Solar not Working Correctly?

[simonpickard]

Hello all,

So I've got my battery monitor installed, good to see what's coming in and out.

One thing that's got me scratching my head is the watts in from the solar. At the height of the day here in the Med (Italy) with 300 watts (2 x 100 watt and 2 x 50 watt panels) pumping into my 12v batteries the monitor is showing I get just over 100 watts. I measured this with nothing turned on.

Does that sound about right? From my searches I looks low to me but I'm not sure if I'm missing a trick here.

The panels are up on my bimini with a 6-7m run to a battery controller and then into the bank.

I know there are a load of different factors all working at once but roughly with 300 watts of panels how many watts would you expect in?

Regards,
Simon

[nimblemotors]

Any shading on the panels?

[simonpickard]

I do have backstays around there but did check and couldn't see much if any shading.

[capt-couillon]

Watts out from the solar panels are going to be dependent on battery state.
Just like your shore power charger, if batteries are up to snuff, the charge controller on the panels will throttle the output depending on the battery SOC.

Of course, depending on your setup, I could be all wet, but that's how it works in my house.

[simonpickard]

This was in bulk mode on the solar controller which I think means it's pumping in as much as it can?

That also confused me as my battery monitor was saying SOC was 100% but it was still in bulk on the solar controller.

Honestly this stuff confuses the hell out of me. Just when I think I've got the basics I release I haven't got a clue.

[Ex-Calif]

Hi Simon. I saw your thread about the battery monitor.

You absolutely need to get the monitor calibration sorted if you are going to have a meaningful dialog about SOC and charge sources.

Clearly you made an assumption about battery capacity when you calibrated your monitor. I think you said 10% down. This cannot be correct if SOC is reading 100% and you are in bulk.

It is a total PITA but you have to learn and apply MaineSails calibration method if you are going to use the monitor SOC function.

As to why the solar as putting out 8amps or so the answers could be multiple. First you need to know if the solar is trying to charge a battery that needs charging - SOC calibration.

Then what I would do is isolate one battery and purposefully discharge it - do this as part of the discharge test by creating a load with incandescent/halogen lights wired in parallel to create the appropriate load.

After you have discharged the battery hook up the solar in the middle of the day and see what you get in a known 20-30% discharged battery.

This is a huge PITA but once you have put the work in you will be an expert on your batteries, monitor and solar system.

[Stu Jackson]

deleted.

[ErikFinn]

Originally Posted by simonpickard

Honestly this stuff confuses the hell out of me. Just when I think I've got the basics I release I haven't got a clue.

I've been experiencing similar feelings recently. There is a LOT of variations to these solar puzzles, and a lot of opinions out there. I'm pondering with my issues here currently:
http://www.cruisersforum.com/forums/...ls-125770.html

Originally Posted by simonpickard

That also confused me as my battery monitor was saying SOC was 100% but it was still in bulk on the solar controller.

MaineSail says there are battery monitors out there incorrectly installed and possibly incorrectly used, have a look at his article here:

Smart Gauge Battery Monitoring Unit Photo Gallery by Compass Marine How To at pbase.com

Also to help learning about solar I recommend Handy Bob's blog, especially the "The RV Battery Charging Puzzle", the "RV SOLAR QUICK ANSWER", and the "HandyBob’s 9 Golden Rules for living on Solar and Battery Power" here:

The RV Battery Charging Puzzle « HandyBob's Blog

A lot of stuff there, but you can not go wrong reading his stuff IMHO.

[simonpickard]

Well how can my solar controller know when that battery is 'full' i.e. goes from bulk into float but my battery monitor can't?

Just read those links. Will read them again before trying to calibrate more.

[sailinglegend]

Originally Posted by simonpickard

Well how can my solar controller know when that battery is 'full' i.e. goes from bulk into float but my battery monitor can't"..."..

That is the whole problem with chargers that don't measure the current actually going into the battery, they have to work on a time basis which means they wil drop to Float at 90% or much less. If this happens with solar there may not be enough hours left in the day at the lower float voltage to get the batteries FULLY charged. They are designed to charge your batteries, not overcharge them! You must get batteries back to 100% regularly or the will Sulfate and die prematurely.

[monte]

Simon I usually look at the amps, not watts. For example right now my solar controller is
My battery monitor is

So this is telling me there is a 10A difference.
As the batteries are around 90% charged the difference is probably a combination of appliances running, and battery acceptance being governed.
Note the voltage level is high because of the charging. If it wasn't charging it would read around 12.6V
This is at 1030 near the med.
1120w of panels

[noelex 77]

Simon the easy way to check your output is to make sure your panels are in full sun with no shade around midday.

Turn on a high constant load that is similar than the the output of your solar panels (300w). This will ensure your battery SOC is not a factor. Measure the draw with solar panels off. Turn on the solar panels and note the difference.

In Italy at this time of year you should be getting about 240w out of the panels if your system is OK.

[capt-couillon]

Well how can my solar controller know when that battery is 'full' i.e. goes from bulk into float but my battery monitor can't?

Ahhh Grashopper, so we wish to delve into the mysteries of the universe?

Who'd a thunk that something as "simple" as a plain ol' lead acid battery could be so complicated, and generate so much confusion, discussion, and debate... Actually LA wet cells while "old" technology, are still fairly sophisticated and dependent on a huge number of factors including temperature, SOC (state of charge), physical construction, discharge rates (Peukert's law), electrolyte stratification, and so on... All of which have been discussed elsewhere on the forum (endlessly).

Anyway, the short answer to your question is that your average "battery monitor" determines battery SOC via voltage. For a 12V LA battery average values are (about) 100% SOC = 12.7V, 50%SOC = 12.2V, 0%SOC = 11.8V These values may (will) vary depending on physical construction of the battery, and composition of the plate materials.

Your "Solar Controller" on the other hand, being a fairly recent innovation, will probably contain some sort of micro-processor and base its transition points on the current acceptance curve of the battery rather than straight voltage measurement.

So what happens is, on a partially discharged battery as the charger kicks on, both voltage and accepted input current will increase to a point where the voltage stabilizes at 12.7 V (your battery monitor now reads 100% SOC (Surface Charge saturation) and the accepted current drops to a "flat rate". Your Solar Controller will continue to supply charging current to the battery until the acceptance current is (usually) around 3% of the rated current. (During this phase, the battery is doing its chemical thing deeper and deeper within the plates and through out the electrolite.) At that point it reduces the voltage to the battery to the "float" level. At this lower voltage level the battery will only accept a minimal amount of charge to make up for self discharge losses. The larger your house bank, the longer the discrepancy between the battery monitor saying 100% and the solar controller still supplying charging current.

Are we confused yet?

In my experience the best way to determine the SOC of a lead-acid battery is the old fashion battery hydrometer




By measuring the specific gravity of the electrolyte, you know the true SOC. Chemistry don't lie.... Electronics might. Of course, we are still dependent on temperature, electrolyte stratification etc...


Another good read on battery charging principles
Charging Information For Lead Acid Batteries – Battery University


(Sorry for all the "smilies" but just in that kinda mood)

[Ex-Calif]

The two terms that continually confuse folks is capacity and state of charge

Until one can separate the two concepts one will be a grasshopper and not a master...

As Cap Cuillon says stuffing amps into a battery is a tricky process. It is a chemical reaction that is impacted by temperature, internal battery resistance and plain old "mechanical" issues. By mechanical I mean the sulfation and materials that make up a battery.

Fundamentally the faster you try to push amps in the more the battery resists. So the battery monitor can get fooled into thinking full, but at a slower rate the battery will still take more amps.

The battery monitor is not magic and it's not smart. It just displays what it knows. The tricky part is that you have to tell it a lot of things for it to "know" accurately anything about your bank.

[barnakiel]

On our system (roughly half your size and half of our plant beyond 10 years old)) we get between 7+ Amps (batteries low) and 0.2 Amps (batteries full).

So I would expect to see anything between 20 and 0.2 Amps on your setup.

About this much depends on how full your batts are.

b.