New Off Grid System - Please help me make a battery decision!

Re: New Off Grid System - Please help me make a battery decision!

Well, I ended up buying 8 blemished Deka 8L16s. These are supposedly brand new batteries. Only thing I could tell as far as blemish is the terminals are a little crooked. Couldn't pass up the price for what seems like a decent quality battery. $1200 for 8 including tax or about $137 each + tax. I will see how it goes once we get the solar panels installed in and possibly get 8 more if overnight DOD is too large. Hoping to get the hydro up and running next winter so maybe 8 L16s will be enough. Our creek is still running strong a week after the last rain and 6 days of sun so I think it's a solid power source. Also spoke to a few micro-hydro turbine vendors and they felt we have a good application. You can switch out the nozzles on the turbines as stream flow varies and realistic output for our head/flow seems to be in the range of 5-24kWHrs/day.

I have 8 8L16 370AH Deka’s and 10 205W panels. I use 60 – 100AH a night (3-5KWH). So I think that’s about 70-75%SOC give or take. IMO these batteries are hard to get to 100%SOC so I probably get them to 90 – 95%SOC most every day. We also use about 2-3KWH during the day. That’s 5 – 8KWH total each day.

My XW bulk and absorb voltage is set to 60.5V, the trimetric shows battery voltage of 49.5 with these settings. I have measured .3V drop @20Amps from all the cables combined. What I am getting at is that I have the voltage set high so my SG gets close to full.

Jeffkruse - thanks for the info. Has using the higher bulk & absorb caused any issues? What is the water usage like? Did you ask Deka about this?

The Deka spec linked below indicates charge voltage of 2.35VPC (56.4V) and float of 2.25V (54V).
http://www.mrsolar.com/pdf/MK_Battery/MK8L16.pdf

What do you have your equalize voltage set at?
How long, and how often do you equalize? The XW6048 can only equalize 1 hour max. I asked Xantrex if I can set it to longer than an hour and they said no but I could change the custom bulk/absorb voltages to equalize level temporarily to do a longer equalize. That seems kind of cheesy. Not sure why they don't just put in a timer option for the equalize button.

Just hooked up the new batteries and charging them now at 60.5V. For the next week or so no solar panels so want to make sure they don't discharge below 50% so trying to make sure the AGS is set up properly.

What is your inverter cut out voltage set at?

I know you said you have grid so not sure if you use a generator. Do you use the AGS (automatic generator start) ?
If so, and if you have the time, would be interested to know how you configured the following?

• Start DCV 30 sec
• Start DCV 15 min
• Start DCV 2 hr

Thanks!

Re: New Off Grid System - Please help me make a battery decision!

I should point out my numbers are based on blemished Deka batteries vs unblemished Surrettes. I was quoted $199 for a new Deka 8L16. Here is that comparison.

8 Deka L16 + tax = $1,739
8 Surrette L16 + tax = $2,613

And there is the time value of money aspect.
For the sake of argument, let's assume Dekas last 6 years, Surrette 12 years:
Deka price today = $1,739
Deka replacement bank year 6 @ 3% inflation = $1,739 * 1.03^6 = $2076
Total Deka price for 12 years = $3,815

Surrette price adjusted for Time Value of Money @ 8% Invested Interest
$2,613-$1,739 (Deka Yr 1) = $874 * 1.08^6 = $1,386 - $874 = $512 lost investment return
$2,613 + $512= $3,125 Surrette cost adjusted for time value of money at year 6

Surrette is $690 cheaper

Re: New Off Grid System - Please help me make a battery decision!

I want to know where you are likely to invest at ~8% (with any security) in the current environment? LOL!

True enough! 8% return is just about as likely or unlikely as counting on 12 years from a Surrette!

Really, that's the whole problem with trying to select a battery bank is none of the specifications are reliable. I don't recall ever having to make such a large purchase with so little reliable information. Ultimately I guess I chose my battery bank the same way I choose my cars. Choose a decent quality product with as little cash up front as possible and don't rely on the warranty.

My wife and I have owned probably 10 cars in the last 10 years between us. Nine of them were used cars over 5 years old. In 2000 I splurged and bought my wife a shiny new 2000 VW Beetle she dreamed of with a full "warranty". We paid more up front for the supposed security that a warranty and new vehicle offers. The car was in the dealer shop 21 times (no joke) before we sold it. Each time at the dealer was a painful multi-day ordeal, much more so than our private mechanic we've used for years who gets us in and out cheaply in hours anytime with no appointment and 1/3 the cost. The 21st issue was bad rear wheel bearings at 8k miles at 1.5 years old. VW said it was not covered under the 100k mile limited warranty as it was a "wear item". I argued to no avail that I have never had a car with worn out wheel bearings and my cars have mileage up to 160k miles. This car had 8k miles! Dealer wanted $2k to fix the bearings. Got it done for $700 at our mechanic and sold the car immediately at a $10k loss and bought a used Chevy with no warranty that we drove for 3 years with no major issues and sold for $1k less than we bought it. Haven't bought a new car since and probably never will again.

Anyways, I personally have no faith in limited warranties, no offense Surrette. Thus I went for the $137 blemished L16 with a decent reputation. I'd rather keep the cash in my pocket and save myself the frustration of an un-honored warranty.

But, if you have good luck with warranties the Surrette may be the right choice for you. It's clearly a high quality product with a good reputation.