Gel Batteries - why are they bad with solar?

[kfetty]

Hi,

We are seeking a battery backup system for our solar array of 36 panels which is a 8000 kWh system. In addition to joining this forum and reading the tutorial and other posts here on batteries, we contacted our local solar installer and asked for a quote which we received today. We did not request that a certain type of battery be used, this was just to get a first stab at how they would approach the project. They quoted a 4500W output backup system including battery enclosure, bypass switch and critical load subpanel. The batteries themselves would be 4 sealed maintenance-free 4D size batteries which would produce 4.4 kWh of usable energy storage. This kind of backup would mean shutting down at least 60% of our heating/cooling in the house (upstairs shut off) and using appliances sparingly.

The batteries are "GEL" batteries and have an expected battery life of 10-14 years. I realize that this forum is dead set against GEL batteries but I'm unable to ascertain exactly why that is. We currently have an automatic generator fueled by propane gas which kicks in when the power goes out. As we just got our solar array installed in December 2012, we are grid-tied for a minimum of 5 years in order to meet our obligation for the NYS tax credits.

We feel a battery backup system fueled by solar would be far more practical in case of protracted outages as propane may be difficult to obtain in an outage scenario. The system quoted by our installer would qualify for NYS and Federal tax credits. The quote total was $14,500 less tax credits of NYS and Fed gives a net cost of $6,500.

Any advice would be appreciated on this subject. We are just beginning our research of this subject and don't expect to install a battery backup system until Fall of 2013.

Thanks,
Karen

[Sunking]

Two very simple reasons. They are very sensitive to over charging.

They have to be charged at a slow rate in most cases of C/20 or less. That would be very rare in any solar application where charge rates are at C/12 and higher.. They also have to be charged at a lower voltage profile.

If over charged the gel electrolyte dries out and forms cracks and voids which is pernament damage. Those cracks and voids raise the battery internal resistance and lowers the capacity.

Lastly they are very expensive and do not last as long as good ole flooded lead acid batteries. There is no reason to use them. You can save money and get better performance with FLA.

[kfetty]

Thanks!

Thanks so much. Clear as can be. I will continue our search but also give feedback to our solar installer.

[inetdog]

Thanks so much. Clear as can be. I will continue our search but also give feedback to our solar installer.

There is at least one manufacturer that offers a special design of GEL battery for RE use and their specifications allow charge rates as high as or higher then the C/5 which is common for FLA batteries. It is not clear what they do differently to allow this, but since they seem to be standing behind their warranties, there must be something.
If your installer shows you manufacturer specifications showing high charging rates, then all you have to worry about are the different voltage profile and the cost.
The ability of GEL batteries, like AGM, to operate in all positions, etc. is just no significant advantage for RE applications, but is good for vehicles, particularly motorcycles, and for portable use.

[Sunking]

There is at least one manufacturer that offers a special design of GEL battery for RE use and their specifications allow charge rates as high as or higher then the C/5 which is common for FLA batteries. If your installer shows you manufacturer specifications showing high charging rates, then all you have to worry about are the different voltage profile and the cost.
The ability of GEL batteries, like AGM, to operate in all positions, etc. is just no significant advantage for RE applications, but is good for vehicles, particularly motorcycles, and for portable use.

I do not disagree. But here is the bottom line. If given the choice between AGM or Gel, AGM wins every time. If given the choice between AGM and FLA. FLA wins every time.

AGM is a niche application as they are considerably more expensive than FLA, but AGM is less than Gel. AGM or even Gel for that matter should only be used where unusual orientation is required like on their side, Extreme cold, extreme mobile applications, in very air tight containers ect where you can justify the cost and lower life cycle capacity.

[Naptown]

I do not disagree. But here is the bottom line. If given the choice between AGM or Gel, AGM wins every time. If given the choice between AGM and FLA. FLA wins every time.

AGM is a niche application as they are considerably more expensive than FLA, but AGM is less than Gel. AGM or even Gel for that matter should only be used where unusual orientation is required like on their side, Extreme cold, extreme mobile applications, in very air tight containers ect where you can justify the cost and lower life cycle capacity.

For back up life cycle is not really an issue. IMHO what is more of an issue is batteries that are out of sight out of mind which generally mean neglected.
Off gridders tend to be anal about battery maintenence as it is a very necessary thing to do.
So that being said my vote is for AGM batteries for back up applications. Not the highest cycle life but they will die of old age before being worn out (Well at least in this country some places not so much) You can slam them with a high charge current meaning a quicker recharge time. Those two attributes alone make them worthwhile.