What batteries should I buy?

[Trukinbear]

yeah, it depends on your situation and why you are trying to put in solar. I thought my situation (off the grid) was temporary and thought I could ease my way into solar using easily sourced locally and used stuff to cobble together a system - a big waste of time, and most importantly money. Once I realized my situation was permanent I realized that I can't cheap my way thru this - this is what it is, and it better last me for the rest of my days. Buy the best quality you can afford, to do otherwise is false economy.

 

[TRW]

yeah, it depends on your situation and why you are trying to put in solar. I thought my situation (off the grid) was temporary and thought I could ease my way into solar using easily sourced locally and used stuff to cobble together a system - a big waste of time, and most importantly money. Once I realized my situation was permanent I realized that I can't cheap my way thru this - this is what it is, and it better last me for the rest of my days. Buy the best quality you can afford, to do otherwise is false economy.

Thanks for that info, I am learning that batteries are not just batteries. I will spend what I need to, but I am getting an education before I do.

 

[Hedges]

If you can do grid-tie with net-metering, or grid-tie zero export, those are ways to dip your toes in solar.
Starting with the right equipment, either batteries can be added to the inverter later, or the grid-tie inverters can play nice with a battery inverter.

Batteries cost several times as much as PV, so should be avoided/minimized.

Truckinbear needed a battery based off-grid system so he has 2.25 times the battery capacity of my system (for no additional dollars) but needs to do some maintenance.

I selected what I did for no time spent on maintenance, but I expect it to last 10 years because it isn't likely to even be cycled 100 times. I will have spent about $3.57/kWh for power stored and retrieved from batteries. The purpose of my batteries is mostly to make the system function during the day, so PV --> AC --> appliances.

 

[Trukinbear]

Yeah, mine get cycled every day - 300Ah out and back in every day on average.

 

[TRW]

Thanks for the added information, I will continue to look at battery technology!

 

[TonyK]

I too am replacing my batteries and saw the Mighty Max brand at Lowes for a good price. No one answered this question in another thread so I'll ask it here. "Is Mighty Max ML a good brand of battery in your opinion?" Is it good or junk? I am considering it based solely on what I can afford now.

 

[snoobler]

I too am replacing my batteries and saw the Mighty Max brand at Lowes for a good price. No one answered this question in another thread so I'll ask it here. "Is Mighty Max ML a good brand of battery in your opinion?" Is it good or junk? I am considering it based solely on what I can afford now.

Assuming you mean:

12V 100AH SLA Battery - MightyMaxBattery

Buy now 12V 100AH SLA Battery. Mighty Max Battery is the name you can trust for all your SLA, AGM, LiFePO, and Power Sport batteries.

www.mightymaxbattery.com

They're cheap, and they likely don't cycle well. Not advertised as "deep cycle." They emphasize "power when you need it." They have a design life of 10 years - that's typical of UPS type batteries that aren't cycled regularly, but when they are, they can deliver a lot of current. They likely don't have good cycle life.

If these are all you can afford, read the data sheet and use absorption/float values at the lower end of the listed ranges. Try to discharge them to no lower than 80%.

 

[TonyK]

If these are all you can afford, read the data sheet and use absorption/float values at the lower end of the listed ranges. Try to discharge them to no lower than 80%.

My other option is using six 35AH Thunderbolt batteries from Harbor Freight instead. I'm told by the company that they are true deep cycle batteries made by Universal Battery, which I know nothing about but are supposedly good.

 

[TRW]

I have no idea on how batteries differ, but I have learned there is a bunch to learn. Is there a good source for me to understand things like why the car battery is not suitable for back up solar storage systems? What is deep cycle, what makes certain batteries better for this application?

 

[snoobler]

Battery University is a pretty good place to get general info on batteries. The more specialized or specific your need, the more you need to transition to manufacturer's spec sheets and recommendations vs. Battery University's guidelines.

 

[Hedges]

[

Is there a good source for me to understand things like why the car battery is not suitable for back up solar storage systems? What is deep cycle, what makes certain batteries better for this application?

You could start here:

List of battery types - Wikipedia

en.wikipedia.org

You'd be surprised at the programs where Wikipedia seemed to be the go-to source for engineering information.

 

[chrisski]

I really like battery university.

I am building my first system. This is going on my RV. The true cost is about four to eight times what I paid for the panels. That real cost that is including the battery bank, wires, cables, mounting brackets, monitoring devices, etc. I find a lot of people will tell you they paid some certain amount, but they left out the price of their trojan battery bank. Or the inverter they use to power their 110 VAC needs. Wire is not free neither.

I also had to temper my requirements. It’s not that the sun does not provide enough power to give me the same amount that I would get from a 50 amp shore jack, its that I run out of roof space to use to get the same amount of power. Actually probably would exceed the campsite space I’m given. So, I‘ve decided we can warch all the TV we want and keep the fan running all day, but we won’t be using solar to power our two A/C units when its 110 out. Actually not using solar to power A/C at all.

Designing this system really makes you conscious of how much energy you use.

 

[Delmar]

My other option is using six 35AH Thunderbolt batteries from Harbor Freight instead. I'm told by the company that they are true deep cycle batteries made by Universal Battery, which I know nothing about but are supposedly good.

So far I have three of them for two different UPS projects. The first one has been in service a couple of years (judging by the dust covering) and is still performing well.

 

[TRW]

Battery University is a pretty good place to get general info on batteries. The more specialized or specific your need, the more you need to transition to manufacturer's spec sheets and recommendations vs. Battery University's guidelines.

OK, I finally got around to looking at your recommended site, Battery University. It is overwhelming. Here is a question that I could not find an answer to. What is the best way to wire up batteries for a large off grid system, that will need a major current draw over night. Should a person go with 12 volt or 24 volt or 48 volt? The overnight draw will be 20 amps at 240 volt.

I will admit I have a bunch to learn yet, but that is something I don't understand.

 

[Trukinbear]

OK, I finally got around to looking at your recommended site, Battery University. It is overwhelming. Here is a question that I could not find an answer to. What is the best way to wire up batteries for a large off grid system, that will need a major current draw over night. Should a person go with 12 volt or 24 volt or 48 volt? The overnight draw will be 20 amps at 240 volt.

I will admit I have a bunch to learn yet, but that is something I don't understand.

Go with the highest voltage you can afford - your 20A@240V is 400A@12V or 100A@48V
My first system was 12V, a waste of time - nothing worked right until we went 48V.

 

[TRW]

Go with the highest voltage you can afford - your 20A@240V is 400A@12V or 100A@48V
My first system was 12V, a waste of time - nothing worked right until we went 48V.

Thanks, I had to assume that this was the way to go, but could not get that for sure from what I read. I understand your post also, it only makes sense. Having that said that, why have I not heard of anyone going with a higher voltage?

 

[Hedges]

Go with the highest voltage you can afford - your 20A@240V is 400A@12V or 100A@48V
My first system was 12V, a waste of time - nothing worked right until we went 48V.

And to continue the math, that's 4800W. Night could be 12 hours, so 57,600 Wh.

I think you should just buy an old submarine.



To put a number on it, consider using 2V AGM cells, so 28,800 Ah needed.
Here's a 1215 Ah battery, so you need 24 of them at 100% DoD (or more for shallower discharge)

Sun Xtender Solar Batteries - Photovoltaic Battery

The Sun Xtender Battery line consists of specialty lead-acid solar, photovoltaic batteries, and renewable energy storage batteries manufactured by Concorde Battery Corporation.

sunxtender.com

Sun Xtender PVX-12150HT AGM Sealed Deep Cycle Battery

Concorde Sun Xtender PVX-12150HT AGM Sealed Deep Cycle Battery

www.solar-electric.com

Conveniently, one series string will be exactly 48V. They can he had for $707 each, so the bank would only set you back $17k
Probably, though, you should discharge no more than 50%, so get 48 of them and wire for 24s2p. $34k, Kaching!

Sunny Island would handle that nicely, up to eight strings.

 

[Hedges]

Thanks, I had to assume that this was the way to go, but could not get that for sure from what I read. I understand your post also, it only makes sense. Having that said that, why have I not heard of anyone going with a higher voltage?

The inverters and charge controllers aren't so commonly available, at least for DIY.
Large UPS usually are - they just have high voltage strings of battery to power transistors directly driving the AC output.
Tesla PowerWall is high voltage.
Sunny Boy Storage uses 400V batteries. Up to three, 10 kWh batteries. Maybe 22 kWh are available now, last I looked.
So that might build a 66 kWh bank for you.

But for just 4800W, 20A 240V, that's in a range that lots of 48V inverters will support.
There are some 120/240V models (or if you're in the European market, 220V models)
Either one Sunny Island with a 120/240 transformer, drawing 100A from the battery, or two Sunny Island each drawing 50A from the battery. Well within their capability and it isn't that much current.

The only problem is lots of watt-hours, so many cells or large ones. The battery will either be made up of 2V lead-acid cells or 3.7V lithium cells. It doesn't really matter what voltage the inverter runs at, it's still the same number of cells. But if lithium, you need BMS to control each voltage, so lower voltage but more cells in parallel will be simpler.

 

[Picasso]

I went over to the higher voltage side of things more to make it easy down the road when I start plugging into EV packs in the same voltage range. Used EV packs is best bang for buck, keep it pack intact. For an all in one units at 400V this is about the cheapest way...... http://www.pomcube.com/netzero-plus-specs.html

see also https://evsiphon.com/products/3kw-setec-power-vehicle-to-load-v2l-system

 

[snoobler]

What in the name of all that is holy takes 40A @ 240VAC? Are you charging an EV at night? That's pretty insane. You realize it's likely buying an EV to charge another EV while you charge the EV that did the charging during the day.