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Old 15-09-2009, 20:24   #1
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Building a Solar Array Gradually

Here is my plan. I'm wondering if anyone has tried this.

I'm planning on putting together smaller cheap 60W solar panels.

My budget dictates that I can't get all I want right away. I'm going to start with a single panel to check out the quality of the panel I'm looking at and make sure it's charging.

It will also give me security in being able to leave the boat in the moorings for a week without worrying about the bilge pump or other issues sucking the battery dry.

Given the purchase of a 60W panel, and then the goal of upgrading to between 240W and 360W of power over time in chunks of 60W.



What charge controller should I look at?


Should I skip the charge controller for the first panel, while evaluating the panel? I'm thinking that it won't explode the battery without the charger, but I've never done any solar applications without a high-end MPPT, which I'm not sure I can afford right now.

Does anyone have any suggestions on a good MPPT that isn't too expensive, but will run up to about 240W or maybe to 360W of input with output for a 12v system (14.8 or so)?


I have a window of 5 days to work on the boat so need these purchases sorted out in the next few days. :-)

Thanks!
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Old 15-09-2009, 21:17   #2
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Hobie;

You can run a panel without a controller only if the output of the panel is no more than a trickle charger. This means that the size and state of your batteries comes into the equation. I am not sure of the exact formula, but I bet either somebody here can chime in with it, or you can find out there on the net.

If you do this, you would also need to install a diode, to keep the batteries from leaking back to the panels at night.

Chris
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Old 16-09-2009, 03:46   #3
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You can safely “trickle charge” a lead acid battery up to about 2% of it’s Amp-Hour capacity (2 Amps of un-regulated charge for every 100 A/H of batt. capacity).

Thus, a pair of parallel 120A/H batteries (or more) should safely accept the maximum charge from an unregulated 60W photo-voltaic cell.
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Old 16-09-2009, 06:04   #4
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How about a cheap panel from the auto parts store if you just want to keep the battery charged for now?.......i2f
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Old 16-09-2009, 07:30   #5
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This route can be a false economy. Figure the $/watt for each size panel. Some of the sources for panels listed in another thread do that for you. IIRC you can be paying $0.50 or more per watt than by buying a larger panel. Of course if you have size constraints, buying a larger panel that doesn't fit on your boat doesn't help either.

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Old 16-09-2009, 09:11   #6
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while I agree with John...

...the cost of solar panels is plummeting at present, and should continue to do so over the course of the next year. Waiting until winter to fill out the array might pay off.
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Old 16-09-2009, 09:18   #7
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charge controller

a 60 watt panel will be able to put out 4 amps. So unless you've got at least a 200 ah battery bank you're going to need a charge controller.
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Old 16-09-2009, 15:30   #8
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I've found someone selling used panels for cheap (around $1.75/watt).

They're a mishmash of brands, but he has pairs of most panels. I think I'm going to start with a pair of 110W panels and maybe grab a pair of 50w panels off him (hard to pass up for $85).

Even if they only output 2/3 their rated power, they are ok with me. I'll obviously be brining a multimeter and testing at least their Voc and see if I can't figure a way to test their current under load as well.

Going to pick up the BlueSky MPPT charger - I like the ability to network them together to go higher power in the future, and the remote display is nice as well.

It'll be a real task to rig up the panels with mounting, given they aren't going to be standard, stock sized. :-)

Wish me luck!
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Old 16-09-2009, 20:09   #9
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If your meter has an amp scale of ten or so, hook it up straight across the panel in full sun. You should get somewhere around ten amps from a 110 watt panel, maybe a little more. A ten amp scale will read over that on a Fluke meter.
Don't overload the milliamp scale or you'll blow a fuse in the meter.

Steve B.
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