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  • Georgia on my mind

    Hello all, just getting myself started in the solar arena. This looks like a good active forum to earn a few merit badges along the way. My current system is a 1386 watt ( and growing) string powering a Power One Aurora 2KW grid tie along with a EPSolar 40A MPPT controller hosting a bank of 4 - 230Ah GC batteries and a Xantrex 1000W sine inverter. The Battery charge controller is running off a tap on the entire string as it can't handle the full voltage or watts.

  • #2
    Originally posted by HOASUNBuster View Post
    Hello all, just getting myself started in the solar arena. This looks like a good active forum to earn a few merit badges along the way. My current system is a 1386 watt ( and growing) string powering a Power One Aurora 2KW grid tie along with a EPSolar 40A MPPT controller hosting a bank of 4 - 230Ah GC batteries and a Xantrex 1000W sine inverter. The Battery charge controller is running off a tap on the entire string as it can't handle the full voltage or watts.
    Hello HOASUNBuster and welcome to Solar Panel Talk!

    I think that if you do the math, you will find that having two different MPPT devices (in your case GTI and CC) connected to the same array of panels (even with a tap) is not going to work out well.
    Without the tap, with both connected at the same point, they will fight each other trying to get the lion's share of the panel output with the result that either the operating power point will be unstable or it will stabilize at less than the panel MPP.
    With the tap, the GTI is going to get shortchanged since some of the current from the lower part of the panel string is being diverted, confusing its attempt to get MPP from the point where it is connected.

    You may be lucky enough to have something close to optimal, but it is very unlikely and I would not recommend that configuration to anyone.
    Have you actually observed and done the calculations on the input power to the two units?

    It is true, however, that splitting the array into two fixed size sub-arrays is not going to give you optimum performance either.
    SunnyBoy 3000 US, 18 BP Solar 175B panels.

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    • #3
      Tap on string

      Inetdog, you are absolutely correct but since one is grid tie and the other is off grid, you have to consider them as 2 separate systems. When I installed them, I pulled wire for 2 strings. One is now the tap for off grid and the other is the entire string for grid tie. Both are switched so I can enable and disable one, the other or both. If I have need to use the off grid system, in order to adequately fund the off grid charge controller, I have to disable the grid tie until the battery bank is recharged. In the event of a power failure, the grid tie is useless so I can devote all the off grid system can handle without worry. They make systems like this but mine cost far less than those and I get the same function. Optimal is one or the other and not both. I am actually thinking of adding a second standby charge controller to put in parallel with my tracer and with a slight reconfiguration of wiring, I can feed both to actively power my home devices and not drain the batteries in the process, at least during a sunny day.

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      • #4
        Originally posted by HOASUNBuster View Post
        Inetdog, you are absolutely correct but since one is grid tie and the other is off grid, you have to consider them as 2 separate systems. When I installed them, I pulled wire for 2 strings. One is now the tap for off grid and the other is the entire string for grid tie. Both are switched so I can enable and disable one, the other or both. If I have need to use the off grid system, in order to adequately fund the off grid charge controller, I have to disable the grid tie until the battery bank is recharged. In the event of a power failure, the grid tie is useless so I can devote all the off grid system can handle without worry. They make systems like this but mine cost far less than those and I get the same function. Optimal is one or the other and not both. I am actually thinking of adding a second standby charge controller to put in parallel with my tracer and with a slight reconfiguration of wiring, I can feed both to actively power my home devices and not drain the batteries in the process, at least during a sunny day.
        Interesting hybrid system you have there. I am not sure why you want to add the complexity of switching so you can use your grid tie solar panels to charge your batteries. Also running any loads off batteries is much more expensive than using the power from the Utility and charging batteries from solar is more expensive than using a standard battery charger.

        The batteries may be your idea of an emergency backup power but with a battery system you still need a generator of some kind. That generator can support you during a power outage and charge your batteries when the power goes out.

        IMO adding the wiring, switching and charge controllers seems to be an added expense that probably will never pay for itself.

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        • #5
          Originally posted by SunEagle View Post
          Interesting hybrid system you have there. I am not sure why you want to add the complexity of switching so you can use your grid tie solar panels to charge your batteries. Also running any loads off batteries is much more expensive than using the power from the Utility and charging batteries from solar is more expensive than using a standard battery charger.

          The batteries may be your idea of an emergency backup power but with a battery system you still need a generator of some kind. That generator can support you during a power outage and charge your batteries when the power goes out.

          IMO adding the wiring, switching and charge controllers seems to be an added expense that probably will never pay for itself.
          SunEagle, My first effort was to have some battery backup that was not dependent on a natural resource that cost me money to actually run beyond the cost of implementation hence the solar battery, inverter setup. That grew along with my interest in the technology into a full emergency system that can run small things by battery along with a tri fuel ( gas, propane, natural gas) 7kw generator and a transfer switch to run anything else for emergencies. The next logical step was implementing something that could help pay for the initial expense of all that with a few more panels and a grid tie. I just had a 1518W peak day today and I think that is pretty good for only having panels rated at 1422 and it rained most of the day. Still trying to figure that one out but not going to spend too much time on it The sun must have been really strong and clear for a few minutes at some point. It has been something that has grown bit by bit and not a total system from the start but it all works together and meets my needs.

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          • #6
            Originally posted by HOASUNBuster View Post
            I just had a 1518W peak day today and I think that is pretty good for only having panels rated at 1422 and it rained most of the day.
            Cloud edge effect - momentary and meaningless.
            [SIGPIC][/SIGPIC]

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            • #7
              Originally posted by russ View Post
              Cloud edge effect - momentary and meaningless.
              Ahh, thanks for bursting my bubble Went and read up on that phenomenon and that is nice to know about in designing systems. Good to know about.

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              • #8
                Originally posted by HOASUNBuster View Post
                SunEagle, My first effort was to have some battery backup that was not dependent on a natural resource that cost me money to actually run beyond the cost of implementation hence the solar battery, inverter setup. That grew along with my interest in the technology into a full emergency system that can run small things by battery along with a tri fuel ( gas, propane, natural gas) 7kw generator and a transfer switch to run anything else for emergencies. The next logical step was implementing something that could help pay for the initial expense of all that with a few more panels and a grid tie. I just had a 1518W peak day today and I think that is pretty good for only having panels rated at 1422 and it rained most of the day. Still trying to figure that one out but not going to spend too much time on it The sun must have been really strong and clear for a few minutes at some point. It has been something that has grown bit by bit and not a total system from the start but it all works together and meets my needs.
                I understand your reasoning although if you take into consideration the cost of the Solar Charge controllers, wiring, fusing and switching hardware I would expect that you can run a propane generator for a real long time. Now if you have a lot of power outages then at some point your "fuel" costs may exceed the cost of all that hardware.

                I chose to build a small solar battery system with the idea of having "free" power after a hurricane took down our normal power. After spending a lot of money (~$2500) for the batteries, panels, CC, combiner box, inverter, etc. I found that my system can put out about 600 to 800 watt hours a day without hurting the batteries which is not really much. That $2500 could have been better spent toward an efficient generator that could run my whole house. Propane is relatively cheap and you can store quite a bit in a 100 gal tank.

                It is just economics and with your grid tie system I would say you have a really good start on reducing your electric bill. As for the "solar emergency backup system" I would say it is not really economical.

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                • #9
                  Originally posted by SunEagle View Post

                  It is just economics and with your grid tie system I would say you have a really good start on reducing your electric bill. As for the "solar emergency backup system" I would say it is not really economical.
                  Thanks. The battery backup was not meant to be economical but to provide some means of providing light and possibly run my refrigerator or furnace in an emergency. It is far too small to run the air conditioner. Storing a large amount of propane or gasoline is not what I want to do either but I can run the generator off the natural gas feed on my house and that is the way it is currently calibrated to run. I have the generator in the event of a large storm Ice damage or tornado damage to infrastructure that would normally take days or more to repair so that I can continue to run and protect my home during such an event so the economics of that part is just not so much of an issue as long as the gas is still flowing. I can easily watch 4 or 5 hours of TV/DVD's and run lights on battery at night and with a mildly sunny day, I can recover the charge to do it again and beyond what I have spent, there is no additional cost to do that. It is when I need to protect pipes from freezing with no heat or if the heat was very hot to be able to periodically run my air that the generator would come in but there is an expense with that and that is more than I pay for electricity. Generators are not known for being efficient and it makes the wheels spin on my gas meter so I don't want it running constantly simply for conservation of expenses unless it is required. I hope to be able to get up to some regular 10KWh days when fully populated and that with my conservation efforts will be half or better of my summer daily usage if I don't run my electric clothes dryer. I am getting some negative spikes on the hourly AMI data so there are times I am making more than I use and I just added 2 more panels so I hope to see more of that if the clouds will go away.

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                  • #10
                    Originally posted by HOASUNBuster View Post
                    Thanks. The battery backup was not meant to be economical but to provide some means of providing light and possibly run my refrigerator or furnace in an emergency. It is far too small to run the air conditioner. Storing a large amount of propane or gasoline is not what I want to do either but I can run the generator off the natural gas feed on my house and that is the way it is currently calibrated to run. I have the generator in the event of a large storm Ice damage or tornado damage to infrastructure that would normally take days or more to repair so that I can continue to run and protect my home during such an event so the economics of that part is just not so much of an issue as long as the gas is still flowing. I can easily watch 4 or 5 hours of TV/DVD's and run lights on battery at night and with a mildly sunny day, I can recover the charge to do it again and beyond what I have spent, there is no additional cost to do that. It is when I need to protect pipes from freezing with no heat or if the heat was very hot to be able to periodically run my air that the generator would come in but there is an expense with that and that is more than I pay for electricity. Generators are not known for being efficient and it makes the wheels spin on my gas meter so I don't want it running constantly simply for conservation of expenses unless it is required. I hope to be able to get up to some regular 10KWh days when fully populated and that with my conservation efforts will be half or better of my summer daily usage if I don't run my electric clothes dryer. I am getting some negative spikes on the hourly AMI data so there are times I am making more than I use and I just added 2 more panels so I hope to see more of that if the clouds will go away.
                    There is no question that your grid tie system is saving you money and will pay for itself. And I understand your viewpoint about running the generator. It is easy to see money going out the door when the gas meter runs but not so easy to see the same happening with your battery. To you it just sits there and provides power. What is really happening is that it is slowly dying every time you charge and discharge. Since there is no "meter" you can't see the dollars going out but they are. When the batteries finally fail they will need to be replaced at a pretty good cost.

                    If you are satisfied with your arrangement then enjoy it. Unfortunately based on pure physics you are spending more running off of your batteries then your gas generator. I am only trying to help you understand the costs.

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                    • #11
                      Originally posted by SunEagle View Post

                      If you are satisfied with your arrangement then enjoy it. Unfortunately based on pure physics you are spending more running off of your batteries then your gas generator. I am only trying to help you understand the costs.
                      I am satisfied and I do understand the expense and the eventual replacement cost of the batteries over time. That is why I only have 4 batteries and not 14 or 24. For short durations, it provides what I need and if I need to replace them in 5+ years, so be it. If I get 1000 cycles, then it costs me about 45 cents a cycle. I spend $2.50 to $3.50 a day on electricity so to have lights and television for an evening costing $.45 I don't think is too bad. It is a trade off I have considered and am OK with. It is a total package that gives me several options. I am more of a utilitarian person and having several options to choose from depending on circumstances is good for me. I can use as much or as little as needed and I have the big guns for total home support if things warrant or just to run my DVD player and have movies from a bad T-Storm knocking out power for an evening. I will however be the only house in my neighborhood with power

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                      • #12
                        Originally posted by HOASUNBuster View Post
                        a bad T-Storm knocking out power for an evening. I will however be the only house in my neighborhood with power
                        Except the guy with a generator that did it for a fraction of the cost or trouble.
                        [SIGPIC][/SIGPIC]

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                        • #13
                          Originally posted by russ View Post
                          Except the guy with a generator that did it for a fraction of the cost or trouble.
                          But is producing sound as well as light....
                          SunnyBoy 3000 US, 18 BP Solar 175B panels.

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                          • #14
                            Originally posted by inetdog View Post
                            But is producing sound as well as light....
                            Exactly right. All I have to do is flip a switch and I have quiet power for limited things. Dragging out the generator and hooking that up would take probably 20 minutes and yes, make noise.Solarwall.jpg
                            Last edited by HOASUNBuster; 08-21-2014, 08:07 AM. Reason: Added photo

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                            • #15
                              Originally posted by HOASUNBuster View Post
                              Exactly right. All I have to do is flip a switch and I have quiet power for limited things. Dragging out the generator and hooking that up would take probably 20 minutes and yes, make noise.[ATTACH=CONFIG]4657[/ATTACH]
                              The generator could be automatic transfer and virtually zero noise - providing you don't go for a cheap Chinese 3,000 RPM type.
                              [SIGPIC][/SIGPIC]

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