Need Battery Bank Advice

[Lancelot1954]

I purchased the following Solar Panel system without batteries a number of years ago and am ready to get the batteries for this system. I am a total novice and would like advice on how much battery power would best match this system and the type of batteries. Also curious what other items I would need to be able to appropriately use this system without hurting the batteries by decharging them to much or any other monitor I should get.

8 - Kyocera 315 watt solar panel w/ MC4 cables. Vmp 39.8 VDC, Voc 49.2 VDC,Isc 8.5 A DC, Imp 7.92 A DC
Single 18' length XRS rail (17lb)
Kit, Mid Clamp F-G 2.50", Mill (4 pcs.)
Kit, End Clamp F 1.81", Mill (4 pcs.)
Kit, Adjustable L-Foot, Mill (4 pcs.)
XRS Splice Kit (one internal splice)
MC4 Solarline 2 (latching) extender cable # 10 AWG 15' Male/Female
MidNite Solar MNPV6 Array Combiner 6 Circuit
PV Array Breaker, 15 Amp 150 VDC DIN rail mount for Midnite or Outback Combiners.
Outback Power MPPT Charge Controller 80 amp 12-60VDC 150 VOC max. input 12v-1250 watts 24v-2500 watts 48v-5000 watts 60v-7500 watts 16.25" x 5.75" x 4”
E-Panel Gray steel chassis with 250 amp 125 VDC inverter breaker for Magnum Energy MS-4024AE
4000 watt 24 volt inverter/105 AMP PFC Charger/120V/240V Input/Output
Digital LCD Display Remote Panel w/50 ft cable

 

[GMB]

Depends on a lot of factors such as what devices/appliances you are running off the solar system, how many days per year is it sunny, how many hours per day is it sunny, how many days of autonomy you need for non sunny days, etc.

This is a good video to get you started. Also, purchase a Kill-A-Watt meter and figure out what devices and appliances you will be running off the system and note the number of watts per hour each device uses and calculate how many hours per day that device/appliance will be running to get a good 24 hour total of the amount of watt hours needed. Then times that number by the amount of days needed for when the sun isn't shinning.

Just for some rough math, your panels will produce about 315watts x 8 panels, x 5.5 hours of good sunlight = 13,860 watts per day. So if you had a battery bank of 13,860 watt hours, it would take the system the entire day to charge it up to full. Again, very rough math here, but hopefully you get the idea.

 

[Lancelot1954]

Thanks for your reply and have watched the video. I will certainly get a "Kill-A-Watt" meter. The problem I have is I can't necessarily say what devices I will be using for how long. So right or wrong I have to work on this backwards. What I am hoping is to get enough batteries to last over a few days if we have rainy or cloudy days. My plan is to have a monitor that tells me when the power level in the battery bank reaches the lowest level it should so I don't ruin the batteries. At that point I will turn off the power. For argument sake lets assume this is for an off grid survival location. So I want enough battery power to last a few days so its a swag for me and hope with this info I can get advice on battery bank size....Likely bigger than the 13,860 watts per day of battery power. Also curious advice on battery type. I think lithium are the best but quit expensive. Curious what lithium battery brands folks would recommend but also other battery types and brands that don't give off gas and have a pretty long cycle rate without being so touchy they are ruined due temperature or lowering battery level too much. Thanks for any help.

 

[Craig]

Well what would you hope to run at the "BUNKER" Lights, Fridge, freezer, stereo ,tv ,bitcoin mine..... This would help give a very rough Idea what you need. personally I could make 13kw last a week if I needed to.

if you did go with 280 AH EVE cells you would be looking at about $3000.00 for 16kw of stored energy give or take depending on where you get them


We run our whole house in the city on 10kw per day without any conservation

 

[GMB]

Lithium Iron Phosphate (LiFePO4) batteries are pretty great. It's what Will recommends and what I see on most higher level systems. They do have an issue with being charged below freezing, but this can be solved with an insulated enclosure, heating pad for the battery bank, adding a temp sense to the battery bank, using a BMS with a temp sensor, etc. Not sure what type of climate you are in so this may not be an issue at all for you.

There is also a device called a BMS (Battery Management System) that keeps the batteries from over-charging and over-discharging. They are about $70-200 per battery pack, depending on which one you decide to purchase and what features you are looking for in a BMS.

As far as LiFePO4 batteries being expensive - yes they can be. Depending on what you're idea of expensive is. I see your equipment list and you have some very nice gear already that is considered "expensive" to some, so we would really need a budget you have in mind to go off of. I purchased sixteen of the 280 amp hour LiFePO4 batteries from Xuba for $1882 delivered to my door in the USA. With these batteries, I made two 24 volt batteries that give me over 14,000 watt hours of storage. Another member here just posted his 32 cells he received from a different supplier and he paid $3335 for his cells. This gives him over 28,000 watt hours of storage.

My Deligreen LF280 28kW build

My order of 32 LF280 cells which I ordered from April Cao at Changsa Deligreen were dropped off this morning by Fedex. I placed the order on 8 May, it generated a tracking number on 18 May and the ship set sail on 18 May, arriving in the port of LA on 12 June. It took until 21 June for them to...

diysolarforum.com

This is a schematic of my system. Our systems are similar in size and nature so this may be of help to you. You could always double my battery bank and run four 24 volt batteries if needed or more. Or start with just 2 and expand if needed in the future as funds become available. But as stated earlier, it really just depends on the devices/appliances you are looking to use and for how long. Hope that helps.

 

[GMB]

I need to add one more thing. If you are looking to DIY your battery bank, this can save you many thousands of dollars. Again, for my battery bank I paid $1882. If I bought BattleBorn LiFePO4 batteries with the same capacity as my bank, it would cost me over $11,000. Now that $11,000 does get you a 10 year warranty and each battery already has a BMS installed so there is that. I chose to save myself $9000 and spend time learning to DIY instead. Figure I can destroy several battery banks and still come out ahead in the long run - worst case scenario...

But in the end, DIY batteries are really not that difficult. All the information is readily available and if you are installing your solar system, then you definitely have the skills to DIY a few battery banks together.

 

[Lancelot1954]

GBM, thanks a bunch for your reply and that helps a great deal in how things are connected and items you have in your system. Again, what I hope is get the best match of batteries for the system I have. I am leaning toward lithium and like the heating idea you had as well. So given I don't ruin the batteries because of charging under freezing, what I am planning is to work at this backward and adjust what ever power usage I need by the power consumption used. Given that I am thinking getting a battery bank with more than the 14,000 KW per day batteries so they can last over a few overcast days. Price rather depends but anything around $5K is acceptable.

 

[Kirk]

Remember that you might not want to keep lithium batteries in the same structure you sleep in. If they are "fire free" 99.999% of the time that's not good enough for sleeping. Check Will's comments on this.

So, assuming your batteries are going in another structure and you can afford a very slightly larger risk there are Nissan Leaf batteries harvested from wrecked cars that you can buy rather cheaply, singly and even if they are pre-assembled into 24V or 48V units, which you can very easily place in parallel for the capacity you'd like. You will still need to add various charging and temperature controls as needed. These are easy to use and very cheap for the watts you get. If you are a genuine cheapskate (like me) you could even buy a wrecked car from the insurance auctions and harvest them yourself. I wish I were younger and could do this but my heavy work years are behind me.

 

[Lancelot1954]

I need to add one more thing. If you are looking to DIY your battery bank, this can save you many thousands of dollars. Again, for my battery bank I paid $1882. If I bought BattleBorn LiFePO4 batteries with the same capacity as my bank, it would cost me over $11,000. Now that $11,000 does get you a 10 year warranty and each battery already has a BMS installed so there is that. I chose to save myself $9000 and spend time learning to DIY instead. Figure I can destroy several battery banks and still come out ahead in the long run - worst case scenario...

But in the end, DIY batteries are really not that difficult. All the information is readily available and if you are installing your solar system, then you definitely have the skills to DIY a few battery banks together.

I have 75-100 yards between my solar panels and my trailer. So is it better to have the solar panels by themselves with wires to the rest of the system beside the trailer or have everything including the batteries and inverter next to the solar panels and a wire to the trailer? From what I can tell I would at least want the inverter next to the trailer since my batteries will be a 24 volt setup like you have in your example.

 

[GMB]

The wires that go from the batteries to the inverter are typically much larger than the wires from the panels (or combiner box) to the charge controller. As you see in my example, I use 2/0 gauge wires from the batteries to the inverter. From the panels to the combiner box, I use 10 gauge, then from the combiner box to charge controller I use 6 gauge, both of which are much, much cheaper than 2/0 gauge wires.

There is a chart in the 'Resources' section on the forum that deals with the length of a wire and how much loss will occur over a distance to help you pick the right size wire for such a long wire run.