Announcement

Collapse
No announcement yet.

Proposed off-grid design attached - would love your input

Collapse
X
  • Filter
  • Time
  • Show
Clear All
new posts

  • #16
    Originally posted by max2k View Post

    unless OP has very limited space / runs his system upside down or his cabin is up in the mountains I don't see rational reason to use AGMs here: for the same price he could get double capacity FLA and not only meet current requirements but also have double autonomy time + increased cycle life. The temperature over there never reaches freezing point.
    "Infrequent visits" as written in the first post could be a rational reason to use AGM's, if there isn't opportunity for the FLA to be properly maintained. At that size and capacity, the OP might also have been looking at UPS batteries, in which case those visits would need to be *really* infrequent for it not to be a regrettable choice.
    CS6P-260P/SE3000 - http://tiny.cc/ed5ozx

    Comment


    • #17
      Hey guys, good point about specifying the battery type. Both partially correct: I'm actually building two identical solar off-grid systems (to the specs posted in the OP). One, for the bush retreat, and one for my brother's daily use on his farm.

      The bush retreat version, I messed up and bought some used AGMs. So, sensij you are correct that these will be used very infrequently at the bush property, and hopefully will last a year or so! (We pay to learn sometimes don't we. These were likely old UPS batteries - yep, I fell for that n00b trap).

      The second setup, for my brother, we need to use reliable batteries that have a high life cycle. This is where I get confused, as I see many types of AGMs advertised for 'solar', but some clearly only have about 300 cycles (so that would mean replacing annually, wouldn't it?) That's a lot of money each year. Flooded, I know nothing about, but might have to look into for the daily-use setup.

      Comment


      • #18
        Originally posted by tombarton View Post
        Hey guys, good point about specifying the battery type. Both partially correct: I'm actually building two identical solar off-grid systems (to the specs posted in the OP). One, for the bush retreat, and one for my brother's daily use on his farm.

        The bush retreat version, I messed up and bought some used AGMs. So, sensij you are correct that these will be used very infrequently at the bush property, and hopefully will last a year or so! (We pay to learn sometimes don't we. These were likely old UPS batteries - yep, I fell for that n00b trap).

        The second setup, for my brother, we need to use reliable batteries that have a high life cycle. This is where I get confused, as I see many types of AGMs advertised for 'solar', but some clearly only have about 300 cycles (so that would mean replacing annually, wouldn't it?) That's a lot of money each year. Flooded, I know nothing about, but might have to look into for the daily-use setup.
        there are LFP prismatic cells now available from China- take a look there as well, might be a good solution for your brother system. Please note LFP have 3.0V per cell vs 2.0V Lead-Acid meaning to compare apples to apples between different chemistries one needs to compare energy stored (capacity x voltage = Wh) and not just capacities. If I was building off grid system myself I'd go with LFP atm: weight / low self discharge / virtually no maintenance / extended cycle life / high charge-discharge rates approaching 1C / not explosive as other Li based types/ ability to utilize capacity better without shortening battery life (can tolerate down to 20% SOC). That is of course if you will be running it daily. If it is just for infrequent visits then Lead Acid would probably be still better due to lower cost. For daily use LFP would be more cost efficient over life span of the batteries at the current prices.
        Last edited by max2k; 09-13-2017, 12:07 AM.

        Comment


        • #19
          I would suggest Flooded lead acid batteries for the daily farm use. It may take a while to learn to use them and flooded is fairly cheap and forgiving. Maintainance is adding water every 2 weeks, till you learn the routine, and then it's maybe every 3-5 weeks.

          LFP is expensive and very easy to mis-configure and ruin or light them on fire.

          AGM is expensive, and slight overcharge can vent fluid & capacity. and not a good choice for a beginner bank.
          Powerfab top of pole PV mount (2) | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
          || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
          || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

          solar: http://tinyurl.com/LMR-Solar
          gen: http://tinyurl.com/LMR-Lister

          Comment


          • #20
            Originally posted by Mike90250 View Post
            ...

            LFP is expensive and very easy to mis-configure and ruin or light them on fire...
            Expensive is relative term- when you account for higher voltage, deeper cycle (and consequently less Ah required) and longer cycle life LFP come out cheaper:
            6V 225ah T105 costs about $200. 100Ah LFP cells are sold at around $100 and only 2 are required for 6V so even initial price is close. If you take into account longer cycle life it becomes no contest.

            I'm curious for the source of setting LFP on fire- everywhere I read these are considered pretty fire safe batteries and fairly tolerant to abuse: "The LiFePO4 batteries are the safest type of Lithium batteries as they will not overheat, and even if punctured they will not catch on fire. The cathode material in LiFePO4 batteries is not hazardous, and so poses no negative health hazards or environmental hazards. Due to the oxygen being bonded tightly to the molecule, there is no danger of the battery erupting into flames like there is with Lithium-Ion." from ttps://www.batterystuff.com/kb/articles/battery-articles/lithium-battery-overview.html
            and many other places. I found this on EV forum and I'd say yes, it could be considered higher fire hazard than FLA but OTOH it was way out of normal use:
            • Shorted the 2 battery output cables during manufacture (seen it twice)
            • Two shorts to chassis, completing the circuit (seen it once)
            • Loose battery connection, arching, nearby combustible materials catch on fire, heat pops the LiFePO4 cells (seen it once)
            • Outboard charger left on overnight, no BMS control (seen it once)
            • Boat captain connecting over-discharged and damaged Li-ion batteries in parallel to fully charged ones (seen it once)
            • On purpose, for testing

            Last edited by max2k; 09-13-2017, 01:28 PM.

            Comment


            • #21
              I have seen 2 LFP systems BBQ'd in the last 6 months, but the pics are not mine to publish.

              I've worked with high power electronics for years, and there are more ways then you can believe for things to go sideways.
              Add a neophyte and a DIY system and someone will be learning an expensive lesson when they practice configuring the charge controller on a LFP bank, Oh - you're supposed to do it that way ?
              Like a chainsaw is perfectly safe, until it isn't.

              more reading about your "safe battery"
              https://www.ncbi.nlm.nih.gov/pubmed/25714114 Just as bad as NMC in an EV test,

              Schneider has pics of 2 burnt commercial systems in this pic: I'm sure there is more to be found. Li-IonFires.png
              Last edited by Mike90250; 09-14-2017, 02:32 AM.
              Powerfab top of pole PV mount (2) | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
              || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
              || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

              solar: http://tinyurl.com/LMR-Solar
              gen: http://tinyurl.com/LMR-Lister

              Comment


              • #22
                Originally posted by Mike90250 View Post
                I have seen 2 LFP systems BBQ'd in the last 6 months, but the pics are not mine to publish.
                can you give overall details- what was the reason and how bad was the damage?

                Originally posted by Mike90250 View Post
                I've worked with high power electronics for years, and there are more ways then you can believe for things to go sideways.
                Add a neophyte and a DIY system and someone will be learning an expensive lesson when they practice configuring the charge controller on a LFP bank, Oh - you're supposed to do it that way ?
                Like a chainsaw is perfectly safe, until it isn't.

                more reading about your "safe battery"
                https://www.ncbi.nlm.nih.gov/pubmed/25714114 Just as bad as NMC in an EV test,
                read the article- interesting but a little off for house systems- they were burning batteries with external fire trying to measure amount of toxic HF produced. This is only applicable when there's fire very close to the bank. They were trying to study what would happen in an accident involving EV and fire.

                LFPs often produce unexpected bursts of energy due to their extremely low input resistance (fraction of mOhm) which leads to extremely high currents both inside and outside the battery in case of short circuiting it. Sort of self inflicted problem- if it had higher resistance such currents wouldn't be possible. External load of 1 mOhm would cause 3000 A and 9kW power draw from single LFP cell most likely melting in the process but it is hardly LFP fault.

                I think I see your point - in case of complete newbie such energy source even perfectly safe under normal operational conditions becomes dangerous object due to amount of energy stored if nothing else. I was more after intrinsic dangers like cells catching fire because of internal manufacturing defects which you can't really do much about. It looks to me LFP are safe in that sense.


                Comment


                • #23
                  > can you give overall details- what was the reason and how bad was the damage?

                  Both banks were made in-house by a local vendor, sold as a "turn key" system to an unsuspecting, non-technical owner. It's likely the vendor did not set hi & lo setpoints properly, the BMS was cheap and maybe failed. If the innards of the "magic box" are set properly, it should safeguard itself against stupid owners, but these 2 didn't,
                  Both banks were totally destroyed, a burnt out shell. One was in a concrete block well house and melted all the plumbing and wiring, & roof. Other was hanging on a tree (all the power gear was outside but dry) and burned, Power in house went out, and he came out and saw the stuff burning and yanked it into the driveway.
                  I don't know if the FD ever connected the 2 incidents
                  Powerfab top of pole PV mount (2) | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
                  || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
                  || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

                  solar: http://tinyurl.com/LMR-Solar
                  gen: http://tinyurl.com/LMR-Lister

                  Comment


                  • #24
                    Originally posted by Mike90250 View Post
                    > can you give overall details- what was the reason and how bad was the damage?

                    Both banks were made in-house by a local vendor, sold as a "turn key" system to an unsuspecting, non-technical owner. It's likely the vendor did not set hi & lo setpoints properly, the BMS was cheap and maybe failed. If the innards of the "magic box" are set properly, it should safeguard itself against stupid owners, but these 2 didn't,
                    Both banks were totally destroyed, a burnt out shell. One was in a concrete block well house and melted all the plumbing and wiring, & roof. Other was hanging on a tree (all the power gear was outside but dry) and burned, Power in house went out, and he came out and saw the stuff burning and yanked it into the driveway.
                    I don't know if the FD ever connected the 2 incidents
                    OK, FLAs are clearly not capable of that and given such 'target market' no wonder LFPs are not favored. If it was me I'd have at least 2 independent systems watching the cells- BMS for what it does and completely separate very dumb threshold detector which would turn the current in case they were reached: BMS could simply have bugs or failed altogether and with amount of energy involved bad things are pretty much guaranteed. Laptop batteries using more dangerous Li-ion type eventually became more or less 'safe' power sources but you're correct end users cannot easily abuse them.

                    Comment


                    • #25
                      Originally posted by Mike90250 View Post
                      Other was hanging on a tree (all the power gear was outside but dry) and burned,
                      Love that.

                      "Well, Mr. Homeowner, the first sign that there might be a problem with your energy storage system is that it's hanging from a tree."

                      Comment


                      • #26
                        Originally posted by jflorey2 View Post
                        Love that.

                        "Well, Mr. Homeowner, the first sign that there might be a problem with your energy storage system is that it's hanging from a tree."
                        look at the bright side- vendor knew their equipment well and spared the house

                        Comment


                        • #27
                          Originally posted by max2k View Post

                          look at the bright side- vendor knew their equipment well and spared the house
                          Or, maybe, like a stomach that knows bad food, the house puked the batteries out.

                          Comment


                          • #28
                            max2k thanks for the info on Lifepo4 - it is really interesting, and something I'll absolutely investigate into the future once I have a bit more off-grid solar experience under my belt. Even for the dream DIY EV project one day. By then the price might be better too, though I can see they'd already pay their way and then some at current prices. I got a couple of Alibaba quotes for interest's sake: 8x 3.2V 120Ah Lifepo4 cells came in at about US$100 a piece. Pretty amazing really. Plus a few hundred USD to ship to OZ.

                            Mike90250 for some reason here in OZ it's less common to find FLA - my solar shop who've given me heaps of advice (and who I'll purchase through to support) stock AGMs, so that's what we'll go with for now. I found it difficult to compare FLA with AGMs, as the latter were far more common here. It could be that in my price range and Ah range (24v total @ 130Ah) there's not a lot of FLA around. I did see them at greater capacities. The only issue here will be making sure I disable equalising charges I think.

                            Comment

                            Working...
                            X