Case study for 2 GT systems with small battery banks.

SolaRevolution

I just recently replaced the old batteries in two grid-tied systems.
The banks were both Deka VRLA group 31 (98ah, 12volt).

One system was 10 years old +/- 4kw PV, a SW5548 (which floated constantly) and two c40 PWM chage controllers (replaced with one FM80 about two years ago) with 8 batteries (2 strings of 4). They were doorstops. Dead. Who ever put in the FM80 did not check the battery health.

The other system was about 8 years old +/- 3.2kw, an Outback GVFX3648 with an MX60 cc and 4 batteries. From what I could gather, they were causing the charger to cycle and frequently dissable the CC.

Fortunately both systems had temp comp sensors. I'd hate to think what could have happened to the constantly floating "doorstops" without.
Both clients wanted similar replacements. They had been told up front that they should expect to need to replace the batteries about every 5 years. A power outtage with no back up finally motivated them. They said they only have one or two utility interruptions in a year and neither could remember for sure when the last one was before the failure. When comparing notes it was found that both had seen their utility bills increasing over the last year or so. They called the original installer who no longer does battery systems and were referred to me.

I asked if thy would want to go bigger with the replacements. They both said they are happy with the back-up they had (when the batteries were good). They both have a few lights and outlets, home offices, garage door openers, one kitchen counter circuit.

So,
The first system had 200ah@48v with 4kw of PV.
The second had 100ah @ 48v with 3.2kw of PV.

Both lasted a bit longer than the original 5 year design. Of course I doubt they were of much use over the last 2-3 years.

Alex Aragon

Cariboocoot

Re: Case study for 2 GT systems with small battery banks.

What did you replace the doorstops with?
I'd be tempted to up the Amp hour capacity, especially if larger batteries were a better price per.

SolaRevolution

Re: Case study for 2 GT systems with small battery banks.

Cariboocoot wrote: »

What did you replace the doorstops with?
I'd be tempted to up the Amp hour capacity, especially if larger batteries were a better price per.

Fullriver DC115-12 AGM Sealed (115 amp/hour, 12 volt) I've never used them before or since. This was last August when there was a brief shortage of batteries. (here in Nor Cal anyway)

They wanted to use the same deka MKs but it would have been a 4 day wait. The other limiting issues were the existing battery enclosures they were designed without much extra room.

Alex