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cptmiker
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# Posted: 10 Dec 2018 01:38pm
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Hello all New here just looking for a bit of help for my dad this question centers around solar panel to battery
how many watts of solar panels are needed to support 1800 amp hr of battery's
Setup=
16 TROJAN T-105 wired to make a 12volts system
3000 watt inverter 12v to 120v
15 100 watt solar panels output
Maximum Power: 100W Maximum System Voltage: 600V DC (UL)
Optimum Operating Voltage (Vmp): 18.9V Open-Circuit Voltage (Voc): 22.5V
Optimum Operating Current (Imp): 5.29A Short-Circuit Current (Isc): 5.75A
Weight: 16.5lbs Dimensions: 47.3 X 21.3 X 1.4 In
1 tristar ts60
1 tristar ts45
There are ancillary parts combiners breakers cutoffs surge and lightning arrestor
auto switch over for generator power.
Basic question is. is there enuff solar panels to maintain the battery assuming 50% or less discharge per day assuming good sun. or am i under powered with panels.
Thanks
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Atlincabin
Member
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# Posted: 11 Dec 2018 11:02am
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What you really need to do is figure your usage per day (watt-hours) and your solar input per day (also in watt-hours and will depend on your location - Arizona is very different from Seattle, for example - use the online program PVWatts to get started) and they should match fairly closely. If that is the case, then the panels will, on average, cover your usage. Of course, the point of batteries is to be able to run stuff when the sun is not shining, so the other calculation you need is the comparison of battery capacity (in watt-hours) to your usage. Most folks will size their battery bank to provide for 3-4 days of no solar gain. Sounds like you have about 22kWh worth of total storage, so if you are willing to accept a 50% discharge (I prefer to stay above 80% when possible), that means 11kWh. Divide by 3 days gives you about 3.5 kWh/day. Will that be enough to run everything you need?
That's a real general description of what you need to know. There are a lot more details that go into designing a solar system with batteries. Lots of online resources to help with this, or find a local solar person.
I would go with a higher-voltage system (24 or 48V) which require smaller wire sizes and are more efficient. I would also go with larger panels, which are probably more cost-effective. Easy to find ~300W panels out there right now for fairly cheap.
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cptmiker
Member
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# Posted: 11 Dec 2018 02:09pm
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battery bank 16 t105 at 225amp hour each configure to 12v =1800amp hours
Battery
8 strings
225x8 = 1800x12 = 21,600 watt hours
total usage per day estimated at 2,766 watt hr per day
if Satellite box are left on 24/7 then usage would be 5,626 watt hr per day.
Solar panels are a total of 1,600 watt hr at 88.96amps x4hr per day average 6400 watt hr per day at 355.84 amps per 4 hour charge time
( note ) Seligman AZ is an average of 6hr per day good sun. so if I calculated by 6hr it would be 9600 watt hours at 533.76 amps for a 6 hour day. backup generator to run on low output days. and to run other high useage appliances like wash and dryer etc. they are never used without the generator.
""Assumes perfect condition and max output""
guessing loss of 20 % efficiency on average leaves
5120 watt hr per day harvest at 71.168 amp per hour at 4 hr per day
So I am not sure why going to 24 or 48v would be that much better aside from efficiency gains and significant cost of hardware. If money was no object I would gladly upgrade solar panels higher capacity battery's to reduce the strings. I'm not knocking anyone or anything and very much appreciate the feed back. But money is an issue to make conversion and I am trying to work with what I have. is this realy that bad. Is 4 to 4.5 years a reasonable time for battery's?
On a side note what would you recomend for a battery charger to run off the generator on bad days?
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creeky
Member
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# Posted: 11 Dec 2018 04:16pm
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Your 8 parallel strings of battery is not a really good idea. With lead 3 parallel strings is considered to be on the outside of good practice.
Also, the high amperage is going to mean a lot of spending on solar controllers. I see you have two. Going 48v and you can use just one.
48v equipment isn't that much more expensive. You really only need a slightly more expensive inverter. The savings on cables, fuses, etc will more than make up that difference. Like just one solar controller. Boom. You're already ahead dollar wise.
Larger panels are much cheaper per watt. Typically around .60/w now.
Also. You should gain close to 10% efficiency at 48v. What's 10% of your cost. Another 20% if you swap lead batteries for lithium.
Is this equipment you've already bought?
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cptmiker
Member
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# Posted: 11 Dec 2018 04:28pm
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All the equipment is already in place and have been for the last 15 or so years. the solar panels were replaced 2 years ago. the batteries just got replaced for the 3rd time. and the two new outback FM80 are installed but not connected yet.. Please remeber that everyone is talking about just buying more stuff. this is not an option at this point. Im trying to understand that with what i have why is it so bad. this system has been in use for just over 15 years and on its third set batterys.
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NorthRick
Member
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# Posted: 11 Dec 2018 05:21pm
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Quoting: cptmiker Basic question is. is there enuff solar panels to maintain the battery assuming 50% or less discharge per day assuming good sun. or am i under powered with panels.
To answer your original question, yes you are under paneled. You have 1,500 watts of panels. Ideally, you'd have around 2,100 or 2,200 watts of panels.
Quoting: cptmiker Im trying to understand that with what i have why is it so bad.
Atlincabin and Creeky pointed out some of the less than ideal aspects of your system.
For starters, you'd likely get more than 5yrs out of a set of batteries if you went to 48v and changed the battery bank configuration to two parallel strings of 8 in series. You would also extend battery life with more panels.
Some of the other stuff is safety. 3000 watts at 12 volts is 250 amps. That takes some thick wire to be safe and it is unlikely that the lugs on your inverter can even handle wire that size.
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cptmiker
Member
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# Posted: 11 Dec 2018 05:50pm
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I agree with the convertion to 24 or even 48 volts DC. Coverting the battery bank to 24volts I would drop from 1800 amp/h to 900. going to 48v woul half that again to 450amp hr. All wires on battery bank and to inverter ar 0 gauge wire with very heavy duty lugs on the wire. The inverter is rated at 250amp to lugs but there is no way I will ever get close to pulling that much power at any time. The goal here is to work with what I have. and every one seem to be missing that no offence to anyone. I will convert to 24v by the end of next year and add 1 more killowatt of panels to the system. since i will need more power converting to 24v to charge the battires. My goal is to work with what I have now.
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cptmiker
Member
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# Posted: 11 Dec 2018 05:56pm
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On a side note please understand I am getting about 4 to 4.5 years out of off the shelf 6v batteris from costo two sets of 16. this is the first time i am going with Trojan batterys. this is the third set in 15 years. So One would think 4 years from a cheap set of $70. each batteries is not bad for 4 to 4.5 years of use. in the setup i have now. so 15year cost of batteris is $4500.
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Atlincabin
Member
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# Posted: 11 Dec 2018 07:10pm
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Sounds like you're killing batteries too fast. That means you are drawing them too low, too often. Even cheap deep-cycle batteries should last 8-10 years if they are not cycled too deeply.
Creeky suggested lithium - I agree with that if/when you get a new set. More expensive per battery by a lot, but they last longer (a lot), and you can draw them down further without damage.
All that said, working with what you have, my suggestion would be more panels so that you don't overdraw the batteries, that is, you keep them closer to topped up.
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cptmiker
Member
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# Posted: 11 Dec 2018 07:23pm
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So based on my calculation as follows
1600amp/h 12v battery bank is 22k watts of power
Drawing 5,626 watts per day
Just found out they use there cable boxes 10hr a day. so i added the power.
drawing 26 percent of the batterys capacity per day.
Charge capacity per day on a good day.
5120 watt hr per day harvest based on 4hr day less 20% efficancy
So just under what i need to recharge the batties. on a daily bassis. So more POWER Muhhaaa. and more MONEY $$$$$$$$
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