Battery Charging Puzzle

[Fuss]

Originally Posted by Fuss

I have 400w of solar.
This has made my generator redundant.

Optimised main engine charging and then running the main engine for 30 minutes a day plus the output from the solar replaces my normal daily use on a boat with no gas only electric.

Another solar advantage for boats running 24v house and 12v starting systems with both 24v and 12v alternators is to have the solar charge both the 24v and the 12v batteries.
In these 24 and 12v systems the 12v alternator on the main engine is a complete waste and should be removed. These alternators usually produce far too many amps for the little job that they have to do.

[noelex 77]

Lead acid batteries do benefit from an occasional 100% charge. However the damage done by not doing this is not very great for flooded wet cell batteries especially when they are still given an occasional equalisation charge.

Given the cost/trouble of acieving 100% charge in your case I would not bother. Not charging them to 100% will not have a very significant impact on their life.

A month of self discharge and occasional bilge pump use should not cause any problem.

(For those with AGM batteries note that with this chemistry it is much more important to achieve an occasional 100% charge. The above advice applies to flooded batteries)

[nigel1]

Have you considered mounting solar panels over the davits?
Should be room for a couple of decent sized panels. For 24V panels, these are available in the UK
24 Volt Solar Panel CS13524V | Professional Grade 135W Monocrystalline

[noelex 77]

Originally Posted by nigel1

Have you considered mounting solar panels over the davits?
Should be room for a couple of decent sized panels. For 24V panels, these are available in the UK
24 Volt Solar Panel CS13524V | Professional Grade 135W Monocrystalline

They list the module efficiency at 21.5 % which is a bit hard to believe.

[nigel1]

Originally Posted by noelex 77

They list the module efficiency at 21.5 % which is a bit hard to believe.

I fitted two of the 12V 135W panels about 8 months ago. So far, I have been happy with them, seem to work pretty well even on the overcast days (which is most days for us)

[noelex 77]

Originally Posted by nigel1

I fitted two of the 12V 135W panels about 8 months ago. So far, I have been happy with them, seem to work pretty well even on the overcast days (which is most days for us)

Good to know they are working well. The module efficiency is related to size /output ratio under STC so does not address low light performance.

It is probably just a typo, but this and the photo of a 48 cell panel instead of a 72 cell panel do not inspire confidence.

[noelex 77]

I have just looked up the specs again and they all look very strange.
The module efficiency of 20.5% is silly it would put them as a higher efficiency panel than the Sunpower E20's (20.4%) the most efficient "normal" panels available.
The size of the panel not surprisingly does not translate to this level of efficiency.

The panel size is about 14% smaller than the Kyocera equivalent. While this is not technically impossible it is very hard to believe for this level of panel.

Their specifications raise questions. I do have some doubt that they are not genuine 135w panels, especially given that they have made bogus claims for the efficiency.

They looks from their website like a reputable company so perhaps my concerns are unwarranted. They could have made a genuine mistake substituting module efficiency for cell efficiency but I would at least encourage some questions before buying these panels.

Nigel is the size they quote on the specs accurate? What is the best current and voltage output you have measured and under what conditions?

[nigel1]

One of the reasons I bought them was because of the slightly smaller size, it was a good fit to go on the davits.
I did spend a lot of time corresponding with the company, as I was initially going for the Kyocera panels.
The ones they advertise are monocrystalline, which I believe are more efficient than the poly, and another difference is that they have one more bypass diode as compared to the Kyocera,
Mine are connected to a BlueSky 3024 controller.
To be honest, I've not looked at the raw input to the controller, I must do this next week.
Few weeks ago on a really sunny day, I happened to glance at the battery monitor and saw a charge of 20A, the wind geny was also running as well.
Since fitting them, I have no need to use the battery charger, and I've used the panels to equalise the batteries.

I'll check the input voltages next week, and report back, hopefully will have some clear skies.

[nigel1]

Just found a picture of my solar install, looks like 120 per panel 120? can that be right), so looks like the picture on the website may be of another panel.
You have got me worried now, I did a quick google search to try and find some more info, came across a French Solar panel site, which also sells these panels, in the description it states

Photovoltaic panel CleverSolar 135Wc CS 12V monocrystalline

The SunPowered SPR series is ideal for all applications for charging batteries.
It offers a very high current load and extremely compact dimensions.

So, gets me thinking, are the panels (or cells) made by Sun Power??
Also noted in the Clever Solar description, that it states the panels original product code is SPR 130, which appears to be a SunPower code.
I googled SPR 130 and found a number of sites, which mention 21.5% efficiency

[noelex 77]

If they are using reject Sunpower cells that's actually very good news. Even the Sunpower "seconds" would still be good cells and explains the better efficiency than Kyocera.
The claim of 20.5 % module effeciency is still bogus but may be a simple translation error. They may have ment cell effeciency and 20.5% would be the correct ball park for Sunpower second cells.

If it has a 120 cells they may be wired in series for about 60v, or 2 lots of 60 cells wired in parallel.
The latter would be my guess. This is fine for a 12v system (with MPPT regulator) but this voltage is too low for a 24v battery system.
The former (all wired in series) is fine for a 12 or 24v system providing the controller can accept the input voltage (with a bit to spare)

The specs should make it clear, but they obviously have some errors.

[nigel1]

Close up picture of the panel
Please excuse the ***** hawk on the panel, not the most efficient way to run the panels

[Captain Dad]

Without discussing solar (have it myself, enough said) here is the truth on your battery 100% charge situation.

The first 90% of charge is rather easy and can happen running the genset for your normal hour or two, but that last 10% is a real pain to get to. You can hot charge the batteries to get them fully charged quickly by manually regulating the voltage somehow, (sorry, can't help you with the details on that, every charger is different) but generally it does involve hacking into the charge controller and doing things your batteries really won't like at all.

your best bet is to either run the genset for the ridiculously long time it takes to charge them properly, or figure out how to live with 80-90% charge.

[nigel1]

Originally Posted by noelex 77

Nigel is the size they quote on the specs accurate? What is the best current and voltage output you have measured and under what conditions?

Managed to get some actual values from the Blue Sky 3024 controller while out sailing last week, see the attached excel file.
Panels are made up from 144 cells each. Lowest state of charge of batteries during the 10 day's of sailing was 12.4V (70%) as measured by the battery monitor.
The best output I saw on the previous sail, was 20 amps (as seen on the battery monitor), this was with the boat heeled towards the sun, no shading and a clear sky

[Dockhead]

To answer my own question:

I have a strong hunch that it's better to break up the gnerator run into a number of shorter runs.

It seems very much to me that the surface charge dissipates somewhat if the batteries are left to sit for a few hours, and the batteries accept more charge.

So if you're trying to efficiently use say 6 hours of generator use, you will get a lot more charge into the batteries by doing it in three runs of two hours each, then if you just leave the genset running for 6 hours. It really seems to me.

Perhaps someone with better knowledge of battery chemistry could comment.

[noelex 77]

Originally Posted by nigel1

The best output I saw on the previous sail, was 20 amps (as seen on the battery monitor), this was with the boat heeled towards the sun, no shading and a clear sky

20A even briefly ( if this was all from the solar panels) is an indication that system is working well.
The 144 cells of your panel must be divided into 4 strings of 36 cells wired in parrallel to produce the voltages you are reporting on the spreadsheet. This is fine.