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Hybrid Ouback Skybox with Nissan Leaf batteries

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  • #46
    Originally posted by Ampster View Post
    ..........
    Yes, that describes one of my friends who recently installed two Powerwalls. He is on grid, has PV solar panels on his entire roof and shade structure. He is on California NEM 1.0 and has a substantial credit each year at true up. Every time I see him he shows me his Tesla app on his phone and the nice graph showing the power he has stored.

    i agree with your last paragraph that definitions are situation variable and user specific. That would be my situation. I chose a hybrid inverter to complement my existing grid tie system because of the risks I wanted to mitigate.
    My point was it's everyone's situation with the cost/benefit analysis being different for everyone depending on their opinion and worldview.

    But I'd still would check the minutia/fine print of my NEM agreement. Just sayin'.

    Not that you are concerned too much about such things as cost effectiveness (or so it seems), but for other readers of this thread, or for your Tesla driving friend, it may be interesting to such readers/folks to note the negative effect on system cost effectiveness the "substantial credit at trueup" represents. Selling back to the POCO at ~ $0.03 - $0.04/kWh makes the cost effectiveness of the excess capacity a whole lot less than the cost effectiveness that non excess capacity can achieve.

    At a grid tie system after tax credit cost of, say, $2.25/STC watt and, say, $0.035/kWh for excess generation, It's a long(er) way to a positive ROI than optimally sized residential PV where average CA residential T.O.U. bill offsets of ~ $450/yr. per installed STC kW are common these days.

    I'm not too sure discussing cost ineffective decisions such as over sizing is necessarily a smart thing to be doing if one want to be thought of as even moderately informed about such things. Sounds more like ignorance based bragging and/or poor design to me, but NOMB or money/concern.

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    • #47
      Originally posted by J.P.M. View Post

      My point was it's everyone's situation with the cost/benefit analysis being different for everyone depending on their opinion and worldview.
      I agree completely with that view. Perhaps I don't make that clear.
      But I'd still would check the minutia/fine print of my NEM agreement. Just sayin'.
      I have read my NEM agreement. It is clear what the limitations are with the system that I have registered with them. They use some language that would imply that they would like to control equipment on my side of the meter..Clearly my Grid Tie inverter is part of that. What is not clear, and I have searched for cases, is what control they have over what I do behind the meter.
      Since I can tell my hybrid inverter to never sell to the grid i am not in violation of my NEM agreement if I don't sell anything from the hybrid inverter to the grid. I can charge the batteries connected to that hybrid inverter at low cost off peak rates. I can use that energy to power my critical loads during the day, which would allow all of solar production to be credited at peak rates. Non of that violates my NEM agreement. That would be the same result as just turning off those loads. Nothing wrong with that. Furthermore after the sun goes down I am still powering my loads with the battery power through the hybrid inverter, saving me that cost of energy at peak rates. That is actually a benefit to the grid because I have taken load off the grid when the grid is often stressed. This is often called the neck of the duck curve.

      Not that you are concerned too much about such things as cost effectiveness (or so it seems), but for other readers of this thread, or for your Tesla driving friend, it may be interesting to such readers/folks to note the negative effect on system cost effectiveness the "substantial credit at trueup" represents. Selling back to the POCO at ~ $0.03 - $0.04/kWh makes the cost effectiveness of the excess capacity a whole lot less than the cost effectiveness that non excess capacity can achieve.
      I actually am concerned about cost effectiveness and used the example of my friend as a complete waste of money when he had all that excess capacity.

      At a grid tie system after tax credit cost of, say, $2.25/STC watt .....
      I"ll finish my thoughts later. This is a good conversation and you bring up some good points

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      • #48
        Originally posted by J.P.M. View Post
        ........
        At a grid tie system after tax credit cost of, say, $2.25/STC watt and, say, $0.035/kWh for excess generation, It's a long(er) way to a positive ROI than optimally sized residential PV where average CA residential T.O.U. bill offsets of ~ $450/yr. per installed STC kW are common these days.
        Yes, I agree and that was my point in pointing out the foolishness of my friend in putting in two Powerwalls when there was no further financial benefit. My idea of the sweet spot for a NEM agreement was what my Radian system helped me achieve in 2016. My total consumption was 5,000 kWhs and my cumulative charge for that year was $30. That meant my net cost for those hours was $0.006/kWh. That consumption was after net generation of close to 1,000 kWhrs at peak and off peak rates and close to 6,000 consumption at super off peak rates. The high usage at super off peak rates was charging two EVs, running a heat pump water heat at super off peak rates and of course charging the batteries which ran the Radian for load shifting.
        I'm not too sure discussing cost ineffective decisions such as over sizing is necessarily a smart thing to be doing if one want to be thought of as even moderately informed about such things. Sounds more like ignorance based bragging and/or poor design to me, but NOMB or money/concern.
        Good advice. I may have left that impression because I was getting frustrated with the naysayers. I had already proven to my self the viability of that load shifting model in my earlier installation in an all electric home that I previously occupied. My first investment was in energy saving devices like an induction cooktop, the previously mentioned heat pump water heater and elimination of inefficient ceiling heat coils in favor of local programmable thermostat controlled individual room heaters. The solar installation was concurrent with the above conservation measures. Then the following year (2015) I installed the Radian for more load shifting.
        I am more frugal than I may have left the impression about. That is why I am using $200/kWh Nissan Leaf Modules instead of the simpler to buy packages like LGChem, SimpliPhi or others that are running closer to $1,000 per kWh of stored energy. One of the things that I like about this approach is that I can add battery capacity in increments of 3.5kWh ($700) until I find the right balance of load shifting with a reserve for backup in case of power outages. All I have to do is fabricate longer copper bus bars of which I already the templates for 6 parallel modules.
        Anyhow, thanks for the feedback. My earlier snarkiness may have been misplaced.
        Last edited by Ampster; 11-24-2018, 01:09 AM.

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        • #49
          My Skybox arrived two days ago. I had to reconfigure my lower wireway/gutter to accommodate it but I got the BOS mounted and rough wiring done to the Skybox. Meanwhile the Leaf modules are being paralleled and I should be up and running in the next couple of days. I also ran some tests on a few random Leaf modules and have picked a charge strategy of charging to 4.15v per cell and discharging to 3.75v. Hopefully that will extend the life of those approximately 5 or 6 year old Leaf modules. I am hoping to avoid early death of those cells that some predict.

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          • #50
            Originally posted by Ampster View Post
            Hopefully that will extend the life of those approximately 5 or 6 year old Leaf modules. I am hoping to avoid early death of those cells that some predict.
            If these are 5-6 years old then they are likely from the first batch which did very poorly at elevated temperatures. If you keep them cool that may help.

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            • #51
              Originally posted by jflorey2 View Post
              ........ If you keep them cool that may help.
              I am hopeful. I live where the wines are great because of the cool evenings. I also have my heat pump water heater in that garage and run it during the day. They will be on an uninsulated south facing wall so I may need some single sided foam faced insulation on that part of the wall that the pack will be located. I will keep an eye on the temperatures. I hadn't given that much thought until you mentioned it. Thanks for the input.

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              • #52
                New member with my first post here, and I am curious about the status of your installation Ampster. Is it working as planned? Things not working as well as they should?

                Additional thoughts on what you would do different or missteps?

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                • #53
                  Originally posted by Ksnax View Post
                  New member with my first post here, and I am curious about the status of your installation Ampster. Is it working as planned? Things not working as well as they should?

                  Additional thoughts on what you would do different or missteps?
                  Thanks for the question. I realize I have made updates partially through several threads. I will provide a summation here.
                  For the most part it is working as planned. My first disappointment was to discover that having Canbus capability doesn't mean that my BMS was going to be able to be understood by the Skybox. I just went to using a contactor to shut down the battery pack if the BMS had an alarm.
                  Using just the battery and the grid I could never get the TOU selling and charging to work consistently. That became less of an issue when I found a very good deal on some used Sunpower panels and decided to install them on a west facing patio cover I had been contemplating. That took most of January and though we did not have any perfectly clear days i saw the system charging my batteries and self consuming some electricity before I left for a vacation in China. Upon my return I am looking forward to tuning it up and I think it will perform as expected.
                  I also have some shade issues and am going to contemplate whether to install a few TIGO optimizers on the affected panels. As I was getting my documents ready to pull the building permit I realized I needed to install a Rapid Shut Down device. I am in the process of determining which version of NEC I need to comply with and will order the parts for that installation.
                  I would be happy to answer any other questions.

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                  • #54
                    I am back from my vacation and have had a few sunny days to see how it performs. I also realized I had not set the Grid Zero function and that may be why I wasn't getting the results from the TOU rates I had programmed into the system. I just set the inverter to Grid Zero mode and it immediately began charging at the lower TOU rate that was below my average cost rate. The average cost rate is user programmable and mine is set at 0.20. The TOU rate for this morning is 0.18 so I believe that is why it began charging from the grid. Later today the TOU rate goes to 0.25 and I am hoping it drops the grid and powers me through that weekend peak period. At least that is the theory.

                    It got cloudy again so it may be a few days before I can report back with meaningful results on how the solar generation part of this works with charging my pack and powering my loads.

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                    • #55
                      More sunshine and my batteries remain near the top. Grid zero mode does keep my grid usage low during peak hours. When the sun shines the inverter shares the generation between by batteries and my load. I have the inverter set for non export and the inverter can modulate the output of the panels to match my loads and charging needs. After the sun goes down the batteries support my load through the peak rate period. Apparently there is about 100 Watts of overhead and some of that I presume is to keep the inverter synced to the grid so the switching from grid use to off grid is as seamless as possible. I did talk to the building department and they are on NEC 2014 so my Rapid Shutdown requirements are going to be easier than I thought.
                      Last edited by Ampster; 03-13-2019, 08:46 PM.

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