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Nickel Iron vs. Lead Acid - Off Grid battery debate

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  • Iron Bran
    replied
    Why C2?

    Ok, this is great b/c you definitely have a lot of experience with using different battery systems!

    [B]Have you ever seen / used a Nickel-Iron set or are you just basing your comments on your experience?
    [/B]
    What I don't understand is why you would require a C/2 charge level to charge ANY off-grid system??? If you are suggesting that you would need to charge the battery in 2 hours, that just doesn't seem reasonable for anyone.

    A C/2 charge rate assumes you are going to reach cutoff min voltage in only 2 hours. That is not the case either. Are you saying that nickel batteries must be charged at C/2 voltage... if so do you have a source on that (please, I would really like to see).

    Also, I am really hoping to hear your constructive reply. I know this is the internet, and you may find this hard to believe, but I am really not trying to argue. I just want to help clarify some issues. Thanks for your help.

    There are at least 3 different types of nickel-iron batteries for renewable energy systems, each with it's own charge / discharge characteristics. Check this out:

    According to different discharge requirements, Changhong pocket type Ni-Fe rechargeable batteries are classified into three types, TNG type (High discharge rate cells), TNZ (Medium discharge rate cells) and TN type (Low discharge rate cell).

    With more than 30 year

    Leave a comment:


  • Sunking
    replied
    I am aware of the variable charge efficiency with NiCd with the higher charge rates be the most efficient. High charge rates are desirable with things like electric vehicles, but are show stoppers for RE application. This gets back to why the Nickel chemistry are incompatible with RE system, in order to obtain high charge rates requires over sizing of solar panel wattage. Typically a RE system working with Lead Acid chemistry runs up to as high as C/10 charge rates. To get to say C/2 of a NiCd requires a 5 time large solar panel thus 5 times the cost. It would be a complete waste of resources and money. Such a system would never ever stand a chance of any kind of payback, nor would it offset any carbon. It would completely defeat the purpose.

    The other downfall of Nickel chemistry is cost which cannot be brought down to compete with Lead Acid and Lithium chemistry. Nickel is a semi-precious metal, and like gold or silver the price of it is likely not ever to come down enough to compete. Thus no one is going to be willing to pay 10 to 40 times more for Nickel chemistry. Not even the Electric Vehicle crowd will buy into it, not so much because of the price, but because of the LOW Energy Density where weight means everything.

    Leave a comment:


  • Iron Bran
    replied
    Thoughts on multiple charge efficency under different conditions

    Hey,

    I am very interested on your thoughts on different efficiencies at different charge levels.

    Here is a detailed writeup I found on charging, and I would like to hear what you think. Especially the 2nd paragraph. Granted, this is for NiCd but I just want to point out that efficiency is not exactly constant. Anyways amigo, check this out...

    To obtain a sufficient voltage drop, the charge rate must be 0.5C and higher. Lower than 0.5C charge rates produce a very shallow voltage decrease that is often difficult to measure, especially if the cells are slightly mismatched. In a battery pack that has mismatched cells, each cell reaches the full charge at a different time and the curve gets distorted. Failing to achieve a sufficient negative slope allows the fast-charge to continue, causing excessive heat buildup due to overcharge. Chargers using the NDV must include other charge-termination methods to provide safe charging under all conditions. Most chargers also observe the battery temperature.

    The charge efficiency factor of a standard NiCd is better on fast charge than slow charge. At a 1C charge rate, the typical charge efficiency is 1.1 or 91 percent. On an overnight slow charge (0.1C), the efficiency drops to 1.4 or 71 percent.

    At a rate of 1C, the charge time of a NiCd is slightly longer than 60 minutes (66 minutes at an assumed charge efficiency of 1.1). The charge time on a battery that is partially discharged or cannot hold full capacity due to memory or other degradation is shorter accordingly. At a 0.1C charge rate, the charge time of an empty NiCd is about 14 hours, which relates to the charge efficiency of 1.4.

    During the first 70 percent of the charge cycle, the charge efficiency of a NiCd battery is close to 100 percent. Almost all of the energy is absorbed and the battery remains cool. Currents of several times the C-rating can be applied to a NiCd battery designed for fast charging without causing heat build-up. Ultra-fast chargers use this unique phenomenon and charge a battery to the 70 percent charge level within a few minutes. The charge continues at a lower rate until the battery is fully charged.

    Once the 70 percent charge threshold is passed, the battery gradually loses ability to accept charge. The cells start to generate gases, the pressure rises and the temperature increases. The charge acceptance drops further as the battery reaches 80 and 90 percent SoC. Once full charge is reached, the battery goes into overcharge. In an attempt to gain a few extra capacity points, some chargers allow a measured amount of overcharge

    Leave a comment:


  • Sunking
    replied
    I do not think you will get many replies as NiFe are just unsuitable for RE applications. They are just too expensive, more than lithium, and extremely inefficient charge characteristics. I know of a couple of people who have toyed with the idea, but with a cost of $2 to $6/wh is just out of the question, plus 40% larger solar panel array to make up for the 65% charge efficiency just makes it unreasonable. Lead acid cost are $0.14/wh for a 10 year battery, and LFP is around $0.50/wh. No one in their right mind is going to pay 10 to 40 times more for a battery

    NiCd are pretty much history because of the cadmium and replaced with MiMh but still too expensive for for RE applications and require special charging algorithms which no manufacture makes a charge controller for. I do some some RC modelers using NiMh for planes and cars using solar panels to charge in th efeild, but they custom design/build there chargers from scratch

    For now and for the foreseeable future lead acid chemistry are king, and soon Lithium LFP may make their mark when prices come down some more and reasonable battery management systems enter the RE market.

    Leave a comment:


  • Iron Bran
    started a topic Nickel Iron vs. Lead Acid - Off Grid battery debate

    Nickel Iron vs. Lead Acid - Off Grid battery debate

    Hi everyone,

    I am interested in learning if you have any experience with non-traditional battery systems?

    Is anyone using ni-cad or nickel iron? I am looking into Nickel Iron (ni-fe), anyone currently using these?

    Thanks!
    Last edited by Mike90250; 09-20-2012, 07:26 PM. Reason: change battle -> debate
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