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  • lithium iron phosphate kit

    So, if i were to get a system up and running designed for off-grid using lithium iron phosphate, what specifically would i need?

    http://www.genasun.com/solarproducts.shtml
    I was thinking i would need 1 of these since they are specifically designed for lithium, but are there other options? they seem pricey compared to lead acid ones.

    System of atleast 1.2kw but not more than 1.5kw.

    Note, i dont think i want an inverter - i was thinking instead i would get appliances that run on DC like the refridgerator from sun frost energy.

  • #2
    Originally posted by muffildy View Post
    http://www.genasun.com/solarproducts.shtml
    I was thinking i would need 1 of these since they are specifically designed for lithium, but are there other options? they seem pricey compared to lead acid ones.
    Are you talking about controllers or batteries? The controllers for lithium are even simpler than the ones for lead acid and the price difference is insignificant. The reason they cost more because there is no demand for them yet because lithium batteries are very expensive.

    If you are talking the difference between lead acid and lithium batteries the price difference is huge. For lead acid batteries you are talking around 15 to 20-cents/watt hour of capacity. For LFP about $1/watt hour for good ones and up to $2/wh for really good ones. We are talking 500 to 2000% more for LFP.

    Originally posted by muffildy View Post
    System of atleast 1.2kw but not more than 1.5kw.

    Note, i dont think i want an inverter - i was thinking instead i would get appliances that run on DC like the refridgerator from sun frost energy.
    OK do not know if this has dawned on you but at 1.5 Kw dictates you run 24 volt battery. MPPT Controllers have maximum panel wattage input vs battery voltage. For example a 80 amp controller has the following panel wattage limitations

    1000 watts @ 12 volt
    2000 watts @ 24 volt
    4000 watts @ 48 volt

    Now you can run 1.5Kw @ 12 volts, but that means buying 2 expensive 60 amp controllers to serve a common 12 volt battery. FWIW 12 volt is very inefficient and really should not be used except in RV's, Boats or very small camping cabins.
    MSEE, PE

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    • #3
      system

      24v system is fine the sunfrost fridge model comes in that voltage possibility.
      batteries i know are going to cost way more than lead acid, but thats just considering up front cost - i think overall cost over the life of the system will be better with lithium because of the fact you can drain them 80% DoD and have a cycle life of 2000 to 70% capacity where as with lead you can usually only do 20% DoD and have a cycle life of 500-900 or so before the battery is dead.

      I was talking about the cost of the controller vs the cost of similar lead acid controllers. Midnite solar seems to offer basically the same 250vdc input 12-120vdc output but costs only 700$ or so instead of 1350$ for the genasun.

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      • #4
        Well you need to look at real deep cycle batteries like Rolls Surrette 5000 series. They come with 10 year warranties and have a cycle life of 5000 cycles @ 20% DOD or 3200 @ 50% DOD
        MSEE, PE

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        • #5
          battery

          not terrible interested in a rolls surrette, or any other lead acid. their efficiency is only 70% typically so i would need many more panels to support it.

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          • #6
            Originally posted by muffildy View Post
            not terrible interested in a rolls surrette, or any other lead acid. their efficiency is only 70% typically so i would need many more panels to support it.
            Same amount of panels - more batteries
            [SIGPIC][/SIGPIC]

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            • #7
              lithium or bust

              more batteries wont change the charge efficiency for the better
              lead acid at 90% SoC typically has a charge efficiency of 50%.
              i would have thought on a sub forum devoted to lithium ion i would have gotten more advice regarding lithium ion rather than lead acid...

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              • #8
                Originally posted by Sunking View Post
                Well you need to look at real deep cycle batteries like Rolls Surrette 5000 series. They come with 10 year warranties and have a cycle life of 5000 cycles @ 20% DOD or 3200 @ 50% DOD
                Not sure where you get that info but FLA is 80 to 90%, and AGM is 90%+. Perhaps you are thinking NiFe or NiCd. FWIW LFP is 80 - 90%
                MSEE, PE

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                • #9
                  http://photovoltaics.sandia.gov/docs...atpapsteve.pdf
                  lead acid = more panels needed
                  lithium charge efficiency is 90+%.

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                  • #10
                    Originally posted by muffildy View Post
                    http://photovoltaics.sandia.gov/docs...atpapsteve.pdf
                    lead acid = more panels needed
                    lithium charge efficiency is 90+%.
                    Very old outdated material that has been found to be incorrect and does not account for new battery manufacturing technology, and multi-stage charging algorithms used today. .

                    Allow me to point out an example of very flawed test apparatus.

                    For this initial test sequence, a single charge and
                    discharge rate was selected. The rate was chosen as one
                    of many that is typically seen in PV systems. For the
                    100Ah Trojan 30XHS battery, a charge and discharge
                    rate of 3.3 amps, or C/30,
                    was selected. PV system
                    batteries will normally have charge rates that vary from
                    about 1/10th the battery capacity to about 1/50th the
                    battery capacity, or C/10 to C/50, with discharge rates
                    varying from about C/10 to C/150. A moderate rate of
                    C/30 was selected from these ranges, resulting in 3.3
                    amps. It is important to select a charge and discharge
                    rate that is similar to that used in PV systems because
                    these rates will have a significant effect on battery charge
                    efficiency,


                    This is a prime example of a very flawed assumption. To start with they used a Trojan 30 XHS which is a hybrid marine cranking battery (Group 30 Marine case), is not a true deep cycle battery used in PV systems. It has much thinner plates and uses lead antimony plate constriction which are inefficient.

                    Next there is no system that would be designed to charge at a C/30 charge rate. That is a ridiculous assumption, coupled with a 5 Sun Hour day minimum. If you charge a battery at C/30 it will be a very low efficiency charge, DUH! Properly designed Solar Systems charge between C/15 to C/8 where the efficiency is 80 to 90%

                    A realistic system, say one that delivers 1 Kwh per day with a whopping 4 Sun Hour Day in December in NV would require a 12 volt, 420 AH battery based on 20% DOD/day. You would need a 375 watt panel and with a MPPT controller would deliver 32 amps or a C/13 charge rate. Move that system north with a 3 Sun hour day requires a 500 watt panel that delivers 42 amps of a C/10 Charge rate. At C/13 to C/10 charge rate with constant current algorithm into a true deep cycle battery and you are in the 80%+ efficiency range.

                    So their test model of C/30 charge rate is seriously flawed. Real system charge at much higher charge rates. If you based your decision on this data.......
                    MSEE, PE

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                    • #11
                      current

                      do you have a link to current research?

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                      • #12
                        Go back and read my edited reply and see what you think.
                        MSEE, PE

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                        • #13
                          efficiency

                          at what rate of charge is it 90% efficient?
                          If i went with 12v ~700ah
                          c/8 is 87 amps, which is more than most chargers can handle (most i see stop at 80amps)
                          so best is probably about c/9
                          is that 90% efficient?

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                          • #14
                            Originally posted by muffildy View Post
                            more batteries wont change the charge efficiency for the better
                            lead acid at 90% SoC typically has a charge efficiency of 50%.
                            i would have thought on a sub forum devoted to lithium ion i would have gotten more advice regarding lithium ion rather than lead acid...
                            Seeing as how no one uses the things it isn't terribly likely you will get much more.

                            Please be our guinea pig - none of has any desire to.
                            [SIGPIC][/SIGPIC]

                            Comment


                            • #15
                              Originally posted by muffildy View Post
                              at what rate of charge is it 90% efficient?
                              Depends on the battery but for quality ones like Rolls C/10 to C/8, however with any desgn you always use worse case or 80%.

                              Think about this. Let's say you need 1 Kwh/day and in December you receive 3 Sun Hours. Design 1 we use FLA batteries with 5 Day reserve capacity or 12 volt 420 AH @ 80% charge efficiency, and the second with 90% 12 volt 330 AH LFP 4 day reserve to be equal with 2.5 day reserves OK.

                              System 1 with FLA requires a 500 watt panel and 40 Amp MPPT charge controller. Cost of panels, charge controller and batteries work out to:

                              Panels = $2/watt = $1000
                              Charge Controller = $500
                              7 year Rolls Battery .22/watt hour = $1100
                              Total = $2600

                              System 2 requires a 475 watt panel, same 40 amp charge, and less battery capacity. Cost look like:

                              Panels $2/watt = $950
                              Charge controller = $500
                              LFP batteries $1/watt hour = $4000
                              Total = $5450

                              So yes it takes more panel wattage for the FLA. So what? The system with Rolls FLA batteries cost 53% less and last twice as long. You don't have to be an engineer like me to figure this one out.
                              MSEE, PE

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