What options do I have - upgrade

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What options do I have - upgrade

Postby Newt » Thu Sep 07, 2017 2:40 pm

Hi folks.

I have an off-grid solar system that has been in place for quite a few years, 16 x 80W panels, 1280kW system , mppt controller. Panels are mounted on a tilting ground based platform.

I wish to upgrade to more watts.

A while back I purchased a PCM5048 mppt controller (max 3250W). My question is: what is my best option?

a) Replace all the 80W panels with new panels - max output of 3250W

This might mean replacing existing wiring, Im yet to measure the wire surface area for current limitations.
Simplifies input to the mppt controller and likely will maximise array performance.
New panels will be larger and fitting to the structure might be an issue.

or

b) Add a second array on the north roof face.

Benefit is to leave the existing array as it is, if one array has an issue I can isolate it and still have the other.
Downside: roof mounting and wiring to battery shed.
Will the MPPT controller be happy with different arrays (different voltages and current) in parallel or will a combiner do the trick ?


Can I use two MPPT contollers - the old and and the new one? I doubt it.

Any advice would be appreciated.

Thanks
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Re: What options do I have - upgrade

Postby Gordon-Loomberah » Thu Sep 07, 2017 8:22 pm

Newt wrote: 16 x 80W panels, 1280kW system


You need to lose the k, it's 1280 watts, or 1.28kW.

If the existing panels still have reasonable output, there is no good reason to replace them.

Facing them all to the north may not be the most useful, you dont want to charge those batteries too hard. This may or may not be an issue, as we don't know their capacity.

Have a read of this thread:
solar-wind-gear/topic5064.html


Will the MPPT controller be happy with different arrays...?


Only if the Vmp of each array is nearly equal.

You can use 2 MPPT charge controllers into the battery, I've been doing it for years.
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Re: What options do I have - upgrade

Postby Newt » Fri Sep 08, 2017 12:08 am

Thanks Gordon

The existing panels are BP Solar I think from memory and still produce good output.

I wish to install new batteries after a panel upgrade to 3.2kW. I intend on 16 x 6V batteries of at least 225Ah each.

What would be the charge limit do you think? The existing array is on a tilting framework and faces north. I do wish to maximise charging to keep the DOD minimal.

Cheers
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Re: What options do I have - upgrade

Postby jaahn » Fri Sep 08, 2017 7:52 am

Hi Newt :)
I would not just tear down a set of functioning panels to replace them ?? Seems counter intuitive to me.
If I was doing it I would either reconfigure the panels so the output matches some new ones which you will then buy. Or run them with a separate controller in the batteries. Perhaps you are short of places to put panels which might affect the outcome.

I think Gordon might be saying is that having all the panels facing the same due north gives a big power spike in the middle of the day which may be larger than recommended for the batteries and would require a large controller. If you pointed some panels east and some west then you spread the power over the day and reduce the peak. Fattens out the morning and the evening power production which might be also matching some of the house usage better too. Gordon has a thread on this called "Virtual Tracker Panel arrangement" which he has referenced for you. 8-)

Undoubtably you will need bigger wiring if you put bigger power panels on to the existing frame. Make the wiring generous as wasting your new big power output in heat losses in the wires is just silly. :cry:
Cheers Jaahn
PS you might be better to ask these questions in the next section as there are more experienced technical people who might give more ideas for you to consider. COMPONENTS INSTALLATION AND PERFORMANCE
solar-wind-gear/
A very friendly informative bunch here :D
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Re: What options do I have - upgrade

Postby Newt » Fri Sep 08, 2017 1:10 pm

Thanks Jaahn

I was wondering about just how must current a battery bank can take and how to work it out. Any clues would be good.

I agree that keeping the existing one is a good idea...it will mean roof mounting a second set. And I need to have the output voltages close as Gordon mentioned. My panels at the moment are around 90-110V I think output, they are 12V panels.

Doesn't it make sense though to have one array facing north as they all are here in the country. I have not seen east/west differentiated arrays anywhere here and if possible maximise the array for charging the bank. I don't quite understand the advantage to a differentiated array system as basically one turns off and then the other comes on as the sun travels.

EDIT: I read the thread about the East/West configuration - it makes sense. Good idea. In my situation the north facing panels which are on tiltable framework would probably be doing most of the work in winter as East/West may not be with the sun so low in the sky.....but in summer the east/west idea would be good. I just don't know how to work out max battery charging.

Cheers
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Re: What options do I have - upgrade

Postby Newt » Fri Sep 08, 2017 2:04 pm

My existing array 16x 80W on tilting framework. Inside shed....MPPT controller left, inverter etc.
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solar small.jpg
16 x 80W panels..tiltable north facing framework
panels small.jpg
inverter, MPPT controller etc
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Re: What options do I have - upgrade

Postby jaahn » Fri Sep 08, 2017 2:23 pm

Hi Newt, :)
What voltage does your system run at. Nominal battery voltage eg 12V, 24V, 36V, 48 V or more ? Do you intend to keep that for the new bigger system ?
Where are you north south east or west. Looks like the outback !

The maximum battery current input is recommended by the manufacturer of the batteries. That is the place to look for their specs sheet for the batteries you are interested in. After that you have to decide if you have some strings in parallel as well as in series. The parallel strings will divide the current among the strings.

When you want some information on the forum it helps the experts who do help on here if you give as much information on the hardware as possible so those familiar with the particular items can speak from experience. I am not as experienced as many others here. Note no question is silly, only the one you forgot to ask ;)
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Re: What options do I have - upgrade

Postby Newt » Fri Sep 08, 2017 2:52 pm

Thanks Jaan

It's a 48V system. I think the best idea so far (as I learn) would be to keep the existing array and place an east and west facing array on the roof which will run on a separate MPPT controller. I now understand the advantage of an east/west differentiated array...I wondered why people in the cities often have them on east/west roof sides....not something I have seen in the country though.

As far as battery current goes...Trojan T105 lead acid for example - which I have been using, the actual current is not mentioned on the specs page...however, Trojan state this:

"Example: A good charging rate for a battery with a 20-hr capacity of 225 amp-hr is about 22 to 29 amps. You can of course go slightly higher or lower depending on what is available on the market"

At the moment I think peak amps the MPPT controller creates is about 12A and 100V roughly off the top of my balding scalp...hah.
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Re: What options do I have - upgrade

Postby Gordon-Loomberah » Fri Sep 08, 2017 3:00 pm

Newt wrote:I was wondering about just how must current a battery bank can take and how to work it out. Any clues would be good.


Trojan recommend max 10-13% of the 20hr rating for their flooded cell batteries, with full charge being reached when it falls to 1-3% of the C20 rating.

At the moment I think peak amps the MPPT controller creates is about 12A and 100V ...


that would be the MPPT input, output will be more like 50V and 24A
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Re: What options do I have - upgrade

Postby Newt » Fri Sep 08, 2017 3:22 pm

Thanks Gordon...yep input sorry. So at 24A the batteries are near maximum charge current? Will charge current from the other MPPT controller be additive, I guess so....therefore how can I add new panels...will I require larger amperage batteries?

Appreciate the advice....been a long time since I have looked at all this.
Last edited by Gordon-Loomberah on Fri Sep 08, 2017 4:34 pm, edited 1 time in total.
Reason: removed unnecessary quoting
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