Helpful Info. What batteries to use for off grid power

[Arcticdude]

Before I bought my battery bank I did a lot of research on all the battery types available. Each one has it's pros and cons. So then I consulted with a couple of off grid solar electric engineers and asked their advice. They suggested that I go with flooded lead acid batteries for my system. They are a better choice for my situation where I depend on my system full time.
I optetd for 8 each Crown 6 volt 430 Ah batteries wired for 24 volt. Cost was around $2600.
They do require a little maintenance, but flooded lead acid batteries can tolerate a faster rate of charge/discharge, depth of discharge etc than sealed batteries can, I.e AGM, Gel etc. Flooded lead acid batteries tolerate heat better too.
With periodic maintenance it's possible to get 10 years out of a lead acid battery bank.

 

[DrHenley]

flooded lead acid batteries can tolerate a faster rate of charge/discharge, depth of discharge etc than sealed batteries can, I.e AGM, Gel etc. Flooded lead acid batteries tolerate heat better too.

It is true that non-sealed flooded batteries handle heat better because the electrolyte can be re-hydrated, while with sealed batteries it can't. My understanding is that AGMs have an excess of electrolyte to compensate for some venting at high temperatures, and that eventually if they are run hot they will get low. I suspect this is the cause of failure for AGMs rather than sulfation, which they are much less prone to than flooded.

But with regards to rate of charge/discharge and depth of discharge, AGMs cannot be lumped with other types of sealed batteries:
http://batteryuniversity.com/learn/article/absorbent_glass_mat_agm

AGM has very low internal resistance, is capable to deliver high currents on demand and offers a relatively long service life, even when deep cycled. AGM is maintenance free, provides good electrical reliability and is lighter than the flooded lead acid type. While regular lead acid batteries need a topping charge every six months to prevent the buildup of sulfation, AGM batteries are less prone to sulfation and can sit in storage for longer before a charge becomes necessary. The battery stands up well to low temperatures and has a low self-discharge.
The leading advantages of AGM are a charge that is up to five times faster than the flooded version, and the ability to deep cycle. AGM offers a depth-of-discharge of 80 percent; the flooded, on the other hand, is specified at 50 percent DoD to attain the same cycle life.​

 

[Digout]

The Telephone company I worked for, installed Pure Lead Positive Flooded Lead Acid Cells to run the exchanges/central offices during a power outage. The largest capacity we installed were 2V 3200AHr. Total Voltage was 48V

With regular maintenance they often had a life span of 15 years or more. Naturally they were also pretty expensive, and I can't recall pricing of them.

They were changing to AGM when I left but some brands of AGM had less than a 5 year life. That was expensive.

I inspected one installation of Nickel Iron batteries that needed refurbishment after 50 years service as the 150Kw Diesel starter battery at a TV transmitter site.

Cost was not a huge factor in the total scheme of things in the commercial environment.

 

[TexasFreedom]

One thing that nobody notices with Nickel Iron batteries is their inefficiencies. Don't get me wrong, I drool over their longevity. But when charging/discharging, you lose half your power. And the daily 'drain'.

 

[Digout]

One thing that nobody notices with Nickel Iron batteries is their inefficiencies. Don't get me wrong, I drool over their longevity. But when charging/discharging, you lose half your power. And the daily 'drain'.

Very true

 

[DrHenley]

That's the great thing about lithium-ion and AGM batteries, very low self discharge. Large lithium-ion batteries are getting close to being commercially viable to use as car batteries.

Does anyone know much about lithium iron phosphate batteries? (LiFePO4) They are technically a type of Lithium Ion battery. They seem to be more affordable than the more common Li-ion (LiCoO2) batteries. Supposedly safer, with even lower self-discharge but lower energy density. They seem to be commonly used in motorcycles and jet skis but not automobiles yet.

 

[MNwr786]

One of the biggest (and very often overlooked) off-grid electrical topics is the actual conservation of power. This is NOT a rant about shutting off the lights.

Most of the devices you use on a daily basis (besides the microwave oven) have internal circuitry to convert the outlet 110AC to low voltage DC, typically 12v. Flat screen tv's, laptops, the stereo... Much efficiency is lost by upconverting the 12v batteries to 110v via inverter just to let said device downconvert it right back to 12"ish" volts.

I know with the archetecture of current switchmode supplies that such conversions are fairly efficient, but the 20 or 30 percent adds up!

Its worth grabbing a volt meter and seeing what devices to which you can add a direct 12v power input (and feedback prevention diode).