Grid connection power meter function

Hey I have a ? concerning utility meter. After a long wait on SCC's Xantrex XW MPPT 80 A 600 V ( the first 2 were bad) I finally started making some power. The system seems to be kickass and watching the meter it seems to be counting my production as power supplied. I haven't got the sell meter installed yet. I want to shut it down until...if this is the case. It seems as long as I have enough load going it evens out what comes in but when it's my inverters are selling the grid meter is reading high 6 kw receive power. Is this a fact that its recording my production as power they supplied? I'll test it for sure when the sun comes up. Just thinking someone might know now and I will save myself the trouble and just shut down till I get the meter. Thanks

2 XW4548 inverters, 4 strings (10) panels each of 245W Yingli , Xantrex XW MPPT 80 A 600 V. 9600 watt total.

Comments

  • Ralph DayRalph Day Solar Expert Posts: 934 ✭✭✭✭
    Re: Grid connection power meter function

    Is it a "smart" meter? If it's digital (likely) and does not say NET somewhere, or you see one number displayed (your consumption) and another number displayed afterward (your production) you are likely paying for the privilage of putting power into the grid. Best to disable until the new meter is in place. Have you got a connection aggreement allowing you to do this, all permits in place etc?

    You should be able to disable the selling to the grid with those inverters...check the manuals.

    Ralph
  • SailawaybobbySailawaybobby Registered Users Posts: 2
    Re: Grid connection power meter function
    Ralph Day wrote: »
    Is it a "smart" meter? If it's digital (likely) and does not say NET somewhere, or you see one number displayed (your consumption) and another number displayed afterward (your production) you are likely paying for the privilage of putting power into the grid. Best to disable until the new meter is in place. Have you got a connection aggreement allowing you to do this, all permits in place etc?

    You should be able to disable the selling to the grid with those inverters...check the manuals.

    Ralph

    Hey thanks a lot. I am brand new at this so I have a little learning curve here. I think I will disable the sell mode. It was interesting yesterday to be running my heating sys. And only showing .25 kw on the smart meter. But I am pretty sure that my inverters and pv system are producing much more than I can use even with everything turned on. I'll post a picture and include performance data in the future. Looking forward to helping others get off grid. Bobby
  • RCinFLARCinFLA Solar Expert Posts: 1,351 ✭✭✭
    Re: Grid connection power meter function

    Most smart meters have RF connection to the power company. It can report consumption and load as often as the power company wants them to. Usually it is at least once an hour. There are several RF comm options selected by particular power company. It can be Wifi, Cellular, or dedicated RF transceiver channel. Most common is cellular with power company having a contract for low rates with cellular network.

    The one I have in FL is default not to allow selling. Any attempt to sell will continue to push meter forward as if power is consumed from utility and will report pushed flow attempt to power company on next reporting time cycle. They may come knocking on your door warning you they will disconnect your grid feed if you have a non-approved, non-permitted, and not inspected system.

    If you have a PV grid tied system, permitted, inspected, and also approved by power company they will RF program the smart meter to allow selling. Depending on the power company they can net meter, or pay you a different rate for any excess pushed power. Some power companies still require a separate meter for selling so they can capture all grid tied PV power, not just the net excess you don't use.
  • ggunnggunn Solar Expert Posts: 1,973 ✭✭✭
    Re: Grid connection power meter function
    Ralph Day wrote: »
    Is it a "smart" meter? If it's digital (likely) and does not say NET somewhere, or you see one number displayed (your consumption) and another number displayed afterward (your production) you are likely paying for the privilage of putting power into the grid. Best to disable until the new meter is in place. Have you got a connection aggreement allowing you to do this, all permits in place etc?

    You should be able to disable the selling to the grid with those inverters...check the manuals.

    Ralph
    I'm not that familiar with how Xantrex inverters work. Question re the "sell" mode: how does the inverter know when your loads are less than production? It seems to me that the load on the inverter is a combination of the local loads and the grid, and unless it is monitoring the utility meter, I don't see how it knows what the net current flow is at the service. Are the connections to the grid and to the house panel separate? Does all the power going to the house from the grid pass through the inverter?
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Grid connection power meter function
    ggunn wrote: »
    I'm not that familiar with how Xantrex inverters work. Question re the "sell" mode: how does the inverter know when your loads are less than production? It seems to me that the load on the inverter is a combination of the local loads and the grid, and unless it is monitoring the utility meter, I don't see how it knows what the net current flow is at the service. Are the connections to the grid and to the house panel separate? Does all the power going to the house from the grid pass through the inverter?

    It doesn't know, nor does it need to. It simply outputs current to the household wiring. If there's loads to use it up, that's what happens. If there isn't, the current goes back to the grid as sold electricity. It's simply the way electricity functions. In short "Sell Mode" is merely a question of whether or not it supplies current to the household wiring if it can, as opposed to not doing so regardless of what power is available from the panels.
  • ggunnggunn Solar Expert Posts: 1,973 ✭✭✭
    Re: Grid connection power meter function
    It doesn't know, nor does it need to. It simply outputs current to the household wiring. If there's loads to use it up, that's what happens. If there isn't, the current goes back to the grid as sold electricity. It's simply the way electricity functions. In short "Sell Mode" is merely a question of whether or not it supplies current to the household wiring if it can, as opposed to not doing so regardless of what power is available from the panels.
    Pardon my density, but huh? I am pretty well versed on how electricity works, but I don't understand your answer. My (quite possibly incorrect) impression of the difference between "sell" mode and... I guess "not sell" mode, is that in "not sell" mode it supplies the household loads but regulates its output so that it doesn't export energy to the grid. Is that correct? If that is so, how does it accomplish that? How does it distinguish the household loads from the loading from the grid?
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Grid connection power meter function

    Sell Mode Off stops the inverter from pushing current to where the utility is connected, operating like an off-grid inverter would. Sell Mode On allows current output to the utility connection, operating like a standard GTI would. At that point the inverter doesn't care where the current goes to; the grid is just another load. It does not discern between one load and another.

    The XW has three sets of AC connnectors: AC1 for the grid, AC2 for generator input, and AC OUT for loads. AC1 is bi-directional, allowing it to back-feed the grid with 'surplus' power when Sell is enabled. Otherwise it is a pass-through to AC Out when the utility is present.
  • ggunnggunn Solar Expert Posts: 1,973 ✭✭✭
    Re: Grid connection power meter function
    Sell Mode Off stops the inverter from pushing current to where the utility is connected, operating like an off-grid inverter would. Sell Mode On allows current output to the utility connection, operating like a standard GTI would. At that point the inverter doesn't care where the current goes to; the grid is just another load. It does not discern between one load and another.

    The XW has three sets of AC connnectors: AC1 for the grid, AC2 for generator input, and AC OUT for loads. AC1 is bi-directional, allowing it to back-feed the grid with 'surplus' power when Sell is enabled. Otherwise it is a pass-through to AC Out when the utility is present.
    So all the house loads are on AC OUT and all the current powering the house loads passes through the inverter (both from the PV and from the grid)? That would explain it; thanks.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Grid connection power meter function

    Oh I wouldn't say all the house loads. Just up to the limit of the inverter(s). :D
  • ggunnggunn Solar Expert Posts: 1,973 ✭✭✭
    Re: Grid connection power meter function
    Oh I wouldn't say all the house loads. Just up to the limit of the inverter(s). :D
    I see the smilie, but I asked a serious question. The way I now understand it (or think I understand it), there are no loads on the conductors between the inverter and the meter, which means that at night, for example, when power cannot get to the household loads except from the grid, 100% of that power is passed through the inverter via the AC1 and AC OUT ports. Is that correct? This is a bit different from an AC coupled Sunny Island installation, something I am more familiar with, where there usually is a protected loads panel on one side of the SI and the main panel on the other side, and only the loads in the protected loads panel draw current from the grid through the inverter ports.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Grid connection power meter function

    Yes; whenever there is no "surplus" power available from the panels (including in daylight hours if the DC Voltage is below the 'sell' point) the AC OUT is powered by the AC IN. If there is sufficient DC Voltage to allow selling, that power is passed to the AC1---AC OUT circuit as current, and will either go to supplying the loads on AC OUT if present or to the main service and any loads there or ultimately to the grid if there is more output from the XW than the household needs.

    SMA's system is different because it is AC coupling GTI's to a separate "off grid" inverter. Within you have a transfer switch which will disconnect the GTI's from the grid in the event of an outage (so will the XW disconnect) but retain their connection to the "off grid" inverter to aid with power the loads and to charge the batteries from solar. The SMA treats the GTI's as a "second grid" in that respect.

    The difference between DC from panels to inverter and AC from panels to inverter. That's why the hybrid inverters are less efficient for GT; the conversion from DC to AC for selling.
  • RCinFLARCinFLA Solar Expert Posts: 1,351 ✭✭✭
    Re: Grid connection power meter function

    XW inverters monitor the voltage and current to/from grid. Also measures voltage on ACout node and current to/from inverter. Inverter, grid, and ACout are all connected together when inverter is sync'd to grid. These measurements include phasing relationship of current to voltage so it can tell power flow direction. With these measurements it can directly measure or calculate what is going in/out of every port (grid, battery, ACout)

    If you disable selling it just modulates the inverter push to prevent any net push back into grid. Any ACout load will be supplied as necessary.

    If selling is disabled and ACout loads do not consume all PV power pushed to batteries, the XW inverter has no where to vent the excess power so it just lets the battery voltage rise, up to max battery voltage limit (70vdc) at which point inverter would shut down. In this situation it is up the PV charge controller to regulate itself to keep the battery voltage in proper float or absorb voltage range so the battery does not get overcharged.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Grid connection power meter function

    I think the thing that's missing here is that not all power for the house has to flow through the XW. As with a standard GTI other loads can be attached to the main service panel. Thus the 'grid' the XW looks at is both the utility and the other loads. It has no way of specifically knowing how much of its output to AC1 is going to the actual grid and how much is being used by loads not connected to AC OUT.
  • RCinFLARCinFLA Solar Expert Posts: 1,351 ✭✭✭
    Re: Grid connection power meter function
    It has no way of specifically knowing how much of its output to AC1 is going to the actual grid and how much is being used by loads not connected to AC OUT.

    It does. It knows vector current and voltage at AC1 port, vector current from inverter along with vector voltage at inverter/ACout node. Inverter minus ACin equals ACout. Everything can be plus or minus. (ACout with reverse flow would be AC coupled GTI at output) It is purely a software thing to invoke prevention of ACin reverse push (no selling).
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Grid connection power meter function
    RCinFLA wrote: »
    It does. It knows vector current and voltage at AC1 port, vector current from inverter along with vector voltage at inverter/ACout node. Inverter minus ACin equals ACout. Everything can be plus or minus. (ACout with reverse flow would be AC coupled GTI at output) It is purely a software thing to invoke prevention of ACin reverse push (no selling).

    Unless it has a way of looking at the grid side of the meter it only knows that power is going out AC1, not that it is going to the house or utility.
  • RCinFLARCinFLA Solar Expert Posts: 1,351 ✭✭✭
    Re: Grid connection power meter function

    Yes, you are correct. I did not catch the end statement of loads not going through XW.
  • ggunnggunn Solar Expert Posts: 1,973 ✭✭✭
    Re: Grid connection power meter function
    Unless it has a way of looking at the grid side of the meter it only knows that power is going out AC1, not that it is going to the house or utility.
    Which was the basis of my original question. It appears that in "don't sell" mode, power cannot be exported from the inverter via AC1, which is connected to the grid and may also be connected to some loads. It's not a problem as long as the grid is up; the loads out there get their power exclusively from the grid. If the grid goes down, those loads go dark and only the loads on AC OUT are powered. Makes sense.

    A downside I can see is that the consumption by the loads on AC1 is not offset by the PV. If the batteries are full and the loads on AC OUT are demanding less than the PV output... what? Does the inverter shut down completely, or can it dial back the power from the PV a la Sunny Island/Sunny Boy systems, and if so, how? It obviously cannot munge the line frequency like SI/SB systems can when operating off grid, since AC OUT would still be connected to the grid.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Grid connection power meter function
    ggunn wrote: »
    Which was the basis of my original question. It appears that in "don't sell" mode, power cannot be exported from the inverter via AC1, which is connected to the grid and may also be connected to some loads. It's not a problem as long as the grid is up; the loads out there get their power exclusively from the grid. If the grid goes down, those loads go dark and only the loads on AC OUT are powered. Makes sense.

    Yes, that's it.
    A downside I can see is that the consumption by the loads on AC1 is not offset by the PV. If the batteries are full and the loads on AC OUT are demanding less than the PV output... what? Does the inverter shut down completely, or can it dial back the power from the PV a la Sunny Island/Sunny Boy systems, and if so, how? It obviously cannot munge the line frequency like SI/SB systems can when operating off grid, since AC OUT would still be connected to the grid.

    Well if the grid is up then the XW will feed AC1 whenever there's power available from the panels. At that point it will offset any loads connected on that side because a load is a load, whether it's the lights in the livingroom or the utility grid's insatiable ability to 'consume' whatever is available.

    When everything is up, AC1 and AC OUT are essentially the same as far as the XW is concerned. Power available that is not used on AC OUT gets fed to AC1 loads (including grid) If the XW's output exceeds the combined loads on AC OUT and AC1, that's power sold back to the grid. The amount of power available depends on the size of the array, the insolation, and the SOC of the batteries. It doesn't need to do the frequency shifting the Sunny Island does because there is no AC coupling. The charge controller prevents the batteries from overcharging and the grid takes and 'extra' power when it is up. When it is down the XW doesn't have 'extra power' because it can detect 'no grid' and the battery Voltage is regulated by the controller. As far as the controller is concerned loads or sell back to the grid simply looks like additional current demand and so it will ramp up whatever its got.

    You could say that the charge controller takes the place of the SI's frequency shifting, controlling panel power on the DC side instead of the AC.
  • ggunnggunn Solar Expert Posts: 1,973 ✭✭✭
    Re: Grid connection power meter function
    Well if the grid is up then the XW will feed AC1 whenever there's power available from the panels. At that point it will offset any loads connected on that side because a load is a load, whether it's the lights in the livingroom or the utility grid's insatiable ability to 'consume' whatever is available.
    Not if it's in "don't sell" mode, right? What I thought you guys were telling me is that in "don't sell" mode, no power is exported through AC1, since the inverter cannot distinguish between local loads on AC1 and the grid. That made sense to me.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Grid connection power meter function
    ggunn wrote: »
    Not if it's in "don't sell" mode, right? What I thought you guys were telling me is that in "don't sell" mode, no power is exported through AC1, since the inverter cannot distinguish between local loads on AC1 and the grid. That made sense to me.

    That is correct. With sell off it won't back-feed to AC1.
  • NorthGuyNorthGuy Solar Expert Posts: 1,925 ✭✭
    Re: Grid connection power meter function
    ggunn wrote: »
    A downside I can see is that the consumption by the loads on AC1 is not offset by the PV. If the batteries are full and the loads on AC OUT are demanding less than the PV output... what? Does the inverter shut down completely, or can it dial back the power from the PV a la Sunny Island/Sunny Boy systems, and if so, how? It obviously cannot munge the line frequency like SI/SB systems can when operating off grid, since AC OUT would still be connected to the grid.

    The power from solar is managed by CCs. They simply maintain the absorb/float voltage. If XW doesn't take enough power, the battery voltage will rise. CCs will dial their output down to prevent this. Part of the harvest is lost.

    When AC1 is on, XW simply connects it to ACOUT and also may use it to charge batteries if so configured. It doesn't take anything from batteries unless you enable "Grid support".

    If you enable "Grid support" then it will synchronize with AC1 and will supply some power. At this moment both AC1 and ACOUT are connected together. It will not output power unless certain conditions are met - there are numerous settings, which are rather complicated that may prevent power output during certain periods etc. When it does output the power, it will regulate its output so that a balance on AC1 is slightly positive - that is it takes some "small amount" (as their tech support told me) from AC1 and supplies the rest. It does that to prevent selling. Small amount is 1A or so, which translates to 240W - at least 5.8kWh per day!!! So, loads on AC1 will not see any power except from the Grid, and loads on ACOUT will receive 1A from the grid and the rest from XW.

    If you enable "Sell" it will backfeed to AC1 (again lots of rules on how much and when), so ACOUT and AC1 loads (still connected together) will be powered by both XW and the grid. If there's not enough loads on ACOUT and AC1 to take all the power from XW, you'll be selling to the grid. You cannot stop this.

    If you want ACOUT loads to be powered only by XW (no grid), the only way to do that is to physically disconnect AC1 from XW.

    When AC1 is out (or disconnected) XW powers all ACOUT loads and will continue to do so until batteries drain out below certain voltage. XW cannot supply any power to AC1 loads in this situation.
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