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Solar by day... Grid by night... without grid tie system possible?

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  • Solar by day... Grid by night... without grid tie system possible?

    Just curious... I've done some searching but came up empty.

    Would there be a way to use solar during the day and automatically transfer back to the grid when the battery bank gets to a certain voltage point or at night when the sun goes down?

    Kinda like how a generator transfer switch functions... but backwards. Run on the generator (solar in this case) as the primary and switch to the grid automatically when solar is down?

    Has anyone heard of doing this? What type of transfer switch would be needed? Is it safe/legal?

    Basically, don't want to back feed the meter or sell power to the power company. I assume a grid tie inverter is the same thing... Im just curious if there is an automatic way of disconnecting completely from the grid when on solar... then back to the grid when not. Make sense? Keep both systems separate at all times is what I'd like to do.
    Last edited by Mr4btTahoe; 09-25-2017, 03:39 PM.

  • #2
    It's not really logical, because you must have battery storage to run the system without the grid during the day. Consider this to double the cost of the installation. So the if you have the grid available to you at night, why not use it during the day? There might be reasons, but they aren't going to justify the added cost unless your doing it for "enjoyment".

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    • #3
      We shift back and forth manually.

      If we are not paying much attention, sometimes at night our battery level will drop to it's Low Voltage Cut-Off level. Then we have to shift back to grid power [assuming the grid is up, sometimes I have gone to grid and it is not up].
      4400w, Midnite Classic 150 charge-controller.

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      • #4
        Originally posted by adoublee View Post
        It's not really logical, because you must have battery storage to run the system without the grid during the day. Consider this to double the cost of the installation. So the if you have the grid available to you at night, why not use it during the day? There might be reasons, but they aren't going to justify the added cost unless your doing it for "enjoyment".
        That is the reasoning given by salesmen trying to sell net-metering system contracts. 'Buy a more expensive net-metering system and save money over off-grid installs because they must buy batteries"

        Batteries are a lot lower expense than the PhotoVoltaics are and without and financing charges, ...

        I attended an Alternative Energy fair this weekend, and I saw this conversation play-out a bunch of times

        4400w, Midnite Classic 150 charge-controller.

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        • #5
          Originally posted by organic farmer View Post
          That is the reasoning given by salesmen trying to sell net-metering system contracts.
          Correct me if I'm wrong but it sounds like you are comparing a financed grid tied system with a DIY battery system. If we compare non-financed DIY grid tied and battery systems, I think the grid tie will win in a financial sense hands down in many (if not most) parts of the U.S. where net metering is allowed. For example, my 4kW grid tie system cost $8K for parts, permit, shipping and taxes, and and after the tax rebate I was out of pocket about $5600. I think you'll be hard-pressed to match that with a battery system, even if you ignore the ongoing battery replacement costs.

          It may be true that the battery cost is lower than the photovoltaics, but not having to buy them at all is even better.

          I think you said that you live in an area where power is expensive and unreliable, and that you have a business that allows offsetting the expense of solar in tax liability, but those two factors don't apply to most of the rest of the U.S.

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          • #6
            Basically, I'd like to work towards going fully off grid but cant swing it all at once. Grid tie (net metering) law has changed in my area... now if we build a grid tie system, we have to sell all the power to the power company and buy it back from them at a higher rate. They kinda like having control... lol. We were planning on going with a grid-tie system however our time has ran out to be grandfathered in. They just changed the law to where now, net metered installations only get back wholesale rate on what they produce... instead of retail. By 2027, net metering will be banned.all together.

            Anyways... that's why I'd like to keep the 2 systems completely separate and switched either automatically (would be nice) or manually. Have access to both systems until our solar system is capable of handling all of our needs. The power company and state can kiss my ass... basically. lol

            This way, while our system is too small, we could at least use it to limit what power we use from the grid.

            Ideas?
            Last edited by Mr4btTahoe; 09-25-2017, 04:57 PM.

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            • #7
              Originally posted by organic farmer View Post
              .....Batteries are a lot lower expense than the PhotoVoltaics are and without and financing charges, ...
              How much time do you spend maintaining your batteries, and what is your projected replacement timeline & expense ?

              Powerfab top of pole PV mount (2) | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
              || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
              || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

              solar: http://tinyurl.com/LMR-Solar
              gen: http://tinyurl.com/LMR-Lister

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              • #8
                Originally posted by Mike90250 View Post

                How much time do you spend maintaining your batteries, and what is your projected replacement timeline & expense ?
                So far I have spent about one hour every quarter in battery maintenance.

                The consensus seems to be that most off-grid homes will replace their first battery bank somewhere between year 10 and 12, regardless of which brand of battery was used. Our batteries cost around $2200.

                This state does not allow DIY net-metering installs. Net-metering is required to be done by certified installers, who are all equipment dealers who refuse to touch any component that they did not sell you [I have asked].

                4400w, Midnite Classic 150 charge-controller.

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                • #9
                  Originally posted by organic farmer View Post
                  This state does not allow DIY net-metering installs.
                  Your profile says Maine.
                  Maine does allow DIY net metering installs.
                  Search "Guy Marsden Solar" for one person's blog about doing a DIY solar grid-tie installation in Maine

                  Net-metering is required to be done by certified installers
                  The installers certainly want you to think that.
                  I know a lot of states have owner-builder exceptions for permits which allow you to do DIY and do everything in a proper and permitted fashion.

                  And some states have solar installers as a special licensed installer - but they also have general electrician licenses, and the licensed electricians can also do the electrical work for solar installs. Usually there's enough electricians around that you can likely find one who will do the work for you on an hourly basis, using equipment you've bought.

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                  • #10
                    There was a guy on another board that was trying to develop a board that would run a refrigerator etc off solar and a small battery. When the battery dropped below a certain point it would switch power over to grid. A fairly simple thing to do with a few caveats. My belief is if you really have to ask, you can't do it. A smart home system will be the future as the utilities start charging different rates for different time periods and premiums for peak demand. I live totally off grid with a battery system that wouldn't even be considered sufficient for a garden shed. Just about everything runs only during the day. Excess PV heats water for showers. Wife even has a dishwasher.

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                    • #11
                      Originally posted by PNPmacnab View Post
                      There was a guy on another board that was trying to develop a board that would run a refrigerator etc off solar and a small battery. When the battery dropped below a certain point it would switch power over to grid. A fairly simple thing to do with a few caveats. My belief is if you really have to ask, you can't do it. A smart home system will be the future as the utilities start charging different rates for different time periods and premiums for peak demand. I live totally off grid with a battery system that wouldn't even be considered sufficient for a garden shed. Just about everything runs only during the day. Excess PV heats water for showers. Wife even has a dishwasher.
                      Building a system that can switch between a battery or the grid is relatively easy using quality transfer equipment. The problem is getting it installed per code and with the permission of your POCO and AHJ.

                      Now if the loads you want transferred are wired to a separate "emergency load" panel then that makes it even easier to install that type of system. But if the "battery powered" loads are using extension cords from a stand alone inverter then the system may not be cheap or easy to have them transferred to grid power.

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                      • #12
                        What if you used a "Grid-Zero" system?
                        The goal is to .... not push any energy into the Grid.
                        The Inverter attempts to just offset your existing Loads.
                        Instead of switching your loads from the grid to/from the battery bank,
                        it regulates the Inverter's output to not exceed your loads.
                        This effectively accomplishes what you want to do.

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                        • #13
                          Originally posted by NEOH View Post
                          What if you used a "Grid-Zero" system?
                          The goal is to .... not push any energy into the Grid.
                          The Inverter attempts to just offset your existing Loads.
                          Instead of switching your loads from the grid to/from the battery bank,
                          it regulates the Inverter's output to not exceed your loads.
                          This effectively accomplishes what you want to do.
                          these systems are possible with and without batteries as well and no switching is needed.
                          OutBack FP1 w/ CS6P-250P http://bit.ly/1Sg5VNH

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                          • #14
                            Originally posted by ButchDeal View Post

                            these systems are possible with and without batteries as well and no switching is needed.
                            I agree if the OP had a Grid Tie system there are a number of options. But if the OP has an "off grid" system for some loads and the grid (without pv) for other loads some type of switching and disconnection is required to keep the off grid system from back-feeding the grid.

                            Seems like a lot of work to keep the loads fed yet lose money due to using batteries to generate electricity. But each to their own ideas.

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