. Thus under best case scenario you could get as much as 18amp hours per day on absolutely LONG COULDLESS SUNNY days. How many of those do you have in Vancouver? Hence taking my original watts divided by 3 as a rule of thumb...you might be lucky to get 15 amphours out of a 48 hour panel on average.
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I just have a few minutes but would like to mention a couple of things, I have 55 watt Evergreen brand panel on my boat (installed 4 years ago), it is a thin film panel, similar to the monocrystaline performance., this is a new class of panel that requires less raw material to make (or was new 4 years ago, since then more companies have started making this type of panel). I bought mine as a cosmetic blemish from sunelec.com in florida, they do not offer kits, but sell panels, charge controllers, etc. they often have great deals.

Ike
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Old 03-28-2008
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Something to bear in mind is that these ICP panels (Coleman licenses out their name, it is not a "coleman" product per se) have 2-year warranty. Panels designed for the marine/off-grid market have usually been sold with a 25-year warranty, and more recently that has been cut down for marine users because the salt air and exposure to spray take a horrible toll on electronics.

I'd want to look at those panels very closely to see how well they could take it, or ask ICP about suitability for semi-permanent use on a boat. They are selling them for intermittent use, i.e. during blackouts and for camping, and that's a very different thing.
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Old 03-28-2008
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Quote:
Originally Posted by camaraderie View Post
Output does vary with temperature...it reduces as things get hot. You will not get MORE than 48 watts out of a 48 watt panel. Indeed...the ratings used to establish a 48watt output include DIRECTLY overhead sun and a 5000ft. above sea level elevation and 70 degrees...which is why the state of California ratings are always less than mfr. ratings. (They rate at sea level and a 45 degree angle). So...there is NO chance that you will get more than mfr. rated power inthe real world.

While it may be comforting to THINK you are getting 3 amps for 10 hours on a 48watt panel....at 50 degrees latitude...you most certainly are not. At full output (direct overhead sun and no clouds or shadows) your panels can put out 3.6 amps at 13.3 V (minimum charging voltage)...on a discharged battery needing a 14.5V charge you can put in a maximum 3.3 amps.
Since 10 hours of USABLE (low horizon angles produce nothing worth mentioning) sunlight is the max and 45 degrees off axis is the AVERAGE sunlight angle...the most you can expect on a bright sunny day is half of the maximum outputs listed above...or 5 hour worth of 3.3-3.6 amps depending on battery state. Thus under best case scenario you could get as much as 18amp hours per day on absolutely LONG COULDLESS SUNNY days. How many of those do you have in Vancouver? Hence taking my original watts divided by 3 as a rule of thumb...you might be lucky to get 15 amphours out of a 48 hour panel on average.
There is something wrong with your numbers. Trickle charging happens at very low voltages not a minimum of 13.3v. My digital readout has my solar panel putting out 14.1 to 14.6 volts most of the day, even on bright cloudy days. Remember, during the summer the days get much longer up here than farther south. The average hours of sunshine per day in Vancouver for July and August is 9 hours (not 5). So with a conservative 3.3 amps per hour for 8 hours you get 24 amps which is much more than your "divide the wattage by 3" estimate. Even after those peak rating hours, the batts are being trickle charged until dark.
Sunrise on 22 June 08 - 3:54 AM
Sunset on 22 June 08 - 8:10 PM
16 hours of daylight!
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Old 03-28-2008
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" Trickle charging happens at very low voltages" No, by definition it refers to a trickle of current, that is, low current charging. See Trickle charging - Wikipedia, the free encyclopedia one of many references that comes up with 13.38 volts for a 12-volt battery based on 2.23V/cell. You will find that each battery maker, for each battery chemistry, supplies a slightly different number for the optimum trickle/float/bulk/acceptance charges, but the voltages they supply are simply guidelines--the charging current is often more important, but less discussed because the casual user has problems measuring or adjusting current.

"My digital readout has my solar panel putting out 14.1 to 14.6 volts most of the day, even on bright cloudy days."
What is your readout reading? A raw solar panel should be hitting 16-17V if it is unregulated and unloaded. When it is loaded up, that will plummet and you may only see 3-7V output as the sun gets lower in the sky (i.e. 7PM on a summer day with a 9PM sunset)

"Remember, during the summer the days get much longer up here than farther south. " You get more hours of daylight--but weaker sunlight because of the extra atmosphere it is crossing. I've measured charge, with an ammeter as well as a voltmeter, and as the day gets late you'll get nothing useful from solar panels. Although using JUST a meter, without an actual load, shows they are still putting out voltage. Add the real load and put the meter in the live circuit, and you'll see the difference.

Pretty much every web site (university, lab, government, industry) that has maps and charts for real solar power from panels, shows the variation by lattitude and they all use the same independently verified criteria. The rule of thumb is "divide wattage by (three, four, six) to get useable amp hours per day" and the only reason for the variation is your lattitude or the time of year.
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