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30kw DIY battery for $310/kwh, which hybrid inverter is recommended?

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  • 30kw DIY battery for $310/kwh, which hybrid inverter is recommended?

    https://www.youtube.com/watch?v=89MyA7zPdYI&t=1s

    This seemed like a very good cost for such a big system about $9500 for a 30kw battery. Lifepo4 so less chance of fire and also takes around an hour to setup and can be shipped ups in several boxes. What would be two 2 or 3 hybrid inverter to use with this system?
    I know of old school sunnyboy "big yellow" ones, but dont' think they can handle that capacity?
    and sma has this newer one but also seems like you would need more than one for this big of a battery.
    SMA SunnyBoy Storage SBS6.0-US-10 Hybrid Inverter 6kW, -25 to +60°C - Solerus Energy

  • #2
    The old school SMA Sunny Island is for low voltage batteries. The SMA sunnyboy storage is for high voltage batteries, but the batteries must be on an approved battery list.. The new SMA high voltage battery solution is 240VAC output. You need two sunny islands (or Sunnyboy Storage) to make 240VAC or use a transformer.

    I have no experience with hybrid inverters to comment. I did research them in the past, but did not pursue it.
    Last edited by oregon_phil; 04-02-2021, 12:07 PM. Reason: New SMA high voltage battery inverter is 240VAC out not 120vac that I originally posted.

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    • #3
      $310 per kWh is not the best cost nor is it the worst cost. My 42kWh pack cost less than $125 per kWh delivered.
      Almost Any UL approved hybrid inverter would be good but the choice should be based on the use case. More details about that would be needed to know which features would optimize the use case. Some names I am familiar with are Outback Skybox, SolArk, Schneider and SMA. Some are better at AC coupling, some are better at optimizing TOU rates, some can be paralleled. Most can provide 240 volt split phase. Typically a hybrid is an inverter that combines some features of a GT inverter and an off grid inverter. There is no industry standard definition and the features and capability will vary between brands and models.

      Usually the inverter capacity is determined by the loads not by the kWh capacity of the battery. Even the smallest of the above inverters could be connected to a 30 kWh battery.
      Last edited by Ampster; 03-23-2021, 04:01 AM.
      9 kW solar. Driving EVs since 2012

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      • #4
        Originally posted by Ampster View Post
        $310 per kWh is not the best cost nor is it the worst cost. My 42kWh pack cost less than $125 per kWh delivered.
        wow who sells a pack that big??? for so cheap?

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        • #5
          Originally posted by khanh dam View Post

          wow who sells a pack that big??? for so cheap?
          LFP cells can be purchased on Alibaba to make DIY packs. Dave Poz makes money off Youtube and affiliate links to products like that battery if that matters to you. I could not confirm the UL certification. That would be a good value if indeed it qualified under the new NEC 2020 rules which specify UL battery systems.

          More importantly, to answer your question about which hybrid inverters, would be recomended, what is the use case? How many Watts of load does it need to serve? Is this a Grid Tie application or grid interactive application? Those are the questions that would help determine the best inverter. Battery size is more about how long a user would want to run the loads in a grid down situation or during load shifting.
          in my view inverter selection is more about features and kW capacity. Perhaps I am biased by my EV conversion experience where the battery choice was shaped by how far I wanted to go and the inverter/motor selection was shaped by how fast i wanted to go. Your mileage may vary.
          Last edited by Ampster; 03-23-2021, 02:32 PM.
          9 kW solar. Driving EVs since 2012

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          • #6
            Originally posted by Ampster View Post

            More importantly, to answer your question about which hybrid inverters, would be recomended, what is the use case? How many Watts of load does it need to serve? Is this a Grid Tie application or grid interactive application? Those are the questions that would help determine the best inverter. Battery size is more about how long a user would want to run the loads in a grid down situation or during load shifting.
            use case would be a for a typical NC home that uses 1100kwh/month and wants to run a 3 ton 30amp 240v central AC unit for 2 days on battery power. The AC will not be running all the time, wild guess is 4-6 hrs a day. Assume 10kw GT array which makes about 65kwh/day in the summer. I probabaly need to reread my book on solar battery systems. My gut feeling is that installing a minisplit that cools one important room would be the best way to go.

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            • #7
              Thank you for the definition of the use case. I also asked for the loads and hoped that you would do the math to articulate them in kW. If you are unable to figure out all the loads in kW then consider the A/C as the biggest one and add some kW for margin.

              The biggest factor will be the startup load of an A/C. To get that, look for the LRA number on the compressor or if it has not been purchased yet, consider one with a soft start or inverter driven variable speed. You will have to weigh the extra cost of low surge A/C versus the cost of a hybrid inverter that has the surge capability you need. If this does not make sense, I suggest you read the book and become informed enough to understand the concepts.

              Once you have a good idea of the running loads and surge loads that need to be served you are ready to evaluate hybrid inverters. Start with the list I gave you. Some have better surge than others. The SolArk have large capacity but may be limited on how much AC coupled GT solar can becoupled. It may be less than the 10 kW you assumed.
              If you haven't figured out by now this is a system design. All the parts have to interact efficiently or you are going to over pay for one part the will or can only be used at less than its capacity. If you want to see how it is done, look at Engineer775 videos. He is in your neck of the woods. Anyone who wants to do this on their own needs to be able do the above calculations and research components to design an efficient system. Otherwise DIY could be more expensuve than paying an installer to do it. Knowledge is power.
              9 kW solar. Driving EVs since 2012

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              • #8
                My gut feeling is that installing a minisplit that cools one important room would be the best way to go
                I agree with ampster. The condenser LRA are going to be one of the largest drivers of the solution set along with running amps. My old condenser was 70LRA and 20 running amps. That's 4800 watts just to run the outdoor condenser! A mini split is a good solution. I went with an inverter condenser and variable speed indoor unit. Power consumption is very low compared to my old unit.

                Other factors to consider: Is the sun going to be out when I need the battery? If I got a battery, I had assumed the sun was going to be out so I could count on solar power. But sunless weeks of 1/4" of wildfire ash and snow/ice on my panels forced me to think otherwise.

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                • #9
                  Originally posted by Ampster View Post
                  Anyone who wants to do this on their own needs to be able do the above calculations and research components to design an efficient system. Otherwise DIY could be more expensuve than paying an installer to do it. Knowledge is power.
                  Well most solar companies just sell a tesla power wall and do zero calculations. Trying to figgure out how long it might last cause someone I know bought one and it has not been installed yet and my mind is blown away that these solar companies just sell products without any research or calculations. How long will a tesla powerwall run a central ac unit is what Im trying to figgure out for my friend. Builders grade Hvac Goodman or Carrier, etc. not high end Trane Variable speed stuff!

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                  • #10
                    Originally posted by khanh dam View Post

                    Well most solar companies just sell a tesla power wall and do zero calculations.
                    I don't know where you get your information but that is not the conclusion I have reached. For example, one of the vendors I have used on a solar panel system install, has installed hundreds of Powerwalls. He is very succesful and does not pay for leads because his referrals come from satisfied customers. When he installed two Powerwalls for my good friend he did the math and I know he understands the physics. He can translate LRA into surge in kWs and know whether the 7kW surge capacity of the Powerwall can handle the surge of that device. I asked you for that number but you did not respond.
                    Trying to figgure out how long it might last cause someone I know bought one and it has not been installed yet and my mind is blown away that these solar companies just sell products without any research or calculations. How long will a tesla powerwall run a central ac unit is what Im trying to figgure out for my friend. Builders grade Hvac Goodman or Carrier, etc. not high end Trane Variable speed stuff!
                    How did you reach the conclusion that they did not do any calculations? Perhaps your friend did not give them the information that they needed to do the calculations.
                    You are asking me to give you a fish and I am trying to teach you how to fish so you can figure this stuff out on your own. I can only make assumptions based on the meager information you provided. There is no standard "Builders Grade" A/C and they vary in surge capacity.

                    Let us assume that your friends A/C can be started by a single Powerwall. Let us also assume that it draws 20 Amps and that there are no other loads. That calculates out to 4.8kWhs each hour. (20 Amps times 240 volts for one hour equals 4800 Watthours). If the capacity of one Powerwall is 13.8 kWhs how long do you think it would last? I assume you can do the math but i am happy to explain it in more detail.
                    The thread title asks about an inverter for a 30 kWh battery but now you are changing horses mid stream and asking about a Powerwall. My apologies if I got side tracked. I never answered the original question because I never got my clarifying questions answered. I made some assumptions in the example above, but the answer will be useless to your friend because his use case may be entirely different than my assumptions.

                    Did you see the figure @oregon_phil gave for LRA? Even though his Compressor only consumes 20 Amps a single Powerwall would never be able to start it. If you want to go back to the question of a hybrid inverter Phil would need to find one that can handle 16.8kW of surge to start his compressor. That is why I suggested earlier that a soft start or variable speed compressor might be less expensive than having to find an inverter solution that can handle the surge. Do you see where this is going?
                    Last edited by Ampster; 03-25-2021, 11:48 AM. Reason: Add calculations
                    9 kW solar. Driving EVs since 2012

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                    • #11
                      Originally posted by khanh dam View Post

                      Builders grade Hvac Goodman or Carrier, etc. not high end Trane Variable speed stuff!
                      A slight correction to my earlier post regarding 20 "running amps". I should have said 20 Rated Load Amps. This AC compressor can be run 20 amps maximum. The actual running amps depends on a lot of things (that I would like to forget about my HVAC classes), and usually runs 50 to 90% of RLA. So 2400 to 4320 watts to run the outdoor condenser compressor.

                      The "High end" trane variable speed outdoor condenser only has a two stage compressor and still has a rating of 60 LRA. I believe an inverter style compressor is the way to go.

                      I'm not a motor guy and can't begin to explain how a soft start device motor device would interact with a battery inverter (powerwall)

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                      • #12
                        Originally posted by oregon_phil View Post
                        .........

                        I'm not a motor guy and can't begin to explain how a soft start device motor device would interact with a battery inverter (powerwall)
                        I don't understand soft starts either. I have an inverter driven refrigerator and agree that for the application of moving heat (heat pump, A/C or refrigeration) true variable speed compressors are very efficient.
                        9 kW solar. Driving EVs since 2012

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                        • #13
                          Originally posted by Ampster View Post
                          You are asking me to give you a fish and I am trying to teach you how to fish so you can figure this stuff out on your own.
                          I truely appreciate that. I'm going to re read my solar battery book and revist this.

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                          • #14
                            my 3 hp well pump takes 15Kva to start, or so says my peak hold fluke meter.

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                            • #15
                              Originally posted by RottenMutt View Post
                              my 3 hp well pump takes 15Kva to start, or so says my peak hold fluke meter.
                              3hp PUMP? I have a 225 foot deep well and it only uses a 1hp pump. maybe you have an above ground pump?

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