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  • Adding batteries to solar PC system (for power outage)?

    I wanted to get thoughts on adding batteries to my newly installed solar PV system. I am pretty new to this technology....

    My understanding (from installer/engineer) is that when there is a power outage (grid) I lose the ability to use the energy created by my panels. I was going to install a portable gas generator as a backup however he also mentioned using a small battery pack. He said the solar system needs to send the power somewhere (for me to use it) but if the grid is down, so am I. He said I can install a small battery system so that the solar system can send the power to it, but then I can also use the power during the day. At night I guess I would use the batteries that may drain rather quickly depending on size. He said I would need an inverter however to convert the AC back to DC (my PC systems uses micro inverters on the roof). Apparently there is no risk to overloading the batteries either <?>

    I suspect the cost would vary by the batteries (size, number, etc.) and the inverter may be expensive too.
    I would not want a large battery system... maybe just something so that I can use the energy from the panels during the day (given sunlight), and maybe just use a generator at night, if needed.

    Any thoughts, insights, are appreciated...
    Wonder if this is something I (or electrician) can easily do.....?

    Thx!

  • #2
    I am going to enjoy the replies to this!

    Essentially you are screwed unless you spend a lot more money - probably more than you have spent so far.
    [SIGPIC][/SIGPIC]

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    • #3
      It means getting rid of all your micro inverters, buying a hybrid inverter,, rewire your whole system and house wiring , install a charge controller for the batteries, and buy a generator. The only thing you can reuse is the panels. Everything else gets chit canned.
      MSEE, PE

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      • #4
        Wow... the EE is going to send me some info. He had mentioned tapping into my breaker box (for the batteries), and it sounded quite straightforward....but no cost estimate yet.

        Originally posted by Sunking View Post
        It means getting rid of all your micro inverters, buying a hybrid inverter,, rewire your whole system and house wiring , install a charge controller for the batteries, and buy a generator. The only thing you can reuse is the panels. Everything else gets chit canned.

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        • #5
          Originally posted by desmo907 View Post
          Wow... the EE is going to send me some info.
          Please share when you get the info.
          MSEE, PE

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          • #6
            Yes,may be &amp; no

            Yes. The electrician is correct. You need batteries if you ever wish to run your loads during night hours (post/pre sunlight).

            May be. Having battery bank and inverter setup should be viable if investment is less than current cost + System size

            No. Battery bank and inverter never come cheap. Also be prepared for operating and replacement cost on long run.

            Regards,

            Saravana

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            • #7
              Thanks. I am not as concerned for night time use (will have a generator) but if we have a power outage I'd like to leverage the energy from the panels. Thus he said I would need batteries. I was suspecting something nominal, as I would probably never run off the batteries when the panels were not producing energy.

              Originally posted by sk_gc View Post
              Yes. The electrician is correct. You need batteries if you ever wish to run your loads during night hours (post/pre sunlight).

              May be. Having battery bank and inverter setup should be viable if investment is less than current cost + System size

              No. Battery bank and inverter never come cheap. Also be prepared for operating and replacement cost on long run.

              Regards,

              Saravana

              Comment


              • #8
                Originally posted by desmo907 View Post
                Thanks. I am not as concerned for night time use (will have a generator) but if we have a power outage I'd like to leverage the energy from the panels. Thus he said I would need batteries. I was suspecting something nominal, as I would probably never run off the batteries when the panels were not producing energy.
                The problem which the electrician may not be taking into account is that to run with a combination of batteries and panels to deliver power to the house when the grid is out will require installation of a transfer switch and also replacing your current grid-tie inverter with a hybrid inverter which can deliver power without using the grid voltage as a reference and the grid as an energy sink.
                From that point, the battery bank could be relatively small, but would have to be large enough to deliver all the load power at least briefly if a cloud passes over the panels, etc. That does not require a large battery storage capacity, but does require a large output current capacity. Which means using AGM batteries instead of FLA batteries, and still having the battery bank fairly large.
                SunnyBoy 3000 US, 18 BP Solar 175B panels.

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                • #9
                  Originally posted by desmo907 View Post
                  He said I can install a small battery system so that the solar system can send the power to it, but then I can also use the power during the day. At night I guess I would use the batteries that may drain rather quickly depending on size. He said I would need an inverter however to convert the AC back to DC (my PC systems uses micro inverters on the roof).
                  OK first I thought you installer was dreaming but I have read a bit more about what you said. He apparently is talking an additional separate system to what you already have. Which is great for him, but not you.

                  Short answer if extended outages are your concern, get a pad mounted generator, LPG, NG, or diesel powered and a Transfer Switch. Last thing you want is a battery system.
                  MSEE, PE

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                  • #10
                    I guess I was not clear.
                    I mentioned to him that if there is a power outage all my solar energy goes to waste so he mentioned I can use it in real-time with the batteries.
                    So it was not to use batteries to store the energy for later use but only so I can still use the electricity I generate from the panels during the day.


                    Originally posted by Sunking View Post
                    OK first I thought you installer was dreaming but I have read a bit more about what you said. He apparently is talking an additional separate system to what you already have. Which is great for him, but not you.

                    Short answer if extended outages are your concern, get a pad mounted generator, LPG, NG, or diesel powered and a Transfer Switch. Last thing you want is a battery system.

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                    • #11
                      Originally posted by desmo907 View Post
                      I guess I was not clear.
                      I mentioned to him that if there is a power outage all my solar energy goes to waste so he mentioned I can use it in real-time with the batteries.
                      So it was not to use batteries to store the energy for later use but only so I can still use the electricity I generate from the panels during the day.
                      Ok complete repacement and configuration which really makes you sales rep really happy.
                      MSEE, PE

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                      • #12
                        Tend to agree with Sunking. The micro-inverters are made not to work unless power detected from grid. Helps to reduce shocks to utility workers. Post if have a way.

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                        • #13
                          Actually it can be done. It will require batteries, a hybrid inverter charger of the Magnum Xantrex or outback class of inverter chargers.
                          A large diversion controller and enough load to bleed off all of the PV power generated. A separate sub panel for the critical circuits.
                          It will void the warranty on the Enphase (not that it will hurt them but by a prior legal agreement they have)
                          These systems are called AC coupled systems
                          NABCEP certified Technical Sales Professional

                          [URL="http://www.solarpaneltalk.com/showthread.php?5334-Solar-Off-Grid-Battery-Design"]http://www.solarpaneltalk.com/showth...Battery-Design[/URL]

                          [URL]http://www.calculator.net/voltage-drop-calculator.html[/URL] (Voltage drop Calculator among others)

                          [URL="http://www.gaisma.com"]www.gaisma.com[/URL]

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                          • #14
                            Cost wise and effectiveness: Get a generator. Far cheaper than a battery system and far more capable of doing what you want without lots of costs, headaches, problems, space usage, etc. A whole-house generator is at most $5K. You can power it with natural gas, propane or gasoline. Propane (LPG) proably is best if you have that already. I have a big propane tank for my house heating and hot water. I may add a generator some day but we only get power failures oh, about 4-hours per year. No way I would spend money on Solar batteries for that. That's an average- one time we had 2 days of outages after remnants of a hurricane came through. Big whoop- we survived. Some neighbors had generators and we didn't, so we lost a refrigerator's worth of food. I can handle that cost until it happens enough to really give us headaches.

                            I'm doing a Solar PV system this year. I may hook up a generator next year as a project but really - in the USA, power outages rarely run more than a few days unless it's a really rural, mountainous situation after a hurricane or big snow dump (NH last October).
                            PowerOne 3.6 x 2, 32 SolarWorld 255W mono

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                            • #15
                              Originally posted by bonaire View Post
                              You can power it with natural gas, propane or gasoline.
                              God I hope not. No one makes a standby emergency generator that uses gasoline. At least I hope not as that would be really stupid if they did. All of them I am aware of use diesel, LPG, or NG.
                              MSEE, PE

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