series vs Parallel

no-carrier

I have a 24v array, can I use a 12v mppt cc?...Is so, what would be the advantage of going with a 24v cc?...520 array, 22vdc and 2 6v 225ah batts..12v...Thanks
Dennis

mike95490

Re: series vs Parallel

check the label on the back of the panel, is the 24V open circuit, or Max Pover ?

BB.

Re: series vs Parallel

MPPT and PWM controllers can use the same solar array (basically Vmp~17.5 volts for a 12 volt battery bank).

And, MPPT controllers can use higher voltage solar panels and arrays (some controllers upwards of Vmp~100 VDC nominal).

The major advantage with MPPT type charge controllers is that they can down convert high voltage / low current from the solar array into low voltage / high current to charge the battery bank (at ~95% efficiency).

This allows you to place your solar array 10's-100's of feet away from the charge controller/battery box and use reasonable size wire (save a whole bunch of money on copper cables between solar array and charge controller).

The main drawback with MPPT controllers is they are much more expensive.

Typically, below 200 watts, a PWM controller will usually be just fine.

For arrays over 400 watts, many times a MPPT controller will be a better solution. A couple of Charge Controller FAQs:

All About Charge Controllers
Read this page about power tracking controllers

-Bill

no-carrier

Re: series vs Parallel

Sorry I didnt make myself clear...My array is 520 watts 12v, wired to 24v...Can I use a 12v
mppt as my cc?...Or does it have to be a 24v charge controller?...
Dennis

BB.

Re: series vs Parallel

All charge controllers have an input and an output rating.

MTTP input ratings are typically anywhere from 35-75-150 VDC maximum input voltage.

Their output voltage rating may be a single voltage like 12 volt battery bank. Or several like 12/24 volt capable. Or anything from 12 volts to 72 volt battery banks.

So, you need a ~35 VDC input capable / 12 volt output MPPT charge controller.

As a start you can look at these couple (low cost vs high cost):

Rogue 30amp 12/24 output MPPT controller
Morningstar TriStar 45 amp MPPT 12/24/48 volt solar charge controller

Both of the above are fine charge controllers and represent the capabilities of MPPT type charge controllers.

-Bill

no-carrier

Re: series vs Parallel

Bill...Thanks for your time...So If I had a 24v array coming in, could I use an mppt that
was like this?http://forsale.stlawson.com/index.php?item=charge_controller
Or would I need a cc that was a 12/24...With my setup, how many amps will I have coming in to the cc? Thanks
Dennis

BB.

Re: series vs Parallel

From your link:

• Output current rating.................... 25A
• System voltage .......................... 12V nominal
• Max. PV Open circuit voltage ............ 30V
• Max. battery voltage..................... 30V

This is a "12 volt only" output charge controller. That is correct.

If you have "12 volt panels" wired two up in series--what you really have is:

• 2x 17.5 Vmp = 35 volt Vmp panels
• 2x 22 Voc = 44 volt Voc (open circuit) panels

These panels will see > 44 volts in cold weather (open circuit voltage).

So, this controller will not work for your setup.

From the Rogue 30 amp MPPT controller (PDF Manual) on Page 43, you will see that its rated Voc is 60 VDC...

So, if your panels are Vmp=17.5 volts wired 2x up in series--then the Rogue (and other higher voltage) controllers will work for you.

My guess is that any controller you need for your current setup will need to be a 12/24 volt capable controller (to manage the >44 volts from your solar array).

You are not doing anything wrong (and actually are doing a good thing--higher Varray to reduce array current and voltage drop)--but you have to get a controller that will support your design.

Regarding what you would typically get from a 520 watt array.. Assuming a 12 volt battery bank charging at 14.5 volts and a 0.77 overall derating factor (solar panels and charge controller losses):

• 520 watts * 1/14.5 volt charging * 0.77 derating = 27.6 amps typical maximum

Note that MPPT charge controllers self limit on current output--so even though in very cold weather with proper conditions, your system should be capable of 35+ amps--That will not happen very often, and in any case, this charge controller will limit its output current to 30 amps (safely).

If you live in very cold climates with snow on the ground (sun reflection into array)--you may want to look at a 45 amp controller--But the extra power collected will not be that much (systems do not exceed the 0.77 conversion factor very often).

-Bill

no-carrier

Re: series vs Parallel

Bill..Would I have to go to a 24v battery pack?....And I am trying to economize as much as possible, If you could look at this cc and give your opinion, I sure would appreciate it..http://cgi.ebay.com/Solar-Charge-Controller-40A-Wellsee-WS-MPPT60-12V-24V-/140487808723?pt=LH_DefaultDomain_0&hash=item20b5b9d6d3
Again, thanks for your time....)
Dennis....ps I live in So.Cal

Cariboocoot

Re: series vs Parallel

Please read this thread before you buy one of those Wellsee units:
http://forum.solar-electric.com/showthread.php?t=9482&highlight=wellsee

Skimping on a charge controller is very often a false economy. Look into the Rogue as Bill suggests.

no-carrier

Re: series vs Parallel

False economy?.....Indeed, you guys are just confusing me with what makes sense....
Thats why I enjoy these forums..Its soooo easy to make a mistake..Looks like I will be
going with a decent cc...Thanks again for all your input guys...)
Dennis

BB.

Re: series vs Parallel

Dennis,

You do have other choices--If these are Vmp=17.5 volt solar panels and you can rewire them to "12 volts" (all in parallel at 17.5 volts)--And the wiring run from the array to the charge controller is not too large, you can look at PWM controllers which are much cheaper and work almost as well for small systems:

• 520 watts of panels / 17.5 volts = 29.7 amps

So, you could look for a 35-40+ amp PWM controller like one of these:

TriStar TS-45 12/24/48 volt PWM solar charge controller Price: $157.08
Xantrex C40 40 Amp Solar Charge Controller Price: $151.05

Some of these less expensive controllers sell their display as an option...

Instead of the optional display--Something that does not cost that much more would be a Trimetric or equivalent Battery Monitor.

A battery monitor logs the current going into and out of the battery bank--Actually a much more important figure for making sure you don't kill your battery bank then the charging current from the Charge Controller display.

For the wiring size from the array to the charge controller, we can start with 3% maximum voltage drop at 17.5 volts (at 30 amps) and use a generic voltage drop controller (trial and error) to calculate the wire gauge needed to support a PWM controller:

• 17.5 * 3% max voltage drop = 0.525 volt max recommended
• 17.5 * 1% max voltage drop = 0.175 volt minimum cost effective
• Calculator=> 15 feet one way run @ 30 amps and 6 awg wire = 0.43 volt drop

Compare that to the MorningStar 45 amp MPPT charge controller with Vmp-max~100 VDC.

You can place ~5x 17.5Vmp panels in series (Vmp-array=87.5 volts, 104 watts per panel).

If this was your 520 watts of panels:

• Imp=520 watts / 87.5volts Vmp = 5.94 amps
• 3% * 87.5 volts = 2.625 volt drop
• Calculator=> 25 feet one way run @ 5.94 amps and 18 awg wire = 2.3 volt drop

So, with PWM and 520 watt array you can make 15 feet on 6 awg wire.

With a MPPT on a 520 array (and an optimum guess of 5 panels in series) you can use an 18 awg wire on a 25 foot (one way) wire run between the array and the solar panels.

No right or wrong answer--but it does show when spending the extra money on a high voltage MPPT type charge controller may be a better solution--in some cases.

-Bill

no-carrier

Re: series vs Parallel

Bill...makes sense......Does living in So Cal. make a difference with the mppt?
Mornings are not cool and the late day is not cool..And I try not to discharge
more than 60%..If this were your system, would you go mppt?...For $150 more,
it wont bother me...Btw my wire run from array to cc is about 30 feet...Thanks
Dennis

BB.

Re: series vs Parallel

To know for sure, we need to know more about your solar panels... How Many Brand/model/wattage/Vmp/Imp/Isc (at least Vmp/Imp and how many panels) and if you can wire these up to "12 volt" parallel configuration.

You can see the drawback for 30 foot one-way run with PWM--You are looking at ~3 or 2 AWG cabling... A real expensive run.

For MPPT, 14-18 awg cable will work fine (although, it really depends on the exact panels and how we can configure them series/parallel for you setup).

You are not in cold weather--so the MPPT for a 17.5 volt array is not going to gain you very much energy over a PWM controller.

For hot weather, solar panel output voltage falls (Vmp decreases as the panels get hot in the sunlight). If you have 100F+ degree days, Vmp can actually fall enough that you may not be able to equalize your battery bank in the middle of a hot summer afternoon--But, that is probably not going to be a big issue.

So--for that distance, I would choose MPPT. The difference between the Rogue (60 vdc max) and the MS Tristar 45 amp MPPT (150 VDC) is worth ~4 gauges smaller wire (depending on how the panels are wired exactly).

For the Rogue--you might need 60' of 10-12 gauge, and for the MorningStar MPPT you might need 60' of 14-16 awg wiring. Not a huge deal--but something to be aware of.

Regarding your battery bank, the recommended size of the array would be around 5% to 13% of the battery rated capacity:

• 12 volts * 225 AH * 1/0.77 derating * 0.13 charge rate = 911 watts
• 12 volts * 225 AH * 1/0.77 derating * 0.05 charge rate =351 watts

So, for that size of battery bank, your 520 watts is somewhere in the middle... Are you planning on adding more solar panels anytime in the near future--or will this be enough for now?

Of course we have not discussed your actual loads--but if you guess 4+ hours of sun with a 0.52% solar panel to AC inverter output efficiency (yes, 1/2 of the energy is "lost" in an off-grid system), your typical usable power per day (9+ months of the year) would be:

• 520 watts * 4 hours of sun * 0.52 eff - 1,082 WH per day (more in summer, less in winter).

That is enough to run a 50 Watt laptop computer + 13 Watt CFL:

• 1,082 WH per day / (50+13)watts = 17 hours per day

-Bill

no-carrier

Re: series vs Parallel

Bill....4 130watt Kyocera 12v 22vdc, the other specs you need I cant find on the back of the panel...2 6v trojans 225ah..And more like 20-25 foot run...Thanks
Dennis

BB.

Re: series vs Parallel

Basically, redoing the previous post with the Kyocera 130 watt panels--Probably these:

Kyocera KC 130TM
Pmax 130 watts
Vmp 17.6 volts
Imp 7.39 amps
Voc 21.9 volts
Isc 8.02 amps
Max system votlage 600 volts

You have two reasonable choices... 0) 4 panels in parallel (any "12 volt" mppt or pwm controller. 1) mount two in series then parallel (for Rogue 30 amp or MS 45 amp MPPT; and 2) 4 in series (for MS 45 amp MPPT)

0) Won't bother with--that was the first system with all 520 watts with 4x panels in parallel: For the wiring size from the array to the charge controller, we can start with 3% maximum voltage drop at 17.5 volts (at 30 amps) and use a generic voltage drop controller (trial and error) to calculate the wire gauge needed to support a PWM controller:

• 17.5 * 3% max voltage drop = 0.525 volt max recommended
• 17.5 * 1% max voltage drop = 0.175 volt minimum cost effective
• 21.9 volts Voc (STC).
• Calculator=> 25 feet one way run @ 30 amps and 4 awg wire = 0.45 volt drop

The Rogue and the Morning Star we can do series parallel (2xVmp and 2xImp):

• 2x17.6 * 3% max voltage drop = 1.056 volt max recommended
• 2x21.9 volts = 43.8 Voc (STC).
• Calculator=> 25 feet one way run @ 2x7.39a= 14.78 amps and 10 awg wire = 0.89 volt drop

And with the MorningStar, we can do 4 panels in series:

• 4x17.6 * 3% max voltage drop = 2.112 volt max recommended
• 4x21.9 volts = 87.6 Voc (STC).
• Calculator=> 25 feet one way run @ 1x7.39a= 7.39 amps and 16 awg wire = 1.8 volt drop

So, the PWM / 4 panels in parallel would not make much sense with 4 awg cable.

The second with 2 panels in series / 2 in parallel, with either Rogue or MS controllers can use 10 awg cable.

The third with MS controller (and other 150 Voc rated controllers) would need 16 awg cable--but you could go to 14 or 12 awg cable pretty cost effectively (and reduce losses below 3%).

As always, double check my numbers (I ain't perfect and I do not do this for a living) and read through the manuals for the controller to understand the configuration that you propose to use. Solar panel's voltages fall with heat and rise with cold... So, a hot panel needs Vmp>Vbatt-charging+Vdrop -- and cold panels need Voc-cold < Vmax-input for the controllers.

Rough out your design, double check the costs and calculations, choose one design, and go through the detail design (min/max voltages, fuse/breakers/wiring, switches, inverters, etc.).

To predict the output power... Using PV Watts, Los Angeles, 0.52 system derating (solar panel to AC inverter output), 1 kW of fixed solar panels (smallest value program accepts):

"Station Identification"
"City:","Los_Angeles"
"State:","California"
"Lat (deg N):", 33.93
"Long (deg W):", 118.40
"Elev (m): ", 32
"PV System Specifications"
"DC Rating:"," 1.0 kW"
"DC to AC Derate Factor:"," 0.520"
"AC Rating:"," 0.5 kW"
"Array Type: Fixed Tilt"
"Array Tilt:"," 33.9"
"Array Azimuth:","180.0"

"Energy Specifications"
"Cost of Electricity:","12.5 cents/kWh"

"Results"
"Month", "Solar Radiation (kWh/m^2/day)", "AC Energy (kWh)", "Energy Value ($)"
1, 4.44, 66, 8.25
2, 5.35, 73, 9.12
3, 5.62, 84, 10.50
4, 6.06, 87, 10.88
5, 6.19, 91, 11.38
6, 6.17, 87, 10.88
7, 6.48, 94, 11.75
8, 6.68, 97, 12.12
9, 5.78, 81, 10.12
10, 5.43, 80, 10.00
11, 4.84, 69, 8.62
12, 4.46, 66, 8.25
"Year", 5.63, 975, 121.88

I like to size a system based the best 9 months of the year (assume the other three months use a back up genset)... That give us February at 73 kWH per month per 1kW of solar panels. For 0.52 kW of panels:

• 73 kWH per month per 1kW panels * 0.52 kW panels * 1/30 days per month = 1.265 kWH per day = 1,265 Watts*Hours per day (average for 520 watts of panels in February)

-Bill

Knd870

Re: series vs Parallel

BB. wrote: »

Basically, redoing the previous post with the Kyocera 130 watt panels--Probably these:



You have two reasonable choices... 0) 4 panels in parallel (any "12 volt" mppt or pwm controller. 1) mount two in series then parallel (for Rogue 30 amp or MS 45 amp MPPT; and 2) 4 in series (for MS 45 amp MPPT)

0) Won't bother with--that was the first system with all 520 watts with 4x panels in parallel: For the wiring size from the array to the charge controller, we can start with 3% maximum voltage drop at 17.5 volts (at 30 amps) and use a generic voltage drop controller (trial and error) to calculate the wire gauge needed to support a PWM controller:

• 17.5 * 3% max voltage drop = 0.525 volt max recommended
• 17.5 * 1% max voltage drop = 0.175 volt minimum cost effective
• 21.9 volts Voc (STC).
• Calculator=> 25 feet one way run @ 30 amps and 4 awg wire = 0.45 volt drop

The Rogue and the Morning Star we can do series parallel (2xVmp and 2xImp):

• 2x17.6 * 3% max voltage drop = 1.056 volt max recommended
• 2x21.9 volts = 43.8 Voc (STC).
• Calculator=> 25 feet one way run @ 2x7.39a= 14.78 amps and 10 awg wire = 0.89 volt drop

And with the MorningStar, we can do 4 panels in series:

• 4x17.6 * 3% max voltage drop = 2.112 volt max recommended
• 4x21.9 volts = 87.6 Voc (STC).
• Calculator=> 25 feet one way run @ 1x7.39a= 7.39 amps and 16 awg wire = 1.8 volt drop

So, the PWM / 4 panels in parallel would not make much sense with 4 awg cable.

The second with 2 panels in series / 2 in parallel, with either Rogue or MS controllers can use 10 awg cable.

The third with MS controller (and other 150 Voc rated controllers) would need 16 awg cable--but you could go to 14 or 12 awg cable pretty cost effectively (and reduce losses below 3%).

As always, double check my numbers (I ain't perfect and I do not do this for a living) and read through the manuals for the controller to understand the configuration that you propose to use. Solar panel's voltages fall with heat and rise with cold... So, a hot panel needs Vmp>Vbatt-charging+Vdrop -- and cold panels need Voc-cold < Vmax-input for the controllers.

Rough out your design, double check the costs and calculations, choose one design, and go through the detail design (min/max voltages, fuse/breakers/wiring, switches, inverters, etc.).

To predict the output power... Using PV Watts, Los Angeles, 0.52 system derating (solar panel to AC inverter output), 1 kW of fixed solar panels (smallest value program accepts):


I like to size a system based the best 9 months of the year (assume the other three months use a back up genset)... That give us February at 73 kWH per month per 1kW of solar panels. For 0.52 kW of panels:

• 73 kWH per month per 1kW panels * 0.52 kW panels * 1/30 days per month = 1.265 kWH per day = 1,265 Watts*Hours per day (average for 520 watts of panels in February)

-Bill

Bill,
I'm still learning this stuff, so I could be wrong (and probably am), but didn't you already take into account the .52 DC to AC conversion with PV watts, so you don't need to multiply it again? In other words wouldn't his production be 2,430 watts instead of the 1,265?

BB.

Re: series vs Parallel

Knd,

There are two different 0.52 numbers here... Just random chance that the system derating for an off grid system efficiency and the original poster's array is the same number (in kWatts).

There is the 0.52 derating for end to end system efficiency--which I plugged into PV Watts.

And there is 0.52 kWatts or 520 watts of solar panels. Because PV Watts has a minimum amount of solar panels of 1 kWatts that it supports--I have to do the calculations using 1,000 watts of solar panels (1kW), then I multiply by the size of solar array that the original poster really has.

If the poster had 600 watts of solar panels, I would have multiplied the PV Watts output by 0.6 kW of panels... If there were 1,200 watts of panels, I would have multiplied February's output by 1.2 kW... And so on.

"DC to AC Derate Factor:"," 0.520"

• 73 kWH per month per 1kW panels * 0.52 kW panels * 1/30 days per month = 1.265 kWH per day = 1,265 Watts*Hours per day (average for 520 watts of panels in February)

Does that make sense?

-Bill

Knd870

Re: series vs Parallel

BB. wrote: »

Knd,

There are two different 0.52 numbers here... Just random chance that the system derating for an off grid system efficiency and the original poster's array is the same number (in kWatts).

There is the 0.52 derating for end to end system efficiency--which I plugged into PV Watts.

And there is 0.52 kWatts or 520 watts of solar panels. Because PV Watts has a minimum amount of solar panels of 1 kWatts that it supports--I have to do the calculations using 1,000 watts of solar panels (1kW), then I multiply by the size of solar array that the original poster really has.

If the poster had 600 watts of solar panels, I would have multiplied the PV Watts output by 0.6 kW of panels... If there were 1,200 watts of panels, I would have multiplied February's output by 1.2 kW... And so on.

• 73 kWH per month per 1kW panels * 0.52 kW panels * 1/30 days per month = 1.265 kWH per day = 1,265 Watts*Hours per day (average for 520 watts of panels in February)

Does that make sense?

-Bill

Thanks Bill, I've got it.

no-carrier

Re: series vs Parallel

Bill...You have gone to alot for work and research to help me, I cant thank you enough...
without folks like you, giving there time freely, there would be alot of uneducated people out there...Thanks again....)
Dennis