Would like to add more batteries

Wilis · September 2009

Hi,
Just setup a solar system last month. Was designed by Dave Ext. 105 NAWS. I have 4 Kyocera's 210, FM80, Magnum MS-4024AE, TM2020 to monitor batteries and 8 T105 plus batteries running 4 serial and 2 strings parallel for a 24v system. Can run a 2Kw load and have backup for my 240v 9amp water pump if needed. I do have a 4KW gen that will do what the solar does but need gas to run. May have ice storm here in Tennessee about every other year and will loose power for 3 or more days. Have about 2 day of running my freezer 24/7 and not use more then 80% battery. I can run my refrigerator on a sunny day and still fully charge my batteries each day. I did have a rainy week that I had to used the Magnum, through the grid, to keep the batteries up. Because we pay less then 9 cent per KW for power from TVA, it will take longer then I will live to reach payback, but have learned so much with this project it is worth it. Now for the question??? I want to double my battery bank and would like to stay with the T105's. I have been able to get them for a good price. I already have two serial lines running in parallel. Can I just add two more serial lines? That would make four. I will also double my PV panels. What trouble will I have with four serial line running in parallel? Is there a better way to do this, short of starting over with different batteries. Thanks for the forum. I have been reading every post and will get through them all someday. Ha Ha Good information for everyone, not just the new starters. You can see what I have done at: http://solar-by-wil.webs.com/ Thanks again for all the help I have received from the forum. Wil

Cariboocoot · September 2009

Re: Would like to add more batteries

Some basic battery configuration info:

Batteries in serial (+ to -) adds voltage, Amp/hrs stay the same.
Batteries in parallel (+ to +) adds Amp/hrs, voltage stays the same.

Right now you have (4) 6V 225 A/hr in series to give 24V times 2 to give 450 Amp/hrs. Eight batteries total.
That battery bank (a collection of batteries wired together to operate as a single power source) requires a certain minimum charge current to maintain its capacity as best it can, regardless of loads.

The load question is one of how long you can run it, now how big of a load. The maximum load size is determined by the inverter: 4000 Watts.

Yes you could add more batteries in parallel, but you start running into issues. First of all, do you have enough solar panel to charge an additional 225 A/hrs? (4) 210 panels = 840 Watts, but how much they average out is another issue. It's usually around 70% or 588 Watts. Divide this by 24 and you get a maximum charge current of 24.5 Amps, which is just over 5% of the capacity of your current bank - the minimum recommendation for proper recharging. From panel charging alone you haven't got enough to handle another 225 A/hrs, let alone another 450.

And there is the issue of wiring multiple banks together so that the current flows evenly in and out of all batteries. It can get very complicated.

If you want to add more batteries anyway, the best choice I think (others may differ) would be to have an entirely separate 'B' bank connected to the inverter & charger via a battery switch. Then if you have surplus solar you can switch to the second bank and keep them both up. Ideally you'd have a second battery meter as well, so you could keep track of each bank in terms of charging/depletion.

Wilis · September 2009

Re: Would like to add more batteries

Thanks Cariboocoot,

Just what I was looking for. It looks like I may add 4 more batteries, one more series string and 4 more PV. That should get my amps higher and keep everything charged. I can charge my batteries from the grid through the inverter if I have to until I get everything set up. I know that is not a way to save electricty but I dont want to kill my first set of batteries. I dont have to use the solar if I dont want to but is nice to have it for backup. I have made buss bars to connect my batteries so everyting is the same length and as close as possible in resistance in the battery box and going to the E-panel. I have wired houses for years and was a tech on 1200 Dell computers before I retired but the solar has a lot of new math. I will learn more as I go. If I was looking for a new job I sure would look into solar. The forum is a great help for new people and will help others get into solar. Thanks Wil

niel · September 2009

Re: Would like to add more batteries

in addition to agreeing with cariboocoot i'll add 2 comments. 1 is i hope you have a series/parallel arrangement for the pvs as all in parallel will not supply enough voltage to the controller to charge the batteries. (maybe it was mentioned?) 2 is you should consider raising the pvs higher as winter snow accumulations will build up at the base of the pvs very quickly. whatever the ground accumulations are will have the added amounts of snow that slide off of the pvs at that point. from a rough guess i'd say a 4 inch snowfall on the ground plus it slides off the pvs is enough to reach the bottom pvs to start covering them. anchor them well against the winds too.

Wilis · September 2009

Re: Would like to add more batteries

Niel,

Yes my pv's are in series-parallel. The snow is not a problem here. If we get any snow it is only 1 or 2 inches and will melt in a day. Only in 1993 did we get 23 inches. Ice is a much bigger problem. My next 4 pv's I would like to pole mount. So far I think I have not made to many big mistakes on this system. The help from NAWS has been great. They were limited by what I was asking for in a system. Like most new comers I had big ideas what a little solar would do. Now I have stated using it I realize it takes a lot more equipment to do what the grid does everyday. Over and over I read on the posts what people want to do and I am learning solar is new to many. I will be calling my local community college to see if they would not have an adult class on basic solar. I have had so many people ask me about what they could do with solar. It is like the blind leading the blind. Thanks again for what the forums are doing. I am sure I will have more question soon. Wil

westbranch · September 2009

Re: Would like to add more batteries

to add to what 'Coot and Niel have said, you could also look at splitting your loads, by bank, to keep both banks from going too low.. ie have one bank just for the fridge or ? and all the rest on the original circuit...

HTH
Eric

Would like to add more batteries

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