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Old 04-05-2013, 15:30   #1
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Sailboat Solar Panel Sizing

Greetings to all!

I will be acquiring a Brown Searunner 34 in the next couple of months and I'm looking around at solar panel options, trying to price out what I'll need. I've been doing a lot of research, but without the actual equipment in front of me it's hard to get real numbers to figure out the required solar panel wattage to keep the batteries topped off.

I'm trying (and not succeeding) to minimalistic about things that use power. For example, anything water related will use manual foot pumps, and the toilet will probably be a 5 gallon MSD port-a-potty so I can still do the "hands off" pump out whenever possible, but also prevent people from screwing up the plumbing and save myself from having to use an energy stealing electric pump and macerator. I considered manual toilets with a holding tank, but I don't think the wife will go for that! Cooking will be propane and AC will be the lovely San Diego weather. :P

As far as what I DO want to have on the boat that draws power, there are a few creature comforts I'd really like to get on board. I'm basically just looking for an experienced solar panel user to recommend total wattage to keep the batteries charged using the following devices:

1) A small mini-fridge with freezer (turned off during the week, but may be used more for extended trips. Gotta keep those steaks from spoiling!)
2) Recharging for two iPads (movies!)
3) Recharging for two smart phones
4) Recharging for laptop (schoolwork at anchor, maybe a movie or two when the iPads are busy)
5) Marine GPS/chartplotter (any recommendations?)
6) Running lights
7) A box fan (helps me sleep at night, but can probably go without if it's too much draw)
8) MAYBE a microwave? Kind of lazy with the cooking sometimes.....

I know this is a very general question and for right I'm just looking for a very general answer so I can start figuring out my budget. I would also appreciate recommended vendors and models.

Thanks!

Dave
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Old 04-05-2013, 15:53   #2
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Re: Sailboat Solar Panel Sizing

A house fridge, a house fan, and a microwave are gonna kill you on electricity. There are lots of 12v fans available, check truck stops if budget is an issue.
We have 600 watts, it's plenty if we don't make too much ice or if the kid doesn't play his PS3 for more than an hour a day. You should be able to get by with about the same just fine if you don't use a microwave much. You can get by on 400 if you're more conservative, but solar panels are really cheap now if you buy Chinese crap like I did and you do have a lot of real estate.
I've never ever heard any cruiser say that they have too much solar.
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Old 04-05-2013, 16:15   #3
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Re: Sailboat Solar Panel Sizing

you didn't mention how you will be using the boat. makes a big difference.

1. daysailing.
2. weekender.
3. 2 week vacation cruise once a year.
4. cruising full/part time.

or something else i haven't thought of.
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Old 04-05-2013, 16:27   #4
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Re: Sailboat Solar Panel Sizing

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Originally Posted by onestepcsy37 View Post
you didn't mention how you will be using the boat. makes a big difference.

1. daysailing.
2. weekender.
3. 2 week vacation cruise once a year.
4. cruising full/part time.

or something else i haven't thought of.
It's going to be mostly weekending, but I'd like to be capable of longer trips on the off chance I get a week to go traveling.
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Old 04-05-2013, 16:45   #5
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Re: Sailboat Solar Panel Sizing

Use some estimates and build a power budget.

The microwave isn't that horrible if you only use it briefly and occasionally. You do need a big inverter and a good battery bank though, since the current drain is quite high. My small microwave takes 90A @ 12V (through the inverter). If you use it 5 minutes a day, that adds up to 7.5 Amp-hours. Since the batteries are more lossy at high current, figure 9Ah.

Your cellphone and iPad chargers will probably draw 0.1A @ 12V each. The laptop charger can take from 2A to 6A @ 12V, depending on the laptop. Use 12V chargers whenever you can, rather than using AC chargers and taking the extra loss from an inverter.

A 12V refrigerator that can keep frozen stuff "mostly frozen" will burn about 3A on average (perhaps more). This is 72Ah per day. An AC-powered refrigerator will typically consume much more than this.

A bare GPS consumes perhaps 0.2A @ 12V. A chartplotter will take a few amps. You're not going to be running the chartplotter continuously, unless you use it for anchor-watch.

For running lights, use LED fixtures. The incandescent ones burn 1 or 2 A each. The LED ones burn one-tenth that amount.

So, make a guess as to what your daily Ah consumption is going to be. Usually, you use more power at sea, and less at anchor, but do the math. The result will tell you how many Amp-hours a day you will consume.

Then, look at your charging sources. Will you be willing to run the engine when the solar panels don't put out due to cloud cover, or if you have shadows on the panels? Or, perhaps you can't, or don't want to fit enough panels to fully replace the power you are consuming. Again, will you engine-charge?

Then look at your batteries. You need to size them to at least provide power through the night. You really only have six hours of good charging sunlight, so the batteries need to deliver power for *at least* 18 hours without discharging below half-charged. More capacity is better, at least to a point.

OK, now the panels. Say you end up needing 100 Ah per day. You will need something like 300 Watts of solar panels. This is a very rough number, and depending on the panel orientation, and the type of charge-controller you may need more, or possibly less.

As you already know, it's much easier to reduce consumption than increase production.
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Old 04-05-2013, 19:47   #6
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Re: Sailboat Solar Panel Sizing

for just weekending you only need, say, 48 hours of power from your battery bank. in that case i would probably have a larger battery bank (say, four golf cart batteries holding 450 amp hours), and a smaller solar panel, say a kyocera 135 watt.

my reasoning is that the panel will charge your batteries to full during the week. on the weekend you can live on your batteries plus whatever the panel will add. when you get back to dock, the solar panel will pick up where it left off.

if you go off for a week, add another solar panel - or two.

all of the above is just my humble opinion based on my past experience. ymmv.
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Old 04-05-2013, 20:25   #7
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Re: Sailboat Solar Panel Sizing

The ipads charge at about 1.5 amps at 12V and full size laptop could be 6 amps or more. A small 3 cf AC fridge on in inverter will use 2.5 amps per hour running about 10 minutes per hour in 90 degree cabin heat. Mine does anyway. I've used one all the time for the last 6 years with much of that time at anchor. Oh it pulls 14-15 amps running but it runs less minutes per hour then a 12v unit. Really its about the same total load btu wise 12V or 120v. Box insulation makes a bigger difference with energy savings.

Don't forget anchor lights and cabin lights at night. Led and florescent are your friends there.

Actually the laptop and ipads are the big energy hogs, the fridge is second. I use a small netbook that runs 8 hours per charge and uses 3 amps an hour for a few hours to charge the battery. I charger the battery powered devices after 11 ish as by then my batteries are over 80% recharged.

I use about 65 amps a day and 230 watts of panels is enough for me to get the batteries charged up everyday. Your going to need at least 330 watts and more likely 400 watts if your panels are fixed. I can pivot my panels in one plane which allows me to adjust the panel orientation a few times a day as the sun and tides change. For me it works great year round.

One thing to consider is the rated panel output and actual output at anchor. For me, my panels put out about 65 percent of rated output with a PWM controller. YMMV. Factors such as mounting location, percent sunshine, shading of panels and temperature all effect solar output.

Good luck
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Old 05-05-2013, 06:16   #8
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Re: Sailboat Solar Panel Sizing

We haven't discussed panel mounting. A sailboat is a difficult place to mount a lot of panels to.

The only place that you can install significant area and not rely on flimsy rail mounts is on top of the bimini. You will need to talk to your canvas shop about installing two exteral bows that go above and across the bimini, but also need to clear the boom.

You can install two of the big 250 watt panels on either side of the boom. This whole rig won't be cheap- maybe $1000 for the SS work, and $1500 for the panels and controller.

Or if you can find a place for one 135 watt panel, maybe mounted on the stern rail, do what the previous poster suggested and use your batteries for the weekend. For short term use, batteries are cheaper than panels.

David
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Old 05-05-2013, 06:16   #9
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Re: Sailboat Solar Panel Sizing

The following figures are ball park for computer/ tablet use. It assumes charging from 12v rather than an inverter. While charging the battery the consumption may be higher, but then the stored energy can used later so the overall consumption remains similar.
iPad 0.5-0.6A
Netbook 1-1.3A
Conventional laptops vary considerably more but 3-4A is typical.
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Old 05-05-2013, 07:02   #10
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Re: Sailboat Solar Panel Sizing

The biggest power hogs on a boat are the refrigerator, laptops and other personnel electronics. In San Francisco Bay, I got my refrigerator down to about 2.5 to 3 amps per hour, but in the tropics 4.5 amps was the norm.

Inverting power to AC uses more power than going with 12v, because you are now converting back to 17 volts or whatever for the laptops and other devices.

You didn't mention your house battery bank and I would start there. Get as much amp hours as you can on the boat. Golf Cart batteries, like the ones I have can store 242 ah each. So as an example, 4 batteries would give you 484 ah. Also upsize your alternator, to the largest your engine can handle without losing performance.

As for solar the best advice I can give is put on as much as you can afford and have space to mount. This accounts for the less then sunny days you will experience sometimes. In full sun my panels make about 45-48 amps, which keeps us on the hook indefinitely, but in cloudy Panama they were usually making around 20 amps or less and I would have to charge the batteries about every 2-3 days.
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Old 05-05-2013, 07:56   #11
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Re: Sailboat Solar Panel Sizing

Quote:
Originally Posted by djmarchand View Post
We haven't discussed panel mounting. A sailboat is a difficult place to mount a lot of panels to.

The only place that you can install significant area and not rely on flimsy rail mounts is on top of the bimini. You will need to talk to your canvas shop about installing two exteral bows that go above and across the bimini, but also need to clear the boom.

You can install two of the big 250 watt panels on either side of the boom. This whole rig won't be cheap- maybe $1000 for the SS work, and $1500 for the panels and controller.

Or if you can find a place for one 135 watt panel, maybe mounted on the stern rail, do what the previous poster suggested and use your batteries for the weekend. For short term use, batteries are cheaper than panels.

David
I have 8 x 85W panels as my bimini, on a 43 feet sloop, no canvas, works great. But yes, the frame design requires some thinking. I think we have a thread here somewhere about the design.
IMHO, can't beat the solar panels, here in the tropics at least, that is.
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Old 05-05-2013, 09:22   #12
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Re: Sailboat Solar Panel Sizing

Silvirus, contact Mark Johnson on the Searunner thread. I think he can give you the exact info you are looking for. Will you be on one of the moorings or in a marina? There is virtually no anchoring in San Diego Bay.
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Old 05-05-2013, 11:16   #13
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Re: Sailboat Solar Panel Sizing

Thanks guys!

As far as lighting, the boat isn't lighted at all...I'm going to have to install that once I take possession. I'm vaguely considering those round push lighting things that stick to the wall. Seems easier than wiring and I can replace the batteries as they run out. Obviously the running lights will require more.

As far as panel mounting, this being a Searunner trimaran, I have all sorts of options for that. I imagine I'll probably end up with two 300 watt panels in the end, one mounted on the aft cabin and the other mounted on the forward part of the hard top bimini I plan to make. I'll start with one just to see how it all works out. San Diego is very sunny most of the time, so I might get more out of it than the rated specs.

With regard to golf cart batteries, do they make them in different voltages? I read somewhere that most of them are 6V, so the rated amp hours can be misleading. 242 Ah turns into 121 Ah when you switch from 6V to 12V. If that's the case, I think I'd rather go with cheap lead acid batteries and suffer through the maintenance.

In response to your query, Roy, my plan at first will be to suck it up and live with parking it at the Marina. The moorings he in the bay tend to have waiting lists so I'll park it at the marina until one becomes available. There is one free anchorage left, but I'm sure that's pretty much full most of the time. Fortunately, my current financial situation should allow me to cover the costs of the slip until a mooring opens up.

My last question is to Erik, with regard to your solar panel bimini. Are the panels sturdy enough to walk on? The searunner has the cockpit in the center of the boat and I am planning on making a plywood cover sturdy enough to walk on so it will make messing around with the mainsail a bit easier. If I end up having to do two panels, I may just use them as the bimini cover if they're safe to walk on. Then again, I imagine the panels get pretty hot.....
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Old 05-05-2013, 11:19   #14
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Re: Sailboat Solar Panel Sizing

Oh, and the boat has a small 9HP out board that raises and lowers via a rope. Not sure if that will be able to be used at all for power, but if all else fails I can get a portable generator for emergency situations.
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Old 05-05-2013, 11:33   #15
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Re: Sailboat Solar Panel Sizing

you will have to figure out where you will be placing these panels and work with that.
if it is a bimini, make it in a place not used by your feet. flexible panels are walk on a ble, but they donot put out as much as the rigid ones you cannot walk on. the glass covers crack a lot--kinda like a car windshield when broken.
as far as amperage is concerned-- do the math---in must exceed out, or you must be in a marina or have an other source of electricity .
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