Announcement

Collapse
No announcement yet.

Question on adding solar to Whole house backup with ATS

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • Question on adding solar to Whole house backup with ATS

    Long time lurker first time poster and I wanted to say thanks for all the great information shared on this board. It has provided my hours of items to research and learn more about. I am posting here as I am considering adding solar panels to my house and wanted some feedback to make sure I wasn't missing something obvious and feedback or ease of future maintenance before I reach out to the power company and electricians. I prefer to be able to know enough that I can have a two way discussion to find the best solution to my needs that meets my local requirements.

    I have a 320 amp service coming to my house which breaks into two 200 amp feeds. These each run to a separate Generac ATS that switches between utility and whole house generators for the 200 amp load centers.

    After reading through the documentation that my utility has online I have two limitations.

    1) Main reason I am here as it prevents the easiest solution. No line side taps are allowed by the utility. All interconnections of the solar system must happen after the point of first disconnect.
    2) Utility implements a hard cap of 20KW capacity, but if I go over 10KW of capacity I start paying a standby charge based on the peak KW utilization. This of course puts a kink in the cost savings of running my own generation capacity if I go over the 10KW capacity. (One of my questions for the utility will be is this based on the total array capacity, the inverter capacity or some other calculated number.

    My hope is to come as close to that 10KW number as possible.

    I realize that I cannot interconnect the solar system to either of my existing load centers as when the utility goes out, the ATS breaks the connection to utility, triggers the start of generator and cuts over to the utility. If the solar system was connected to the existing load centers, then I would risk backfeeding the generator and causing expensive damage to either the generator or electrical system.

    The couple solutions I have come up with:

    1) Split the solar panels between two 5KW inverters. Place a 200 amp load center with built in pass-thru lugs between the meter and the ATS. This becomes my point of first disconnect. This allows me to connect 5KW of solar capacity to a 30 amp breaker meeting the requirements of the 120% rule within the panel as well as keep the connection before the ATS so that when the utility goes offline and the ATS switches over to generator, the solar system is not connected to the same grid as the generator. When the utility comes back, the ATS monitors for stable power, cuts the generator and switches back to utility power. Solar inverter should see the utility is back on and start sending power again as well. Everything should be pretty well automated and I shouldn't have to touch it other than regular maintenance items. My concern with this design is that I wonder if I am risking back feeding the two inverters to each other when I am tied to the utility power since both inverters are tied to the same grid at the meter? This is most economic method of adding the 10KW I have found.

    2) Install a 225 amp load center with a 200 amp main breaker with add-on pass-thru lugs between the meter and one of the ATS, leaving the other ATS as is directly connected to the meter. I can connect the single 10KW inverter to the load center via a 60 amp breaker. Feed the ATS through the add-on pass-thru lugs. More expensive and takes up more space due to the larger load center size, but does reduce the number of components in the system. (Simplification)

    Thoughts, comments suggestions welcome.

  • #2
    Set your Generator to run at 58-59 hz, assuming the inverter(s) will not qualify *. The slight reduction in frequency will only be noticed by clocks synced to line frequency. No other gear should notice this difference. (most everything is rated 50-60hz globally)

    * some smart inverters may try to qualify thinking the utility is wanting more/less solar output

    Other ways involve a relay coil connection to the generator side of the ATS, and the relay contacts control a Inhibit function on the Inverter (inverter may not have this feature)
    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

    Comment


    • #3
      My ATS has a contactor for grid and 1 for gen, I added a next contactor that feed the solar to my house panel.
      The control of that contactor is wired in parallel with the one for the grid.

      Comment


      • #4
        Are generators not able to deal with power coming form a second source? I figured the reason Solaredge and other grid tie manufacturers say not to connect to a generator is because cheap generators don't always regulate voltage and frequency very well.

        Comment


        • #5
          Originally posted by reader2580 View Post
          Are generators not able to deal with power coming form a second source? I figured the reason Solaredge and other grid tie manufacturers say not to connect to a generator is because cheap generators don't always regulate voltage and frequency very well.
          Generators need to be synced together so they produce the same phase angle and frequency. Most small stand alone generators do not have that ability so it is not good to connect them to a second power source.

          Comment


          • #6
            Sync'd generators can be easily paralleled.
            But a GT inverter is not a generator, it wants to raise the voltage of the line it's connected to. Since the entire grid is there, it cant raise the grid voltage. But when you hook up to a generator, it might sync up to a really good expensive generator and if there is enough solar, it will raise the line voltage above 250VAC. What the generator will do, when it's got voltage running into it like that, usually becomes real expensive before the inverter over-voltages and resets and trys again in 5 min to fry your generator.
            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

            Comment


            • #7
              Originally posted by reader2580 View Post
              Are generators not able to deal with power coming form a second source? I figured the reason Solaredge and other grid tie manufacturers say not to connect to a generator is because cheap generators don't always regulate voltage and frequency very well.
              No, because they are power sources, not loads.

              Comment


              • #8
                Thank you all for your replies and suggestions. Gives me more things to research and see what the best solution is for to work with.

                Comment

                Working...
                X