New off-grid install...questions

johnT

Hi guys,

I am going to be putting up my solar system very soon and would like feedback as to what I might need to do...things I'm missing, etc. So far I have a prebuilt MidNite Magnum 4400 48v system on the way... http://www.solar-electric.com/misoprmasy4w.html , 9 Sharp 235 watt panels (3 strings of 3), 8 6v 250ah batteries (extremely cheap "learner" batteries:D) and a Honda eu2000i backup generator. I know the prebuilt e-panel is a little overkill for the rest of the system, but I figured when I've made my mistakes and the cheap batteries kick the bucket I will (hopefully) add 3 more panels and get some bigger batteries.

I am going to have about 12-15ft from panels to CC and the batteries will be very close to the e-panel (is putting the batteries directly below the e-panel ok, or is that a potential hazard? they would be in a box vented to the outside).

Does anyone have any knowledge of the aforementioned e-panel? Do I still need a combiner box or an array disconnect (or both)? I am in Belize and finding such things is going to be very difficult (I had the rest of the components shipped in a friends container and being the newbie that I am I didn't think about all the little details (they did cross my mind, but thought I could get anything else I needed here...I found out differently once I was here). Things such as MC4 extensions and combiner boxes...they don't have those here in my area as far as I can tell. I asked a local guy how they combine them and run them to the CC and he said they just solder them together. So if I do need a combiner box does anyone have any good info/ideas on a DIY box? And with no MC4 extensions I am not sure the best way to "extend" them.

I bought the prebuilt with the hopes that it would be just a matter of wires in from the panels, wires out to the batteries and wires to the AC box. As a total beginner I was hoping to have all the breakers/shunts/etc already done so I didn't have to figure it out or bother you guys with it:D. But I'm not sure what all is taken care of inside there as I don't have it yet and I can't seem to find a manual or diagram on it. Any and all feedback would be greatly appreciated.

Here are the panel specs...Thanks in advance

Maximum Power (Pmax)*: 235 W
Tolerance of Pmax: +10%/-5%
Type of Cell: Monocrystalline silicon
Cell Configuration: 60 in series
Open Circuit Voltage (Voc): 37.0 V
Maximum Power Voltage (Vpm): 30.0 V
Short Circuit Current (Isc): 8.60 A
Maximum Power Current (Ipm): 7.84 A
Module Efficiency (%): 14.4%
Maximum System (DC) Voltage: 600 V
Series Fuse Rating: 15 A
NOCT: 47.5°C
Temperature Coefficient (Pmax): -0.485%/°C
Temperature Coefficient (Voc): -0.351%/°C
Temperature Coefficient (lsc): 0.053%/°C
Dimensions (A x B x C below): 39.1” x 64.6” x 1.8”/994 x 1640 x 46 mm
Cable Length (I): 43.3”/1100 mm
Output Interconnect Cable**: 12 AWG with MC Locking Connector
Weight: 44.1 lbs / 20.0 kg
Max Load: 50 psf (2400 Pascals)
Operating Temperature (cell): -40 to 194°F / -40 to 90°C
UL Listed: UL 1703
Fire Rating: Class C

vtmaps

Re: New off-grid install...questions

johnT wrote: »

is putting the batteries directly below the e-panel ok, or is that a potential hazard?

I don't know how hazardous it is, but it is a violation of NEC. Sometimes the best way is to build a wall and mount your electronics on one side of the wall. On the other side is your battery box. If you elevate the battery box a bit you will make for shorter cables from battery to epanel, and the batteries will be easier to service.

Does anyone have any knowledge of the aforementioned e-panel? Do I still need a combiner box or an array disconnect (or both)?

The epanel has an array disconnect. You do need a combiner box. Midnite makes a nice box for 3 parallel strings, and you can special order it with built in MC4 connectors, circuit breakers, and lighning arrester. Since you are thinking of expanding your array, you may want to start out with their 6 circuit combiner.

But I'm not sure what all is taken care of inside there as I don't have it yet and I can't seem to find a manual or diagram on it.

How about: http://www.midnitesolar.com/pdfs/MNE-240_Manual_new_Cover.pdf

--vtMaps

Photowhit

Re: New off-grid install...questions

vtmaps wrote: »

I don't know how hazardous it is, but it is a violation of NEC. Sometimes the best way is to build a wall and mount your electronics on one side of the wall. On the other side is your battery box.

While I agree that it's good to have a break between the batter box and Epanel, I don't think there is a NEC code in this regards. You have to have reasonable access to the breakers, and if they are not sealed batteries, I would consider a battery box, to seal off potentially harmful/explosive fumes from electronics.

niel

Re: New off-grid install...questions

yes, those things do come back to haunt you. you should obtain the mc4 cables and cut them in half so as to splice to the wires going to the combiner. cutting off the mc4 connectors on the pv wires often violates the warranty on the pvs. one spliced wire with mc4 connections wil allow the connection to the - string output and + string output of 1 string. if you've got 3 strings you need 3 mc4 extension wires. obtain another one for each string you plan to add in the future too.

you will need to fuse or circuit breaker each string as problems can arise that leads to the destruction of your pvs and it is also a safety hazard. you have 3 strings now, but you plan on expanding by another string so you need at least 4 breaker positions minimally. after they are combined then they go off to you cc through the epanel. inside the epanel it will have a breaker to feed the cc and that you can use as a disconnect to the cc. another breaker will be present that also is the output of the cc. you can look over the wiring diagrams over at midnite solar and you will see what i mean. don't forget to look at where the spds are wired to as well so you know where they intended what to go where when you put the wires going into it from your pvs and batteries.

the epanel is made for the basic in and out configurations and such things like load centers and combiners are external to the epanel. down there i can't say what the requirements are as far as electrical codes go and i'm sure they exist somewhere even if they are lax in enforcement. do not just solder the pv strings together regardless of electrical codes and advice from others down there.

also, be aware the breaker before the inverter will not protect you against any shorts between the breaker and the batteries and we do recommend a breaker near the batteries to help alleviate that potential hazard. i put one on my battery box before the wires are allowed to exit the box.

one other note is that it is recommended to have a 100ah minimum capacity per kw of inverter power capability with 48v battery banks. you may have ripple problems going with only 250ah as it really should be twice that. it would become obvious to you that the 250ah will not handle the full 4400w of load anyway. battery voltage would quickly get sucked down until the inverter thinks there's insufficient voltage to operate. it may help if you limit your loads to about 2kw max and if using the built in charger then cut the charge current back there to roughly 13% of battery ah capacity or .13 x 250ah = 32.5a. i'm not sure of the actual settings allowed on the charger, but i wouldn't go higher than 35a or 40a unless you have loads present to the batteries to offset the high charge rates.

johnT

Re: New off-grid install...questions

Thanks for the input guys.

Just found out that I have a friend coming down for a visit in a couple weeks and they can bring a combiner and some mc4 cables (if they come in time)...:cool:

Niel...what size breaker for the batteries would you recommend and does it require a special box to put it in? Are these things normally available at a hardware, or do I need to order this from NAWS also.

And yes, I realized as I said in my other post that the e-panel was overkill for my current setup, but from what I've read on here one should always plan for system expansion. And I was also under the impression that the 100ah per kw of inverter power was more important with grid-tie systems and not so much with off-grid.

At this point I don't think my loads will go over 2kw...at least it will be rare, if so.

I'm not sure what you mean by ripple problems...I guess the question is: will this system work without major problems (theoretically of course) or do I need to make changes before I go ahead with it? I knew the batteries were a little on the small size, but I got them super cheap and thought they would be great to learn on. When they flat line I was planning on getting something more in the 400ah range (which would put me in the range of the 100ah to kw of inverter power).

Thanks again

inetdog

Re: New off-grid install...questions

johnT wrote: »

And I was also under the impression that the 100ah per kw of inverter power was more important with grid-tie systems and not so much with off-grid.

Off grid is where you specially need to have enough battery capacity since you are dependent on the inverter for large loads (unless you have an auto-start generator.)
A pure grid tie system will not have batteries at all, and a hybrid system with both grid tie and batteries does not make economic sense for most people unless you have frequent long POCO outages or power quality problems.

mike95490

Re: New off-grid install...questions

With the inverter generator - check your actual LOAD rating, I think the 2000w is a short term PEAK load, not continuous load. You will have to program the charger to not consume full power from the generator. Also, you need to look up the PF (power factor) of the charger, as that will reduce the efficiency of the generator feeding the charger. There was a thread here a while ago, regarding charger PF and generator sizing that hopefully, someone will post a link to for you.

niel

Re: New off-grid install...questions

sorry for the delay in getting back to the thread, but ripple is an unwanted ac component and the pumping on the batteries high and low for current will cause large voltage fluctuations as the batteries get bogged down and then lightened loads. this effect is not limited to gt operation. the voltage dip will at some point even stop operation of the inverter even though there's still some usable ahs left in the bank.

inetdog

Re: New off-grid install...questions

niel wrote: »

sorry for the delay in getting back to the thread, but ripple is an unwanted ac component and the pumping on the batteries high and low for current will cause large voltage fluctuations as the batteries get bogged down and then lightened loads. this effect is not limited to gt operation. the voltage dip will at some point even stop operation of the inverter even though there's still some usable ahs left in the bank.

The relationship between the current ripple and the voltage ripple at any point in time is directly described by the internal resistance of the battery, which tends to increase as the battery SOC decreases and as aging and wear take their toll on the battery.
That the voltage ripple can cause a low voltage trip even though the average voltage remains high is a very important observation. But the extent will depend on whether the relevant protection circuit uses low pass filtering or not.