Solar panel question

Hi guys, I have 3 panels charging a battery bank and running a load. My question is why do I have really high voltage(over 100) but less than 2 amps and other times they are both high or both low? I understand that they combine for power output, but some days I have really high voltage but hardly any amps to charge my batteries. Is it the power or amps that is charging the batteries? Thanks for your help.

Rob

Rob Sigg wrote:Hi guys, I have 3 panels charging a battery bank and running a load. My question is why do I have really high voltage(over 100) but less than 2 amps and other times they are both high or both low? I understand that they combine for power output, but some days I have really high voltage but hardly any amps to charge my batteries. Is it the power or amps that is charging the batteries? Thanks for your help.

Rob

Rob, what is the rated voltage and wattage of each panel and how is the array configured? What kind of charger are you using? What is your battery voltage?

I have YGE panels I believe they are 240 watt each, Standard test conditions and 29.5 Volts. They are configured in series I believe, pos to negative etc. Im still learning. Im using a TS MPPT 60amp tied into a 24 volt battery bank. 4 12 volt batteries in series, and then parallel.

That what you are looking for? Early in the morning it goes into mppt mode when the voltage for the arrays is higher than the battery.

Rob Sigg wrote:I have YGE panels I believe they are 240 watt each, Standard test conditions and 29.5 Volts. They are configured in series I believe, pos to negative etc. Im still learning. Im using a TS MPPT 60amp tied into a 24 volt battery bank. 4 12 volt batteries in series, and then parallel.

That what you are looking for? Early in the morning it goes into mppt mode when the voltage for the arrays is higher than the battery.

Make sure all the switches on the controller are in the proper position to correspond to the type of battery you are using AND the voltage of the battery bank (switches should be in the following positions for a 24 volt battery: 2-ON, 3-OFF. Switches 4,5,6 should be positioned depending on what kind of battery you are using - AGM, flooded, etc.). Beyond this consider the possibility that the state of charge on your battery is so high that the controller is doings its job to limit the charging rate (i.e. the current). You can test this by discharging your battery to drop the voltage, then verifying that the charge rate increases accordingly. If you find that this is the "problem", then your controller is working properly and it's happy days, .

thanks for your reply. I have all of the settings correct. Im following your logic but I didnt think the controller determined the amps on the array, just from the array input to the batteries. Am I wrong? Im still not really clear on what actually charges my batteries, is it the voltage that is important, the amps or both?

I'm pretty sure the controller's readout will tell you the amperage going into the battery, so this will vary depending on sun, loads, and the battery's state of charge. It should only approach the maximum if the batteries are quite discharged. The function of the controller is to shut the panels off if need be to keep the batteries from being overcharged....

Yes, it does show the charging current, which makes sense that it is being controlled. I wouldnt think that the actual amps the panels are producing could be controlled though. For example, right now at 4:35PM Im getting 44.03 volts but 0 amps from the panels. the charge current is .1 amps, and the battery voltage is 25.35 volts. If its trying to stay in float stage then it should be up to 27 volts. Now I realize the the sun isnt real strong right now, but why does it have that high of voltage then?

Rob, how is your solar system working out? Did you find any problems with the configuration or components?

Hi Marcos, I didnt find any problems so far. It seems my voltage and amps output from the panels are going up somewhat proportionally....Ill have to post a pic of the stats when I get a few more days of logging. Im just not clear on what is important the volts or amps, or both...when it comes to charging the batteries. Its hard to track since I have loads on the system while its peak charging time. I dont think its really a problem, just a lack of me understanding and Im hoping to wrap my head around it so I can optimize my system and make some decisions on more equipment. It looks like alot of this is trial and error/monitoring.

Thanks for the follow UP

Rob Sigg wrote:Hi Marcos, I didnt find any problems so far. It seems my voltage and amps output from the panels are going up somewhat proportionally....Ill have to post a pic of the stats when I get a few more days of logging. Im just not clear on what is important the volts or amps, or both...when it comes to charging the batteries. Its hard to track since I have loads on the system while its peak charging time. I dont think its really a problem, just a lack of me understanding and Im hoping to wrap my head around it so I can optimize my system and make some decisions on more equipment. It looks like alot of this is trial and error/monitoring.

Thanks for the follow UP

I'm curious to know what kind of loads you have on the batteries. Have you yet tried heavily discharging the battery to take the battery voltage down and see how the system responds? As long as the battery voltage remains high the controller will limit the charging rate. During a sunny day, please try putting a heavy load on the battery to take its voltage down in increments. Record the data and see how the charge rate (amps on the battery side of the controller) responds.

BTW, it's amps that is most important to consider when charging the batteries, but only on the battery side of the controller. I understand that the current on the panel side of the controller should be less than the current on the battery side by a factor of battery voltage/array voltage. They will not be the same because they are separate circuits that interact through a transformer (among other components). The voltage on the panel side of the controller should be roughly the panel voltage ratings (depending on how the panels are connected in the array) except during particularly low solar incidence which would drop the voltage considerably.

Please note that I am no expert on solar PV installations, nor am I an electrical engineer. So, don't take my advice too seriously.

Good discussion on MPPT controllers here: http://www.solar-electric.com/whatismppt.html

Ill post some data when I get it. Its rare that Im home during a sunny afternoon to do testing, the only load I have on it right now is a freezer 5 amps, and a radon fan probably less than 2 amps.

Rob Sigg wrote:I have YGE panels I believe they are 240 watt each, Standard test conditions and 29.5 Volts. They are configured in series I believe, pos to negative etc. Im still learning. Im using a TS MPPT 60amp tied into a 24 volt battery bank. 4 12 volt batteries in series, and then parallel.

That what you are looking for? Early in the morning it goes into mppt mode when the voltage for the arrays is higher than the battery.

I take it you're running a 24 volt system. The panels should be tied in parallel, positive to positive and negative to negative.

It sounds like you have the batteries connected properly... two in series in parallel to two other in series.

Two 12 volt batteries in series = 24 volts. Two 24 volt pairs in parallel = 24 volts.

The YGE 240s are 24 volt panels, correct? They should be connected in parallel. If you have them in series, you have, in effect, one large 72 volt solar panel, whose open circuit voltage will be 100 volts or over. If the panels were tied in parallel, the open circuit voltage would never climb to 100 volts.

The TS MPPT 60amp charge controller is designed for input from 12, 24, 36, or 48 volts. It probably is not functioning properly with the voltage you are applying.

My panels are in series, so you are correct. A solar installer friend of mine set them up that way. And yes I have a 24 volt system. Not sure why he would have set it up wrong are we missing something?

I don't know if you are familiar with equations for current, voltage, resistance, and power. If not, this might help:

"I" stands for current (in amps).

"V" stands for voltage (in volts).

"R" stands for resistance (in ohms).

"P" stands for power (in watts).

I = V / R

Consequently, using simple algebra:

V = I X R, or more simply expressed, V = IR

Likewise, R = V / I



Now for power. The power in a circuit equals the product of the voltage and the current.

P = VI



If you have a 24 volt system running at 1 amp, you have a system delivering 24 watts. 24 volts X 1 amp = 24 watts.

If your 24 volt system is running at about 31 amps, it'll be delivering about 746 watts, which approximately equals 1 horsepower. Watts and horsepower are both expressions of power, in different units of measurement.



These things should help you understand what is going on with your panels, batteries, and charge controller. Volts, amps, resistance, and power are all related through the above equations. One factor does not change without a corresponding change in one or more of the other factors. The changes are dictated by the relationships described by the algebraic equations.

Rob Sigg wrote:My panels are in series, so you are correct. A solar installer friend of mine set them up that way. And yes I have a 24 volt system. Not sure why he would have set it up wrong are we missing something?

Your batteries are configured to 24 volts, which means you have a 24 volt system.

The panels are 24 volt panels. If you configure three 24 volt panels in parallel you have 24 volts. If you configure three 24 volt panels in series you have 72 volts. You don't want to charge a 24 volt system with 72 volt panels. The open circuit voltage of each of your panels is almost 35 volts. Under full load, the panels should be a little over 24 volts.

Try reconfiguring the panels to parallel and see how things work out.

Remember that by putting the 3 panels in parallel, you are getting 3 times the current. Parallel configuration means that no matter how many panels you parallel, you still have only 24 volts. However, for each panel you add in parallel, you get an additional approximately 8 amps.

The power output of your panel array increases by 240 watts with every panel you add. The increase in power comes from the increase in current (amps), not from any increase in voltage. A 24 volt system is a 24 volt system. All your additions of panels should be in parallel.

I completely understand, but IM not sure why my friend would have put them in series based on what you ar saying. I have a call into him to find out his reasoning. He does large commercial installation everyday. Not trying to be a pain, just very confused. Thanks for your explaination as well, that was helpful.

OK I got the skinny. My MPPT controller can handle up to 150 volts and it will take any combination to put the max amount of power into the batteries etc. He tells me that its always better to have the higher voltage rather than amps since there is no line loss with voltage. If we went parallel our amps would be much higher, but the net gain would be less due to loss. Now I understand why my volts are so high but my amps arent

Rob Sigg wrote:OK I got the skinny. My MPPT controller can handle up to 150 volts and it will take any combination to put the max amount of power into the batteries etc. He tells me that its always better to have the higher voltage rather than amps since there is no line loss with voltage. If we went parallel our amps would be much higher, but the net gain would be less due to loss. Now I understand why my volts are so high but my amps arent

Okay that's a new one on me. I don't do large commercial installations and am not familiar with the technicalities involved. Obviously your friend knows more about this. The controller can handle the high voltages but I don't think that is at the core of the problem.

I have a small set up, which I used for years although since the last time the batteries went bad on me I haven't replaced them. I'm not home much (over the road trucker) so I haven't gotten around to getting my panels useful again.

I'm not qualified to rebut your friend on the advantages of series configuration of panels, other than to remind you that you have a small system, and the issues which may add up to large losses or gains in a large system may not be the same ones with which you must deal.

If your panels are not far distant from your charge controller, and the parallel connections are made near the controller, taking advantage of the extra conductivity in 6 wires versus 2 wires (were the panels paralleled where they are located), then the resistive losses should be comparatively small for your system.

On the brightest day of the year, at high noon, the most you will probably see from a 240 watt panel is 8 amps. I'm taking for granted that the wires supplied by the manufacturer are capable of transmitting 8 amps without significant loss. I believe this to be true because it would not be in their interest to manufacture powerful panels only to have the loss in the output wire so high that the buyer and user would experience poor performance.

If your panels are configured in series, the highest current you can expect is 8 amps. If the panels are in series, the voltages will add but the current will not. One panel produces 8 amps. Three panels in series produce 8 amps. The voltage may have gone to 72 volts because of the series configuration, but the current will still be 8 amps.

Now, if your batteries are in a configuration supplying you with 24 volts, then no matter how many volts you have coming out of your panels, you won't go much higher than 24 volts at the battery end. Actually, fully charged, you'll get about 28 volts, as 12 volt lead/acid batteries are about 14 volts at full charge. The batteries will not climb to the 72 volts of your panels. Again, the batteries will stay at about 28 maximum. To simplify the discussion and for the sake of understanding, let's stick with nominal whole numbers. At noon on a bright day, with your present configuration, you can charge 24 volt batteries at 8 amps, 72 volts or not at the panel end of the circuit. Three solar panels will not provide the current of an automotive alternator, so your 12 volt batteries will probably not climb much beyond 14 volts even while charging. For power, let's say you'll have 8 amps X 28 volts = 224 watts. If the panels were configured in parallel, you'd be charging with 24 amps at 28 volts, and your power would be 24 amps X 28 volts = 672 watts. I know the panels are rated at 240 watts maximum, but the rating is taken from test conditions rather than the actual operating environment, so these numbers from a 240 watt rated panel are actually pretty much okay.

Losses in power lines are a major factor in the transmission of electricity. It is because of this that the high tension wires one sees strapped all over creation are run at such extremely high voltages. In your case, the losses in the relatively short lines from the panels to the charge controller, resulting from the relatively low current of 8 amps, are relatively small, perhaps a few percent. However, the loss of 16 amps of charging current resulting from the series configuration versus parallel configuration is a huge loss. You're losing 2/3 of the capability of your panels.

If you had 6 batteries configured in series to equal 72 volts, then yes by all means the series configuration of your panels would result in less resistive loss. There is no doubt about that and all the calculations would back it up. But again, your batteries are at 24 volts. Lead/acid batteries do not climb to triple their nominal voltage ratings.

You need to get all of the current you can into your batteries. I know this from experience. Solar power is great, but it has its disadvantages. Perhaps the greatest disadvantage is the lack of sunlight. When the sun is shining, you need to have everything right so that your batteries will not sit in an uncharged state for long. If they do, they'll die. Desulfators are not all they're made out to be.

If you tell me you're getting much more than 8 amps with your present configuration then I have a lot of studying to do and I'll have to rethink everything I've stated above.

You are correct mostly, I get a bit over 8 amps. IM getting it right now actually. I think a good test would be to rewire them to compare. My panels are about 35 to 50 feet away from the charge controller, but batteries are 2 feet.

Rob Sigg wrote:You are correct mostly, I get a bit over 8 amps. IM getting it right now actually. I think a good test would be to rewire them to compare. My panels are about 35 to 50 feet away from the charge controller, but batteries are 2 feet.

When you rewire them, run the wires from the three panels down to the charge controller and make the parallel connections at that point. The more wire you have carrying the current, the less loss you'll have.

Another way to do it would be to parallel the panels where they are, then go to Lowes or Home Depot, etc., and buy heavy duty wire for the trip from the panels to the controller. The heavier the wire, the lower the loss.

If the wires haven't been cut in order to facilitate the series connections, I'd go with the former.

very handy charts




easier to read

Thanks for the info. Ill have to try this out as I get time. For now mystery solved

Rob Sigg wrote:OK I got the skinny. My MPPT controller can handle up to 150 volts and it will take any combination to put the max amount of power into the batteries etc. He tells me that its always better to have the higher voltage rather than amps since there is no line loss with voltage. If we went parallel our amps would be much higher, but the net gain would be less due to loss. Now I understand why my volts are so high but my amps arent

This is absolutely correct. There is no reason whatever to wire your panels in parallel provided your controller is working properly and configured properly. If you're getting 8 amps from the array, then you should be getting amps in the mid to high 20's into the battery (multiply the current from the array by the array voltage, then divide by the battery charging voltage). If not, then there's something wrong the the controller, or it's not installed properly.

Thanks for that. It seems all is working well.

Rob Sigg wrote:Thanks for that. It seems all is working well.

So everything was ok from the get go?

Yeah I was confused as to why my voltage was so high but my amps werent. I forgot that since they are in series the amps dont add up just the voltage. That was why I started the whole post, but in the process I learned alot of new things thanks to you guys. So thanks!

Rob Sigg wrote:Yeah I was confused as to why my voltage was so high but my amps werent. I forgot that since they are in series the amps dont add up just the voltage. That was why I started the whole post, but in the process I learned alot of new things thanks to you guys. So thanks!

Excellent, and you're welcome. That's what this forum is for (and thank you Paul Wheaton for hosting us). I was interested in your system because it's very similar to what I have in mind (although I'll have a few more panels). I've done a lot of research, but have no experience yet. By all accounts the new MPPT controllers are just plain awesome (especially the one you got), so I was particularly curious to know if you just happened to get a faulty controller. I'm glad to know it's working, for your sake and mine (I was planning on getting the same controller, .

Rob Sigg wrote:Yeah I was confused as to why my voltage was so high but my amps werent. I forgot that since they are in series the amps dont add up just the voltage. That was why I started the whole post, but in the process I learned alot of new things thanks to you guys. So thanks!

I was right. I did have some studying to do.

I was not aware that the MPPT controller involves the use of a DC to DC converter.

Your panels put out about 72 volts and 8 amps, but the MPPT controller can turn that into lower voltage and higher current.

Then I take it the current you measured was between the panels and the controller. If you were getting 8 amps at that point, then the current between the controller and the batteries was much higher.

Robert Harsell wrote:

Rob Sigg wrote:Yeah I was confused as to why my voltage was so high but my amps werent. I forgot that since they are in series the amps dont add up just the voltage. That was why I started the whole post, but in the process I learned alot of new things thanks to you guys. So thanks!

I was right. I did have some studying to do.

I was not aware that the MPPT controller involves the use of a DC to DC converter.

Your panels put out about 72 volts and 8 amps, but the MPPT controller can turn that into lower voltage and higher current.

Then I take it the current you measured was between the panels and the controller. If you were getting 8 amps at that point, then the current between the controller and the batteries was much higher.

Yup you are correct. This controller is really cool, Ive been very pleased with it to date.


Marcos, Id be happy to share any data or things that Ive found out so please dont hesitate to ask questions. Right now I have one 5 amp freezer, one 1.5 amp fridge, a radon fan, 2 ballest flourescent light...not sure total watts. I have everything on a timer so its 2-4 hours on, 4-6 hours off etc throuhout the day so it can get fully charged. Provided I have enough sun every day it goes into absorption mode easily within 2 hours. Ive been draining to about 50% DOD.

Rob Sigg wrote:Marcos, Id be happy to share any data or things that Ive found out so please dont hesitate to ask questions. Right now I have one 5 amp freezer, one 1.5 amp fridge, a radon fan, 2 ballest flourescent light...not sure total watts. I have everything on a timer so its 2-4 hours on, 4-6 hours off etc throuhout the day so it can get fully charged. Provided I have enough sun every day it goes into absorption mode easily within 2 hours. Ive been draining to about 50% DOD.

Ok, well, I'm curious about how you have set up your timers and how you came to decide on that configuration. Based on what you've written, it seems you want the battery to go to absorption on a regular basis. Is this what you were targeting?...or, are you trying to prevent the battery from becoming significantly discharged?... or, am I wrong on both counts?

I had an unusual idea to load my freezer with a thermal mass in the form of bottles of salt water of a concentration to get the freezing point to 5-10F, then lower the thermostat setting all the way on the freezer. It would take some experimentation to get right. The idea is to try and get the freezer to cycle only once each day. I would then place the freezer on a timer to where it can cycle only during the day while the panels are producing. This should buy some time for the freezer during periods of poor sun, enhance the longevity of the compressor, and increase the yield from the panels by minimizing battery losses.

BTW, what kind of inverter are you using?

You were right on both counts I want them to go to apsorption every day if possible since im discharging them down to 40-50% daily. The timer makes sure there is a nice balance since the longest runs are during the max sun time as you pointed out. Ive found that my freezers can go 10-12 hours easily with no power as long as they are full, I have all meat in it now which helps with thermal mass. I try to leave it off in the early morning and late afternoon to help the process. Right now Ive been loading it up slowly to see just how far I can push it. I have 105 amp hour batteries, so 210 total Ah. I could leave the freezers off more, but for now Im leaving as is until I have time for more experimenting. My radon fan is plugged into it as well because that is how I vent my battery fumes too.

I have a PowerBright 2300 24 volt inverter. Its not top of the line, but it works great for what I want, at least for now. IM looking to get another 4 batteries so I can plug my second freezer into it. I have it set up so that I can easily go to grid power by plugging into outlets if my batteries need a break, or I can disconnect everything and trickle charge from the A/C.

BTW does anyone know how often the batteries should go into absorption stage? I typically drain them down to 50% daily and get to absorption daily as long as there is sun. When there is a cloudy day my batteries drop to 22 volts(24 V system) and my inverter will shut it self down at 21 volts. IM just wondering how long I can stay between 21 and 24 volts before I start to damage my batteries long term. More of a worse case scenario planning than a day to day use question.

Rob Sigg wrote:BTW does anyone know how often the batteries should go into absorption stage? I typically drain them down to 50% daily and get to absorption daily as long as there is sun. When there is a cloudy day my batteries drop to 22 volts(24 V system) and my inverter will shut it self down at 21 volts. IM just wondering how long I can stay between 21 and 24 volts before I start to damage my batteries long term. More of a worse case scenario planning than a day to day use question.

I have read sources that suggest the battery should be fully charged once each week as a preventive maintenance practice. Absorption will not fully charge the battery until it is completed and takes the battery to float. The weekly procedure that makes the most sense to me is to take your battery to absorption with a generator, and do so early in the day. Let the panels complete the absorption stage and take it to float (*). There is also the matter of periodically equalizing the cells, and I've read several accounts that this should be done either monthly or quarterly. NOTE: Battery charging is particularly inefficient once it gets into the absorption stage. Bulk charging is efficient. Therefore, a generator should be limited to bulk charging.

Based on my research it seems you're risking damage to your battery system by allowing the voltage to drop so low. Perhaps you should get more panels.

(*) Note that there is no need to use a generator if you don't have to. However, if the capacity of the array is not sufficient to take the battery to float on a regular basis, then it makes sense to either use a generator to fully charge the battery or get more panels.

If your batteries are reaching absorption each day but being discharged to 50% or less each night, you need more batteries, not panels. 200 some amp hours is a bit low for 750 watts of panels. i've got 660 watts of panels and 1060 amp-hours of batteries - my system is 12v though. the system rarely drops below 12.5v.

MPPT controllers are the way. boost that voltage! i had to run 3 pairs of wire to my 3 60 watt panels (through a PWM controller), and only one pair to my 480 watt array (through the MPPT). MPPT technology makes solar PV feasible in rainy/cloudy location.

Rob Sigg wrote:BTW does anyone know how often the batteries should go into absorption stage? I typically drain them down to 50% daily and get to absorption daily as long as there is sun. When there is a cloudy day my batteries drop to 22 volts(24 V system) and my inverter will shut it self down at 21 volts. IM just wondering how long I can stay between 21 and 24 volts before I start to damage my batteries long term. More of a worse case scenario planning than a day to day use question.

if you are regularly dropping your batteries below 24.2v, you are wearing them out. if you can, reprogram the inverter to shut off at 24v and buy more panels/batteries (or use less power!) and save yourself money in the long run. my batteries are 8 years old and i expect another few years out of them. those suckers get boiled every sunny day, and watered often. Rolls-Surette 480's or 530's are well worth the hefty price tag.

Robert Harsell wrote:
I take it you're running a 24 volt system. The panels should be tied in parallel, positive to positive and negative to negative.

An MPPT controller is capable of taking a high-voltage, low-current input and transforming it into a lower-voltage, higher-current output. The parallel advice is largely left for PWM controllers.

Robert Harsell wrote:
If you tell me you're getting much more than 8 amps with your present configuration then I have a lot of studying to do and I'll have to rethink everything I've stated above.

You are thinking PWM controllers.

My two 240 watt panels, (37.7 voc, 8 amps) are wired in series. They typically push 7 or so amps at 50-60 volts. Were I using a Pulse Width controller, I'd be getting only seven amps at 12 (or 24) volts. However, I am using an MPPT controller, which takes the input, turns it into AC, and converts that to a lower-voltage DC current, but does so with great efficiency (92 + per cent), meaning that on the really sunny moments, when 420 watts is coming in, the current fed to the batteries is some six to eight times what a PWM controller could create.

Thank you for the reply. I came to the same conclusion. Ive looked into a small wind generator to just charge batteries, but it would require alot more investment than I can afford right now. That cost would be well over $1,000; more batteries to double my current capacity would less than $550. They both have pros and cons, so Im still doing research. For now Ive removed the loads and Im waiting til spring to see how it goes.

The batteries give of power at night and so would the windmill due to night wind. So in a sense you could think of it as a night battery. that does not need to be replaced every 5 years.