Firstly let me say, I have no knowledge whatsoever of solar panels.
I was just talking the other day to my daughter’s partner about maintaining battery charge in the boat.
He tells me he knows nothing either then a couple of days later gives me one of these (see picture)
IMG_0135.jpg
My question from those that may know, will this maintain my boat battery charge level.
Shakey - If only I lived near the coast
Shakey,
My neighbor has one fitted to his car trailer, the idea being to keep his battery that powers his winch always charged, but unfortunately not doing the job for him. Unsure if it is because of the battery condition but he is disappointed with it and i think his is a 10W.....
JN
Will a 3.5 watt panel charge anything? At max efficiency, it is probably delivering less than 300mA, ie, 0.3 amp. And that is during daylight hours, in full sunlight. If your boat is wired correctly, with no parasitic drain when everything is turned off, it "may" keep you up to 12.4 volts. It can't do any harm at that level of charging, anyway.
It is a simple calculation. I=P / E , where I=current, P=power, and E=voltage. So, given your theoretical rating of 3.5 watts, at 12v, divde 3.5 by 12, gives you about 0.29 amps. The charge voltage is probably higher than 12v, would need to be at least 12.7 to get any charge. At 12.7v , it is 0.27 amp. So, a tiny charge indeed, more suited to a very small rechargeable battery. Minimum size I would use for that application would be 20w, and you would want a proper regulator , so the charge will cut down if you do get a really good run of sun and no battery drain.
Any solar panel needs full sun, at the right angle, to get full efficeincy. Laying them horizontal really cuts down the rate unless the sun is directly over head, and, of course, any shade takes them to nothing. In my experience, if you put 180w of panel tilted towards the sun directly, at the correct angle, it will give almost twice the charge rate of 240 watts of panel alongside it, mounted flat.
I experimented with mounting panels on the roof of my ute canopy this year for an extended camping stay. 3 x 80w=240 watts of panel up there, should be fine? Nup, pathetic, nothing much till mid morning, then a poor rate anyway. I had been using four of those panels (320w) in a frame, hard to manage , but great charge rate. I just wanted to save the effort of putting it all together, was prepared to drop some charge rate for convenience. Luckily, I had my old 180w hinged panels along, and even more luckily, they matched voltage well enough to be able to parallel them up. Made up an andersen plug double adaptor, hey presto, getting 18 amps when the sun was well up. 10 amps from the 180w, 8 amps from the 240w. And the 180's facing the rising sun had good charge as soon as the sun rose., the flat mounted ones started to contribute about 3 hours later.
I purchased a 20W 12V solar panel with cutout/inbuilt Regulator off Fleabay For somewheres around the $20/30 ?? , couple of anderson PLugs and just plug it tin when i get home or after ive cleaned the Boat and it trickle charges my Batterries just fine
Just sit the panel on box cushion when its trickle charging and remove and store when taking the boat out..
There are a lot of variables but that should work Shakey.
Solar panels are very interesting. The 3.5 watt panel would help maintain a good fully charged battery but don't expect it to top ip a battery that has some level of discharge or is getting a bit old in the tooth.Originally Posted by Fed
I once had a BP Solar 10W panel, it was like chalk and cheese compared to many panels, a setting sun on the panel would still be putting out quite a reasonable charge. My much newer 200Watt panels don't put out anywhere near the same when the sun is at an oblique angle. Solar panels aren't all the same, even the ones on your roof can vary from barely adequate to very good. Also you have to remember that solar panels also degrade, over 10 years they'll lose anywhere from 10% to 50% or more efficiency depending on quality. Earlier models you will notice was broken into a number of grids. Bird shit in just the corner of one of those grids and that grid will not produce anything.
Solar panels are like most things these days, there are many that are useless to those that work well and their technology is constantly changing.
And a 3.5 watt panel will do virtually nothing on an AGM battery, hardly enough power to overcome the internal battery resistance.
I think Ranmar nailed it -
The efficiency that you get out of a solar panel can be pretty low ...... from my experience it probably is 25% over a 24 hr period ( at best)
I run a 80W solar on my canopy to keep the battery charged up - when the fridge is going in the car ...... now it's probably only drawing 1-2 amps / hr on average over a 24 hr period when the fridge is running a 2 deg C . that 80 amp panel just stays ahead on average during winter ( cloudy / wet / short days) . Summer it's generally seeing the battery fully charged by mid morning.
My point is ....... even with good isolation , you could still lose an amp or two / day - if you dont & having things like a stereo connected - you can lose a lot more ..... that 20W solar panel is going to give you 1.66 amps / hr at full efficiency - so more like 0.4 amps / hr over the course of a 24 hr day (9.6 amps) . Teamed with a quality regulator ..... you battery will be well maintained - even on those shitty cloudy wet days. ...... & that's what you want.
Chris
Give a man a fish & he will eat for a day !
Teach him how to fish
& he will sit in a boat - & drink beer all day!
TEAM MOJIKO
I couldn't be bothered looking any of this up but by memory a lead acid battery drops about 3% per Month or around 0.1 AH per Day and by Ranmars calcs the panel should put out way more than that.
The 80 w panels I was referring to above are actually original BP Solar. They are from the original Kalbarri Solar Farm project, commissioned in 1995. This was, at the time, a cutting edge solar plant, complete with sun tracking. It did its 20 year life, and was dismantled in 2015. I bought 10 panels at $20 ea from it. When I tested them they were all at over 90% of original spec, very good quality panels indeed. And still going strong, now at 25 years old.
One thing to be mindful of is the need for a good regulator. Even the very cheap ones can be quite good and reliable nowadays, just make sure you get an MPPT, instead of a PCM. The PCM's are normally the very cheapest but they are all so cheap nowadays the difference is really negligible. You will get more charging current per watt of panel with an MPPT, in general circumstances. For small setups like we are talking here, there are sub $50 regulators that work fine, For larger setups I wouldn't cheap out, too much energy involved. There is a bit to it, this page has a good explanation. https://www.solar4rvs.com.au/buying/...oller-regulat/ As all the panels I've ever used produce over 19V open cct voltage, MPPT's are the go. My first solar regulator was the Plasmatronics PL20, the gold standard for solar regulators 10 years ago. Expensive at $320. It finally expired this year. I have a $95 model bought a short time after that, still doing good service. I have a $35 MPPT ebay job on the boat, extracts up to 9 amps from a 120w panel on the roof, been good for 18 months. We'll see how long it lasts--it does reduce charge rate as the battery voltage rises to max levels, fully configurable via menu. And, while we are at it, don't just assume your regulator comes all pre-set and ready to go--my son's wasn't getting a lot of charge into his when he used it for the first time this year, , and the settings for charge voltage levels were all wrong out of the box.
Guys what happens when the regulator fails the panel will still be producting energy which if not directed will turn into heat unless the regulator is just passed thry and the panels true operating voltage is pumped into the battery untill noticed
How do they work and possibly fail?
I plan on running 1-2 panels on my t top to recharge 1 start battery and 2 deep cycles as either 2x12v or 2 in series for 24v
I would love to go out sat or sun and have all the batteries recharged within 4-5 days
Sent from my SM-G900I using Ausfish mobile app
From my understanding you really shouldn’t be relying on trickle charging to recharge batteries....... trickle is to keep a battery topped up. Unless your panels are supplying 5-10% of the battery capacity you are probably going to reduce the life of the batteries. Batteries are meant to be brought back to full charge as soon as possible within specification (varies between battery type).
Chris
Give a man a fish & he will eat for a day !
Teach him how to fish
& he will sit in a boat - & drink beer all day!
TEAM MOJIKO
I have been doing this for years and it works fine. I have a 40W panel that I have now built in to the bimini and attaches via an Anderson Plug. I think the most important thing is a good inverter. I got the smallest model Victron Smart Solar and it is streets ahead of the normal PWM junk out there. Much more intelligent battery management and conidtioning and my batteries are always topped up - the other good thing is the app confirms how your battery is charging.
I have just replaced my last set of batteries after 7 years - they were still in great condition but I thought after 7 years in the marine environment that it was time. They were always on the solar charger when not using the boat.
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