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  • small hybrid system

    I have a customer who wants to put only 1kw of Pv on the roof, charge a battery and have grid tie as a backup only. She will just run the furnace(in a power outage), fridge, tv and the like on an ongoing basis. The Hybrid charger/inverters i have seen are much bigger than this and, to complicate matters, I have lots of 250w grid tie panels in stock which i want to use up, but of course they are 37V and not 24V. Any ideas?

  • #2
    Well an mppt controller is first off when using a 12v system if that is what is intended
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    • #3
      Yes, but it would be nice of there was a charger/inverter with grid backup that can use a 37V panel (all in one package). I haven't seen one yet and I wondered if you gods of PV have (blatant ass kissing, if you haven't noticed )

      This system won't be running any 12v appliances, only 120vac stuff

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      • #4
        Originally posted by MikeSolar View Post
        I have a customer who wants to put only 1kw of Pv on the roof, charge a battery and have grid tie as a backup only. She will just run the furnace(in a power outage), fridge, tv and the like on an ongoing basis. The Hybrid charger/inverters i have seen are much bigger than this and, to complicate matters, I have lots of 250w grid tie panels in stock which i want to use up, but of course they are 37V and not 24V. Any ideas?
        I am a little unclear what your customer wants.

        Either she wants to have 1kw of solar panels that only charges a battery to run specific loads if there is a Utility power outage,

        Or she wants a 1kw "grid tie" solar system that also has a battery backup in case the power goes out.

        The first is possible but a very expensive backup power system when you figure in the cost of the batteries and panels as compared to a backup generator.

        The second doesn't make much sense either because such a small solar array will be very expensive $/watt as compared to a normal size grid tie system around 5kw. On top of that adding batteries just runs the price up a lot more.

        Also 37volt panels will work just fine charging batteries when they are matched up with a good MPPT type charge controller. So why does matter if they aren't 24volts?

        So help me out and again tell us what she is looking for?

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        • #5
          Originally posted by SunEagle View Post
          I am a little unclear what your customer wants.

          Either she wants to have 1kw of solar panels that only charges a battery to run specific loads if there is a Utility power outage,

          Or she wants a 1kw "grid tie" solar system that also has a battery backup in case the power goes out.

          The first is possible but a very expensive backup power system when you figure in the cost of the batteries and panels as compared to a backup generator.

          The second doesn't make much sense either because such a small solar array will be very expensive $/watt as compared to a normal size grid tie system around 5kw. On top of that adding batteries just runs the price up a lot more.

          Also 37volt panels will work just fine charging batteries when they are matched up with a good MPPT type charge controller. So why does matter if they aren't 24volts?

          So help me out and again tell us what she is looking for?
          It's no problem to be 24V and the cost is not the biggest issue. She wants to be able to run her TV and fridge off solar and if there is not enough battery, to flip it over to the grid. I don't think she cares to be monitoring the system so it will have to be autonomous. I will have to come in periodically and service the system.

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          • #6
            Originally posted by MikeSolar View Post
            It's no problem to be 24V and the cost is not the biggest issue. She wants to be able to run her TV and fridge off solar and if there is not enough battery, to flip it over to the grid. I don't think she cares to be monitoring the system so it will have to be autonomous. I will have to come in periodically and service the system.
            Why would she want to run her tv and fridge off of a battery instead of the grid? Using a battery as your power source will cost you 10 times as much as just using the grid.

            The grid should be the main power source and then while costly the battery is the backup power source. She has it ass backwards.

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            • #7
              Originally posted by SunEagle View Post
              Why would she want to run her tv and fridge off of a battery instead of the grid? Using a battery as your power source will cost you 10 times as much as just using the grid.

              The grid should be the main power source and then while costly the battery is the backup power source. She has it ass backwards.

              Yup, I know this and have explained it to her but this is what she wants to do so I need to help her do it.

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              • #8
                Originally posted by MikeSolar View Post
                Yup, I know this and have explained it to her but this is what she wants to do so I need to help her do it.
                You know this whole Solar vs Grid thing in regards to cost is like buying a $55,000 hybrid vehicle thinking you are going to save in the long run in gas.

                It is more about saying you are off the grid than really being off grid.

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                • #9
                  Originally posted by MikeSolar View Post
                  Yup, I know this and have explained it to her but this is what she wants to do so I need to help her do it.
                  I think I understand her motivation. Unfortunately that type of hybrid system she wants is neither small or cheap.

                  If she won't go for a full scale grid tie system then maybe providing her a solar battery system that meets her power needs and has the ability to charge the batteries from the grid through a battery charger. You can set off a warning when the battery voltage is getting low so she could then plug in the battery charger. Getting that all done automatically will be expensive.

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                  • #10
                    Originally posted by SunEagle View Post
                    I think I understand her motivation. Unfortunately that type of hybrid system she wants is neither small or cheap.

                    If she won't go for a full scale grid tie system then maybe providing her a solar battery system that meets her power needs and has the ability to charge the batteries from the grid through a battery charger. You can set off a warning when the battery voltage is getting low so she could then plug in the battery charger. Getting that all done automatically will be expensive.
                    Well, I have convinced her to do something like the Outback GFX 1548 (due to the 37v, 250w panels i have) but I will need a 48v battery bank which is a pain for a system with only 1kw of panels. Not too sure what to get for those as I don't want to over size the batteries.

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                    • #11
                      Originally posted by MikeSolar View Post
                      Well, I have convinced her to do something like the Outback GFX 1548 (due to the 37v, 250w panels i have) but I will need a 48v battery bank which is a pain for a system with only 1kw of panels. Not too sure what to get for those as I don't want to over size the batteries.
                      You have your work cut out for you. Too little battery and she will be draining them quickly. Too much and that 1kw of panels will have a hard time getting them properly charged. She has painted herself into a corner but doesn't know she is already stuck. Good luck with your design.

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                      • #12
                        Get 8 6volt 225 amps golf cart batteries and an automatic transfer switch, get an inverter can program the low battery cut off or a charge controller which can do the job. you also need an AC battery charger if the inverter doesn't come with it.
                        After I check the inverter you mention it has all the features so you only need the battery and the automatic switch to transfer to the grid when the battery go low.

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                        • #13
                          Originally posted by paulcheung View Post
                          Get 8 6volt 225 amps golf cart batteries and an automatic transfer switch, get an inverter can program the low battery cut off or a charge controller which can do the job. you also need an AC battery charger if the inverter doesn't come with it.
                          After I check the inverter you mention it has all the features so you only need the battery and the automatic switch to transfer to the grid when the battery go low.
                          It appears to have a transfer switch built in.

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                          • #14
                            Don't know if you can program that internal transfer switch backward, the external transfer switch will allow you to choose which power source is primary which is secondary.

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                            • #15
                              Originally posted by paulcheung View Post
                              Don't know if you can program that internal transfer switch backward, the external transfer switch will allow you to choose which power source is primary which is secondary.
                              Which takes me back to my comment in post #6 about the system being backwards with Battery as primary and Utility as secondary or backup. This system can be costly due to the way it is expected to work.
                              Last edited by SunEagle; 09-01-2014, 12:37 PM. Reason: spelling

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