Conflicting advice on series vs. parallel for charging 12v Bank. Please advise.

[driscolldb]

I've researched my eyes out and have called a few people, but I seem to get a lot of conflicting information.

My system is small and doesn't move. All panels get ample light at the same time and are never shaded. My panels are less than thirty feet from the charge controller and the batteries are less than five feet from it.

This system is for emergency power and charging. Everything thing I have is 12V DC, or well within the ability of running off my small inverter (which is almost never used). I estimate that if I were to hook up everything I could think I'd ever need at the same time, I would use 1.5 Kwh over 24 hours, most of that being a slow constant draw.

The batteries (stats below) I have are wired in parallel staying at 12V. I do not wish to go to 24V.

Right now I have one 300 Watt panel that is doing OK. I recently got a great deal on four 280 watt panels (stats below) and want to hook them up to my system (removing the old panel) and add more batteries to run a DC Fridge and Freezer.


Now for the problem:

Some people are telling me to put the panels in parallel and some are telling me to wire them in series. The parallel-minded people are saying that the panels have enough volts already and this would bring you to a higher amp rating the batteries can definitely handle. Thus charging faster/better.

The series-mined people are saying that with an MPPT controller you always want to wire in series as along as the charge controller (stats below) can handle it. Maxing the Volts out while staying inside the battery's amp charging rate. Thus charging faster/better.

Of course I want to charge as fast as possible and do what is best to prolong the life of the batteries.

Could you please tell me what configuration you would put these panels. Parallel, series, or 2X2 in series and then each pair linked in parallel? Does it even matter? Other than wire sizing, is there an advantage to either setup?

Personally I'm leaning toward all parallel. The Midnite Solar string sizer says that all 4 panels in series would be excessive. Others say it can handle it.

Thank you.

Here is my equipment:

(6) SLR124 VmaxTank Batteries in parallel AGM
Nominal Voltage 12V
20Hr Capacity 125AH
RC (Min) 260
Energy (kWH) 1.7
Charging Current 8A-35A
Charging Voltage 14.4-14.9V
Float Voltage 13.5V-13.8V

(4) STP280S-20/Wew Solar Panels
Max Power 280W
VMP 31.5V
Imp 8.89A
VOC 39.4V
Max System V 1000V
Max Series Fuse 20a

(1) Midnite Classic 200 Lite Charge Controller
Operating Volts In: 200VDC
Max Hyper VOC 200+battery
Battery Charge Volts 12-93
Absolute Curent Output 74a at 12V Battery

[Sunking]

Quit listening to people who do not know WTF they are talking about. It is all abou twhat kind of panels and controller you use.

If you do not know WTF you are doing, you buy very expensive Battery Panels and dirt cheap PWM controller. When you go that route you must parallel the panels not to exceed 18 volts. Battery Panels are 18 volts. Then they cheap out and buy a cheap PWM controller, so they turn their 100 watt panels into 65 watt panels. It takes a 300 watt PWM system to equal a 200 watt MPPT system. A 300 watt PWM system will cost you $600 to $800, you have to wire all th epanels in parallel requiring combiners, fuses and extra large wire to handle that low volt and high current. Up around a $1000 because they did not know WTF they were doing.

Smart Money buys dirt cheap higher voltage higher wattage grid tied panels and a good MPPT CONTROLLER. Smart Money wire as many panels in series to get voltage up and current down. A 200 watt MPPT system you spend $$200 on panels, and $200 on a 15 amp MPPT controller for a total of $400 to $500, less than a 300 watt PWM system and they do the same thing. Additionally with the panels wired in series much smaller wire over longer distances, id Two strings or less no combiners or fuses needed., life is simple and efficient running high voltage on your panels up to 60 to 200 volts . Unlike what you will be doing operating at 12 volts.

[driscolldb]

Sunking,

Thank you for the reply. Its a little convoluted, but I think what you're saying is to wire them in series.

"Quit listening to people who do not know WTF they are talking about." I haven't listened to anyone, yet, so I cannot quit. What I've done is a lot of research and have asked a lot of questions. When things contradict I continue to ask questions. This is a small system that I have built myself, to learn as I go. How am I supposed to magically know who knows WTF they are talking about? If I knew who knew WTF they were talking about, after all the research I mentioned doing, I wouldn't be here asking more questions, would I?

“If you do not know WTF you are doing, you buy very expensive Battery Panels and dirt cheap PWM controller “

I don't see how this applies. I do not have a dirt cheap PWM controller. I think what you're doing is giving an example of someone that has done something I'm not doing. Also you're giving examples of the difference between PWM and MPPT, which I'm aware of. You're advocating an MPPT controller over a PWM; we agree, already. As you can see in my post I already own an MPPT controller. This is an entire paragraph about PWM expense vs. MPPT expense; if there is relevance here I don't see it.


“life is simple and efficient running high voltage on your panels up to 60 to 200 volts . Unlike what you will be doing operating at 12 volts. “

I think what you're saying here is that my life (solar system) isn't simple and efficient because I'm running 12V. Running at higher volts would require me to step everything back down to use almost every piece of DC equipment I own on a system used to charge flashlights and run a couple of appliances you'd see plugged into a car. I didn't arbitrarily choose to keep the batteries at 12V. I will add to my knowledge base that having a 12V system is neither simple, nor efficient and mention that to others. I wonder if anyone will tell me to stop listening to people that don't know WTF they are talking about.


This is what I consider simple. A few decent panels (which I have), run to an MPPT charge controller (which I have), hooked to a battery bank that runs at the V for everything I want to run or charge. The question I was asking was whether to run them in series or parallel.

[MichaelK!]

A few decent panels (which I have), run to an MPPT charge controller (which I have), hooked to a battery bank that runs at the V for everything I want to run or charge. The question I was asking was whether to run them in series or parallel.

The answer is both. I plugged your panel's specs into the sizing calculator, and it doesn't like all four of your panels in series; wattage is too high. It does like two parallel strings of two panels in series. Wire it up that way with your MPPT controller and you're good to go.

[driscolldb]

MichaelK!,

Thank you!

[Sunking]

I plugged your panel's specs into the sizing calculator, and it doesn't like all four of your panels in series; wattage is too high. It does like two parallel strings of two panels in series.

There is someone you should not listen too because they have no idea WTF they are talking about or even what they just said.

Has nothing what so ever to do with wattage. The Wattage of the 4 panels is exactly the same if in all four panels are in parallel or series. The difference is the VOLTAGE is too high with all panels in series, and with 4 panels you only have 3 option. All in parallel which is the last thing you want with a MPPT Controller, All in Series which is what you want if it does not exceed Voc input of the controller, and Series/Parallel in 2 x 2.

[MichaelK!]

There is someone you should not listen too because they have no idea WTF they are talking about or even what they just said.

Has nothing what so ever to do with wattage. The Wattage of the 4 panels is exactly the same if in all four panels are in parallel or series. The difference is the VOLTAGE is too high with all panels in series, and with 4 panels you only have 3 option. All in parallel which is the last thing you want with a MPPT Controller, All in Series which is what you want if it does not exceed Voc input of the controller, and Series/Parallel in 2 x 2.

Honestly, you should have an attitude adjustment! If you actually plug the specs into the sizing calculator, the calculator itself states "Array power (Wattage) excessive". It's not my verbage, it's the verbage of the calculator itself. I CAN add you know. Four panels in series is 157V, which I think maybe might be less than 200V. When you input the number however as two 2-panel strings, the calculator gives you a green OK.

panelgif.GIF

[Sunking]

Honestly, you should have an attitude adjustment! If you actually plug the specs into the sizing calculator, the calculator itself states "Array power (Wattage) excessive". It's not my verbage, it's the verbage of the calculator itself. I CAN add you know. Four panels in series is 157V, which I think maybe might be less than 200V. When you input the number however as two 2-panel strings, the calculator gives you a green OK.

What does that tell you?

Power = P1 + P2 +P3..... Makes no difference if the panels are series or parallel 4 panels of 280 watts = 1120 watts all day long everyday. You are trying to compare 3 different Controllers with different power ratings at 12 volt battery. The maximum Power Input at 12 volts is:

Classic 150 = 1380 watts
Classic 200 = 1137 watts
Classic 250V = 878 watts
Classic 250KVS = 800 watts

From the charts it is real easy to see only the Classic 150 and 200 should be considered operating at 90/70 volts or less input voltage. The OP IMO should only be looking at the Classic 150. Regardless either the Classic 150 or 200 with those panels are 2 x 2.

[Gajetest]

Wow! A poor guy ask for a little help and yu'all get into a equipment measuring match

And I'm keeping this PG you know what I mean when I say you 'all measuring your equipment.

I see you have a 12 volt system. Well right there even for emergency situations 12 volt systems tend to be a might unstable 24 volt is better 48 is best 96 volt I think is a might overkill. You have to series and parallel just like you have to do with your power storage system. To get the all-important amp hours you need to get your watt hours without spending or purchasing to many panels. I went for solar trackers gives me the most sun power time as it moves my panels like a sunflower always facing the sun.
You say your system uses 1.5KWH or around that I’m too lazy to scroll back up and get the number you placed I hope I'm close, and mean no disrespect like I said I’m just lazy. There are about a hundred calculators online that will tell you what you need in power and panels and some good math was demonstrated here.

The average American household of 4 uses 16.5KWH in a 24 hour period. Mine is 2 people and I use 17.5KWH in a 24 hour cycle, computers and gadgets I’m always working on puts me in a higher power bracket plus there is no energy crisis so I use electricity in abundance. And I sure as hell don’t give my CLEAN energy to a power company who sells me trash power to use in my home. Hook an oscilloscope to your pure sine wave inverter, and then do the same test to what’s coming out of your wall from the Power Company. Your inverter power will look like spring water compared to the Mississippi Mud they send through all their capacitors and whatnot. However, if you have been keeping up with the power companies; then you know their switching to micro-grids. Like they are already doing in Europe, and will start leasing and charging for equipment and wattage hours.

So you might want to start thinking on a larger scale before they jump and catch you by the short hairs. All I'm writing is documented so if some ijit wants to try and bash me; better do some reading. And you’ll find I really will not care or listen to negative junk. We got a good thing here I’m glad I joined. I like to see all the information that is available open and to be shared. We in America are behind in renewable energy systems. Above 90% could not even tell you what an inverter is or 99% wouldn’t have a clue to what a Gasifier-generator is. Let’s keep the dialogue to the point please. I’m a wind bag and I know it. But I’m reaching 60 years too fast and I’m tired of the damn 1%-ters treating us like mushrooms.

All I'm saying we got some CEO's out there that are planning more nuclear reactors, can you wrap your head around that? We don't need them. Anyone can go Off-Grid at a low cost. Don't look at brand names look at specifications of the equipment you buy. Let’s use good forums like this one to come together to share and take back what is already God given and free. Well I probably wrote too much, but I can’t help it. We need to help each other and not wait for some company to drop a ready-made will fit all power system on our door. And to all of you fellow tinkerers well met gentlemen.

[MikeB]

need advice

I have two 12v-150W panels that I plan to wire in series for 24V, with tracer 20amp mppt CC, and 4-6v batteries connected in series, with 12/24 1500W inverter to run a small fridge. Is this the best plan or should I connect the batteries in series, parallel for 12V.
Thanks in advance.

MikeB

[Mike90250]

is your fridge 12V or 24v ? That's your answer.

If it's 120VAC, then you need a pure sine inverter to run it, and I would advise to use a 24v system with a 1,000w inverter. You need a large inverter to be able to start the motor in the fridge.

[MikeB]

is your fridge 12V or 24v ? That's your answer.

If it's 120VAC, then you need a pure sine inverter to run it, and I would advise to use a 24v system with a 1,000w inverter. You need a large inverter to be able to start the motor in the fridge.

The fridge will be 120V and I had planned on 1500W pure sine wave inverter. So if I get this correct, you are saying going 24V with the batteries then a 1000w inverter will do the job?

The Tracer 20A controller is rated for 200W. Will it work for the 2-12v 150 panels wired in series. Am I correct that would be 24v, 150w?

[Mike90250]

Mostly - yes

a 24V battery system needs to charge at nearly 31V at times - Will the "12v" panels in series go that high? What is the
Vmp _____
Voc _____
spec on the label ?

[MikeB]

Mostly - yes

a 24V battery system needs to charge at nearly 31V at times - Will the "12v" panels in series go that high? What is the
Vmp _____
Voc _____
spec on the label ?

No it's 8.29 & 22.92. So I assume I can still have the panels in series, for 24v, and the batteries in series and parallel for 12v. And I assume that's my only choice without buying more panels for the time being. I also have a 50w panel I used for years for lights & small tv at this cabin and I had planned on just leaving it out of this new array. However I'm curious, is there any way to include the 50w panel or is it simpler and better just to leave it out.

I really appreciate your time and expertize. I don't know if you're allowed to recommend controllers & inverters, but if you are, what would be an adequate choice on a limited budget.

thank you again

MikeB

[cmclane28]

No it's 8.29 & 22.92. So I assume I can still have the panels in series, for 24v, and the batteries in series and parallel for 12v. And I assume that's my only choice without buying more panels for the time being. I also have a 50w panel I used for years for lights & small tv at this cabin and I had planned on just leaving it out of this new array. However I'm curious, is there any way to include the 50w panel or is it simpler and better just to leave it out.

I really appreciate your time and expertize. I don't know if you're allowed to recommend controllers & inverters, but if you are, what would be an adequate choice on a limited budget.

thank you again

MikeB

If your charge controller is only rated for 200 watts (I assume that's if you have a 12V battery bank), and you are going to use a 12 V battery bank, your 2 - 150 watt panels are going to be too much because they will be putting out 300 watts no matter which way you wire them (Series: 36+v x 8.29 amps or parallel: 18+v x 16.58 amps). Typically the wattage rating for the charge controllers is double if you go with a 24V battery though, so assuming that's the case I'd wire the panels in series and wire your 4 - 6v batteries in series for a 24 volt system. Assuming they are rated around 230 Ah that would give you about 2,700 usable watt hours (realistically less because of normal inefficiencies), so as to not run your batteries down past 50%. Not sure what your fridge uses in watts, but you mentioned it was a small one so I think that would work fine. Of course if you have a couple cloudy days in a row you'll need to find a way to help charge the battery bank.