Unlimited solar panels, overcharge guaranteed?

[travissand]

Up Date Sept 28th 2018:
User Matrix in comment Number 18 provides a link to the solution for people who have Midnite classic charge controllers like myself http://midniteftp.com/forum/index.php?topic=3796.0
Does anyone know if this can be accomplished with other systems as well?
Youtube video about the subject. https://youtu.be/UqfU7Q5NRH0

Original Post:
I've done a lot of reading but one question I have that hasn't specifically been answered is this. Let's assume you had an unlimited wattage solar system. And you have a small battery Bank. I don't want to lower the maximum amps my charge controller can put out because then that amperage is not available for the inverter. People keep telling me that I'll overcharge and cook my batteries. But it seems to me if I set the maximum voltage at a reasonable amount the batteries will only take what they can safely handle. So I guess I would use the hydrometer to teach me when they are full so the charge controller could back off to float voltage. And assuming it's never cloudy I suppose I could lower the voltage in order to slow the charge down so I wasn't speed charging them.
Is my logic correct?
Is this particular balancing act so tedious that I need to turn down the maximum available amps?

That brings me to a second question. Assuming the above at what depth of discharge could I get down to and still return the battery to full within solar producing daylight hours?


With these theoretical questions answered it will help me to understand even beyond my new setup. I'm trying not to get into what size my system is and stuff but I know you'll ask. In reality it's not unlimited wattage but it does seem to be possibly around double what most people would have for my size battery Bank. Off grid 6 kilowatts of solar panels & a 19 kilowatt hour battery. This system is in Hawaii in a place with no obstruction to the Sun and rarely cloudy. The panels do not track the Sun. They're currently producing 1300w already at 7:30 a.m. Im currently using one kilowatt hour overnight. That will probably increase to 2 kilowatt hours nightly once I get confident in this new setup. I think C/8 is 2400w which can be reached at 9 :30 a.m.


A fun side note, for a quick test when I faced them directly at Sunrise they produce like High Noon. Seems like people underestimate single access Sun tracking. Especially near the equator where the second axis is not quite as necessary and or can easily be manually set every few months.
It's a satisfying thing running high-wattage devices in the daytime knowing that I don't have to run that dang generator anymore.

[organic farmer]

I've done a lot of reading but one question I have that hasn't specifically been answered is this. Let's assume you had an unlimited wattage solar system. And you have a small battery Bank. I don't want to lower the maximum amps my charge controller can put out because then that amperage is not available for the inverter. People keep telling me that I'll overcharge and cook my batteries. But it seems to me if I set the maximum voltage at a reasonable amount the batteries will only take what they can safely handle. So I guess I would use the hydrometer to teach me when they are full so the charge controller could back off to float voltage. And assuming it's never cloudy I suppose I could lower the voltage in order to slow the charge down so I wasn't speed charging them.
Is my logic correct?

Those are all 'presets' that can be pre-programmed into my charge-controller.

... That brings me to a second question. Assuming the above at what depth of discharge could I get down to and still return the battery to full within solar producing daylight hours?

That is a common system variable.

My system can get our batteries up to 99% State-Of-Charge by noon on any sunny day.

[jflorey2]

I've done a lot of reading but one question I have that hasn't specifically been answered is this. Let's assume you had an unlimited wattage solar system. And you have a small battery Bank. I don't want to lower the maximum amps my charge controller can put out because then that amperage is not available for the inverter. People keep telling me that I'll overcharge and cook my batteries. But it seems to me if I set the maximum voltage at a reasonable amount the batteries will only take what they can safely handle.

Nope. You can overcharge both lead-acid and lithium chemistry batteries. There is a limit to how much charge they can accept during bulk charging (constant current for the li flavor.)

To avoid that set the maximum charge current at the charge controller to what the battery can accept. For FLA it's generally C/8, for AGM C/4, for LiFePO4 usually C/2. However ALWAYS check the manufacturer's specs first; they are the final word in how to care for a battery.

Is my logic correct?
Is this particular balancing act so tedious that I need to turn down the maximum available amps?

There's no balancing act. Just turn down the charge current to a safe level, and you're done. If you want to have all that current from your billion-watt solar array available to other devices, get a charge controller that lets you set charge current to the BATTERY rather than charge current output.

That brings me to a second question. Assuming the above at what depth of discharge could I get down to and still return the battery to full within solar producing daylight hours?

From an energy perspective? You could go down to zero percent charge. If you have enough power available you can always charge at C/8 until fully charged (unless you live near/in the Arctic Circle or something,)

However, from a real world system (i.e. not a billion watt system) you have to estimate what energy you will get on your worst day and plan for that. Which means that in many cases you will NOT get a full charge.

From a battery perspective? For lead acid, never go below 50% charge.

With these theoretical questions answered it will help me to understand even beyond my new setup. I'm trying not to get into what size my system is and stuff but I know you'll ask. In reality it's not unlimited wattage but it does seem to be possibly around double what most people would have for my size battery Bank. Off grid 6 kilowatts of solar panels & a 19 kilowatt hour battery. This system is in Hawaii in a place with no obstruction to the Sun and rarely cloudy. The panels do not track the Sun. They're currently producing 1300w already at 7:30 a.m. Im currently using one kilowatt hour overnight. That will probably increase to 2 kilowatt hours nightly once I get confident in this new setup. I think C/8 is 2400w which can be reached at 9 :30 a.m.

OK. So you will likely need a charge controller that can limit BATTERY (not total current to keep your battery currents under control.

A fun side note, for a quick test when I faced them directly at Sunrise they produce like High Noon. Seems like people underestimate single access Sun tracking.

I don't think they underestimate it. I think they are making the decision between buying a $2000 tracker, or spending that $2000 on another 4kw of solar and roof mounting hardware.

BTW if you want all the benefits of tracking, mount two solar arrays 45 to 60 degrees off dead south - one to the southeast, one to the southwest. If your array is small it can be cheaper than a tracker. It also allows you to put one array where you get morning sun and the other where you get afternoon sun.

[Mike90250]

You have to decide how you want things to run:
1) flat out full power and risk damaging batteries from overcharge
2) reasonable charge limits, and if heavy loads arise, slower battery charging.

i don't know any reliable method to allow full battery charging, and nearly unlimited loads, from 1 charge controller.
Generally, on a clear day, as the sun ramps up power to the panels, a lead acid battery will self-regulate, as it also slowly charges up.
But that all goes out the window on a foggy or cloudy morning, and the full sun breaks through at 11am, and blasts 60A into your little battery that is still low from overnight.

[travissand]

So if my batteries were really hungry for a recharge and the sun breaks out at High Noon I'd be charging at C/3.2. Or if I don't round any of the of the numbers before multiplying an error to be exact it would be C/3.8. And that would rarely ever happen considering I don't drain my batteries down that far. & being aware of this issue if I did drain them enough to except unhealthy current I could simply run the generator during the cloudy morning so this doesn't happen. Or I could put a current limiter or second charge controller in between the charge controller I'm using now and the batteries but that would require an insanely huge diode.
I may see one day a year where the clouds here are thick enough to considerably stifle energy production. Really it seems like from what I've read flooded lead-acid batteries can handle a little bit of overcharging anyway. I guess for now I'll keep an eye on the amperage. Maybe I'll even disconnect the solar panels until noon just to see how many amps are really consumed. 100 Amps x 0.01ohms =1v So float + 1v should equal the voltage I should set my Max volts to in order to stay under 100 amps? Lol I think I'll opt for the real world test.

And if it's too many I know that turning down the voltage a little would lessen the amperage. Truthfully I'm disappointed if the top of the line charge controllers don't mesure the amount of amps going into the batteries versus in to the batteries versus being consumed by the loads so that way they can adjust their maximum current output on the Fly. All this high-tech and we're still living in the Stone Age with these designs.

The solution to my particular problem would have been purchase AGM batteries instead of flooded lead-acid. But for that price I could have probably doubled my flooded lead-acid battery Bank to relieve the problem and possibly create a undercharged condition LOL.

now I'm even more mad at the charge controller manufacturers. What a ridiculous Balancing Act they make us do. Solar panels are cheap now and we're no longer cutting Corners with the amount of Watts of our solar array. This is going to be a problem more and more often that needs to be addressed.

and of course this brings me to think that a surge load maybe pulling power out of the battery unnecessarily instead of pulling it all out of the charge controller when you are floating which is unnecessarily cycling the battery and reducing its life. Electricity follows the path of least resistance and if you have a battery Bank willing to put out 2400 amps and a charge controller only willing to put out 230 where do you think the power will come from for a surge load? The batteries may have more resistance but will the charge controller respond quickly? Sorry for my rambling these other questions should probably be in a difference thread and I haven't searched for their answers yet but I do remember a guy complaining he saw this problem happening with his Midnite classic.

[travissand]

I don't think they underestimate it. I think they are making the decision between buying a $2000 tracker, or spending that $2000 on another 4kw of solar and roof mounting hardware.

In Hawaii solar retail panels are $1 a watt plus the cost of your mounting hardware, charge controller and wiring. So on my 6000 watt system I could double my kilowatt hours if I purchased a cheap eBay Sun Tracker and since I have room I could ground Mount them on top of a chain link fence. Guaranteed I could keep the cost under $1000. I could even program the tracker to keep it under 100 amps until the batteries were in absorb mode. That way my inverter is only withheld from full solar panel wattage during the bulk mode. This could be a good compromise.
by the same logic it seems like the charge controllers Max Amps setting should only be valid during bulk charging otherwise it should pass through its full capability. That's a simple software setting does anybody know how they function?

[jflorey2]

In Hawaii solar retail panels are $1 a watt plus the cost of your mounting hardware, charge controller and wiring. So on my 6000 watt system I could double my kilowatt hours if I purchased a cheap eBay Sun Tracker

Nope. You might get 30% more out of a single axis tracker, or 40% out of a dual axis tracker (or a single axis with elevation adjusted 4x a year.) I know at least one company who advertises 45% more, which is probably stretching it.

No one even _claims_ 2x more, much less delivers. I am afraid you are the victim of a sleazy salesman.

and since I have room I could ground Mount them on top of a chain link fence. Guaranteed I could keep the cost under $1000.

You can't mount trackers on top of chain link fence posts. That sounds like a joke.

A Zomeworks passive tracker that will carry 3-4kW is about $6000. Could you build one for cheaper out of Unistrut and the like? Probably. But if you are going to go that route, I can buy panels for 30 cents a watt via Ebay or Renvu and get another 4kW for $1200. It's all about watts per dollar.

About the only way that solar tracking makes sense with today's panel prices is if you are putting up an array so large that you can use one central motor to aim an entire 10-100kw section of the array. That way you are taking advantage of economies of scale, and the delta cost for the tracking isn't very much.

[travissand]

Nope. You might get 30% more out of a single axis tracker, or 40% out of a dual axis tracker (or a single axis with elevation adjusted 4x a year.) I know at least one company who advertises 45% more, which is probably stretching it.

No one even _claims_ 2x more, much less delivers. I am afraid you are the victim of a sleazy salesman.

You can't mount trackers on top of chain link fence posts. That sounds like a joke.

A Zomeworks passive tracker that will carry 3-4kW is about $6000. Could you build one for cheaper out of Unistrut and the like? Probably. But if you are going to go that route, I can buy panels for 30 cents a watt via Ebay or Renvu and get another 4kW for $1200. It's all about watts per dollar.

About the only way that solar tracking makes sense with today's panel prices is if you are putting up an array so large that you can use one central motor to aim an entire 10-100kw section of the array. That way you are taking advantage of economies of scale, and the delta cost for the tracking isn't very much.

I'm not blessed with cheap eBay savings when it comes to large items that are hard to ship. However I am blessed with clean air in the middle of the Pacific Ocean. I have not been scammed by sneaky salesman. My calculations are done off of real world use and what I have seen with my own eyes with my own system. Right now you're getting near full power for only 4 hours a day. Yet there's 12 hours of Sun here. Imagine getting near full power for 12 hours instead of 4. In fact I'm on a 8000 foot mountain with ocean views in both directions technically I get the sun before anybody at sea level. And I'm still in the sun when it's already set on everyone down below. Though I doubt this extra Sun helps much. I'm just trying to show that I don't have any blockage near the horizons other than further distance from the Sun

[travissand]

I just got off the phone with Midnite classic and the tech support guy had no idea what I was talking about and recommended emailing the developers who apparently will not return communication with me

[jflorey2]

I'm not blessed with cheap eBay savings when it comes to large items that are hard to ship. However I am blessed with clean air in the middle of the Pacific Ocean. I have not been scammed by sneaky salesman. My calculations are done off of real world use and what I have seen with my own eyes with my own system. Right now you're getting near full power for only 4 hours a day. Yet there's 12 hours of Sun here. Imagine getting near full power for 12 hours instead of 4

That would be great! But due to the Sun passing through a lot of atmosphere you don't get anything near full power towards the beginning and the end of the day.

Take a look at the power curve for a PV panel on a tracker vs on a fixed mount. If we were on the Moon, the fixed panel would look like half a sine wave and the tracker would look like a square wave. Here on Earth they both look like sine waves - the one with the tracker is just somewhat fatter.

[Mike90250]

> I may see one day a year where the clouds here are thick enough to considerably stifle energy production.

Light haze will reduce your daily peak, but enhance the pre & post noon harvest.

Clouds, to the point you loose crisp shadows, will reduce your harvest 70-90%.

[Matrix]

What charge controller do you have? The Midnite Solar Classic has a little known internal programing setting (not the one in the menu) that I believe will limit charge amps only, but will not limit amps available for loads (not sure but I think it works this way). It is a different setting than the Limit output amps setting in the local app or menu. It does require a WhizBang Jr though and the Classic must have firmware version 2096 or newer.

[travissand]

What charge controller do you have? .

yes this is awesome! thank you thank you Matrix for bringing this to my attention. That's what this form is for. Better tech support than Midnite themselves Yes I do have Midnite 150 classics. Between the systems I manage I have 5 of them.
But their tech support was not aware of this. I specifically asked him if I installed a whiz-bang would the software give me this ability. He had no idea what I was talking about and The Wiz bang only tells you battery charge level. My response was it would give the charge controller the ability to monitor how much power was going in to the inverter provided the software was programmed that way. He said The Wiz bang could not possibly tell the controller anything about what the inverter was using and said the controller is hooked to the batteries only it's not even hooked to the inverter at all. I said it's hooked to both and The Wiz bang will let it differentiate how much power is going to each. He even tried to say that the battery somehow communicates with the charge controller. My response to that was the charge controller may be able to study the voltage and consumption but I wouldn't call that communication.

[Matrix]

Well this is Odd that MN did not know this, it is their white paper. Anyway, here it is (see link or attached pdf). Maybe this will work for you ... may be not?

http://www.midniteftp.com/support/kb/faq.php?id=37

[Matrix]

The tweak can only be done from the MNGP (MidNite Graphics Panel). You cant do it from the local app.

A few things I have "discovered" while messing with this embedded menu option:

1. Once you get to the 4405 address, know that the default for address 4405 = 30000 in case you ever need to set it back.
2. That being said, the 30000 number might as well be 30 million zillion, because you will have to adjust it down to probably below 1000 ONE DIGIT AT A TIME using the appropriate arrow key. Plan to be there about 30 minutes. BUT I figured out you can speed adjust the value by Pressing and holding the Upper Left Button (shift) while pressing and / or holding the Up or Down arrow buttons
3. I set my CC to 430 which should limit the current to 43 amps charging or C/10 (See the MN white paper for the formula). If I recall, it did limit the charge amps but not the amps for loads. In the end I set it back to default because my array was not large enough to really bother with it - Because ...
4. You will need to Watch Heat when limiting the current of the Classic. Might cause the heat of the FET to go up ... but should cause the heat of the battery to be lower during charging. As I experimented with it, both were true.

Good Luck, hope this helps