Hi Larry;
I agree, that in normal circumstances the battery will only be
discharged daily15 to 25%. I just completed some system modeling using
HOMER, and actually the battery is cycled to 80% many times a year
(approx. inverter shutdown), unless you have a generator, or load
reduction. The annual cycles seem to be a combination of light cycling,
and then in cloudy weather deep cycles.
The 80% number is just to be able to do an apples to apples comparison
at the worst case scenario. It also gives you an idea how a battery
behaves when you need it the most, after several days of cloudy weather,
and when it might not reach full charge again for awhile. If I can only
look at one cycle life #, I'd prefer the 80% rate than the 10%.
Here's an interesting study done by Sandia labs that tried to create a
more realistic cycle testing for solar. It used a combination of light
and heavy cycles. (Just what you were saying Larry)
http://www.cleanenergy.com.ph/projects/CBRED/TA%20RE%20Manufacturers%20Sub-Contract/Compendium%20of%20References/Solar%20References/Sandia%20Standards/PV%20battery%20cycle%20life%20test.pdf
R.Ray Walters
CTO, Solarray, Inc
Nabcep Certified PV Installer,
Licensed Master Electrician
Solar Design Engineer
303 505-8760
On 12/18/2013 3:37 PM, Larry Crutcher, Starlight Solar Power Systems wrote:
Ray,
To question 2: I find Rolls batteries to be outstanding. Our oldest banks are
over ten years now and trouble free. I can say the same about Crown CR-390
batteries if your doing comparisons. Can't say that about Trojan and defiantly
not Deka AGM's (run away!).
The 80% DoD thing is a poor way of measuring battery cycle life in RE systems.
If your only talking about floor scrubbers, sure, use 80%. But for RE purposes,
a 15% to 30% discharge is more realistic. Who discharges to 80% daily? More
importantly, who would design such a system? Perhaps 80% DoD is useful for some
but I sure wish we had a more realistic standard for the RE world.
(Did I vociferate?)
Larry
https://www.crownbattery.com/applications/renewable-energy-systems
On Dec 18, 2013, at 2:28 PM, Ray Walters <[email protected]> wrote:
Hi;
I was just doing some cost comparisons of different batteries for a customer.
I found that on Rolls website, they've apparently upgrade their cycle life of
the S5000 series to 2100 cycles (or more) at 80% DOD. It has been 1500 cycles
at 80% DOD for quite a while, so:
Question 1, what new technology is Rolls now employing in their batteries to
boost cycle life by 40% from before?
Question 2, are folks' real world experiences in line with that incredible "best in
the business" claim.
Question 3, at what rate of charge and discharge are cycle life tests normally
done. Can companies exaggerate their cycle life, by running the tests at 100 hr
discharge rate, for instance.
Question 4, Is there any independent confirmation/ testing being done?
Off List replies are fine, for those of you not wanting to publicly share your
experiences.
Thanks,
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