Safe + Inexpensive Battery(s) For MPP Solar 800W W/250W panels

[solarfather]

Hello,

I have a MPP Solar 800W SCC and Two 250W Santan Solar Panels. Specs for all below.

Goals: 1) Reduce home electricity usage during the day and 2) Have a grid down backup for day use

Problem: I need a battery so the system can work (it seems the 800W MPP solar requires a battery), I don't intent to run off the battery for power reserve if can be avoided, will be relying on the auto transfer switch to grid power when solar doesn't have enough power to keep the freezer going (sun down).

*In the 1% case where grid is down, I'm ok just using the solar during the day when sun is out for now. I may have other devices on the MPP solar, of course limiting to less than 800W.

Thoughts?

Thanks

Current System:


MPP Solar:
Electrical Specifications
Continuous Output 800W
Surge Rating 5 seconds max, 2X
Input Power Factor 0.8
Input Voltage Range 90~280VAC (Appliance mode), 170~280VAC (UPS mode)
Input/Output Frequency 50Hz / 60Hz
Output Voltage 230VAC±5%
Output Waveform Pure Sine Wave
Output Regulation < 3% RMS for battery voltage range
Peak Efficiency 90%
Nominal DC Voltage 12V
Max DC Voltage 15.5V
Transfer Time (2 Modes) <10ms (UPS mode), <20ms (Appliance mode)**
Charging Mode 3-stage
Bulk Voltage (Flooded, AMG/GEL) 14.6V/14.1V
Float Voltage 13.5V
Max AC Charging Current 20A
No Load Power Consumption <15W
Power Saving Consumption <5W

Solar Charger
Max PV Input / Output 500W
Max Charging Current 40A
Max PV Input Voc, MPPT Range 102V,15V~80V
Algorithm MPPT


Specs for Solar Panels (I have multiple but will use just 2 for this setup):
Specifications:
Rated Power: 250W
Open circuit voltage (VOC): 37.6 V
Max power voltage (VMP): 30.3 V
Short circuit current (ISC): 8.85 A
Max power current: 8.27 A
Power Tolerance 0/+3%
Maximum system voltage: 600V (UL)
Fuse Rating: 15 A

 

[MisterSandals]

I may have other devices on the MPP solar, of course limiting to less than 800W.

How long do you wish to run on battery power?
Using 800w since you provided it, if you wanted to run for 10 hours, it would require batteries...
800w/12v = 66.6amps x 10 hours = 666 amp hour battery x 2 = 1333ah
Using 2x multiplier because lead acid batteries should only be discharged 50%.

1333ah is quite a bit of battery(s).

 

[solarfather]

I don't plan on running battery much at all. Will be relying on ats

 

[solarfather]

AGM's are affordable, and can handle about 30% of their amp hour rating in panel wattage input (so one 100 amp hour AGM can take 300 watts in panels) so there is your minimum. Not less than 200 amp hour AGM to keep them from "over charge " voltage problems. Any more just adds power into the night. This is the battery I chose, its got good ratings, but don't drain them below 12 volt. (50% ) if you expect a long life out of them. I keep them in the house, climate controlled so I never suffer excess heat or cold and they perform like new 3 years in now. They do not off gas, are maintenance free, and are perfectly safe, I don't care what anyone sais ;P https://www.ebay.com/p/3033166895?iid=401742018311
I run 800 amp hours worth at 12 volt and have no problem with my ancient maytag frig running all night unless I use my gaming computer too long

Ah thank you! I was hoping for something even less expensive though, since I don't really intend to use the battery for any energy storage needs, just so I can use the Auto Transfer Switching feature of the MPP solar to pop back and forth from grid to solar daily.

 

[solarfather]

I know there is a huge fad now on LI, but These UB 121000 are really strong and reliable batteries, perfect for your application, and you can put them in your home, no off gassing, no maintenance, no spill, can stack in any position. Hook up and forget They are actually designed for low discharge without suffering too much damage, and can be charged to 15 volt and like it. When you do the math on LI, recommended full is 85-90% , and discharge not below 20% for max life. UB AGM 100% full charge to 50% discharge. So you get good power out of them because you don't have to stop charge at 90% like LI. AGM 50%, LI 65% recommended for max life,, is it really worth so much money? I say no, better technowlogy is coming down the pike as we speak for home storage capacity, don't need to pay for light weight.

Thanks, not necessarily comparing the Lithium, but just comparing to not using a battery at all, looking for the cheapest possible battery just to make the system work while switching back and forth from grid to solar. I don't know if a cheap $40 car battery can work? It is my understanding I should be able to set the battery level so that it is never discharged close to 50% life before switching to grid.

 

[solarfather]

Most automotive batteries are used to about 1000 watts coming in from your alternator at 12 volt, but don't have an real capacity, they charge quickly and discharge large "cranking amps". They are also know to "explode" under stressful situation, I have had it happen, its dangerous and terrifying, and fire did start. I DO NOT recommend you do this,, get a good deep cycle battery that can take a reasonable charge . (100 amp hour minimum)

Thanks, so this wouldn't be large enough even though I will be just bypassing to grid: https://www.amazon.com/ExpertPower-Rechargeable-Battery-EXP12330-Replaces/dp/B00KQX5FPQ/ref=sr_1_4