Expand a 12v solar system

[Solarson]

18 months on and my small 12v solar system has been great, but now I need to expand it for full time living. The MT50 meter tells me 21kwh have been generated and 12kwh discharged in the first 20 days of October. I now want to consume an additional 1kw / day through an inverter for ac power. I'm looking at a Victron 1600w.

How do I expand my solar capacity and especially the battery bank?

Currently have:
2 x 235w pv's
40 amp MPPT - Tracer 4215BN
4 x 105ah 12v AGM batteries

Winter sun is 4 hours a day and I'm aiming for 4 or 5 days cover.

[Logan5]

I would not expand until your batteries start to show signs of diminished capacity. there are many choices for expansion, all of them expensive. IMHO the best one is to purchase 8 new t-105's and upgrade to 24v inverter.will give you double the daily capacity. you can not mix old batteries with the new ones.

[Solarson]

8 new t-105's and upgrade to 24v inverter will give you double the daily capacity

. New t-105's sounds good - they'd have to be agm as the battery bank is in the living area. 6v I'm assuming?

What would be the spec of the new charge controller and how would I convert from 24v to 12v for the current wired consumer network?

[Logan5]

sure AGM's if you don't mind them cost twice as much and last half as long. Why not build a battery box and save a grand.

[ButchDeal]

. New t-105's sounds good - they'd have to be agm as the battery bank is in the living area. 6v I'm assuming?

What would be the spec of the new charge controller and how would I convert from 24v to 12v for the current wired consumer network?

AGMs should be in a battery box as well. Any lead acid battery should be in a battery box that is vented to outside, to prevent contact with the conductors, contain any acid leak, and vent any hydrogen. Yes AGM is sealed but they can still leak if over charged.

A simple wooden sealed box, with plastic liner in the bottom and gravity vent is all that is needed.

[Solarson]

Hey Logan and Butch. Didn't realise AGM would halve the battery life or cause a health risk. Think I will have to reconsider and relocate the battery box outside. I can't vent from inside as floor is below ground level.

[Solarson]

If the battery box is outside that then I'd ideally need to locate the charge controller and inverter(s) in the cabin due to external build and access restrictions (built into rock, protected area). How far away can these be from the batteries?

[ButchDeal]

Hey Logan and Butch. Didn't realise AGM would halve the battery life or cause a health risk. Think I will have to reconsider and relocate the battery box outside. I can't vent from inside as floor is below ground level.

Why can't you vent from inside? mine is in the basement and vented out. Remember that Hydrogen rises so you need the vent higher than the batteries.

here is mine for reference, at the end of the album:

https://plus.google.com/u/0/photos/104762377056878727516/album/6112049346938017457

[Solarson]

" Hydrogen rises so you need the vent higher than the batteries." ...Butch.

Ah, when you said 'gravity fed' I mistakenly assumed the vent had to run lower than the case. Can it run vertically 8 feet to ground level then horizontally 3 feet to outside? I guess a rising slope through the wall would be good.

[ButchDeal]

yes as long as it is rising. you want a coper return tube inside it. The return is copper to conduct temperature back so that you don't get a thermal syphon going sucking hot air out of the box.
The return should go down to a few inches of the bottom and the main vent right at the top.
think of it as an upside down drain.

don't put any electronics in the box other than batteries and fuses.
no openings in the box above the lowest battery top (and seal them all as best as possible)

[Solarson]

Nice pics Butch. My cabin's footprint is smaller than the area of your pv's!

Can I combine the 2 cost saving ideas - Logan's wet batteries and Butch's externally vented internal battery box?

[ButchDeal]

yes the battery box will work for flooded batteries as well as AGM. For flooded I would paint the inside with some good exterior paint.

[Logan5]

next thing I would do is upgrade to 24v you are wasting a nice set of batteries, parallel wiring batteries to keep using an old junk 12v inverter.

[Solarson]

So that's eight 6v t-105's in a sealed externally vented box. Stepped up to 24v (series and parallel) , then into a charge controller. What's the spec for that?

I know an inverter can convert as required to ac but how do I get 12v dc for the legacy wired setup?

[Logan5]

I would work with and rewire the batteries you already have until they need replaced. you are not ready for new batteries, you have more learning to do.

[Solarson]

Learning is what I've been doing with my current system and reading these forums for a couple of years. Now I've hit a knowledge wall. If i said I'd spent a couple of hundred hours researching, it's not an exaggeration. Just looking for advice on how to upgrade to output another kilowatt a day with plenty of cloudy day storage. For all sorts of reasons (health, location, help, age, opportunity) I only have a small window to get a total upgrade done to see me through the rest of my retirement. If I need to replace all the current equipment, it's not an issue, as I can install the current system in another location. I just want to keep using the pv's and in-house 12v appliance wiring.

I appreciate the advice given so far - thanks - just looking for more to get it done.

[Sunking]

How do I expand my solar capacity and especially the battery bank?

Currently have:
2 x 235w pv's
40 amp MPPT - Tracer 4215BN
4 x 105ah 12v AGM batteries

Winter sun is 4 hours a day and I'm aiming for 4 or 5 days cover.

I am going to jump in here and rain on the parade.



Real simple, you cannot expand, you are already maxed out. You built yourself a trap, you are trapped inside a 12 volt toy box. At 12 volt with a 40 Amp Controller, 500 watt s is all there is. You are already at 470 watts, there is no place to go except 24 or 48 volts. But you trapped inside a 12 volt box, and that is where you went terrible wrong from the start.

Next your batteries are to old to expand. Last thing you want to do is have parallel batteries, and you did that 4 times because you are Trapped inside a 12 volt box. All you know is 12 volts. That is fine for RV's and Toys, has no place in a real home system. If you needed 420 AH batteries why did you not buy 420 AH batteries? I can tell you why, because you are stuck inside a 12 volt box and there are no 12 volt 420 Amp Hour batteries. But there are tons of 2, 4, and 6 volt 420 AH batteries.

So if you insist on using 12 volts there is only one possible way to expand. Buy a 80 Amp Controller, that will allow you to go up to 1000 watts maximum, and support your new 12 volt 800 AH that will self destruct in a short time if you parallel your batteries again. Avoid that by buying 2-volt 800 AH batteries and wire them in series for 12 volts.

Now if it were me and I was in your shoes, I would replace the batteries and reconfigure for 24 or 48 volts. At 24 volts with a 40 amp MPPT controller you can grow to 1000 watts and 48 volts up to 2000 watts.

Heck I bet you even wired your panels in parallel didn't you? Wrong, wire them in series even if you stay with 12 volts. But until you get out of that 12 volt box, you are going nowhere. You are stuck right where you are at. You cannot add any more panels because you are already maxed out on a 40 amp controller operating into a 12 volt battery. You cannot add any more batteries because you do not have enough panel wattage to support any more batteries, and even if you did last thing you want to do is add new batteries to old batteries.

So to expand you must move up in Battery voltage, replace the batteries, and add more panels.

Here is a crying towel to dry off with.

[Sunking]

As for the batteries gassing, well not sure where everyone is getting ventilation is a problem. It can be is you are abusing your batteries. Here is a small battery plant I built a few years ago in the lower basement of the Prudential Building in Boston. Only ventilation used is the buildings HVAC and the room is kept at 78 to 80 degrees. Only thing code requires is a Hydrogen Monitor. I have built around 50 large plants in many sky scrapper basements. In fact I can tell you every large high rise building has fairly large battery plants in every basement for the communication network. serving the building.

FWIW those are 2-volt 4000 AH cells. There are 48 batteries making two strings for a capacity of 48 volts @ 8000 AH or 384 Kwh capacity. Small for a telephone system.