solar setup advice

davo

Hello all would like some advice on my setup currently I have 4x 6v trojan batteries linked up to make 470 ah 12v bank to charge this I currently have 2x 100w 17v pv running through 30a pwm on a good day I see 9a from these bad winter days as little as .6a I need more power and would like to know what would be best for me,I have the option to buy 250w 30ish V Lg brand panels at less(£150.00) than it would cost me for two 100w 17v pv (£170.00) so my question is can I run 4x 100w panels through current pwm even if they are different brand or would it be better to buy 2 2ler50w lg panels and get a mppt charge controller?cos I can sell my current system to a friend for approx 150 so for only a little more than I would spend on 2x100w i could have 2x250w pv and 30a mppt charger I have found mppt controller on ebay for approx 50.00 howwver theres a voltage limit of 350 odd volts...dors this mean i couldnt put 2x250 watt panels through it? I am confused.com and any advice would really help me!hpp this all makes sense and apologies for typos I am typing on my phone!
Kind regards Dave

niel

Re: solar setup advice

welcome to the forum.
let's start off with the general requirement for a 470ah battery bank. it is usually about a 10% rate for trojans, but can vary a tad from that. that would mean 47a from the charging source. you will need far more than the smallish pvs you've already bought and even staying with that type of pv you would most likely need to upgrade the current capacity of the controller be it pwm or mppt. to go with the present day high wattage bargain pvs with 60 cells you would certainly need an mppt cc as the voltage would otherwise not be well suited for a pwm type.

a rough calculation for the pv wattage might be the battery ah divided 10 divided by .77 times the battery voltage for stc pv watts. your proposed 500w in pv would be 500w/12vx.77/470ah=6.8% which might be doable during the summer months, but winter would be a problem. most likely 3 of the 250w pvs for 750w total in stc would be more accommodating for your battery bank by the ideal 10% charge rate, but again, winter will be low. 750w/12vx.77/470ah=10.2%. you could up this to 4 of those pvs for better winter coverage. this is a bit on the high side for summer, but giving more maintenance will certainly allow this to work out.
1000w/12vx.77/470ah=13.65%.

as i stated the higher wattages means a higher capacity on the controller. many 60a mppt controllers are limited to about 60ax12v=720w. an 80a cc will be 80ax12v=960w and 1000w in pv may be ok to use with an occasional maxing out on the controller. probably the midnite classic 150 would insure full capacity with 1 controller at 12v.
hope this helps you.

Cariboocoot

Re: solar setup advice

Another detail to add to what Niel said: those 250 Watt panels are likely to be 30 Vmp, which means you will not be able to realize their full power potential without an MPPT type charge controller.

If you've been running that 470 Amp hour bank for very long with only 9 Amps of power for charging it could be damaged. You need to check the specific gravity of every cell, recharge it from some source capable of 40-50 Amps, and see if you can still get full SG on each.

davo

Re: solar setup advice

Ok thanks for the advice really helpful,does it make a difference that they rarely go down?I use 12v 35w 2.6amp for 6 hours and 8x 1w leds would it make more sense to halve the bank ? Its a new bank as before I had approx 200amp of random batteries and lost charge quickly so replaced

niel

Re: solar setup advice

ok, now you've succeeded in losing me. what rarely goes down?

"I use 12v 35w 2.6amp for 6 hours and 8x 1w leds"
ok are these both loads? if so then how long on the other one?
assuming 35w x 6hrs = 210wh
assuming 8w x 6hrs = 48wh
total is 258wh
258wh/12v=21.5ah used in a 24hr period. this represents about 4.6% of the capacity. that's more than 10 days autonomy to 50% of battery capacity. a smaller battery bank would've been fine unless you plan on expansions for more loads later. the pv requirements were for the capacity of the battery you have and will easily do for your stated loads as 500w-1000w of pv is by far overkill for the loads.

generally it is a good idea to size your loads (possible future expansion and extra days of autonomy as well) and then the batteries to match. after that the pvs and method of feeding to the batteries by either pwm or mppt.

Cariboocoot

Re: solar setup advice

I have to say this sounds like a classic case of too much battery. Only discharging them a very small amount and having too little solar to fully recharge them from a deeper DOD means they 'float' at the top few percentile of capacity. This is a waste of money in batteries. Deep cycles actually should be discharged significantly and fully recharged both to keep them in best condition and get your $ out of them.

If your loads are that small you probably should have a smaller battery bank and cycle it deeper. The two 100 Watt panels you now have could provide about 400 to 500 Watt hours AC per day. You seem to be using less than 300 (like Niel, I'm confused about your usage info). You could use 100 Amp hours @ 12 Volts to provide this with 25% DOD (roughly: 25 Amp hours * 12 Volts = 300 Watt hours, not including losses).

If those are actually your needs the cheapest thing to do would be sell the batteries and buy a smaller one, rather than add panels and an expensive controller to handle them.