batteries for off-grid systems

[electro7]

I was wondering what type of batteries are best for off-grid systems? I have been told in the past that AGM batteries are best (for interactive with battery back-up systems), but have recently heard that wet cell lead acid are better/last longer, is this true?
How long can I tell my customer the batteries will last?
Also, are 6 volt batteries better to use than 12 volt batteries? or doesn't that matter?
Thanks for your thoughts ahead of time!

 

[GoldDigger]

For any given capacity (AH) AGM will cost more than Flooded Lead Acid (FLA). And will last maybe half as many cycles.
The "zero maintenance" aspect is offset by the fact that they are harder to monitor and therefore easier to damage without realizing it.
One factor where AGM shines is in faster recharge time because of the higher charging amperage allowed. This makes solar PV more possible in areas where there are only a few equivalent hours of sun per day.
Do not under any circumstances use GEL type sealed batteries, since they are easily damaged by high charge current.
Use either 12V, 6V or even 4V or 2V batteries as needed to allow you to get the AH capacity you need without having to put batteries in parallel. And choose the total bank voltage based on the maximum inverter power you will regularly need.
Dereckbc can give you very authoritative advice and may reccommend some other sites and resources.

Tapatalk!

 

[electro7]

Thanks GoldDigger! I have heard various opinions on what type of battery to use. It sounds like the FLA's are the way to go. Do you think it the same for grid-tie with battery back-up systems as well? I heard that in that case, since the batteries may not be used as much as an off-grid system, the agm will last longer- true?
Would love to hear from Derekbc and get some recommendations on other resources too.
Thanks again!

 

[GoldDigger]

Thanks GoldDigger! I have heard various opinions on what type of battery to use. It sounds like the FLA's are the way to go. Do you think it the same for grid-tie with battery back-up systems as well? I heard that in that case, since the batteries may not be used as much as an off-grid system, the agm will last longer- true?
Would love to hear from Derekbc and get some recommendations on other resources too.
Thanks again!

The AGMs will probably last longer than they would in deep cycle use, but so would FLA batteries in the same use and the FLAs can still be expected to outlast most AGMs in that service.

 

[electrofelon]

I was wondering what type of batteries are best for off-grid systems? I have been told in the past that AGM batteries are best (for interactive with battery back-up systems), but have recently heard that wet cell lead acid are better/last longer, is this true?
How long can I tell my customer the batteries will last?
Also, are 6 volt batteries better to use than 12 volt batteries? or doesn't that matter?
Thanks for your thoughts ahead of time!

I live off grid. I have only used l-16's and had good luck with then. I had some Deka's and now I have trojan l-16 REB's. There doesnt seem to be any free lunch with batteries - you get what you pay for. The Very best batteries are the HUP solar one and they will last many cycles and years, but they cost an arm and a leg too. I really dont think there is much difference in "cycles per dollar" .

My opinion is that with the low cost of PV now, this really changes how battery banks can/should be designed. I argue that the battery bank can be much smaller since it is affordable now to throw more PV at it to get charged on even a cloudy day. PV is cheaper than batteries now, so size with small battery bank and larger array.

 

[GoldDigger]

Just be careful that you do not try to put too much charging current into your bank during bulk charging stage.
Flooded batteries should not get a current higher than about C/8 where C is the amp-hour capacity of the bank.
If you need to recharge in just a couple of hours in winter, then AGM batteries which can accept C/4 may be necessary.

Tapatalk!

 

[electrofelon]

Just be careful that you do not try to put too much charging current into your bank during bulk charging stage.
Flooded batteries should not get a current higher than about C/8 where C is the amp-hour capacity of the bank.
If you need to recharge in just a couple of hours in winter, then AGM batteries which can accept C/4 may be necessary.

Tapatalk!

Yes I agree that can be a concern with my philosophy. I will be putting in 3250 watts soon and that will exceed the recommended charge rate of my small bank quite a bit. I will have a diversion system to domestic water heating to keep the charge rate in check.

 

[electrofelon]

Paradoxically, with a nice large array, you may never have a high charge rate issue because the bank will always be in absorption.

 

[GoldDigger]

It will also let you use really large time shiftable loads during the day.

Tapatalk!

 

[electrofelon]

Yes that is a big advantage too. I will be able run power tools right off the array when the sun is out which was one of my goals with this system upgrade. My place can get hot in the summer so I could run an air conditioner too. I would just need some sort of control so that it doesnt run off the batteries when it clouds over. Probably just a voltage controlled switch could handle that task.

 

[Besoeker]

My place can get hot in the summer so I could run an air conditioner too. I would just need some sort of control so that it doesnt run off the batteries when it clouds over.

If it doesn't run off the batteries what will it run off if you are not grid tied?
Or will it just not run at all?

 

[mgookin]

If it doesn't run off the batteries what will it run off if you are not grid tied?
Or will it just not run at all?

I think he means it will shut the a/c system down if it's drawing from the batteries.

We make a control for a group who sends solar systems to impoverished communities in Africa and it keeps a well pump from running off batteries at night. It only lets the well pump run a short time each side of solar noon when there's more power than they can store in the batteries. This way they don't need to spend money on batteries for that load. Their systems are packaged into conex containers. Open that conex and you have your panels, charger, batteries, a microwave oven and a well pump for potable water and for irrigation to grow food. There is no a/c.

 

[rogertaylorlive]

yeah, i have been using lead acid batteries and they are working really, i have purchased them 2 years ago and are running in a smooth conditions.