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Old 01-29-2023, 05:12 PM   #1
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Solar Panel Advice

I have a Cape Dory Trawler 28. (Yes, I know not technically a trawler, but thatís what itís called).
Two 12 volt deep cycle group 27 lead acid batteries. Limited mounting options. I have 44Ē of aft fly bridge rail that I could mount a panel on. I can fit a 100- 150 watt panel there. At anchor, I use the stereo, charge cell phone, one or two LED lights, the LED anchor light and possibly the small refrigerator.
My questions are.
1. Will that size panel recharge the house battery?
2. Could the 12 volt battery power my small refrigerator through the night and then get charged up with the panel the next day?
3. Will it need a controller?
Not sure what to expect. What do you think
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Old 01-29-2023, 05:24 PM   #2
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1. A controller is always good. Not very expensive for your small application.
2. Ballpark numbers, a 150W solar panel will produce about 60AH@12v per day. More in summer, less in winter.
3. I have a small 2.4 cf 12VDC fridge in my camper van - it consumes about 50AH per day, though varies based on ambient temps. So not much power left over if all you have is your solar.
4. Your battery setup has roughly 100AH of reserve energy storage.

If you are careful with consumption, and don't hit too many cloudy days in a row, you should be able to get by just fine with a 150W solar. A lot depends on your fridge consumption, and how much other stuff you have running, but you should be okay, especially since you presumably have charge capacity off your alternator. Will you be solidly "Net Zero?" I don't know, but close enough that it's worth the effort. Right now you probably stress being out overnight - with solar, stress of one overnight will disappear, and likely you'll be good for over 2 overnights (at least).

There are some good solar minds on the forum - guessing some others will chime in.

Two thumbs-up on the CD 28. It's a pocket trawler.

Peter
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Old 01-29-2023, 05:43 PM   #3
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And just so you know... If you have group 27 la batteries they are not deep cycle regardless of what the label says. Gell or AGM might be a different thing
The most economical alternative for actual deep cycle batteries are golf cart batteries from one of the big Box stores
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Old 01-29-2023, 05:47 PM   #4
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I didn’t know that.
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Old 01-29-2023, 05:55 PM   #5
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And just so you know... If you have group 27 la batteries they are not deep cycle regardless of what the label says. Gell or AGM might be a different thing
The most economical alternative for actual deep cycle batteries are golf cart batteries from one of the big Box stores
Interesting - can you elaborate? Autozone has one HERE that is clearly labeled as deep-cell. What should someone look for to understand capabilities of the battery?

Peter
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Old 01-29-2023, 07:52 PM   #6
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As I have said, many, many times, the only deep cycle battery you can trust to have thick plates, more room for sulfate under the plates and extra headroom for electrolyte is 6V golf cart batteries. The others almost always lack these features. The foregoing is true for flooded cell lead acid batteries. AGMs have an entirely different construction and do not cause the problems noted above.

So working from the bottom up of the OP:

Yes you do nead a controller, otherwise when your batteries are fully charged your panels will keep dumping current into them and ruin them.

These can be as cheap as a $47 Renogy 20A PWM or better a 20A Renogy MPPT controller for about $90. The latter is about 15% more efficient than the former.

Just guessing, your fridge will use about 50Ah in 24 hrs and other loads such as lights, device charging, etc will run another 15 Ah.

Two group 27 batteries have approximately 150 Ahs of capacity, of which only 75 is usable for best life. So, with no other charging sources, you can last a bit more than 24 hours without starting up your engine and recharging.

A 150 watt solar panel can produce 50Ah if it is the summer at lower latitudes, less if not. That can help extend your no engine running time to several days.

It is all about balancing charging sources with loads with battery capacity.

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Old 01-29-2023, 08:30 PM   #7
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Thanks, that makes sense.
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Old 01-30-2023, 05:13 AM   #8
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I agree with the previous posts on the use of 6 golf cart batts instead of the Group 27's. For what it's worth you can fit the GC batts in place of the 27's without any real problems. 2 Duracell GC batts from Sam's Club will give you 230 AH's of power at very minimal cost and no real changes would have to be made to your system.

I have been running a small stand alone frig off that setup without problem on a sailboat. But you'll need more solar to keep it charged up if you're not running the engine. I have 2 - 100 Watt panels and they do fine.

As an alternative you could run the engine for an hour or so in the morning to give the batts an initial charge and then let the panel finish it off. And ideally if you could add one more battery somewhere to be your "engine start" reserve as a "just in case" that would be good.
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Old 01-30-2023, 08:12 AM   #9
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Put the largest solar panel you can fit aboard. Use 10-awg cable to the controller. You will notice a big difference in battery capacity right off the bat.

Epever makes a good basic controller - they white label for Outback, a respected name for off grid. They have a decent display panel with current and capacity. I'm not a fan of Renogy - their products are fine if they work. If they are DOA, a problem to RMA them. Victron would be expensive and is really best suited to an integrated system.

EPEVER 20A MPPT Solar Charge Controller 12V 24V Auto, Max 60V Input Solar Panel Charge Regulator Negative Grounded with LCD Display for Lead-Acid and Lithium Batteries https://a.co/d/0Avfj11

Peter
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Old 01-30-2023, 09:00 AM   #10
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I know that Renogy may get its bad rep due to one test that Marine HowTo did of its 100 Ah Li battery where they measured only 70 Ahs. Do you know of any others?

I have had good luck with Renogy products.

David
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Old 01-30-2023, 11:54 AM   #11
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Quote:
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I know that Renogy may get its bad rep due to one test that Marine HowTo did of its 100 Ah Li battery where they measured only 70 Ahs. Do you know of any others?

I have had good luck with Renogy products.

David
Any idea what year? I go to the Marine how to HERE and do a word search for Renogy on the site. There is no Renogy 100 Ah bat test. The word is used in one sentence recommending not to go Renogy, the word is used in another such as Renogy talking about solar panels.
I suspect the test you mention is no longer valid and was scrubbed from the site. With constant improvements even in china what was may no longer be.
Then there are lemons everywhere in all products.

In my comparison shopping I am finding many batteries that look identical but are branded by different names of resellers. I am reminded of when I discovered that GE was making appliances for multiple well known brands which were identical except for the label.
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Old 01-30-2023, 10:59 PM   #12
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Just another chime in from someone who did this about 4-5 yrs ago with minimal room. I managed 260W though. They goof up the use of a lot of my flybridge but the panels were worth it.

Instead of freaking out at the two to three day mark even with fully charged batteries we can last more than a week. By then we are moving again. If you can fit a 150 watt panel do it, forget the 100. But the 100 , if that is all you can fit, will be FAR better than not doing it.

As pointed out you WILL need a controller or the 150W , even the 100W, panel will damage the batteries eventually.

I agree too that the so called deep cycle batt. you pictured is deep cycle only in an advertiser's mind. THe golf cart units are deep cycle units. You just need 2 of them in series to get 12 volts. And amp hour to amp hour they are less expensive than some other battery types. But you do have to keep the water level up or they too will suffer damage.
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Old 01-30-2023, 11:40 PM   #13
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Good advice all round. Solar is pretty addictive.

If you get to the point where you consider multiple panels, consider dedicated controllers. Just mentioning for planning purposes.

I love the cape dory flybridge. If you ever want to trade up in size give me a knock.
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