expanding my system with 2nd system

[binkino]

Hi there,

I am thinking about to expand my system.


But first you should know about my PV system:

In 2014 a company installed a PV system to my house.
They installed 3 rows with each 4 PV modules, and connectet the modules in pair (no joke!)
The batteries were 4x 200Ah AGM = 48 Volts.
The VOC never reached the full charge state. Also it discharged the batteires down to 20% and killed them - and more things, you would cry.
After a lot of trouble with the company and the system, I had enough of this, they also gone bankrupt, and I stripped everything and build it from scratch new and bought the Classic Lite 200 and rewired the modules to 4/string to have a 148VOC, that gives me a good use of energy.

Last year I added a 4th string with 4 more modules with 255Wp to the system on the roof.
Now this is about 3.900 Wp power. (12x 240Wp + 4x 255Wp ... do I calculate correct?)

For the winter time, the 4th string was a good idea. Every watt counts

So 2 of the old batteries are really broken, and the other 2 I think I can use them for playing.
Possible a couple of really good charging cycles, they can come back to full life.
When I reinstalled the system, the money was small, so it was only possible for me to buy cheaper 4 x 230Ah AGM batteries (=48V)
The inverter is a Westech Combo 3000 / 48V



The situation is, that, also in the sunny summer time, the battery bank with 230Ah AGM batteries will not deliver enough energy for the night. Sometimes I have to work longer at the computer in the night, so they will be empty to early and the inverter switches to normal grid.


Yes, I better expand or replace the battery bank, but I want to use them now as so long as they will work, and put money to the side, to buy better batteries one day.

So using existing hardware ... I have a APC 1400XL UPS (USV we say) that works great and has perfect sinus wave, and from the old installation I have these 2x 200Ah AGM batteries here.
I allready tested it standalone. I connected the batteries to the UPS and it gave my long time using my computer. But the APC can not charge the AGM correctly, so I need a charger like the classic and use the 4th string.

So why not connecting these two batteries in series to 24V, charged by another Classic connected to the 4th string (complete electrical independend from the other system!)
and to the DC input of the APC
and its 230V output to the input of the Westech inverter?


The VOC of the strings is about 148 Volts DC.
Because I do not want to rewire the modules every time, I think it is a good idea to feed it into a 2nd Classic 200 - like I allready own it - and let it transform for the 24V bank.

Then, if the 230Ah / 48V system is 'empty' - it would switch back to the APC and gives me more PV energy time, before this will have to switch back to power grid I have to pay for.

OR I connect only the basement electric (small freezer, light, ...) to the APC, that could relieve the 48V system.
The APC will have to be allways 'ON', so it will use energy from the batteries so or so.
I have not found a way to switch it on/off like other inverter can do,
that only works with the button pushing some seconds and again for some seconds.



What do you think about this idea?
Will 255Wp be enough to charge the old 200Ah batteries?




And please excuse, again, my english, as it is not my first language.
If you have a question, because I wrote something stupid, please correct me.

[mike90045]

Q1)  why are you using short lived AGM battery instead of flooded batteries.

Q2)  You must calculate the watts used by computer and appliances, to get the size of the batteries right. 

If you consume 2700 watt hours in a day, you need  at least 3x that much in battery capacity 8100watt hours

8100 wh @ 50V = 162 ah     Then you need enough solar PV to recharge that battery the next sunny day, while your loads are running, and then you have a balanced system

[binkino]

I didn't know enough about it. In the old system were 200Ah and I bought in consideration of my budget (about 1.000 Euros were possible, at least 1.080 Euro. Today I know other options, like Trojan T-105 and others) and what I could get for the money. These were the 230Ah. They are not bad, but really cheap: 2 had to be replaced in warranty in the time. But its running now.

Right your calculation. I am not sure how much energy is needed actually. I better calculate this for present time. But estimating double of the capacity I have now?
I also could use more energy from the PV, if the Classic would different between charging amps and needed amps, not to charge with to much amps, but give the inverter what it needs. So I can only charge with max. 23A, have set it to 30A in the Classic, and hope that this is in balance with the needed power and the max. charging amps) (see my request) Would make this system much more effective a bit. Yes, this would be no problem, with double capacity or other batteries.

So till I can buy better batteries, I want to use existing hardware to make the best out of the situation.

[dgd]

Binkino,

I wouldn't waste money buying more AGMs or even smallish capacity T104 or equivalents, or mess about making two separate systems, one at 24V and other at 48V.
That current limiting to 23A just seems crazy when you can generate so much more power
You appear to have a decent size PV array and appropriate Classic controller.
I would suggest L16 FLA batteries to get a 48V 400Ah bank. Although that may seem too large it will mean shallower depth cycles each day hence longer battery life and a greater reserve for bad weather times. Also FLA more serviceable and there are some excellent prices if you shop around (eg Crown L16)
Just IMO.

dgd

[binkino]

Thank you for the recommendation, that is a thing when I will replace the AGMs.
I agree, investing money should makes sense.


That is what I mean, I waste energy by limiting to 23 (30) Amps, while the energy could be stored in batteries or used.
In the summer, when the sun is top of my house, my PV don't know where to put the energy

Understand this not ingratitude, I appreciate the advice

But this gives me no idea, about my idea will work.
This "extension" is a possible solution to expand with existing hardware (charger is another thing, I had an offer to get one, so not much money I have to invest)


One day - may be next year (=2017) - I will replace the 230 Ah AGMs for sure.
But I don't throw the AGMs away now, so long they do their job and also if they fail earlier, I will come back to your advice
New batteries will cost me money, I guess I will have to invest about > 2.000 Euros for a big beast that fits the need?
IF the AGMs are good next year, I can use them as "emergency reserve" in bad weather time, charged by the 2nd charger.
One string could keep them by good condition / if the main batteries are full, a relay or like that can switch a string to them and keep them alive or something, I will think about when it is time

[Westbranch]

In the summer, when the sun is top of my house, my PV don't know where to put the energy

This is where ;opportunity loads'' come into play, mostly it will be up to you to do something to use the energy like doing a laundry...  or use one of the more costly and complex setups that diver the power to a storage water heater or such, when the batteries go into Float...

hth

[binkino]

Yes that is what I do, if the sun is high and much power, then I start the laundry / washing machine