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sizing solar panels

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glivs
Admiral

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USA
836 Posts

Initially Posted - 01/29/2009 : 12:10:15

In what may be the first in a series of questions....

What is your estimated daily DC load for your boat? I'm estimating minimum usage of about 18Ah/d on the hook (w/ LED anchor light) and with little effort (hardwired GPS, autopilot...), could easily double that.

In computing solar panel needs, do you work in Watts or Ah? Since we are a 12V system, I computed load in Ah. However, some of the on-line recommendations are to compute everything in Watts to take advantage of the higher output voltages of the panels (~16-18V) even though I would think a solar regulator would limit output under most conditions to <14.4 VDC.

Bottom line it would appear a 20W panel(~1.2A output)would require between 3-5 d to recharge the battery from 1 day on the hook assuming 5.2 hr solar irradiance near the summer solstice, a little inefficiency in the charging process, and a bit of variability in solar input due to clouds, etc. Does that seem to be in the ballpark with your experiences?

Gerry Livingston, Malletts Bay, VT
"Great Escape" 1989 C-25 SR/WK #5972

Edited by - on

Voyager
Master Marine Consultant

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USA
5358 Posts

Response Posted - 01/29/2009 : 23:05:20

Gary -
I've looked at this problem extensively, as I don't have shore power, and my engine charging circuit misbehaved by overcharging the battery last summer. I have two 18W solar panels that I purchased from Amazon / Target which came with a 7A regulator. Turns out it is pretty much right on the money for my needs.

I began by creating a power budget, it is just a spreadsheet listing everything on the boat that takes power, both in Amps and Watts:
the VHF radio - I assumed it's receive-only 99% of the time, but motor-mouths should rate it differently
the GPS/chartplotter, depth gauge, knotmeter, weather station, etc
the running lights - this month's SAIL mag has a basic article on LED fixtures
the anchor light - again LED
Steaming or bow light - LED
Spreader lights - I got a couple of sealed LED fixtures for this
Cabin lights - I found a nice pair of 1156 LED "bulb" for $14 at the Pilot truck stop that fits right into the cabin fixtures.
Music/radio/audio system
Laptop power / cell phone charger / Blackberry charger
Fans, bilge pumps, autopilot, coldplate etc
110VAC Inverter

Once you list out all the components then calculate, estimate or measure the current draw in Amps and measure or estimate the number of hours of use under normal conditions. You can also record Watts and convert to amps, but I use Amp Hours.

At peak solar intensity, I can get about 1A from each panel. Typically, however, with non-optimal sun tilt, shadows created by lines and shrouds, dust accumulation and whatever else, I derate the panels to 800 mA each.

In April you'll get about 13 hours of daylight, but you only get peak power from 2 hours after dawn to 2 hours before sunset, so you're down to 9 hours. In June, you get 15 hours, with 11 hours of peak sun. By September, you're back down to 12 hours with 8 hours peak. Because of lower sun angle in Sept, you actually get less.

With clouds, CT has 51% overcast days and VT is probably similar, so again, you have to derate somewhat. Bottom line, I assume 1.6 AH for a maximum of 11 hours in June/July, then in Sept its 1.5 AH for 8. Peak summer I get 17.6 AH a day and in Sept I get 12.0 AH. This is still quite good.

Now, I only have one 80 AH battery, and so the most I can take out is 40 AH. As a rule of thumb, I use Don Casey's voltage equivalent to % dischage figures which for a standard lead acid battery is:
12.6 V . . . . . 100%
12.4 V . . . . . 80%
12.2 V . . . . . 60%
12.0 V . . . . . 40% (now I'm in trouble)
so the lowest I should go is about 12.1 V

but!!!!!! You can go a little lower because while the battery is being discharged, it will read lower than it is. If you stop using it for 20 minutes, it will "recover" by 0.1 or 0.2 V. I never push my battery below 12.0V

If you have a gel battery, these numbers should start at 12.8V and go down correspondingly. 12.2V for example is 40% discharge, which is too low, and you risk killing the battery.

I recently purchased a LED-based voltage detector from Defender marine which will indicate at a glance your level of charge. It shows 11.8V, 12.2V, 12.6V and charging voltages of 13.4V (float charge), 14.4V standard charge) and 15.8V (overcharge) right on the panel.

If I sail for two days on the weekend and put the battery down to 12.2V, that's about 1/2 way or 40 AH. Over the course of several sunny days, I can make that back and have enough for an evening sail each week.

Finally, if the battery gets completely hosed, I take it home and charge it on the charger in the garage.

I hope this helps.

Edited by - on

OLarryR
Master Marine Consultant

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USA
3442 Posts

Response Posted - 01/29/2009 : 23:40:20

My 20 watt rigid Kyocera solar panel ideally will put out 1.2 amps/hour. However, over the course of a regular day and not always having the panel exactly perpendicular to the sun, also my neck of the woods geographically...the panel averages .6 or .7 amps and over the whole day of charging ranges from .4 to .8 amps. Then there are those days when the sun just does not come out. So, I would figure capacity of a panel conservatively figuring it will charge for about 5-6 hours a day at about 2/3 it's design capacity and perhaps for 5 days a week. Some will experience a higher charging rate than that and some less depending on the quality of the panel (some will charge a bit even if partially shaded in say one corner of the panel - Has to do with how the internals are connected in the panel), the panel's orientation, geographical location and the number of sunny days common for your area.

Edited by - on

britinusa
Web Editor

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USA
5404 Posts

Response Posted - 01/30/2009 : 07:00:02

Using an 18w panel here with my newly designed solar mount (sweet!) Wish I had two.. soon!

Bruce, great description of the loads.
Curious to know which LED lamps you purchased.

The main cabin lights on the C250 are 15w !!! You have LED replacements, but I don't think the lamp wll fit our light fitting, still have not found an LED replacement for them. Also looking for LED festoon lamps. Replacing the lamps with LED's must make a dramatic drop in consumption.

And a cool plate!! Don't let peggy read this! Which one?

Paul

Edited by - on

Prospector
Master Marine Consultant

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Canada
3159 Posts

Response Posted - 01/30/2009 : 08:28:42

Brit - It may not be as hard as you think to get LED replacements.

Go to the *GASP* Dollar store and buy a couple LED flashlights. Most of these run of 2 or 3 AA batteries so you can figure out the volts easy enough (1.5 V per battery) bust up the light and take out the bulbs. I know they aren't "Marine" bulbs, but what the heck, you only have $1 invested. Run 'gator clips from the light fixture to the bulb. If it doesn't work, reverse the leads (you may nave the negative lead on the positive end). If it still doesn't work, you need to drop the volts. a quick trip to radio shack will get you the bits you need for under $5. Hot glue the bulb into the original Catalina fixture and you have an LED light.

I found a light that runs on a 9V battery (the little square ones) and it wired directly into the catalina fixture with no issues. I bought the light at Princess Auto for around $5, but saw similar ones last night at the dollar store. What I found though was that the LED light does not go through the original plastic "Lens" well, and it is considerably dimmer than the old bulb with the lens on. With the lens off, it is considerably brighter. I can't explain that. So I live with it looking ugly for the time being.

Edited by - on

JimB517
Past Commodore

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USA
3285 Posts

Response Posted - 01/30/2009 : 11:59:33

I have a total of 33 watts on 3, 11 watt panels. These produce about 2.5 amps at 25 volts (voltage drops when you hook them up to your system). Augmented with limited time on the engine, I can live full time on board with this power. Load = Lights, stereo, computer, cell phone charging, autopilot, fish finder, GPS.

Adding in my new 12 volt cooler (4 amps) overwhelmed this system.

I have a voltage regulator but don't use it when cruising.

Edited by - on

glivs
Admiral

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USA
836 Posts

Response Posted - 01/30/2009 : 18:25:14

Thanks all - that is what I was looking for.

Edited by - on

Voyager
Master Marine Consultant

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USA
5358 Posts

Response Posted - 01/30/2009 : 21:18:36

Paul -
You had a few questions about sourcing the LED lamps . . .
<blockquote id="quote">quote:<hr height="1" noshade id="quote">Curious to know which LED lamps you purchased.<hr height="1" noshade id="quote"></blockquote id="quote">
I purchased different bulbs for different applications.
For the cabin lights, I purchased the automotive "1156" replacements from the Pilot trucking store along I-95. 1156 is a standard tail light or parking light bulb used for a car or truck.

Anchor lights have to be done differently, as you need an ALL AROUND type. See MastLight.com at http://www.mastlight.com/Products/1156T18W.html
<blockquote id="quote">quote:<hr height="1" noshade id="quote">looking for LED festoon lamps<hr height="1" noshade id="quote"></blockquote id="quote">
Check West Marine, DoctorLED or Ancor for your favorite application. Dr LED makes a nice replacement for an Aft Nav light.

Here's another http://www.superbrightleds.com/cgi-bin/store/commerce.cgi?product=OTHER

Happy hunting

Edited by - on

Prospector
Master Marine Consultant

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Canada
3159 Posts

Response Posted - 01/30/2009 : 21:24:13

Bruce - did you find the same thing that I did with the LEDS - thta the cloudy plastic covers dimmed them considerably compared to the old bulbs?

Edited by - on

Voyager
Master Marine Consultant

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USA
5358 Posts

Response Posted - 01/30/2009 : 21:34:48

By the way, I've been looking for a cold plate or a powered cooler. Coleman makes the latter available at your local dept or sporting store as the model 5640B. Running a 4A cooler for 10 hours is enough to run the battery 1/2-way down.

At this point, I guess I will stick with my five day maxcold ice cooler.

Edited by - on

skrenz
Captain

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USA
351 Posts

Response Posted - 02/03/2009 : 18:07:37

Bruce,
What I'm looking for are LED festoon replacement bulbs. those are the bulbs, as I'm sure you know, that are either 1/2" or 1" long and have to pointy ends. If I could find a reasonable price for these I could replace my running lights and a couple of internal lights too. Anyone have any ideas on where to get these?

Edited by - on

Voyager
Master Marine Consultant

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USA
5358 Posts

Response Posted - 02/03/2009 : 19:49:47

Chris - you are right, the frosty covers did dim the lights. When you look at the light output, they have two disadvantages over incandescents or fluorescents: (1) the light output is less, and (2)they are very directional. The latter makes the lights seem dim unless you point them in the direction you need the light. That's why they are pretty good flashlights. It will take a while until manufacturers perfect the placement of the lighting elements.

Steve - Festoon LED bulbs are available from several sources including DoctorLED, Mastlight.com and Ancor (carried by West Marine). You have to look at the festoon bulbs though.

If you want a festoon to point only one direction, you can purchase them very cheaply from a variety of sources. The light elements are all mounted on one side of a PCB, and you get about 90 degrees (45 degrees on a side) of light, but the strongest beam points perpendicular to the PCB, with light intensity tailing off quickly away from the main beam.

Other LED festoon bulbs have light elements on 3 or 4 sides, and provide more or less uniform light intensity all around. You get some dimming near the 45 degree points, but its generally ok.

MastLight has created a four-sided LED bulb inside a glass envelope that fits into a bayonet-type receptacle for the Anchor light at the top of the mast.

Edited by - on

britinusa
Web Editor

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USA
5404 Posts

Response Posted - 02/04/2009 : 06:09:47

Chris(Prospector) good idea about the LEDs from the dollar store!

regarding the dimming of LEDs by the festoon lamp covers, I tend not to use turn those lamps on, I can hear the amps rushing out of the battery! But with LEDs, I would not be such a miser. Will let you know how it works out.

One of the nice things about my solar controller is the digital load readout. So I'll be able to get an instant load saving indication when I put the new lamps in.

Paul

Edited by - on

Gloss
Master Marine Consultant

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USA
1916 Posts

Response Posted - 02/04/2009 : 08:10:47

I have a unisolar flexible 11 watt panel. It goes to a Morningstar digital charge controller with a digital readout of amps in from the panel, amps going out to accessories, and voltage of the battery bank. This is very handy. On a sunny day with the panel pointed at the sun I will get .6 amp.

so buy the biggest panel you can afford and which will fit.

the thing I like about the Unisolar flexible panel is that it has a grommet in each of the 4 corners so you can clip in the panel. It also has multiple blocking diodes so if part of the panel is in shade, it will not draw down your output.

Edited by - on

Voyager
Master Marine Consultant

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USA
5358 Posts

Response Posted - 02/04/2009 : 22:05:24

Found a very cool LED website yesterday that has a lot of interesting LED lamps available, but I was particularly interested in the following:

http://www.superbrightleds.com/cgi-bin/store/commerce.cgi?product=CAR&cart_id=7129925.23479

If you scroll down to the 21st item on the list, you'll find an 1156 socket with a PCB containing 36 white LEDs.

........1156-PCB-W36 White LED lamp
........12VDC 1156 Base with 1-1/2 inch square circuit board
........With 36 Super White LEDs, 57 lumens
........Designed for overhead lighting in boats, campers, box trucks, etc.
........With Wide 100 Degree Beam Pattern $ 16.95

This seems awfully hard to beat, and will probably produce a lot more light than a 20W incandescent at 2-4 Watts.

I just saw several LED Headlights tonight as well. Bright!

Edited by - on

HeelinPatrick
Navigator

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USA
102 Posts

Response Posted - 02/16/2009 : 16:45:10

Anyone have any problems with the LED's cutting out if the battery voltage gets two low. Do they just cut out, or do they go dim like a regular bulb?

Edited by - on

Voyager
Master Marine Consultant

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USA
5358 Posts

Response Posted - 02/16/2009 : 21:52:56

I've tried reducing voltage with multiple LED lamps, and most of them dim as voltage is reduced, however some with zener diode-type regulators will cut out below a certain voltage level.

I also just purchased several 6" fluorescent fixtures (GE makes them) that take 8 AA batteries. I rewired them so that I could run the lamps off the 12V battery.

I was quite surprised to find out that they will cut off below 11.5V, making them none-too forgiving on a boat where you could see voltage drops of 1/2 volt in some areas.

I also found it curious that a battery-powered fixture would cut out at such a small amount of dischage (~0.1V per cell on average)

They are cool when they're working however.

Edited by - Voyager on 02/16/2009 21:53:35

Turk
Admiral

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USA
736 Posts

Response Posted - 02/17/2009 : 17:24:40

Here are some sources for LED lights. I purchased these for my 250 and have yet to install but will be doing so in a few weeks.

Steaming,transom and deck light:

http://www.marinebeam.com/44felednaliw.html

This is a high powered festoon in a bright (cool) white recommended for white nav lights and 2 mile visability.

http://www.bulbamerica.com/High-Power-5W-LED-MR16-Flood-Warm-White-GU5-3-Bipin-Base-5081-prod.htm

This deck light is a full 20 watts but at 1/10 the power consumption. It has a warm color perfect for not attracting the bugs.

Interior lights:

http://www.marinebeam.com/42feledbu.html

These are high powered interior lights. Can get them in cool, warm and red. These are very bright and equivalent to the interior festoons in brightness.

As a note: Most LEDs for cars are very basic and will shut off if voltage drops. These will all stay on to 3v. I bought a OMG red green LED for the bow on Ebay for $48. Great price.

Edited by - Turk on 02/22/2009 08:17:08

Voyager
Master Marine Consultant

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USA
5358 Posts

Response Posted - 02/21/2009 : 11:10:46

Turk - These all around festoons are exactly what are needed for the anchor light and running lights. Apprx equal brightness all around. The flat ones are great for the interior lighting.

In reading the section on constant current regulation on the marinebeam website, you can see why they're better than generic LEDs - they can take a wide variations in boat voltage (14-15V while charging, 11.5V after a long night at anchor) and put out roughly the same amount of light power.

The prices don't break the bank either. When you think about what it costs to replace the $3 incandescent bulb at the top of the mast once or twice, they'd be cheap at $100 each. But you can't beat it at $20 to $25 each.

Edited by - on

Turk
Admiral

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USA
736 Posts

Response Posted - 02/22/2009 : 08:15:27

I received the lights today and after testing them I have to say I am impressed. The cylinder looking festoon for the transom and steaming light is very bright. I hooked it up on my workbench at home and It is actually very hard to look at. It is bright!

These are the new high output LEDs that are larger than the "yellow" looking LEDs of the past (yellow when off) . Each LED is much larger in size. The halogen 20 Watt has one very large LED and is every bit as equivalent to what I had before in an incandescent.

LEDs have arrived! Our batteries will love us. Except for the new 7 1/2 digital flat screen TV I bought for the cabin.

Edited by - on

Voyager
Master Marine Consultant

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USA
5358 Posts

Response Posted - 02/22/2009 : 21:18:29

Turk -
Nice screen! You're gonna love it.

How many amps did the transom/steaming light draw at 12.8V?

Edited by - on

Turk
Admiral

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USA
736 Posts

Response Posted - 02/22/2009 : 22:26:38

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by Voyager
 Turk -
Nice screen! You're gonna love it.

How many amps did the transom/steaming light draw at 12.8V?
<hr height="1" noshade id="quote"></blockquote id="quote">

Should be .187 amps. Ohms law.

Edited by - on

Voyager
Master Marine Consultant

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USA
5358 Posts

Response Posted - 02/22/2009 : 22:31:57

Like compared to 1.667A for an incandescent lamp. Keeps the batteries up even after a night at anchor.

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