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  • Flywheel instead of battery storage?

    One of the biggest headaches of managing any off-grid solar electric system is the batteries. The need to ensure lead acid batteries regularly reach a 100% state of charge to avoid an early grave can be daunting. Ensuring they reach this 100% state of charge often involves wasting PV power during the absorbtion stage so as to ensure the voltage does not drop too low. Without a very clever management system this inevitably leads to wasted amps!

    Professional flywheels aligned parallel to the Earth's axis of rotation have comparable energy storage capabilities of lead acid batteries with an almost limitless cycling capability and no need to reach 100% SOC before discharging to prolong service life. There is no need to check weather forecasts to plan your energy use the night before for fear of using too much power and not having enough sun the next day to charge your batteries! You can simply withdraw whatever was stored in the flywheel and that's that.

    I have not checked what the cost of such an energy storage system is nor whether or not it is feasible to DIY.

    Inherent dangers are obviously explosive destruction due to overspeed or manufacturing defects. locating the flywheel underground could perhaps best deal with those risks.

    Has anyone ever given this much thought? Are the costs perhaps far too high?

  • #2
    Lots of thought has gone into the flywheel concept - it is used for frequency stabilization by a few utilities.

    DIY - no way

    Useful? Apparently not really as it is in use and has not caught on.
    [SIGPIC][/SIGPIC]

    Comment


    • #3
      Originally posted by Dave3011 View Post
      One of the biggest headaches of managing any off-grid solar electric system is the batteries. The need to ensure lead acid batteries regularly reach a 100% state of charge to avoid an early grave can be daunting. Ensuring they reach this 100% state of charge often involves wasting PV power during the absorbtion stage so as to ensure the voltage does not drop too low. Without a very clever management system this inevitably leads to wasted amps!
      If you are REALLY concerned about not wasting power in absorb, instead of flywheels, we've already had batteries that don't need an absorb, but they have been commonly overlooked for about 5 years for the typical storage-power user like us: LiFePo4. Specifically, Lithium-IRon-phosphate. In large prismatic cells, from CALB and GBS. (there are others too that might be suitable). These are not the small cylindrical cells. Nor does it have to be complicated - those that have something to sell make it seem so.

      There is so much misunderstanding, FUD, well-intentioned but misleading information from those outside the storage application such as ours that it can sometimes be hard to have a rational discussion about batteries that you can have landed on your doorstep tommorrow - from 20ah to 2Mw or more. You do not have to go directly to China to get them. They do much more than just not needing absorb and make a perfect fit for mppt. Of course this draws in detractors and conjucture like flies unfortunately. Ok, 2Mw might take a week.

      At the risk of thread hijack, I'll just ask that if you want some serious answers from an actual hands-on owner, with no BS, fanboy, or salesmanship attached to it, I'll be happy to help.

      If you want to continue about flywheels, then that's cool, but just didn't want to hijack the thread. If it's about lack of absorb, I'm all ears!

      Comment


      • #4
        Originally posted by PNjunction View Post
        If you are REALLY concerned about not wasting power in absorb, instead of flywheels, we've already had batteries that don't need an absorb, but they have been commonly overlooked for about 5 years for the typical storage-power user like us: LiFePo4. Specifically, Lithium-IRon-phosphate. In large prismatic cells, from CALB and GBS. These are not the small cylindrical cells.

        There is so much misunderstanding, FUD, well-intentioned but misleading information from those outside the storage application such as ours that it can sometimes be hard to have a rational discussion about batteries that you can have landed on your doorstep tommorrow - from 20ah to 2Kw or more. They do much more than just not needing absorb. Of course this draws in detractors and conjucture like flies unfortunately.

        At the risk of thread hijack, I'll just ask that if you want some serious answers from an actual hands-on owner, with no BS, fanboy, or salesmanship attached to it, I'll be happy to help.

        If you want to continue about flywheels, then that's cool, but just didn't want to hijack the thread.
        No objection at all to "hijacking the thread"! I was pretty certain there's a good reason we dont see flywheels in every off-grid system. It's good if threads like these stimulate discussion on alternatives to the king lead acid!!!

        There is no solar panel owner out there who wants to see even 1 watt/hour of precious power go to waste and unfortunately batteries are the biggest wasters in the entire system...

        I've seen many threads featuring LiFePo4 batteries, but again price and compatibility with charge controllers seem to be an issue.

        Here in South Africa there is the much hyped "Lead Crystal Battery" which can apparently be cycled repeatedly using 100% DOD, it's even been "tested" by an independent enthusiast in Cape Town but no reputable solar installation company here recommends them? They tend to stick with the much tried and tested 2V deep cycle tubular cells.

        I'm currently stuck with an inferior bank of 12v 102AH sealed lead calcium batteries which I've wired together to make a "Big" 24V 400AH pack to serve my energy storing needs. When that day comes to replace them with something better I'd like to do it properly, make the best informed decision possible and hopefully find myself beyond criticism on these forums at last...

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        • #5
          Ok, here's a small laundry list of advantages. In fact, the lack of an absorb grabbed my attention first, and along with the other stuff, this had to be a lark. Not so.

          No absorb - well, a teeeny bit if charging over 0.5C typically. The charge/discharge curve is essentially flat, except for two extremely steep knees at the beginning and end of charge. The mantra here is to stay out of those knees. Now your charge controller stays in bulk until finished, and if using mppt takes advantage of that as well all the way to the end. When you are finished charging, you are done.

          Simple one-step CV charging. No float. No EQ. No temperature-compensation. Disable these in ordinary controllers, or if float is not able to be disabled, set it lower than 13.8v to become benign more or less.

          Up to 1C charge / discharge. Up to 3C for limited time. Best for life is .5C or less, which is what we'd do for a typical solar house-bank scenario.

          80% DOD at 2000 cycle life. 70% DOD to 3000 or more. However, these are predictions in our hands. Skeptical, yes, but so far so good. They aren't lying about the other stuff, but we'll see.

          No need to fully charge. In fact, it is even better if you don't have to. You are rewarded for PSOC or partial state of charge operations.

          Minimal Peukert effect, or voltage sag, especially under a typical house-bank situation. If you are a high-current EV user, then you might see some. The setting in some controllers for the Peukert effect is 1.06 I believe.

          About 1/3 to 1/2 the weight of lead.

          When comparing prices, be sure to take into account you can take these down to 80% DOD, vs a lead-acid down to 50% in normal use. Most find them on par with larger capacity, high quality agm when looked at from that perspective. These are prismatics remember, not the cylindricals that are higher priced and have far more current capability that a house-bank would ever use. Think deep-cycle vs sli. The cylindricals are more suited for sli duty. Some hobbiests cross-purpose these and pay a heavy price for that.

          Unless you get them from specialty battery stores, the major place to get these are the shops that specialize in EV-conversions. BUT, we don't treat them like EV users do with high-voltage and high-current, so in effect, these batteries will lead a very sheltered life compared to them. The EV conversion guys are all over the globe and on the net. Most deal with CALB and GBS. Some seem to have Winston.

          Typically, they consist of four, 3.2v nominal cells wired in series (or parallel-series for huge capacities).
          And on and on.

          The best part is that you don't have to believe a word of any of this. You can prove it to yourself with the smallest of capacities, the 12v 20ah version that looks more like a 12ah agm.

          Gotta run - eyelids closing....

          Comment


          • #6
            As russ stated, a lot of research has gone into Flywheel technology. They are used in commercial and industrial applications where a "short" power outage (a few minutes) is mitigated by the flywheel power generator.

            Unfortunately no one has come up with (although some people have claimed to) a commercial flywheel application that has the ability to provide power for a longer time period.

            The idea is interesting but a DIY project would be very hard to do considering the cost of equipment and safety requirements needed for a large system.

            Comment


            • #7
              Originally posted by SunEagle View Post
              As russ stated, a lot of research has gone into Flywheel technology. They are used in commercial and industrial applications where a "short" power outage (a few minutes) is mitigated by the flywheel power generator.

              Unfortunately no one has come up with (although some people have claimed to) a commercial flywheel application that has the ability to provide power for a longer time period.

              The idea is interesting but a DIY project would be very hard to do considering the cost of equipment and safety requirements needed for a large system.
              I've been away from energy storage via flywheels for some years. Back in the day, the energy density was not as good for flywheels as other forms of energy storage, and that was before electric battery improvements. Scaling up on size seemed to offer some promise, lending some credence to the opinion to not being too good for small/DIY applications.

              Comment


              • #8
                Originally posted by J.P.M. View Post
                I've been away from energy storage via flywheels for some years. Back in the day, the energy density was not as good for flywheels as other forms of energy storage, and that was before electric battery improvements. Scaling up on size seemed to offer some promise, lending some credence to the opinion to not being too good for small/DIY applications.
                I don't remember the size I have read about but they were utility scale.

                The problem is a lot of mass is required in the flywheels - same as for pumped hydro - it takes a special situation.
                [SIGPIC][/SIGPIC]

                Comment


                • #9
                  Originally posted by russ View Post
                  I don't remember the size I have read about but they were utility scale.

                  The problem is a lot of mass is required in the flywheels - same as for pumped hydro - it takes a special situation.
                  And probably more containment than a nuke (but for different reasons) should a very big flywheel come apart at some very high angular velocity. Some thought putting it underground or under water would help that.

                  Comment


                  • #10
                    Originally posted by Dave3011 View Post
                    Professional flywheels aligned parallel to the Earth's axis of rotation have comparable energy storage capabilities of lead acid batteries with an almost limitless cycling capability and no need to reach 100% SOC before discharging to prolong service life. There is no need to check weather forecasts to plan your energy use the night before for fear of using too much power and not having enough sun the next day to charge your batteries! You can simply withdraw whatever was stored in the flywheel and that's that.
                    Well, if you run at a deficit you will kill your flywheel storage as surely as you will kill a battery bank. They just handle low states of charge better.
                    I have not checked what the cost of such an energy storage system is nor whether or not it is feasible to DIY.
                    Not feasible at all. Too much to go wrong, too catastrophic when something does go wrong.
                    In general flywheels are excellent when you need a lot of power, not great when you need a lot of energy.

                    Comment


                    • #11
                      Originally posted by J.P.M. View Post
                      I've been away from energy storage via flywheels for some years. Back in the day, the energy density was not as good for flywheels as other forms of energy storage, and that was before electric battery improvements. Scaling up on size seemed to offer some promise, lending some credence to the opinion to not being too good for small/DIY applications.
                      I worked at a company that had a small (30kw) flywheel system to "ride through" very short duration power dips (maybe 2 a year). The cost for that system (in the late 80's) seemed more economical than a battery UPS system considering the few times it was needed and the cost to maintain and replace batteries.

                      Big issue with flywheels is friction. Put one in a "zero gravity" environment and you may have something that works.

                      Comment


                      • #12
                        For any useful energy output, the wheel would have to weigh several if (not dozens of) tons.
                        They are a good way to store energy, but, yes, friction is not our friend here.

                        Even with the strongest Neodymium magnets available today, they could not levitate that kind of axle.

                        Shame really, it would work on a smaller scale, but you'd need lots of them for any real output...
                        Dem

                        Comment


                        • #13
                          Ah, ok. Flywheels it is then.

                          I'll back out. To save a lot of thread drift, even though the Op seemed genuinely interested in lifepo4, you can continue here:
                          http://forum.solar-electric.com/show...and-40ah-batts

                          Off to the flywheel store!

                          Comment


                          • #14
                            Here's one potential approach if it can get beyond a prototype. Needs a vacuum of course for reduced friction.

                            Circa 1980, I was part of a research group at Bendix Corp. looking into potential projects in the area of advanced composite materials. One of those considered was using high performance composites in flywheels for energy storage. Ultimately, we passed on that but it's interesting how far back flywheel energy storage development goes.

                            Comment


                            • #15
                              Originally posted by PNjunction View Post
                              Ah, ok. Flywheels it is then.

                              I'll back out. To save a lot of thread drift, even though the Op seemed genuinely interested in lifepo4, you can continue here:
                              http://forum.solar-electric.com/show...and-40ah-batts

                              Off to the flywheel store!
                              No. I was trying to convince the OP that a Flywheel is not viable energy storage solution. And yes I think LiFePo4 batteries are a very good way to store energy.

                              I just read an article about the new 14.5MW solar array in Anahola HI. Along with the PV array they will be installing a 6MW Lithium-ion battery energy storage system. That is one big battery.
                              Last edited by SunEagle; 06-30-2014, 04:09 PM. Reason: added info on Anahola pv & battery system

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