Off-grid solar charge controllers

[Mike90250]

Sunking your statement ""The bad news for RE users is solar charge controllers do not lend themselves well to an EQ charge. Many units have the feature built in them, but unfortunately due to the time and power limitations of the system in low insolation areas, they cannot often apply a EQ charge long enough to accomplish the job. In which case one really needs a generator and a standard AC charger to accomplish the job."" Is just so spot on but it is usually never thought much about,,
As its usually about 2pm in the afternoon even in high solar isolation areas(5Hrs) before the batteries are charged close to "full"' and that only leaves about 2 hours at most to do the equalization.. If you live in a 4hr zone or less then there is not ever going to be enough time to do a good equalization.

and that's why my big honking generator shed is next to the battery shed. Summertime, I rely on long absorb times to bubble and stir the electrolyte, but winters, I'll have to crank the beast up and bulk the batteries for a couple early morning hours, and then let the sun do it's share. Winters with their deeper discharges, is when cells are more likely to get out of balance, and need Eq.

And another reason to look at LiFe or NeFe

[john p]

Sunking your statement ""The bad news for RE users is solar charge controllers do not lend themselves well to an EQ charge. Many units have the feature built in them, but unfortunately due to the time and power limitations of the system in low insolation areas, they cannot often apply a EQ charge long enough to accomplish the job. In which case one really needs a generator and a standard AC charger to accomplish the job."" Is just so spot on but it is usually never thought much about,,
As its usually about 2pm in the afternoon even in high solar isolation areas(5Hrs) before the batteries are charged close to "full"' and that only leaves about 2 hours at most to do the equalization.. If you live in a 4hr zone or less then there is not ever going to be enough time to do a good equalization.

[Sunking]

Jonathon in my 33 years of working with DC plants I can tell you there is nothing special about L-16 batteries over any other kind of deep cycle battery. Al L-16 means is it has specific physical dimensions. In fact they are not designed for RE applications. They are like golf cart batteries in that they were designed for something else. In the case of L-16 batteries they were designed for floor scrubbers.

Like golf cart batteries they just happened to be available when RE applications started taking off, and re branded with RE labels by the various manufactures. What made them popular is the physical size.

As for Equalization, they are like any other flooded lead acid battery. They only require an Equalization Charge when specific gravity falls below 1.250 or wide ranging specific gravity of greater than 0.030, after being fully charged.

The bad news for RE users is solar charge controllers do not lend themselves well to an EQ charge. Many units have the feature built in them, but unfortunately due to the time and power limitations of the system in low insolation areas, they cannot often apply a EQ charge long enough to accomplish the job. In which case one really needs a generator and a standard AC charger to accomplish the job.

[Jonathan Cole]

In response to Mike, the manual for my brand new Morningstar 60 Amp PWM Tristar charge controller says:
"The L16 battery has some special charging requirements in a solar system. A study found that nearly half of the L-16 battery capacity can be lost if the regulation voltage is too low and the time between finish-charges is too long. One standard charging program in the TriStar is specifically for L-16 batteries and it provides for higher voltages and more frequent equalizations......

A good reference for charging L-16 batteries is a Sandia Labs report (year 2000) titled "PV Hybrid Battery Tests on L-16 Batteries" website:www.Sandia.gov/pv "

As far as sulfation goes, it is a complex subject, and in general in solar energy systems is an issue for chronically under-charged batteries that do not see enough equalization charges. Equalization softens sulfate and drives it off of the electrode. Sulfation may start after 24 hours, but it may take many months before it is irreversible. The larger flooded lead-acid deep-cycle solar batteries can often go for several months without an equalization charge if they are kept reasonably (80-90%) charged up.

Jon

[john p]

Here in Brisbane it rarely gets below 50deg F at night time in winter most of year its about 60 to 90F My other home in Philippines it never gets below 60 deg F on the coldest winters night.
My favourite PWM charger for small 12v systems is a Chinese copy of an old Steca model. No brand name but available here in Aus from a few big electronics stores.just about impossible to destroy it. Rated max input is 26v but it will take 36 v no problems and still never gets warm. Not like MPPT chargers that tend to die when operated 50% above rated input. They know they not that reliable as only 2 years warranty.. Another reason not good value most PWM as you know give 5 years, as they know there not going to be problem

Picture of it added its a 30a model

[Jonathan Cole]

Hi John,

As you know, I generally agree with your assessment. If you have to pay a large premium to get small improvement then more solar panels are a better choice. With 20-25 year warranties on solar panels, it is hard to beat their economic advantage over expensive, marginal increases derived from higher-tech more expensive equipment that may fail at anytime after their 2 year warranty is expired. However, it seems that in the more northern regions where there is less sun in the winter, cooler temperatures and the batteries which are more regularly deeply discharged (giving them a low voltage), MPPT controllers might make sense. I also agree that mechanical trackers are not a good investment. I think you get more bang for your buck by spending that tracker money on more panels in a fixed installation. Not to mention that properly mounted fixed panels have no maintenance other than occasional cleaning.

Jon

[Mike90250]

Moved to new thread.

[john p]

ramblings of me

Jonathan Cole here are extracts I wrote on another thead.. yingli yl185p-23b panel.

Mike90250.. Please dont take offence at my asking this.You make this statement.. You will need a MPPT type charge controller to down convert the 23V to 16V to charge the battery. If you just use a PWM controller, you throw away about 35% of your panel capacity The person asked you about one panel 23v to use on 12v system.. Have you ever done a real comparison between a PWM and a MPPT charger under that condition and you really got 35% more into the battery using the MPPT charger.?????

Mikes reply
I've not done the actual test, but the math is solid (if i only did the math instead of pulling numbers out of the air.) So you must first understand how the solar panel IV curve works, and then you can see that as the voltage goes lower, the amps stay the same (or very close) so it's a simple ratio, if peak power is at 23V, and battery voltage is 12V, 12/23= 0.52 or 52% of full power ! Gads, even worse than I thought. back to 16V it's 16/23=0.69 or 69% of full power [31% loss ]

Then my reply
Maths is wonderful.. But you have never tried it for real.. And if you did im more than willing to bet the result will be nothing like 31% more charge into a battery from that panel.

Why do I say this.??/ I have done many many test comparisons in real to show people that the real difference on a system smaller than 500w of solar panels the figure is somewhere between 4% to 9% , Have never got a higher figure..
Granted on big systems you do get higher results but in the 10 to 20% range..
To give an example of what im saying I have 3x 80w panels open circuit voltage about 21 if used with PWM charger I get 78 ahr into the batteries if Iseries the outputs of the panels I get 81 ahr.... I have used many different types of MPPT chargers and always about same result,, NO MATHS INVOLVED just looking at AHR reading for the day.

Just asking.. If you were correct where does the 31% of the power go ?? compared to using the MPPT charger???

Mike
It's lost as a mis-match between PV panel and battery. And if you use 12V panels (Vmp @ 18V) there is very little difference between PWM and MPPT. But a 23V panel was mentioned, and that's where there is enough difference with a 12V battery.
And the new Morningstar and Midnight Classic charge controllers are super efficient, with only about 1% losses, where older MPPT controllers were in the 5-10% loss range.

And also depending on battery state of charge, a nearly full battery will not accept much charge from any controller

Me
Mike90250 The only part of your last post I accept is..And also depending on battery state of charge, a nearly full battery will not accept much charge from any controller. That is why I have always started the test at early in the morning after the battery is is in a discharged state.Then measured the total ahr into the battery at end of day.. I gave one result done many times PWM 78ahr MPPT 81ahr about 4% even if you want to use the latest super dooper MPPT charger it is most likely at best add 4% to that making a total of about 8% Along long long way short of 31%.. If you think im wrong and you can do the test comparison starting with a battery about 50% discharged and can produce the figures there is a 31% loss then I will believe mabe i have been testing them all wrong over the last few years..
And you not say where the 31% of panel output went?? disipated in the charger as heat?? in the wiring as heat? in the panel as heat??

I really believe many of the claims made for MPPT chargers are theory only.. Not actual real life measurements.when used on under 500w systems..
And not good value for money.. here a good 30a PWM costs about $120 a MPPT charger above $600 if you had 1 to 3 panels about the 100w range it far better value for money to buy another panel and you definately will get a worthwile improvement under every condition..

Nothing beats real life testing. Its my job to do that and compare results with theory .. You would be supprised the differences you get..

Mike
Ah ha ! Now I know what's wrong on your end. You are measuring total daily recharge. That will always be the same, if you have sufficient PV array.

Look at what I put in BOLD

I don't have the resources to actually DO the test, as I'm in a situation where I am running off my PV, and can't afford to change the system.

Here's another way to visualize it. (internal circuit losses ignored)

System 1: 24V 100W 4.16A PV, PWM controller, 12V battery charging at 15V. 9V mismatch (24v-15V) gives:
15V * 4.16 = 62W
9V * 4.16 = 37.4 W Lost as not being able to be used at all, sort of like power factor losses in an AC circuit
You must realize, that the way the PV IV curve works, you cannot get 100W at 15V, because that would require 6.6amps which is more than the panel is spec'd at [4.16A]

System 2: 24V 100W 4.16A PV, MPPT controller, 12V battery charging at 15V.
15V * 6.6A = 100W
The DC-DC downconverter (like an AC transformer only DC) preserves all the power, and your battery charges.

That's a free, >2A gain, from the otherwise wasted, 9V mis-match.

Till now, john p , nobody disputes this fact. In fact, I've seen several people upgrade to a MPPT controller, and they can't believe their battery monitors, and have gone and measured their actual charge current, and it's right, magic power just from a different controller.
There are internal losses in both PWM and MPPT, and varied MPPT algorithms, so it's not always as perfect as the math says, but the difference and gain IS there.

Me
Mike this is the start the middle and the end of my point.. and it nice now you agree with it..Ah ha ! Now I know what's wrong on your end. You are measuring total daily recharge. That will always be the same, if you have sufficient PV array.Now you see where in real life there is NOadvantage in using the very expensive MPPT charger. You are far better buying another bpanel with the money difference..

Me last time
Mike I will tell you why im not a believer in using MPPT chargers on small systems.. Here at work we have multiple solar arrays of various types on the roof and on ground mounted trackers.. We have just about every type of solar battery charger available,, many are sample units from manufacturers.. At the end of the day testing has shown on small systems there is very little gain using less reliable and far more expensive MPPT controllers.
You most likely would not believe the failure rate of MPPT chargers when abused compared to PWM chargers.
The only valid test for real world (not a 5 minute test that shows""magic free power"") is how much energy is put into a battery pack starting from a known discharged amount over a set amount of hours..
Trackers fall into the same useless catagory ,, it far better to buy more panels than try to get more power from trackers, and removes the need foor unreliable motor and actuators.

I now just hope Mike 90250 the moderator is not unhappy with me reposting all of this..

[Mike90250]

According to Sandia National Laboratories, between 10% and 85% state of charge, a deep cycle flooded lead acid battery is 90% efficient. Above that, the efficiency drops to 50-60%. True, you need to occasionally charge up all the way in order to equalize, but yopu only would want to do that as much as necessary (L-16 batteries require 6 hours per month of equalization according to Morningstar).

I see 2 very wrong things here.

1) Charge efficiency. between 10% and 85% SOC =90% eff True enough, but that's also where suflation sets in after 24 hours. This kills batteries in just a couple of months. That same study also addressed the sulfation issues.

2) Equalization. I don't know of any battery mfg that even hints at 6 hours of monthly equalization. Usually, it's suggested only when cells are imbalanced, and then for only 30 minute intervals.
Morningstar's monthly EQ is an hour or less in their modern chargers.

I'm concerned that you are/have been writing some very dated advice, and don't have current data to back it up.

[Jonathan Cole]

Off-grid solar charge controllers

There are several approaches to charge control. These are Pulse Width Modulation (PWM), Maximum Power Point Tracking (MPPT), and in some cases power diversion when the batteries are full. See the descriptive technical articles in the Appendix.

You can simply connect the PV panels directly to the battery or inverter. The older charge controllers, simply turned the panels on or off according to the battery voltage and capacity. This is not advisable, however, due to over-voltage conditions, over-heating, shortened battery life and decreased battery capacity. The investment in a charge controller is well worth the savings in battery life and capacity.

As a result of the deficiencies of these older on-off devices, a class of charge controllers using Pulse Width Modulation (PWM) were developed that give an optimal charging regime for the deep cycle batteries used in solar applications. Highly efficient and very low cost per watt of controlled power, these have become very sophisticated and usually include volt, amp, and accumulating kwHr metering.

The Maximum Power Point Tracking (MPPT) charge controller differs in that it calculates the voltage at which the module is able to produce maximum power. The MPPT system then operates the PV modules to extract the full wattage, regardless of present battery voltage. A high efficiency DC-to-DC power converter converts the module voltage at the controller input to the appropriate battery voltage at the output.

With MPPT, if the whole system

[Sunking]

There is one fact, or Ohm's Law that cannot be ignored with respect to charge controllers:

With a Shunt Controller current in = current out.
With a MPPT controller input current does not = output current.

OK let's now debate. :becky:

[john p]

Jonathan Cole sart another thread And I will tell you a lot more about my everyday connection with all types of solar controllers.. BUT NOT GT ones, I at the moment know almost nothing about them

[Jonathan Cole]

Jonathan Cole you are a similar thinking man to me as far as MPPT controllers go. In real life (despite the maths and the advertising hype" on small systems the gain is very low most cases below 8%. And the huge price difference makes it a better deal to go buy another panel with a 20 year at least guarantee..
mabe you like to read my other post on this sites in replying to others about same subject..read the thread ..yingli yl185p-23b panel Sunking will totally disagree with all I write about it . but thats ok, I think we just have very different ways of testing things..

Hi John,
I believe you and I are correct in most cases, unless you are talking about high latitude locations where it is very cool for substantial parts of the year. Then MPPT may be worth the cost. Although I am a bit wary of why an Outback 60 amp MPPT contoller costs twice as much as a Morningstar 60 Amp PWM controller and also that the Outback has two years warranty against the Morningstar's 5 year warranty. Is there something inherently less reliable about MPPT controllers? I would be interested in hearing about people's experience with MPPT controllers.

Jason the moderator has asked me to start a new thread, since this charge controller thing is only slightly related to LiFePo batteries. So I will do that by posting my original piece about the difference between charge controllers and the economics of their use. Derek disagreed with me which is fine because what we should all care about here is not who is right but what is factually correct. Without facts, we can make expensive errors and then people can say, See? I told you solar doesn't work! Gr-r-r!! that gets me mad since I have been living off-grid with all the amenities for decades and never had a power outage or burned out a light bulb, so I know it is superior to grid power.

[john p]

Jonathan Cole you are a similar thinking man to me as far as MPPT controllers go. In real life (despite the maths and the advertising hype" on small systems the gain is very low most cases below 8%. And the huge price difference makes it a better deal to go buy another panel with a 20 year at least guarantee..
mabe you like to read my other post on this sites in replying to others about same subject..read the thread ..yingli yl185p-23b panel Sunking will totally disagree with all I write about it . but thats ok, I think we just have very different ways of testing things..

[Jonathan Cole]

John first let me say WELCOME, you are a VALUED CONTRIBUTOR.

With that said i respectively disagree with your oppinion. A shunt (PWM) regulator by nature is 70% efficient, whre MPPT is 90% or more regardless of weather.

Hi Derek,

Thanks for your comments.

By the way it is Jon not John.

While it is true that my opinion is as I stated, it is an opinion with some basis in fact and experience. I have lived off the grid on solar PV systems for more than 2 decades and have researched and written a book about the topic.

For example, I have a Morningstar 60 Amp PWM charge controller that is connected to 750 (peaking at 1000) watts of solar panels. You say that it is only 70% efficient. That would mean that 30% of the energy going in is not passing through to the battery. This would require the charge controller to dissipate 225 watts of energy, yet the heat sink is always cool to the touch.Perhaps you mean that the pulse width modulation switching turns off the power source 30% of the time. I do not believe that a PWM charge controller is 70% efficient the way it is used in a practical solar energy system. But I have written to Morningstar to see what they have to say about it. Maybe you are right and that 225 watts of heat is well spread out in the heat sink. But I can boil water in minutes with an immersion heater of that size. I will pass along what I receive from Morningstar.

A pulse width modulated charge controller does its work by chopping the electrical flow with distinct on-off times. In bulk charging mode, the off-time would be negligible and that is by far the largest part of the energy flow unless your batteries are undersized. In absorption, float and equalization modes, the pulse-width off-time is much greater when the panels are generating substantial energy. However, long-time users of solar know that to make your batteries last a long time you try to keep the energy use at a rate that prevents these end-stage and inefficient charging regimes. According to Sandia National Laboratories, between 10% and 85% state of charge, a deep cycle flooded lead acid battery is 90% efficient. Above that, the efficiency drops to 50-60%. True, you need to occasionally charge up all the way in order to equalize, but yopu only would want to do that as much as necessary (L-16 batteries require 6 hours per month of equalization according to Morningstar).

In any case, I would be interested in your reasoning beyond just a blanket statement of opinion. I think that this is an important issue for solar economics and the design of practical and durable systems.

Jon