Need Help Calculating Solar Panel System

Solar Expert Posts: 62 ✭✭✭✭
Hi,

I'm currently have 5 panels of 100W solar panel, a 30A Morningstar PWM charge controller and a 300W Morningstar suresine inverter and I will be acquiring 2 150AH batteries tomorrow.

I'm planning to use energy acquired from solar mainly for lighting and in case of blackout I'll use it to power a water pump (125W continuous) about 30minutes (I get around 3-6 hours blackout everyday in this country).

Since my home 90% bulb is LED bulb, the power needed should be low.
I assumed a total of 100WH for lighting.
====================================================================
I read in an article how to calculate the system.

1) How much energy battery could store.

300AH*12V = 3600WH or 150W/hour available

2) How much energy usages

I assume 100W for 24 hours (for worst case) not included the water pump yet.

100W*24H = 2400WH

3) Energy solar panel could produce

5 hours of sun

500W * 5 * 0.85 (losses) = 2125 WH

====================================================================

From the counting above, it seems that my panel isn't producing enough power to fully charge my battery, not to mention autonomous in case of bad weather. Hmm...

I was wondering if the calculation above is true. Please help me to correct my system.

Thank you.

Comments

• Banned Posts: 17,615 ✭✭✭
Re: Need Help Calculating Solar Panel System

Well not quite.

300 Amp hours @ 12 Volts is 3600 Watt hours (DC), but you can not use 100% of that capacity and expect the batteries to recharge at all (or at least not for very long). So with a maximum Depth Of Discharge of 50% you really have 1800 Watt hours available.

So there's the first problem: you won't get 2400 Watt hours of lighting from them, even without including the conversion loss and inverter consumption.

The second problem is that solar panels will not produce their nameplate rating. On average your 500 Watts of PV will put out 385 Watts over the 5 hours of equivalent good sun. That's 1925 Watt hours (again on the DC side; no conversion or inverter losses).

You should get about 26 Amps from that array with a PWM controller. That's an 8.6% peak charge rate. So whereas the panels will recharge the batteries, neither will supply the desired 2400 Watt hours of lighting.

The end-to-end calculation for what that system could supply looks like this:
500 * 5 * 0.52 = 1300 Watt hours AC.

If I were you I would be re-evaluating the power needs first, then looking at buying a couple of GC2 batteries to put in series instead of the two 12 Volts in parallel (more suited to the available charging). If the load and supply can't be aligned one of them has to be changed.
• Solar Expert Posts: 62 ✭✭✭✭
Re: Need Help Calculating Solar Panel System

I've been looking for a good battery for a long time... I think it will take forever..

It's hard to find a good battery here. Even a standard deep cycle battery cost very much here. But, I still afford to buy a better one here.

There are lots of china-made brand here, but I'm not sure of their quality. I planned to buy indian-made battery, it's a deep cycle tall turbular battery, what do you think about it?

If I keep using 12V battery and paralleling it using this

is it okay? Will it charge equally?

So, in order to get at least 2400W hours AC to supply 100W bulb for 24 hours, I will need at least 10 panel of 100W or 1000W panel, right?

1000 * 5 * 0.52 = 2600 Watt hours AC.
• Banned Posts: 17,615 ✭✭✭
Re: Need Help Calculating Solar Panel System
mulia wrote: »
I've been looking for a good battery for a long time... I think it will take forever..

It's hard to find a good battery here. Even a standard deep cycle battery cost very much here. But, I still afford to buy a better one here.

There are lots of china-made brand here, but I'm not sure of their quality. I planned to buy indian-made battery, it's a deep cycle tall turbular battery, what do you think about it?

Without more specifics I don't think anyone could render an opinion on it.

If I keep using 12V battery and paralleling it using this

is it okay? Will it charge equally?

Yes! That is the correct way to parallel two batteries!

So, in order to get at least 2400W hours AC to supply 100W bulb for 24 hours, I will need at least 10 panel of 100W or 1000W panel, right?

1000 * 5 * 0.52 = 2600 Watt hours AC.

Batteries supply the load, panels recharge the batteries.
To get 2400 Watt hours DC from 12 Volts you need 200 Amp hours used, or a minimum 400 Amp hour battery bank. This would be two parallel strings of GC2's for example.

Then to recharge that much the short cut is to look at the peak charging current of 10% of capacity, or 40 Amps. On a 12 Volt system with a PWM controller that's roughly 40 * 17.5 or 700 Watts. Note that the current is equivalent to the combined Imp of the panels regardless of what Voltage they are. It is slightly different if an MPPT controller is used.
• Solar Expert Posts: 62 ✭✭✭✭
Re: Need Help Calculating Solar Panel System

I'm sorry about that.

After deep browsing, I found several seller of Trojan T 105 battery in my country although very far away, it's commonly used as golf cart battery, is it a good battery to start with?

It's around \$200 in my country. If possible, I'm going to buy 4 of it. If it's done, I'll end with 12V 450AH available as power bank. How many wattage of solar panel you will suggest in order to have it charged and also supply at least 2400 Watt hours AC?

I hope it could supply 2 days without sun too.
Batteries supply the load, panels recharge the batteries.
To get 2400 Watt hours DC from 12 Volts you need 200 Amp hours used, or a minimum 400 Amp hour battery bank. This would be two parallel strings of GC2's for example.

Then to recharge that much the short cut is to look at the peak charging current of 10% of capacity, or 40 Amps. On a 12 Volt system with a PWM controller that's roughly 40 * 17.5 or 700 Watts. Note that the current is equivalent to the
combined Imp of the panels regardless of what Voltage they are. It is slightly different if an MPPT controller is used.

I didn't get it. Where 17.5 came from?

Is the peak charging current depends from the capacity of battery? (10% * Capacity?)

What's the difference if I use an MPPT controller?
• Banned Posts: 17,615 ✭✭✭
Re: Need Help Calculating Solar Panel System

The Trojan T105 is often used in RE applications. Very good battery with only two drawbacks: it's expensive and its charging Voltage requirements can be too high for some controllers (14.8 Volts on a 12 Volt system) and inverters (they will high Voltage Fault under certain conditions).
I didn't get it. Where 17.5 came from?

17.5 Volts is the 'normal' Vmp for "12 Volt" panels. As such the quick way to find approximate Wattage when using a PWM type controller: current needed * Vmp = Watts.
Is the peak charging current depends from the capacity of battery? (10% * Capacity?)

Yes. The Amp hour capacity (regardless of Voltage) at the "20 hour rate" which is the standard used for RE.
What's the difference if I use an MPPT controller?

Let's look at 12 Volts 450 Amp hours (four T105's). You want 45 Amps as the peak current at the minimum 12 Volts. So 45 * 12 / 0.77 (typical panel & controller derating) = 701 Watts. 700 would do, or you could round up if that fits the available panel selection better (for example to keep the number of panels even if that makes the array easier to plan).

On PWM it would be 45 * 17.5 Vmp = 787.5 Watts. As you can see there's about 11% advantage to the MPPT providing the panels with those specs are used. If you are looking at particular panels note that the Imp rating needs to add up to around 45 regardless of the Watts or Vmp. For example some 100 Watt panels have Vmp 18.9 and Imp 5.3: you'd need nine such panels in parallel to provide the 45 Amps. Put the same panels on an MPPT controller and you'd only need seven!
• Solar Expert Posts: 62 ✭✭✭✭
Re: Need Help Calculating Solar Panel System
The Trojan T105 is often used in RE applications. Very good battery with only two drawbacks: it's expensive and its charging Voltage requirements can be too high for some controllers (14.8 Volts on a 12 Volt system) and inverters (they will high Voltage Fault under certain conditions).

Attachment not found.

Attachment not found.

Trojan has different absorption, equalization and floating rate compared to MS 30 CC, will they match without decreasing the battery lifespan?

Let's look at 12 Volts 450 Amp hours (four T105's). You want 45 Amps as the peak current at the minimum 12 Volts. So 45 * 12 / 0.77 (typical panel & controller derating) = 701 Watts. 700 would do, or you could round up if that fits the available panel selection better (for example to keep the number of panels even if that makes the array easier to plan).

On PWM it would be 45 * 17.5 Vmp = 787.5 Watts. As you can see there's about 11% advantage to the MPPT providing the panels with those specs are used. If you are looking at particular panels note that the Imp rating needs to add up to around 45 regardless of the Watts or Vmp. For example some 100 Watt panels have Vmp 18.9 and Imp 5.3: you'd need nine such panels in parallel to provide the 45 Amps. Put the same panels on an MPPT controller and you'd only need seven!

So, in order to calculate panel size needed to charge my battery bank, I will take 10% of the power bank size, then multiplying it with voltage and dividing it with derating rate. right?

I'll need to print this formula.

Calculation on PWM depends on the Vmp while on MPPT depends on the wattage of the panel?

I currently have 5 of this panel.

Attachment not found.

If I buy more panel, with different Vmp and Voc like this

Attachment not found.

Will they match and working properly? In case an MPPT controller used.
• Banned Posts: 17,615 ✭✭✭
Re: Need Help Calculating Solar Panel System
mulia wrote: »
Trojan has different absorption, equalization and floating rate compared to MS 30 CC, will they match without decreasing the battery lifespan?

No. This is indeed the problem. Without having that 14.8 Volt Absorb the Trojans will never be fully charged and this decreases lifespan. You need to program the controller to the specs the batteries require. If this is not possible you either change the batteries or the controller.
So, in order to calculate panel size needed to charge my battery bank, I will take 10% of the power bank size, then multiplying it with voltage and dividing it with derating rate. right?

Yes, for MPPT type controllers.
Calculation on PWM depends on the Vmp while on MPPT depends on the wattage of the panel?

PWM controllers depend on Imp: the current at maximum power. They can't do anything with "additional" Voltage, unlike MPPT type controllers.
I currently have 5 of this panel.

Those would be Renogy 100 Watt panels. I was just discussing these with someone else as a matter of fact. They will actually work better on MPPT than on PWM due to the unusually high (but still within range) Vmp of 18.9.

On a PWM controller one of these would produce its Imp of 5.3
On an MPPT controller one of these would produce 6.4 Amps. A 20% increase in current.
(NOTE: For comparison of performance of the two controller types for the panel under controlled conditions, not an actual measured output.)
Will they match and working properly? In case an MPPT controller used.

These other panels will not match with the others in any configuration. Two of the 18.9 Vmp in series is 37.8 Volts, far above the 31.4 Vmp of the others. In fact it is over the Voc of the others meaning there would be significant power loss as the second panel type would have its Voltage 'pulled above' its Vmp by the first ones. And the current is too different between the two to run one each in series. A bad match. The only way to use these in combination without power loss is on separate controllers.
• Solar Expert Posts: 62 ✭✭✭✭
Re: Need Help Calculating Solar Panel System
No. This is indeed the problem. Without having that 14.8 Volt Absorb the Trojans will never be fully charged and this decreases lifespan. You need to program the controller to the specs the batteries require. If this is not possible you either change the batteries or the controller.

OMG, seems like I'm going to spend much more money..

I've read lots good news from using this GC battery, I wish to use this but I see that PS 30M isn't capable to be programmed. I've wrote a letter to Morningstar to ask about this matter.

I wish to know your opinion, which is better, to stick to trojan and buy another MPPT CC or stick to my PWM and buy another battery which is not as good as this trojan?
Yes, for MPPT type controllers.

Then, how about PWM controller?
Those would be Renogy 100 Watt panels. I was just discussing these with someone else as a matter of fact. They will actually work better on MPPT than on PWM due to the unusually high (but still within range) Vmp of 18.9.

On a PWM controller one of these would produce its Imp of 5.3
On an MPPT controller one of these would produce 6.4 Amps. A 20% increase in current.
(NOTE: For comparison of performance of the two controller types for the panel under controlled conditions, not an actual measured output.)

In my country, these are locally manufactured panels which all component are imported from Japan (according to the seller). And for sure these panels are so expensive (for my wallet) compared to chinese made panel... I'm so hesitated to buy it for first since chinese made one really seems to be a good deal in price. *depressed

These other panels will not match with the others in any configuration. Two of the 18.9 Vmp in series is 37.8 Volts, far above the 31.4 Vmp of the others. In fact it is over the Voc of the others meaning there would be significant power loss as the second panel type would have its Voltage 'pulled above' its Vmp by the first ones. And the current is too different between the two to run one each in series. A bad match. The only way to use these in combination without power loss is on separate controllers.

So bad. Seems like I'll need to spend another bucks for another cc if I want to use larger wattage panel..

But, that 245W panel will works with MPPT cc right? I'm afraid to lose another money for doing more mistake.

And what do you think about this panel?
Attachment not found.

Will it match with current 100W panels? They have nearly many similarity, except for the Ipm.

Btw, if I'm to buy an MPPT CC, will MS Tristar 60 doing fine?
• Banned Posts: 17,615 ✭✭✭
Re: Need Help Calculating Solar Panel System
mulia wrote: »
OMG, seems like I'm going to spend much more money..

That is practically the RE mantra. :roll:
I've read lots good news from using this GC battery, I wish to use this but I see that PS 30M isn't capable to be programmed. I've wrote a letter to Morningstar to ask about this matter.

I wish to know your opinion, which is better, to stick to trojan and buy another MPPT CC or stick to my PWM and buy another battery which is not as good as this trojan?

Crown and East Penn/Deka/US Battery as well as other makers have similar GC2's which do not require the high Absorb Voltage that Trojan does. They are also usually cheaper but just as good quality. Availability where you are is a matter you'll have to sort out yourself.
Then, how about PWM controller?

The output current for a PWM controller is Imp of panels * number of panels in parallel.
In my country, these are locally manufactured panels which all component are imported from Japan (according to the seller). And for sure these panels are so expensive (for my wallet) compared to chinese made panel... I'm so hesitated to buy it for first since chinese made one really seems to be a good deal in price. *depressed

I feel your pain. I live in Canada and look at how cheap this stuff is in the USA ...
So bad. Seems like I'll need to spend another bucks for another cc if I want to use larger wattage panel..

But, that 245W panel will works with MPPT cc right? I'm afraid to lose another money for doing more mistake.

Yes, an MPPT controller can adjust the panels' 30 Vmp to proper Voltage for the system and turn the 'extra' Voltage into additional current. But of course they are not cheap. Nor will they adjust for panels that are incompatible with each other in the same array (a frequent mistake people make).

And what do you think about this panel?
Attachment not found.

Will it match with current 100W panels? They have nearly many similarity, except for the Ipm.

Those panels with their 18.6 Vmp will work fine in parallel with the ones at 18.9 Vmp. Hardly enough difference to bother about.
Btw, if I'm to buy an MPPT CC, will MS Tristar 60 doing fine?

I would avoid it. There's better ones out there. MidNite makes the best available at the moment, although they are more expensive than Morningstar. But MS needs a separate meter to match features so that's \$500 for the controller + \$96 for the meter and suddenly \$610 for the MidNite (which is also larger capacity) doesn't look so bad. Probably the best bargain in a 60 Amp MPPT right now is the Outback FM60 @ \$500 with built-in display. Prices and availability where you are will affect the choice of course.

Frankly Morningstar needs to get its act together and update their controllers.
• Solar Expert Posts: 62 ✭✭✭✭
Re: Need Help Calculating Solar Panel System
Crown and East Penn/Deka/US Battery as well as other makers have similar GC2's which do not require the high Absorb Voltage that Trojan does. They are also usually cheaper but just as good quality. Availability where you are is a matter you'll have to sort out yourself.

None of them available here, it seems that most of GC here used to use Trojan as their power source. How bad will this 14.4 from CC to will affect Trojan which have 14.8 absorption charge? I think I've no choice here, Trojan is the best I can found here.
I feel your pain. I live in Canada and look at how cheap this stuff is in the USA ...
Worse here. No credit tax for using renewable energy. No grid tie system can be used (can't sell that power to utility company). Power outage happen everyday ranging from 3-6 hours, already happened for 10 years. All my gears for solar panel bought overseas(inverter, CC, breaker,fuse) being heavily taxed and import duties both item price and shipping cost taxed.

I believe such things won't happen in Canada.

Yes, an MPPT controller can adjust the panels' 30 Vmp to proper Voltage for the system and turn the 'extra' Voltage into additional current. But of course they are not cheap. Nor will they adjust for panels that are incompatible with each other in the same array (a frequent mistake people make).
I came with a plan to have 2 separate system to charge a battery bank. One will be that 5 panels with PWM and the other will be a system consist of 4-6 panel of any below panels 245/260W with MPPT. They will charge the same battery bank. What do you think of it? I'm thinking of buying that new panels in few months after first system running smoothly.
Attachment not found.
Attachment not found.
I would avoid it. There's better ones out there. MidNite makes the best available at the moment, although they are more expensive than Morningstar. But MS needs a separate meter to match features so that's \$500 for the controller + \$96 for the meter and suddenly \$610 for the MidNite (which is also larger capacity) doesn't look so bad. Probably the best bargain in a 60 Amp MPPT right now is the Outback FM60 @ \$500 with built-in display. Prices and availability where you are will affect the choice of course.

Frankly Morningstar needs to get its act together and update their controllers.

Ups, thank you for pointing that out. Midnight seems to be a good deal for sure. If I were to come with decision to have 6 panels of 260W as above, which version will you suggest to acquire? I think Classic 250 will cover it, don't you? (Voc 38.10*6 =228.6V while Classic will handle 250V)
• Banned Posts: 17,615 ✭✭✭
Re: Need Help Calculating Solar Panel System
mulia wrote: »
Worse here. No credit tax for using renewable energy. No grid tie system can be used (can't sell that power to utility company). Power outage happen everyday ranging from 3-6 hours, already happened for 10 years. All my gears for solar panel bought overseas(inverter, CC, breaker,fuse) being heavily taxed and import duties both item price and shipping cost taxed.

I believe such things won't happen in Canada.

Actually they do. Which ones depend on where in Canada you are. We have GT here in British Columbia, but the utility power is so cheap the payback time is never. Tax credit? No. They even put the provincial sales tax back on all solar stuff the last time they played with taxes. We don't have much in outages here, but other parts of the country do. It's a big country; second largest in the world.
I came with a plan to have 2 separate system to charge a battery bank. One will be that 5 panels with PWM and the other will be a system consist of 4-6 panel of any below panels 245/260W with MPPT. They will charge the same battery bank. What do you think of it? I'm thinking of buying that new panels in few months after first system running smoothly.

This is actually a viable plan, even if the Absorb Voltage on one of the controllers is too low for the Trojans. The other being able to reach 14.8 will take the batteries to that point regardless; the lower set one will merely contribute current during Bulk, which is when you need it the most.

The two sets of panels you list have Vmp close enough to work together in parallel. But neither would work properly on a PWM controller.
Ups, thank you for pointing that out. Midnight seems to be a good deal for sure. If I were to come with decision to have 6 panels of 260W as above, which version will you suggest to acquire? I think Classic 250 will cover it, don't you? (Voc 38.10*6 =228.6V while Classic will handle 250V)

They don't make the 250 anymore, and you probably don't need it. You would not put all six panels in series. Not only does it put the Voc in 'danger land' it also decreases controller efficiency having the array Vmp that much higher than system Voltage.

Six 260 Watt panels is 1560 Watts, so the output would be (1560 * 0.77 / 12) 100 Amps. The Classic can not handle that much current, but will do about 96 Amps on 12 Volts. That is a lot of power - perhaps more than you need? It would be better on a 24 Volt system: same power, double the Voltage, half the current.
• Solar Expert Posts: 62 ✭✭✭✭
Re: Need Help Calculating Solar Panel System
Actually they do. Which ones depend on where in Canada you are. We have GT here in British Columbia, but the utility power is so cheap the payback time is never. Tax credit? No. They even put the provincial sales tax back on all solar stuff the last time they played with taxes. We don't have much in outages here, but other parts of the country do. It's a big country; second largest in the world.
Urgh.. at least it's safe, peaceful and beautiful country with lots of nice community.

They don't make the 250 anymore, and you probably don't need it. You would not put all six panels in series. Not only does it put the Voc in 'danger land' it also decreases controller efficiency having the array Vmp that much higher than system Voltage.

Six 260 Watt panels is 1560 Watts, so the output would be (1560 * 0.77 / 12) 100 Amps. The Classic can not handle that much current, but will do about 96 Amps on 12 Volts. That is a lot of power - perhaps more than you need? It would be better on a 24 Volt system: same power, double the Voltage, half the current.

So if I decided to acquire 6 of that panel, what configuration do you suggest me to build? in case of 12V and 24V battery bank system.

And regarding the CC, is Classic 150 enough for these config?

But that also means that I'll need to use a 24V inverter, since I can't take 12V to power my Suresine from 24V battery bank without making the battery bank system uneven.
• Banned Posts: 17,615 ✭✭✭
Re: Need Help Calculating Solar Panel System
mulia wrote: »
Urgh.. at least it's safe, peaceful and beautiful country with lots of nice community.

Relatively safe outside the major cities anyway.
So if I decided to acquire 6 of that panel, what configuration do you suggest me to build? in case of 12V and 24V battery bank system.

And regarding the CC, is Classic 150 enough for these config?

But that also means that I'll need to use a 24V inverter, since I can't take 12V to power my Suresine from 24V battery bank without making the battery bank system uneven.

Yes, the 12 Volt limitation of the existing inverter is an issue.

But those panels will work with a 12 Volt system through the Classic. At 30 Vmp the most efficient configuration is all in parallel. That means there is a need for combiner box & breakers/fuses for every panel.

Do you really need six 260 Watt panels? I can't remember what battery bank size we worked out. Think it was 450 Amp hours @ 12 Volts to provide up to 2400 Watt hours? Based on Trojan T105's which is what you ca get.

That would require 45 Amps of peak current which only needs about 700 Watts of PV. If you used four 240 Watt panels you'd get 61 Amps @ 12 Volts and 'max out' an FM60. Cheaper, meets the power needs by far (13% peak charge rate) and you could wire the array as two parallel strings of two in series (slightly less efficient due to the 60-ish Vmp but saves combiner box and fuses/breakers on array).
• Solar Expert Posts: 62 ✭✭✭✭
Re: Need Help Calculating Solar Panel System
Yes, the 12 Volt limitation of the existing inverter is an issue.

But those panels will work with a 12 Volt system through the Classic. At 30 Vmp the most efficient configuration is all in parallel. That means there is a need for combiner box & breakers/fuses for every panel.

Do you really need six 260 Watt panels? I can't remember what battery bank size we worked out. Think it was 450 Amp hours @ 12 Volts to provide up to 2400 Watt hours? Based on Trojan T105's which is what you ca get.

That would require 45 Amps of peak current which only needs about 700 Watts of PV. If you used four 240 Watt panels you'd get 61 Amps @ 12 Volts and 'max out' an FM60. Cheaper, meets the power needs by far (13% peak charge rate) and you could wire the array as two parallel strings of two in series (slightly less efficient due to the 60-ish Vmp but saves combiner box and fuses/breakers on array).

4x 245 with 2 parallel of 2 in series?

Did you mean like this?

Attachment not found.

So, Vmp = 62,88V and Imp= 15,68A?

Okay, will be acquiring a Classic 150 soon..

I don't understand, why the parallel give the most efficient rather than two parallel of two series while MPPT can accept any voltage and current (within its limit) and convert them to proper charging current and voltage?

For the start, I'll learn to build the system to provide 2400WH for lighting system of my house. After the system running smoothly, I'll buy another panel, 245/260 (the bigger wattage, the cheaper price/watt here) because I have a 'dream' to have my whole house off-grid to power small fridge, seldom-use water pump and rice cooker, so I won't have any worry about blackout anymore. At that time, I'll for sure, need a 24V system, smaller mm cable (much cheaper) and much stable system.

I've contacted a seller, the Trojans are available on tuesday, and it will take about 2 weeks to deliver from seller to my house through land. Can't wait to use solar power for the first time after long waiting.

As for now, system will be built is going to be like this

Attachment not found.

The panel is 100W panel, Vmp=18.90V, Imp=5.33A, Voc=22.54V, Isc=5.79A.

The breaker is Midnite Solar MNEPV 150VDC, 5pcs of 12A and 1 pc of 30A.

CC is Morningstar PS-30M PWM

Can you give opinion regarding the current design please?

Is there any mistake in the wiring?

Regarding inverter wiring, I'll follow manufacture wiring and fusing size.
• Solar Expert Posts: 203 ✭✭✭✭✭
Re: Need Help Calculating Solar Panel System

You don't need a breaker between the combiner box and charge controller, the individual panel breakers are sufficient.
• Solar Expert Posts: 62 ✭✭✭✭
Re: Need Help Calculating Solar Panel System
Plowman wrote: »
You don't need a breaker between the combiner box and charge controller, the individual panel breakers are sufficient.

Thank you for taking a look.

How about the entire diagram? Is that anything wrong?

I think Cariboocoot is a bit busy at the moment. (S)He helps a lots.
• Super Moderators, Administrators Posts: 33,548 admin
Re: Need Help Calculating Solar Panel System

How long is the distance between array and the charge controller--And what AWG wire are you planning one.

Also, the same question between charge controller and battery bank wiring.

And you have a choice... 2 panels in series and a 2/4/6 panel array. Higher voltage array, smaller AWG wire needed from array to controller, and fewer circuit breakers in the combiner box.

If you are commited to 5 panels, then your wiring is the only choice.

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Solar Expert Posts: 62 ✭✭✭✭
Re: Need Help Calculating Solar Panel System
BB. wrote: »
How long is the distance between array and the charge controller--And what AWG wire are you planning one.

Also, the same question between charge controller and battery bank wiring.

And you have a choice... 2 panels in series and a 2/4/6 panel array. Higher voltage array, smaller AWG wire needed from array to controller, and fewer circuit breakers in the combiner box.

If you are commited to 5 panels, then your wiring is the only choice.

-Bill

Distance between array and charge controller will about 30cm (er... about 12 in inch) and I'm planning to use 35mm or 50mm ( about 2AWG or 1/0AWG) welding cable from combined array to CC.

The same wire will also be used between CC and battery bank.

But... I think there's not much choice when using a PWM CC, since higher Voltage will get less efficient, isn't it?

Yes, for temporary I'll be utilizing this 5 panels, after it's running, I'll get another panel, and for sure, making it in even number..
• Banned Posts: 17,615 ✭✭✭
Re: Need Help Calculating Solar Panel System
mulia wrote: »
I don't understand, why the parallel give the most efficient rather than two parallel of two series while MPPT can accept any voltage and current (within its limit) and convert them to proper charging current and voltage?

The efficiency of an MPPT controller goes down as the array Voltage moves higher in relation to the system Voltage. It may take 150 Volts in, but if it has to convert that to 15 Volts charging then a lot of work has to be done to make the conversion. In that work power is lost to heat in the controller. We're not talking massive amounts, but sometimes enough to make a difference. In general you try to balance this with overcoming resistance loss in the wiring between array and controller.

Your diagram for the MPPT array is correct: two parallel strings of two in series. Array will produce 2X the Vmp and 2X the Imp of one panel.

Your diagram for the PWM controller is also correct, except that there should be fuses or breakers on each panel rated for their "maximum series fuse" current or if not listed 1.56 * Isc rounded up. Probably 15 Amps. This is to prevent problems should one panel short and receive the full current of the remaining panels.

You are correct that the PWM controller can not utilize panels in series without significant power loss. With the "12 Volt" panels on a 12 Volt system half the panels would be doing nothing for you.

30 cm from array to controller is unrealistically short. That would put the controller outside in the weather. With an output of <27 Amps @ 12 Volts 10 AWG (2.5 mm diameter) would allow a distance up to 2 metres. You will find 2 AWG or 1/0 impossible to fit in the connectors.
• Solar Expert Posts: 62 ✭✭✭✭
Re: Need Help Calculating Solar Panel System
The efficiency of an MPPT controller goes down as the array Voltage moves higher in relation to the system Voltage. It may take 150 Volts in, but if it has to convert that to 15 Volts charging then a lot of work has to be done to make the conversion. In that work power is lost to heat in the controller. We're not talking massive amounts, but sometimes enough to make a difference. In general you try to balance this with overcoming resistance loss in the wiring between array and controller.

Your diagram for the MPPT array is correct: two parallel strings of two in series. Array will produce 2X the Vmp and 2X the Imp of one panel.

Your diagram for the PWM controller is also correct, except that there should be fuses or breakers on each panel rated for their "maximum series fuse" current or if not listed 1.56 * Isc rounded up. Probably 15 Amps. This is to prevent problems should one panel short and receive the full current of the remaining panels.

You are correct that the PWM controller can not utilize panels in series without significant power loss. With the "12 Volt" panels on a 12 Volt system half the panels would be doing nothing for you.

30 cm from array to controller is unrealistically short. That would put the controller outside in the weather. With an output of <27 Amps @ 12 Volts 10 AWG (2.5 mm diameter) would allow a distance up to 2 metres. You will find 2 AWG or 1/0 impossible to fit in the connectors.

I got it. Thank you for explaining it, So people will need to choose, to sacrifice efficiency by joining many panels in series and save combiner, fuse and wire or joining them in parallel with lot of fuses and heavy expensive wire.

I did put breaker on PWM diagram, a breaker on each panel, it's a 100 panel with Isc of 5.33A. 1.56*5.33 = 8.3A. Well, I put in a 12A, it's a bit higher A, should have a 10A rather than 12A.

Yes, I planned to put it outside nearest as possible from array to prevent loss voltage due to distance if I put it indoor, but on second though, I'll just put it inside . *sigh* Just read the manual, the max cable is #6 AWG. Glad to be warned first, I'll need to find another cable.