Newbie question regarding solar system

martinruss7

Any help would be greatly appreciated! I want to add additional panels to an existing solar system. My question is what panels are compatible? This system is composed of four 72 cell 24v SOLARWORLD 320 watt panels. Connected as pairs in series for 48 volts. Each pair utilizes a 30amp breaker in a midnite combiner box. It also has a pwm diversion controller it's the C440-hva from Missouri wind and solar. Also has a 16 battery golf cart bank@48v with 416ah capacity, with a 6000 watt 48v aims inverter charger with transfer switch to pull line from grid to charge batteries when there is days with minimal sun. Systems is running great but would like to upgrade. ANY SUGGESTIONS?
Panel info is as follows
Vmpp - 36.7
Impp- 8.78
Voc- 45.9
Isc- 9.41
Pmpp- 320 watts

BB.

Assuming your Charge controller is large enough to add more panels and you are adding panels to the existing charge controller...

You need to add 2x72 (144) "cells" worth of panels... That can be 4x 36 cell panels (typically "12 volt" <150 Watt panels--Vmp~18 volts), or 2x 72 cell panels (Vmp~36 volts per panel for 72 volt Vmp).

Or--If you got 30 cell panels (common "GT" panels >200 Watts @ Vmp~30 volts). You cannot put these in series and get Vmp-array~72 volts (STC standard test conditions). If you wanted to use these panels, you would need to buy another MPPT charge controller and parallel that to your battery bus (will work fine with properly programmed multiple charge controllers charging the same battery bank).

Regarding your battery bank--48 volts @ 416 AH--In general, the maximum solar array wattage and AC inverter would be around ~4,160 Watts "cost effective maximum".

For the solar array, if you have very high charging current, you need to watch the battery temperature--High charging current can overheat the batteries and cause thermal run-away (not a common problem, but one we like to be careful of).

And for flooded cell lead acid batteries, they really cannot manage much more than ~4,160 Watts of continuous AC output. The 6 kWatt inverter is a bit on the large size--But if you are happy with how everything is running, there is no reason to change (and if you run heavy loads when the sun is up--The solar panels definitely help reduce battery bank loading (and will nicely support the larger AC inverter).

-Bill

martinruss7

Did not expect such a prompt response, thank you. Anyways My charge controller allows for no more than 125 amps of solar. I would like to change my pwm controller to a midnite classic. With that said which one should I go with, and with that controller would your technical advise be the same. So as far as getting additional solar panels if I go with the 12v panels this won't create any issues as far a mixing panels. Also with a midnite classic how many panels max can I have on one controller .

vtmaps

If you upgrade to a Midnite Classic you should reconfigure your panels to a higher string voltage.  Most controllers require some headroom, in other words the string voltage needs to be higher than the battery voltage.  An MPPT controller needs a few more volts headroom than a PWM controller. 

Since your four panels are true 24 volt panels (configured two to a string for 48 volt nominal), they have just enough headroom for a PWM controller.  That's a good match because a PWM controller can't utilize higher voltages.

Several folks have been disappointed when they switch from PWM to MPPT because of the headroom issue.  You might be better off configuring the panels with a string length of three (that means adding two new panels).

The other option is to leave your present system alone and just add new panels and a controller for them.  Two controllers, each with its own array, is a reasonable design and offers some advantages (like redundancy).

--vtMaps

martinruss7

So if I upgraded and added these extra two panels in 3 panel strings would the classic go into hypervoc to soon

vtmaps

martinruss7 said:

So if I upgraded and added these extra two panels in 3 panel strings would the classic go into hypervoc to soon

Yes.  You would need a Classic 200.   I should have mentioned that.   If you can find a couple of 12 volt panels with an Imp very close to 8.78, you could put one of them in each of your strings and use a classic 150. 

72 cell panels are becoming more popular and in a 48 volt system they are not the best match for a classic 150 (except, perhaps, in the tropics where Voc will stay low). 

In a 48 volt system, three 60 cell panels in series is perfect for a classic 150.

--vtMaps

martinruss7

As close to8.78 imp as possible? Please explain

BB.

If your present panels have Imp~8.78 amps, then "matching" series panels with your existing panels that have Imp+/-10% is "close enough" (some here like +/- 5% better--your choice as to "how close"):

• 8.78a * 1.10 = 9.66 Amps maximum Vmp for series connection
  
• 8.78a * 0.90 = 7.9 Amps minimum Vmp for series connection

Panels used to be rated +/- 5% or sometimes wider tolerance ranges so a 10% mismatch was very possible with off the shelf "identical" panels.

-Bill

martinruss7

Ok so say I add one more 24v panel @ or around same specs to make the 3 panel strings. Does this change the breaker size? I'm currently using a 30 amp

BB.

Adding a panel(s) in series only changes the operating voltage--The current flow remains about the same. No change needed for breaker (if correct breaker and I understand your question correctly).

-Bill

PS: I should add--This is true on the Solar Array side...

You are adding more Watts to the array, so the output current of the solar charge controller will go up--You need heavy enough cable and large enough breaker for the Controller to Battery Bus connection.

martinruss7

So I think I have the wrong breaker size for the two panels I have in series right?!

BB.

I am not sure--I did not find the "series fuse rating" in the data sheet... I would expect around 15 amps (or possibly 20 amps).

You only need series fusing/breakers if you have (typically) 3 or more parallel strings.

-Bill

martinruss7

Ok. So the plan is to purchase two more 24 volt 72 cell panels and add one to each string. This will give me two string of 3 with a 6 panel array. Add it to classic 200 charge controller. I am using 1/0 cable from controller to batteries with a 125 amp dc breaker and also 1/0 from battery to inverter with a 250 anl fuse. Any objections before I spend the hard earned money? And again thank yous very much for all your expertise.

martinruss7

Oh I almost forgot to ask about angle of panel in winter for my area(81003)

Raj174

I believe the largest cable that the Classic 200 will accept is a 4 AWG and shouldn't need any larger than an 80 amp breaker for it.

BB.

The Midnite 200 is rated for 79 amps maximum (from the main page spec)... If using standard US/NEC rated breakers and wiring, it is a good idea to mulitple by 1.25 (NEC derating) forwiring/breakers (79a*1.25=98.75a~100a).

As always, read the details--Ratings are sometimes voltage/temperature specific:

http://www.solar-electric.com/inverters-controllers-accessories/chco/misoclchco/misocl/misocl200mpc.html

200

200VDC

12-93 Volts

74A @ 12V

70A @ 24V

65A @ 48V

66 Amps De-rated Current at 40°C (104°F)

The short answer--Many times, there are no short answers.

-Bill "long answer" B.

vtmaps

martinruss7 said:

r and also 1/0 from battery to inverter with a 250 anl fuse. Any objections before I spend the hard earned money?

From battery to inverter you want a circuit breaker, not a fuse (because the breaker is also a switch).  Also, 250 amps is a bit high for 1/0 cable. 

What inverter do you have?  Most inverters come with instructions for cable and circuit breaker size. 

--vtMaps

martinruss7

I have the aims 48v 6000 watt to 120 single leg low frequency

vtmaps

martinruss7 said:

I have the aims 48v 6000 watt to 120 single leg low frequency

What do they recommend for cable and circuit breaker size?  I will admit to being surprised if they recommend 1/0 cable and a 250 amp fuse.

--vtMaps

martinruss7

No the manual actually says 1/0 and I can't find in the book where it talks about fuse size. Now this inverter does have two built in breakers for the charger input and AC output.

vtmaps

I just looked at the specs on that inverter... OMG!  it draws 200 watts on idle!  The highest you can set the low battery cut off is 42 volts... this thing sounds like a battery killer.   And it can surge to 18,000 watts for 20 seconds... that's over 428 amps when it shuts off at 42 volts. 

Maybe that's why they recommend 1/0 cable... the cable resistance will keep the inverter from ever putting out that type of power.

--vtMaps

martinruss7

My manual says 87 watts at idle and i can set it as high as 46v for low battery shutdown. But I never let my batteries drop below 48.8 v.

vtmaps

martinruss7 said:

My manual says 87 watts at idle and i can set it as high as 46v for low battery shutdown. But I never let my batteries drop below 48.8 v.

That's better, but it's still 2 kwh per day idle consumption.    Maybe I was looking at the wrong Aims inverter...  This is what I see on the Aims website:

Input Specifications

• Nominal Input Voltage: 48.0Vdc
• Low Battery Alarm: 42.0Vdc-44.0Vdc
• Low battery Trip: 40.0Vdc-42.0Vdc
• High Voltage Alarm: 64.0Vdc
• Low battery Voltage Restart: 62.0Vdc
• Idle Consumption: 4.16 amps DC
• Power Saver Mode Idle Consumption: <0.83 amps DC

4.16 amps X 48 volts = 200 watts.

--vtMaps

martinruss7

What is the experts opinion on the cenergy frameless 320 watt 24v solar panels? Has anyone had any experience with them. Or the hightec solar panels.

BB.

Check the Vmp rating of the panel... "24 volt" panel may be Vmp~30 volts or Vmp~36 volts--For Battery Based systems--It can make a difference when choosing an MPPT charge controller (brand/model) and configuration of the array.

I would suggest staying away from frameless panels--Mounting them properly/securely for 20-30+ years can be a pain.

-Bill

martinruss7

Thanks for all the info .

martinruss7

What about the classic 250? According to the sizing tool I can have up to four of my 320 panels in series and still be within tolerances. With around 55 amps out.

vtmaps

martinruss7 said:

What about the classic 250? According to the sizing tool I can have up to four of my 320 panels in series and still be within tolerances. With around 55 amps out.

The Classic controllers need some headroom... that is, PV input voltage needs to be higher than battery charging voltage.  But too much headroom leads to inefficient operation.  In other words: heat is produced.   More heat is produced (power lost) when reducing 140 volts to 48 volts, than when reducing 90 volts to 48 volts.

If you look at the Classic power handling charts, you will see that as input voltage goes up, power handling capacity goes down.  The Classic protects itself from melting by throttling back its output as it gets hotter.

In a 48 volt system, the Classic 150 can handle over 5000 watts (if the input voltage is low enough).  A Classic 250 caps out at 3212 watts.   So yes, you can go four to a string with the Classic 250, and if you do not expand your system it will work OK.  Do not try to approach the limits... it's not good to run these things continuously on the verge of melting.

If I recall, you want to upgrade your system by adding more panels.  Why not keep your present system and just add three 60 cell panels with a Midnite Kid controller?

--vtMaps

martinruss7

One last question guys. If I decided to just add two additional 24v 320 watt panels to my existing 48v system, can I add the two in parellel to increase my amps. Keep in mind these are 24v panels.

vtmaps

martinruss7 said:

One last question guys. If I decided to just add two additional 24v 320 watt panels to my existing 48v system, can I add the two in parellel to increase my amps. Keep in mind these are 24v panels.

What charge controller are you using?  As long as you do not exceed its ratings, you will be OK.  When you move from two to three strings of panels, you must have a combiner box with a circuit breaker for each string.

check out: http://www.solar-electric.com/installation-parts-and-equipment/midnite/pvarco/mnpv3.html

--vtMaps

martinruss7

I'm using the Coleman Air C440-HVA Controller.


This controller is capable of handling up to 125 Amps of continuous solar power, but open collector voltage should not exceed double the nominal battery voltage. So with that info, can run a third string of two 24v solar panels in parallel? Just to increase amperage. And yes I have a combiner box with breakers.