Best way to expand this system?

Chris Miller

Hi all,

We are completely off-grid and need to add a little bit more power to our system. We're doing good most days but on cloudy days our inverter will hit the low voltage cut off around 7am the next day before the sun comes up. I want to add more batteries and either more panels and maybe a wind generator. For right now though, I wanted to discuss solar panels. I want to add more but no longer have access to the panels we bought before. The specs are:

Hareon Solar - 100w
Imp 5.81a
Vmp 17.2v
Isc 6.46a
Voc 21.6v

I have 10 of these total, in 2 strings of 5 panels each. They feed into my combiner box with one breaker per string.

The panels are approx. 50ft from the charge controller. Charge controller is an Outback FM-80

I would like to add another 1000 - 2000 watts of solar, but I don't know what panels I should buy or what size / configuration to work best with what I already have.

I've tried the sizing tool on outbacks website but it won't load right for me. I'm really not even sure that my current configuration of 2 strings is the best bet but it's what was recommended to me.

BTW... system voltage is 48 volts. I am running Trojan T105 RE's right now.... I'd like to add another string of 8 if i can soon.

Any recommendations? Thanks in advance for any / all help. It would be much appreciated!

Cariboocoot

Re: Best way to expand this system?

Well let's see.
Right now you're running an array with a Vmp of (5*17.2) 86 and an Imp of (2*5.81) 11.62 through an FM80 so you might see (1000W * 0.77 / 48 ) 16 Amps of peak charge current. That's pretty low for a string of T105's (225 Amp hours); 7% before loads. I can see where you'd want more panel, especially on a cloudy day.

The good news is that those are basically "12 Volt" panels. There would be no problem adding another string of five similar Vmp panels to the mix. Even if their Vmp were 18 it would come to 90 Volts; only 4.6% higher than the existing string.

So say you put five KD140's on it: string Vmp 88.5, string Imp 7.91. That would add 700 Watts bringing you up to 1700 Watts and about 27 Amps peak charge current (12%).

The FM80 could handle a lot more than that, but the existing batteries would not like much more current. So at that point you could still add panel, but limit the output current. Kind of a waste of panel, but it would improve output on a cloudy day.

If you do add batteries, make sure the existing ones are right up to snuff or else the new ones will be immediately 'pulled down'. And of course more battery = more panel.

northerner

Re: Best way to expand this system?

I was in a similar circumstance just over a year ago where I had several 12 volt panels and looked to upgrade. I was not off grid like you, however, the fellow I was dealing with recommended selling them and going with larger 24 volt panels. I'm sure glad I made that move! The 24 volt panels are more cost effective, and the array won't be a mismatch of various panels. The 12 volt panels are well suited for those with RV's or trailers, so it may not be too difficult to unload them. Of course you do have more panels, plus you're off grid, so that may way into your decision. Good luck with your expansion!

Cariboocoot

Re: Best way to expand this system?

Good point, northerner. Let's do some math and see what we get.

Five KD140's for $284 each = $1420 (brings existing array to 1700 Watts).
Seven Conergy 245's for $223 = $1561 (replace whole array with 1715 Watts).
$141 difference.

Obviously if you want to expand beyond that point it could be more economical to replace the whole array (although changes to mounting and wiring would be necessary). Especially if you can sell the old panels.

Photowhit

Re: Best way to expand this system?

If you match the Vmp with the cheaper grid tie type panels and add in what you have I think that would be the best option.

You cumlitive VMP of 86 so 3 panels in the 29 volt range or there is a pretty good deal on the ConEnergy panels mentioned above. There should be minimal losses with strings of 3 of those panels. So long as the current panels are mono or polycrystaline they should have similar curves, you should be able to just add the strings.

Since you currently only have 2 strings, likely you will also need a combiner box, a fuse or breaker box for the panels.

Leave the panels you have and add 1 or 2 strings of 3 of those should work out nicely. Now how long has your battery bank been hitting low voltage in the morning? since it likely has very little loads at this time (unless your up and using a microwave or some heavy draw items) Your batteries may be on their way out.

Chris Miller

Re: Best way to expand this system?

Thanks for all of the replies so far guys. I am looking at all options mentioned and trying to come up with a workable solution. I could probably sell these smaller panels here but it would be a pain. I have a 4 spot combiner box already and it has 2 more spots open for breakers so adding on would be simple enough. Being as anal as I am though, it would be great to have a nice matching array out there and hopefully with a panel that doesn't change size / design in 3 months like our current ones did.

The batteries have got down to 43 volts about 3 times now in the mornings. It has to be the combination of the fridge and freezer hitting at exactly the same time while voltage is already low because as soon as the magnum shuts itself down the voltage jumps back up to 47+

I really need to find someone close by with these Trojan's and get them bought soon. That would be a huge help I think.

Chris Miller

Re: Best way to expand this system?

Here is what the outback usually looks like around this time every day with the sun high in the sky and no clouds (2pm).

Hope this looks good?Attachment not found.

Cariboocoot

Re: Best way to expand this system?

Chris Miller wrote: »

I really need to find someone close by with these Trojan's and get them bought soon. That would be a huge help I think.

Except that your existing array may be having trouble charging the batteries you already have. If you add more batteries the problem could get worse.

Check the SG with a hydrometer at the end of charging on a good day and see if you are getting full recharge. If so, you could expand the battery bank to carry you through the night better.

But I suspect it's a case of being short of capacity in both areas.

Cariboocoot

Re: Best way to expand this system?

Good output on the charge controller.

But ...
50% capacity of the batteries is about 5kW hours. Evidently you are using this much because you're getting battery Voltage way down to 43 (much too low for cut-off in my opinion). If the array can only get 3kW hours per day, then adding batteries will only result in a delay before the deficit charging takes over again.

Do you have a daily kW hour usage figure? Not the number from the controller; that just shows what it harvested.

Chris Miller

Re: Best way to expand this system?

Cariboocoot wrote: »

Good output on the charge controller.

But ...
50% capacity of the batteries is about 5kW hours. Evidently you are using this much because you're getting battery Voltage way down to 43 (much too low for cut-off in my opinion). If the array can only get 3kW hours per day, then adding batteries will only result in a delay before the deficit charging takes over again.

Do you have a daily kW hour usage figure? Not the number from the controller; that just shows what it harvested.

I don't have a current figure because it's variable right now with construction projects and other stuff but I am going to get the kill-a-watt's back out and figure it out. I can guarantee it's hitting 5kwh though. I am still trying to wrap my head around a lot of this solar stuff while dealing with the many other projects of a sudden off-grid move. We're getting 6-7kwh per day in production according to the outback and I guess I assumed it was just all there for the taking. Probably in the same way I assumed that with 1000 watts of panels I have 1000 watts of power available to me at all times when the sun is out without ever touching the batteries. (grin).

NorthGuy

Re: Best way to expand this system?

Chris Miller wrote: »

Hope this looks good?

The charging current is about 9% of your bank. At such current, the voltage should be much higher in that conditions. 51.6V at this current indicates batteries at the beginning of bulk. They should be in absorption by 2pm or at least very close to it. There are two possible explanations:

1. You have too many loads, which take current from the solar charger and it doesn't go to batteries

or

2. Your batteries are in a very bad shape.

Before you do expansions, it is a good idea to figure out what your loads are. This way, you will know what is happening.

Also, it's a good idea to measure specific gravity with hydrometer in every cell and also measure voltages on every battery. The voltage may be so low because you have shorted cell(s).

Cariboocoot

Re: Best way to expand this system?

It's a bit more like:

1000 Watts of panel * hours of good sun * 0.52 efficiency factor. So if you do get 6 hours equivalent good sun then that 1kW array should be good for just over 3kW hours AC.

Note that use of power during daylight hours helps; if the batteries are full then the panels can produce power which is not realized without loads drawing at the time. But there are still losses from powering the inverter and converting to AC.

It is really important to see if the batteries are getting fully charge, by when, and how much power is being used between then and the start of the next charge cycle. Too much of this low Voltage in the morning stuff and you won't be buying a second string of batteries, you'll be having to replace the ones you've got.

Chris Miller

Re: Best way to expand this system?

NorthGuy wrote: »

The charging current is about 9% of your bank. At such current, the voltage should be much higher in that conditions. 51.6V at this current indicates batteries at the beginning of bulk. They should be in absorption by 2pm or at least very close to it. There are two possible explanations:

1. You have too many loads, which take current from the solar charger and it doesn't go to batteries

or

2. Your batteries are in a very bad shape.

Before you do expansions, it is a good idea to figure out what your loads are. This way, you will know what is happening.

Also, it's a good idea to measure specific gravity with hydrometer in every cell and also measure voltages on every battery. The voltage may be so low because you have shorted cell(s).

Just put a hydrometer on order so we'll see.

Come to think of it, I haven't been seeing much absorb cycle lately. Mainly just MPPT bulk and snoozing. I'm sure the freezer sitting outside in the sun all day isn't helping.

Chris Miller

Re: Best way to expand this system?

Hmm... just realized my float is set to 52.8 on the outback but it's 54 right now and still sitting on bulk?

Cariboocoot

Re: Best way to expand this system?

Chris Miller wrote: »

Hmm... just realized my float is set to 52.8 on the outback but it's 54 right now and still sitting on bulk?

It has to go through the Absorb stage in order to switch to Float.

westbranch

Re: Best way to expand this system?

Chris, it would help us all if you described your system in your Signature line, so we can understand any limitations of your system and give appropriate advice. You need to 'BULK' those batteries soon as you have been Deficit charging from what you have said.

Do you have a Generator?

tallgirl

Re: Best way to expand this system?

Everything I've read so far, including the low voltages, sounds like insufficient PV is the first cause of problem.

Panels are getting to be cheap enough that I'm starting to tell people to consider east or west facing exposures. The efficiency loss isn't all that bad, considering the drop in panel prices.

Chris Miller

Re: Best way to expand this system?

westbranch wrote: »

Chris, it would help us all if you described your system in your Signature line, so we can understand any limitations of your system and give appropriate advice. You need to 'BULK' those batteries soon as you have been Deficit charging from what you have said.

Do you have a Generator?

I did get em back up with a generator and they have been staying steady above 50 volts for a couple of days now. I will work on the signature....

I'm also close to knowing my total usage every day. The freezer sitting out in the sun was pulling close to 2 KWH / day and we had a rogue light in one of our bearded dragon enclosures that was pulling a lot of power too. Addressed both issues and I think things are looking up!

inetdog

Re: Best way to expand this system?

tallgirl wrote: »

Panels are getting to be cheap enough that I'm starting to tell people to consider east or west facing exposures. The efficiency loss isn't all that bad, considering the drop in panel prices.

For people in high latitudes who need winter production and do not have South-facing roof area, the combination of roughly equal East and West facing panels can do almost as well as the same number of panels facing South.

In equatorial areas, Up seems to do very well. :-)

Chris Miller

Re: Best way to expand this system?

Hey guys,

Thanks for all your help on this one. I decided to sell the 100 watters and now i'm trying to decide which way to go with new panels and more batteries. I made a new post here:

http://forum.solar-electric.com/showthread.php?19537-Help-me-expand-this-system

Would you let me know your thoughts?