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  • #16
    Originally posted by Ampster View Post

    I looked up my location and installation specifics on PVWatts which gave me a factor of 1438 times nameplate to estimate my annual production. In 10 months since it has been installed my system is on tract to exceed that projection. To be conservative and account for degradation I only used a factor of 1200 for my calculation above.

    As calculated in the post above, the cost of my battery storage is $0.139/kWh. That is significantly below your estimate of $0.50. How did you calculate that number and what assumptions did you make?
    When considering your gross savings from PV generation, you'll find that because of T.O.U. pricing/times, the value of the electricity your PV system generates will be less than the peak pricing value. For example, using PVWatts numbers for my system, at current SDG & E rates - not too unlike PG & E rates - my system generates ~ 1,720 kWh/yr per installed STC kW. If I feed all of it to the grid, and using PVWatts hourly option and published SDG & E T.O.U. rate sheets and times for T.O.U. rates and times it will have a value of about $414.

    $414/1,720 kW = ~ $0.240/kWh.

    I think I'm pretty informed about CA mandated NEM policies and SDG & E rates, and somewhat but admittedly less informed about PG & E rates. I cite my information as an example only. But my suspicion is that your rates, times and billing situation may not be so different than mine.

    As for the cost of storage, everyone throws numbers around, mostly without any explanation of how the numbers are arrived at. Maybe the "cost" is a buck per stored kWh. Maybe it is $0.139/stored kWh. Or delivered kWh per year. Or something else. Unless the basics of the analysis are defined, the costs quoted are mostly useless. Problem is most folks don't know that the concept of something called the time value of money even exits, much less know what to do with it, so they usually grab the last thing they heard someone say and see if it sticks when the throw it against the wall.

    You provide some explanation of your costing logic, but it's pretty simplistic compared to what's considered necessary if one claims to know something or attempt some verification with respect to solar process economics.

    As long as you're claiming a cost for storage, I'd respectfully suggest you consider digging into what the possible (+/- some model's tolerance might be) generation might be for your system by hour and then put a NPV on that generation based on some form of recognized life cycle costing method(s), and then compare that to the NPV of the cost of what you are considering doing, including maintenance and battery replacement.

    One other thing to perhaps consider in your analysis: Electricity rates do actually go down as well as up. Example (only): on 12/01/2017, the peak T.O.U. rate for SDG & E , T.O.U. for residential PV systems was $0.54297/kWh. On 07/02/18 it was $0.53773/kWh for the same billing schedule. On 09/17/18, it dropped to $0.44566/kWh. That doesn't make any analysis any easier and adds uncertainty (or perhaps more accurately said, highlights the problem of assumptions always present in any cost analysis).

    Lastly, and only FWIW, suit yourself, even with accurate input, PVWatts is already rather conservative in terms of annual output. Many folks have found the 14 % system loss parameter to be a source of what's usually a low annual output number from the model. Many have found changing that parameter from 14% to 10% gives a better match of the model's output to what their system actually seems to produce. Sill +/- maybe 10 % on individual years, but the running day/day 30 day model averages get closer to the actual running 30 day average outputs. There is such a thing as compounding conservative assumptions , and that may not always be the best way to go. Just sayin'.

    Take what you want of the above. Scrap the rest.

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    • #17
      Originally posted by SunEagle View Post

      Unfortunately your calculation is based on a paper estimate and not real time usage. The big question is, will any of those Li battery systems provide the rated kWh each day and last 8 years that they say they will. I do not believe they will yet. They are too new a battery technology to have a proven track record.

      My $0.50/kWh is based on current FLA type battery costs, kWh output and cycle life. While an FLA might not last very long, it still costs much then any professionally installed Li battery systems. Heck even the Powerwall2 is about $9k to $10k installed.

      But you might find used batteries for less. The key term is USED. Can you trust them?
      I understand I am taking a gamble on used Leaf batteries. 3 years ago I purchased a complete pack for $1500 and some of those modules are still running a GEM and the rest I am putting into this experiment. It looks like It will be difficult to find more at that cost but even at $200/kWhr I have room for rejects and degradation. Nobody is telling me that those Nissan Leaf modules will last 8 years, that is merely my assumption but I have room for error because if they last half as long as I predict my cost is still below your estimate for FLAs. I am also comforted by the fact that Sunking has enough confidence in them to use them in his golf carts. Stationary storage is less stressful than motive power and I can control the discharge rate in my situation.
      With regard to the cost of a PowerWall, I received a quote of $12,000 and that included paperwork for California SGIP incentive, Ater incentives and tax credit that system would have a net cost of under $5,000. I am going this route because it gives me the flexibility of adding more battery capacity and adding more solar that I would not have had with a Powerwall. I am not recommending my approach to everyone but for the DIYers who have the desire, this may be another approach to a cost effective system if one has the time and skills to put it together

      You are correct, the key issue is that they are USED and whether I can trust them. In my case the answer is, I have evaluated the risk and it makes sense for me. Maybe Sunking can give us some insight as to how long his Leaf modules are lasting?

      Comment


      • #18
        Originally posted by Ampster View Post

        I understand I am taking a gamble on used Leaf batteries. 3 years ago I purchased a complete pack for $1500 and some of those modules are still running a GEM and the rest I am putting into this experiment. It looks like It will be difficult to find more at that cost but even at $200/kWhr I have room for rejects and degradation. Nobody is telling me that those Nissan Leaf modules will last 8 years, that is merely my assumption but I have room for error because if they last half as long as I predict my cost is still below your estimate for FLAs. I am also comforted by the fact that Sunking has enough confidence in them to use them in his golf carts. Stationary storage is less stressful than motive power and I can control the discharge rate in my situation.
        With regard to the cost of a PowerWall, I received a quote of $12,000 and that included paperwork for California SGIP incentive, Ater incentives and tax credit that system would have a net cost of under $5,000. I am going this route because it gives me the flexibility of adding more battery capacity and adding more solar that I would not have had with a Powerwall. I am not recommending my approach to everyone but for the DIYers who have the desire, this may be another approach to a cost effective system if one has the time and skills to put it together

        You are correct, the key issue is that they are USED and whether I can trust them. In my case the answer is, I have evaluated the risk and it makes sense for me. Maybe Sunking can give us some insight as to how long his Leaf modules are lasting?
        Well my hat is off to you and your Li storage system. I really hope it works out better then expected.

        I just happen to be a pessimist and I do not think the current battery technology is the most cost effective type for an energy storage system for the near future.

        Comment


        • #19
          Originally posted by SunEagle View Post
          ........I really hope it works out better then expected.

          I just happen to be a pessimist and I do not think the current battery technology is the most cost effective type for an energy storage system for the near future.
          I will be happy if it works out at 75% of expectations. My goals were not as much financial as they were to give me flexibility for future evolution of the system as my needs evolve. Those goals emphasized backup and resiliency.

          I am a pessimist as far as the Investor Owned Utilities are concerned. I think that the industry is going through some disruption and I don't think they will be able to provide efficient delivery of energy in the near term. That is partially driving my strategy.

          I have noticed your pessimism regarding Lithium battery technology. You have more experience than I and I am sure you have some very good reasons for your pessimism. I have looked at the industry trends, especially in the area of utility storage and those systems are almost entirely Lithium based. I have confidence that AES, Excel, United Power and others have done their analysis. They are accountable to shareholders and are investing big bucks.There has to be a reason those companies have chosen Lithium over FLA.

          Comment


          • #20
            Originally posted by Ampster View Post
            How much money I save depends on how much I use. Remember in summer my peak rate is $0.47 /kWhr. If I save 1000 kHrs per year I get my money back over 15 years
            Your batteries won't last 15 years.
            I can't achieve my other goals with a generator and that is why I prefer to use storage supplemented by solar than maintain a generator.
            OK, what are your other goals?
            I am very familiar with relays. That is my fallback if I can't get CAN communications to work with the BMS. If I can't get Outback's AC coupling to control the grid tie inverter when the grid is down I will use relays there triggered by high voltage battery signal to knock the grid tie inverter off line.
            You really have to do it via battery charge state, not voltage. When you hit CV you're not fully charged, especially at high rates (i.e. large array/small battery.) You can do this via an accessory like a FlexNetDC (Outback's system.)
            I am not sure I agree with your statement about Lithium chemistries not working with Skybox. You maybe thinking of package systems like SimpliPhi or LG Chem where the issue may be the communications between the Skybox and the integral BMS of those systems.
            SimpliPhi has no communications and generally doesn't work well with inverter/chargers. LG Chem does, but you also need the right SW/adapter.
            Lithium is easier for me than FLA or AGM. It requires just a constant charge voltage, the correct Amperage and a BMS to control or cutoff the charging and discharging. No float just a simple voltage setting.
            OK. Not sure why that is easier than FLA, which does not need a BMS.

            Comment


            • #21
              Originally posted by J.P.M. View Post

              When considering your gross savings from PV generation.......
              ...........

              Take what you want of the above. Scrap the rest.
              Thanks, all of that was helpful. This conversation with you and others did help me establish some cost benchmarks. As explained in another post my goals are not as much financial as they are to give me flexibility and resiliency. I call it a hobby so that I don't have to go through the rigorous financial analysis that I was accustomed to in my career. I also have a low cost of funds and do not need a high ROI on these adventures. That should be a cautionary note for others who might be tempted to follow in my footsteps without adequate analysis.

              Comment


              • #22
                Originally posted by Ampster View Post

                I will be happy if it works out at 75% of expectations. My goals were not as much financial as they were to give me flexibility for future evolution of the system as my needs evolve. Those goals emphasized backup and resiliency.

                I am a pessimist as far as the Investor Owned Utilities are concerned. I think that the industry is going through some disruption and I don't think they will be able to provide efficient delivery of energy in the near term. That is partially driving my strategy.

                I have noticed your pessimism regarding Lithium battery technology. You have more experience than I and I am sure you have some very good reasons for your pessimism. I have looked at the industry trends, especially in the area of utility storage and those systems are almost entirely Lithium based. I have confidence that AES, Excel, United Power and others have done their analysis. They are accountable to shareholders and are investing big bucks.There has to be a reason those companies have chosen Lithium over FLA.
                Well most POCO's have been regulated into installing storage of some kind and the big HV voltage systems all happen to be Li chemistry. They would not do it unless they had been forced into it by the politicians.

                I would take it with a grain of salt to think they are installing energy storage because it is economical. Since they can pass on the cost to their customers it probably doesn't mean it will cost them much at all in the end.

                But who knows. Maybe the holy grail of batteries is just over the next hill.

                Comment


                • #23
                  key information on Lithium (LiFePO4) battery and Lead Acid
                  https://www.youtube.com/watch?v=0E7aDcUNric&feature=youtu.be

                  Comment


                  • #24
                    Originally posted by jflorey2 View Post
                    Your batteries won't last 15 years.

                    OK, what are your other goals?

                    You really have to do it via battery charge state, not voltage. When you hit CV you're not fully charged, especially at high rates (i.e. large array/small battery.) You can do this via an accessory like a FlexNetDC (Outback's system.)

                    SimpliPhi has no communications and generally doesn't work well with inverter/chargers. LG Chem does, but you also need the right SW/adapter.

                    OK. Not sure why that is easier than FLA, which does not need a BMS.
                    Yes 15 years is a stretch for any battery chemistry. I mentioned 15 years as a system payback. I assumed 8 years for batteries.

                    My goals as stated in the beginning of this thread are:
                    - Shift loads so that all my solar production gets credited at the Peak Rate.
                    - Have a backup in the case of a power outage.
                    - AC couple the Outback inverter to my Grid tied system so that during a power outage the additional capacity if that system can supplement my back up.
                    A generator won't help me much to shift loads and leverage my existing grid tie system.

                    I have picked a voltage parameter based on the charge curve of my battery. I pick that voltage to avoid the knee of the curve. I do not want to fully charge my Lithium batteries. That strategy should lengthen their life. My BMS allows me to tell the charger to turn off when the Amperage in the Constant Voltage stage reaches a specific value. That point in the curve corresponds to a State of Charge. I think we are describing the same phenomena. The Skybox can charge from the grid or from solar panels. I don't need a FlexNet because all that is integrated in the Skybox.

                    I don't have any interest in how SimpliPhi or LG communicate with the Skybox. My comment was trying to understand your original statement, "There aren't many lithium chemistry batteries yet that work with the Skybox." You have still not answered my question about what you mean by that statement. Any examples? My belief, and Outback seems to agree, is that the Skybox will work with any chemistry. I am looking forward to working with them on integrating my Orion CAN bus communication with the Skybox.

                    I like complexity especially if it makes things simpler for me. That is why I find a BMS easier than FLA. It offers me the ability to look at the health of my pack in terms of capacity and balance. I can do that from the comfort of my laptop by looking at charts and graphs. I don't like menial tasks like looking for a hydrometer, unscrewing the tops of each cell and measuring their specific gravity. I like data and analysis. It is a personal preference and I do not wish that everyone be like me.
                    Last edited by Ampster; 11-20-2018, 05:16 PM.

                    Comment


                    • #25
                      Originally posted by SunEagle View Post

                      Well most POCO's have been regulated into installing storage of some kind and the big HV voltage systems all happen to be Li chemistry. They would not do it unless they had been forced into it by the politicians.

                      I would take it with a grain of salt to think they are installing energy storage because it is economical. Since they can pass on the cost to their customers it probably doesn't mean it will cost them much at all in the end.

                      But who knows. Maybe the holy grail of batteries is just over the next hill.
                      I agree the POCOs have been forced into installing storage but they have not been forced into choosing Lithium. There is a market reason that the big HV systems are Lithium.
                      I think storage is competitive with Peaker Plants and that is where it is currently being utilized. Gas Peakers are not efficient but they are fast. The best solutions are described as hybrids using combined cycle gas turbines which are clean and efficient. The battery supplies the grid until the gas turbine ramps up.Then the exhaust from the turbine heats the water for the second phase of the combined cycle plant.

                      Holy grail of batteries? A week doesn't go by that someone says they have discovered a new amazing battery technology. All that is left is to find out how to manufacture it. Yes, someday Lithium may be considered yesterdays old technology, and I don't know where that leaves Lead Acid. Was the last great breakthrough AGM? No capacity increases?
                      Last edited by Ampster; 11-20-2018, 05:27 PM.

                      Comment


                      • #26
                        Originally posted by BMSengineer View Post
                        key information on Lithium (LiFePO4) battery and Lead Acid
                        https://www.youtube.com/watch?v=0E7aDcUNric&feature=youtu.be
                        Please stop posting videos concerning BMS equipment.

                        Comment


                        • #27
                          Originally posted by Ampster View Post

                          I agree the POCOs have been forced into installing storage but they have not been forced into choosing Lithium. There is a market reason that the big HV systems are Lithium.
                          I think storage is competitive with Peaker Plants and that is where it is currently being utilized. Gas Peakers are not efficient but they are fast. The best solutions are described as hybrids using combined cycle gas turbines which are clean and efficient. The battery supplies the grid until the gas turbine ramps up.Then the exhaust from the turbine heats the water for the second phase of the combined cycle plant.

                          Holy grail of batteries? A week doesn't go by that someone says they have discovered a new amazing battery technology. All that is left is to find out how to manufacture it. Yes, someday Lithium may be considered yesterdays old technology, and I don't know where that leaves Lead Acid. Was the last great breakthrough AGM? No capacity increases?
                          What the POCO's don't publish is the final installed cost for those battery systems along with what it cost for them to produce each kWh. Sure they help stabilize the grid faster then a Peaker but trust me you would not want to own or have to maintain a battery system if you did not have to.

                          I base my answers on my 40 years in the electrical engineering field. Batteries are not cheap and the POCO's know it.

                          Comment


                          • #28
                            Originally posted by Ampster View Post
                            Yes 15 years is a stretch for any battery chemistry. I mentioned 15 years as a system payback. I assumed 8 years for batteries.
                            Right. So your payback time has to include regular battery replacements.
                            My goals as stated in the beginning of this thread are:
                            - Shift loads so that all my solar production gets credited at the Peak Rate.
                            - Have a backup in the case of a power outage.
                            - AC couple the Outback inverter to my Grid tied system so that during a power outage the additional capacity if that system can supplement my back up.
                            A generator won't help me much to shift loads and leverage my existing grid tie system.
                            Agreed. But:

                            1) is a money issue. This system will not save you money due to battery cost.
                            2) and 3) are for backup power and your needs will be better served by a generator. (That's why pretty much every off-grid system has a generator; it's the reliable backup for the less reliable solar system.)

                            I have a feeling that you just really, really want to build a solar battery system, even if it isn't cost effective. If so, that's fine - it's your money. But let's state that up front.
                            I have picked a voltage parameter based on the charge curve of my battery. I pick that voltage to avoid the knee of the curve. I do not want to fully charge my Lithium batteries. That strategy should lengthen their life. My BMS allows me to tell the charger to turn off when the Amperage in the Constant Voltage stage reaches a specific value.
                            That works as long as you always charge at full power. Will your solar array always provide full power? Or will the amperage drop sometimes due to clouds, evening etc?
                            I don't need a FlexNet because all that is integrated in the Skybox.
                            I didn't think the Skybox had a current shunt. I could be wrong.
                            I don't have any interest in how SimpliPhi or LG communicate with the Skybox. My comment was trying to understand your original statement, "There aren't many lithium chemistry batteries yet that work with the Skybox." You have still not answered my question about what you mean by that statement. Any examples? My belief, and Outback seems to agree, is that the Skybox will work with any chemistry.
                            The battery has to have the right BMS to be able to communicate with the Skybox. I have no doubt you could spoof it by telling it (for example) that it's a lead acid battery or something, but per Outback the way it's supposed to be used is with a battery that can communicate with the Skybox.

                            The chemistry itself doesn't matter. The fact that lithium chemistries need BMSes is what matters. If people had sodium-sulfur batteries that needed a BMS the same comment would apply.


                            Comment


                            • #29
                              Originally posted by Ampster View Post
                              Okay, if I buy more Nissan Leaf batteries at $200/kiloWatt and I replace them every 8 years.
                              You are dreaming if you think the batteries will last 8 years, and that you can utilize the energy.

                              MSEE, PE

                              Comment


                              • #30
                                Originally posted by Sunking View Post
                                You are dreaming if you think the batteries will last 8 years, and that you can utilize the energy.
                                How long have yours lasted?

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