MPPT 80 600 CC down

Photowhit · September 2015

Hi Masterjoe, I'm not sure what you expected from your solar setup.

There are so many wrong things going on in this thread.

A hybrid system is designed for maximum reliability, NOT to save money. The battery bank is a backup, not intended for regular use, some regular use is good for the bank but not it's intended purpose!

12 - 6 volt 390 ah batteries creates a battery bank of 3 strings of 4 - 6 volts batteries, so each string has 24 volts at 390 ah, 3 strings in parallel makes a 3 x 390ah = 1170ah 24 volt battery bank.

A 24 volt battery banks resting voltage when full is @ 25.4-25.6 volts, nothing wrong with 25.7 at night (this might be the wrong figure, but something in that range)

First, I don't think he's the "sharpest stick in the woods" if you indicated you might switch to a 48 volt system, he should have had you, have a battery back up that could be configured as a 48 volt battery bank! No way to configure 12 - 6 volt batteries as a 48 volt bank. You do NOT add new batteries to old particularly if you are designing a system from scratch.

This is a hybrid system. The charge controller only needs to top off and maintain your batteries so that you can use them in an emergency. You appear to want to use them over night... Most modern charge controllers can handle being 'presented with more current than they can handle, they just don't use it. Your 1170 ah battery bank needs about 5% charging current to be maintained as a backup or about 60 Amps the array and single charge controller can do this with out a problem.

I don't know how the XW system works, if once charged the current from the array feeds the inverter to back feed the grid then, I would think you have the correct sizing of array to inverter, as others (Vic?) pointed out a 4500 watt array can typically produce 3375 watts so a 4000 watt inverter should not be over taxed.

As Bill has described it, the inverter works from the battery voltage, so an additional invert might well be needed. You might even consider a high voltage backfeeding inverter and split your array to that...

Really like to know what you had expected and what you were told, in terms of over all cost of electric

Vic · September 2015

Hi Masterjoe,

There is probably very little re-wiring required -- none on the PV or CC, and almost nothing for the inverter, BUT, you will have 1.5 battery strings at 48 V. So, you would need to drop one string at 24 V, OR buy an additional four batteries and interconnects to make it two strings at 48 V.

Multiple battery strings, generally are not such a good idea, but the batteries are young, so it should be OK. AND, two strings is much better than your existing three-string 24 V battery.

Doubt that there is much, if any change in the PDPs, etc between the new model 48 V inverters and the older XW4024s, except possibly the paint color.

FWIW, Good Luck, Vic

Dave Angelini · September 2015

It could be common in Florida.....

Masterjoe · September 2015

Well I have to say you guys are awesome. You have all been very kind in answering a lot of my questions. I was not getting a clear answer on what full battery voltage was. Yes when the sun goes down we sit anywhere from 25.4v-25.7v. Right now with the CC down we are at 25.5v sitting. My concern before which is why i wanted to run the batteries at night was because I never saw the batteries getting any usage during the day. Charles did not explain to me very well when he said we skim off the top of the batteries during the day. What we are actually doing while the batteries are at 26.7 (float voltage) is running the loads off the array and the excess is going back to the grid. So correct that I want the batteries ready for an emergency and now I know I do not need to exercise them often. The differnce between the XW4024 and the XW6048 is roughly $1,000 give or take. The inverter running off the batteries explains why the inverter is charging the battery bank every 5 or so days. My only concern is the inverter is set as a 2 stage no float. So I hope until we can afford a new CC I am not killing the life of the batteries. That would be the last thing I need to replace. I am going to contact Charles on Monday and see if he won't replace the CC. We have 12 6v batteries so I would think we would need 4 more to have all 16 wired into 2 strings of 8 for 48v if I am correct? We are expecting a daughter the first week of November. We sank everything we had back in March to get this system. It took until 1 Aug to get it up and running. So besides my other bills we have been paying over $600 a month between electric bill and loan payment. So this CC going after only 1.5 months in does not help. My guess for April would be tax return time since we do our own taxes and e-file we get it in under 5 days. If I am lucky again my end of year bonus of $1700 will get us to where we could do both the CC and the 48v upgrade. But I am demanding lightning arrestors installed. If I read right we would need 4 one at each end of the array and one on AC in and DC out.

Masterjoe · September 2015

Photowhit said:

Hi Masterjoe, I'm not sure what you expected from your solar setup.
There are so many wrong things going on in this thread.
A hybrid system is designed for maximum reliability, NOT to save money. The battery bank is a backup, not intended for regular use, some regular use is good for the bank but not it's intended purpose!
12 - 6 volt 390 ah batteries creates a battery bank of 3 strings of 4 - 6 volts batteries, so each string has 24 volts at 390 ah, 3 strings in parallel makes a 3 x 390ah = 1170ah 24 volt battery bank.
A 24 volt battery banks resting voltage when full is @ 25.4-25.6 volts, nothing wrong with 25.7 at night (this might be the wrong figure, but something in that range)
First, I don't think he's the "sharpest stick in the woods" if you indicated you might switch to a 48 volt system, he should have had you, have a battery back up that could be configured as a 48 volt battery bank! No way to configure 12 - 6 volt batteries as a 48 volt bank. You do NOT add new batteries to old particularly if you are designing a system from scratch.
This is a hybrid system. The charge controller only needs to top off and maintain your batteries so that you can use them in an emergency. You appear to want to use them over night... Most modern charge controllers can handle being 'presented with more current than they can handle, they just don't use it. Your 1170 ah battery bank needs about 5% charging current to be maintained as a backup or about 60 Amps the array and single charge controller can do this with out a problem.
I don't know how the XW system works, if once charged the current from the array feeds the inverter to back feed the grid then, I would think you have the correct sizing of array to inverter, as others (Vic?) pointed out a 4500 watt array can typically produce 3375 watts so a 4000 watt inverter should not be over taxed.
As Bill has described it, the inverter works from the battery voltage, so an additional invert might well be needed. You might even consider a high voltage backfeeding inverter and split your array to that...
Really like to know what you had expected and what you were told, in terms of over all cost of electric

In terms of overall cost, it is yet to be determined what our bill will be. We have not had a full month running yet. But I was told 50-60% lower. As long as my wife can stop running the AC during the summer we ought to be able to best that. I just understood more in your post than I have so far listening to Charles lol.

MPPT 80 600 CC down

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