few questions about solar (a newbie)

Nabiru3 · April 2018

Hello guys

my name is Nabil, and I am new to the solar power world and I have got few simple questions (just to be on the safe side)

question 1) I have got 1 MPPT morningstar tristar 30A charge contoller and 2 LG 315 panels (around 33Vmpp each) and 2 12v batteries wired in series (24v system) now I have the options of both wiring the solar panels in parallel or in series (cause the charge controller can take up to 30A and 150V). now (as the old legend says) if you have a 24v battery bank you should connect it to a 24v nominal panel array, right ? BUT, with an MPPT controller it is different as it can handle large volts to make them charge lower battery nominal voltage (boost current feature) so now i am confused as I can connect both panels in either way and still get the same output, so which method should I go with series or parallel ???
(btw, in the manual it says it is better to charge low nominal voltage battery using a higher nominal voltage panel(s) NOT the opposite though)

question 2) My 24v system inverter(which is indian btw) has a battery type switch in the back where it says I should either choose (Tubular or Flat plate), I know that Lead Acid batteries are categorized as (VLA & VRLA) and some VRLA types are GEL and AGM batteries, but I really don't know what kind of battery classification (Tubular and Flat plate) is. so if you please tell my which battery type option i should go with ? btw, my batteries are of type (Trojan VRLA AGM 12V)

question 3) (I am really sorry this is being overly annoying

) I have a 0.5hp (370w 1.7a rated) domestic water pump, if we say I run it for 1 straight hour on a 300AH 12v battery(which 100% full), how much of battery juice I will get remaining (considering both the continuous running wattage and the starting Amp (LRA) consumption of the pump motor)

Thanks in advance for any help provided

Photowhit · April 2018

on question 1, you should hook the panels up in series, the MPPT charge controller needs about 30% higher voltage than the charging voltage.

On Question 3, It sounds like you will be running a 24 volt battery bank, so I think you have something out of sync here...

... but it's a bit of a trick question, assuming the load is a AC load, you will also have the inverters inefficiency to consider. The inverter will use 7 to as much as 20% more energy than the load. so I'll use 420watts for the total load. So 420watts at 12 volts will be about 420/12=35 amps per hour. Now we run into another problem. Batteries are rated based on a discharge rate of 1/20th or their capacity (C20). If you draw current off faster than 1/20th, their effective capacity is lower. This changes by battery type and plate design. This is called Peukert's Law, This might help explain it...

https://www.batterystuff.com/kb/tools/peukert-s-law-a-nerds-attempt-to-explain-battery-capacity.html

So I'd give a rough guess of around 255-260 Amphours at C20.

mcgivor · April 2018

Welcome to the forum Nabil

With question 1, being that the panels are 24V nominal panels it would be possible to connect either way, in theroy, but series would probably be better to allow more headroom for the MPPT to work it's magic. Another consideration is high ambient temperatures tend to lower the output voltage so again series would probably work better. Input your relevant information in the fields of this string calculator http://string-calculator.morningstarcorp.com/ this is the best way to find tho optimum arrangement.

Question 2. Flat plate would be most likely the setting for regular Trojans, can you post a link to the exat battery?

Question 3. This is tricky question to answer because although the pump is rated at 1.7A at 230V, it is an inductive load, so power factor comes into play, which will increase the draw from the system. From experience with a 1/2 Hp pump, the draw should be approximately 24A at 24V nominal lower if the voltage is higher and higher if the voltage is lower. The trick is to run the pump once the battery is fully charged, this way the panels will supply the bulk of the current requirements allowing the batteries to recover afterwards. So let's use 24A at 24V as a guide, that would equate to 24Ah, so if you were to pump after the sun has set, the battery which has a usable capacity of 150 Ah (to keep within the 50% state of charge for longer battery life ) 150-24=125Ah remaining. If pumping is done as suggested when the charging is complete, the capacity would be back after a few hours or less, leaving the nominal capacity available. This method is referred to as opportunity loads, using production that would otherwise be wasted.

Hope this helps, others will surely have valuable input, there are some very helpful members here who will offer advice, good luck.

Horsefly · April 2018

mcgivor said:

....
From experience with a 1/2 Hp pump, the draw should be approximately 24A at 24V nominal lower if the voltage is higher and higher if the voltage is lower.

Hey @mcgivor, I'm not sure what the difference might be between your 1/2 HP pump and mine, but my 1/2 HP well pump pulls about 60A continuous from my 24V battery bank.

EDIT: I just went back and looked at my notes from last summer, and it looks like it was actually more like 57A most of the time.

mcgivor · April 2018

Horsefly said:

mcgivor said:

....
From experience with a 1/2 Hp pump, the draw should be approximately 24A at 24V nominal lower if the voltage is higher and higher if the voltage is lower.

Hey @mcgivor, I'm not sure what the difference might be between your 1/2 HP pump and mine, but my 1/2 HP well pump pulls about 60A continuous from my 24V battery bank.

EDIT: I just went back and looked at my notes from last summer, and it looks like it was actually more like 57A most of the time.

Is your pump 120V? in India the voltage would be double, or 230V so the current would halved, or there abouts, which would equate to being about the same, yas, no?

Horsefly · April 2018

I'm talking about the current out of the battery, not the AC current. I thought you were too. That would be (or should be) independent of what the output voltage was for the Inverter, right?

Estragon · April 2018

If it's [email protected], that would be [email protected]?

Estragon · April 2018

If it's [email protected], that sounds close-ish to what I see on my (240vac) submersible in the lake ([email protected]) into pressure tanks.

mike95490 · April 2018

1) does your battery have caps to add distilled water to ? if so, it's very likely flat plate.

2) wire the panels in series, and let the Controller manage it, easy.

3) Pump. Watts AC = V x A. then convert the watts to DC 24V and you will learn how many amps at 24V the battery must supply

Here's a power chart for pumps. My pump, 240V 3wire, 1/2 hp, consumes about 1,000w exactly when running. At 24V that would be 41 amps, plus about 15% more for internal inverter losses

Image: https://us.v-cdn.net/6024911/uploads/editor/bp/d5hgjjytt62a.jpg

mcgivor · April 2018

Horsefly said:

I'm talking about the current out of the battery, not the AC current. I thought you were too. That would be (or should be) independent of what the output voltage was for the Inverter, right?

You are correct the battery current would be based on the power requirements not the voltage of the pump, for a given power, the battery if the same voltage, would be equal current. My mistake, credit to you for the clarification.

Nabiru3 · April 2018

Great thanks for all of your answers which helped me a lot in understanding some of the basics.

few questions about solar (a newbie)

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