Load sharing between grid and inverter

[sensij]

That would be a hybrid inverter, they cost big buck$, and lower efficiency. It can all be done, how much money do you have?

Sensi FWIW I am experimenting with SMPS right now tinkering with BMS and motor controllers for a start up. Exact same principles.

Well, SolarEdge has the ability to limit grid feed in if you install a consumption meter that it can communicate with. More info here.

Your experimenting sounds fun... what type of motor controllers do you work with? I hope the smoke all stays where it belongs.

[inetdog]

...I hope the smoke all stays where it belongs.

From the tires only? Although with an infinitely controllable torque independent of speed, tire spin has no benefits that I know of.

[Mike90250]

Back to the OP actual Question

The OP wants to Load Shave. No backfeed to the grid. That means the normal GT inverter will not do the job, it requires a Hybrid Inverter, with outboard Charge Controller and 100ah of battery for every Kw of inverter load.

I know they can work, but I don't know if they are 100% no backfeed. There may be a few inconsequential watts here and there as the control circuits throttle the inverter with varying loads. I know the XW series does Load Shave (or Grid Support, AC1) pretty well, the control circuits are all there for the Gen Support (AC2) and it's not ever blown up my genset from backfeeding.

And yes, in Load Shave/Grid Support more, idle losses are over 100w, and it's tricky to get the battery cut-in/out points set properly. It's all in their manual and appendixes.

[inetdog]

Back to the OP actual Question

The OP wants to Load Shave. No backfeed to the grid. That means the normal GT inverter will not do the job, it requires a Hybrid Inverter, with outboard Charge Controller and 100ah of battery for every Kw of inverter load.

Actually, there is no reason not to be able to operate a pure GTI in a mode where it does not export power to the grid. No battery needed, just a power flow sensor between the POCO meter and the rest of the wiring system and the right programming of the MPPT input stage.
Whether there are any such GTIs available at this time is an open question (I believe that there are some currently used outside the US), but there is no technical reason to require a battery or a hybrid inverter for this function.

It is indeed possible to do this with some (but not necessarily all) off the shelf hybrid inverters.

[sensij]

Again, Solaredge inverters can be set to limit the feed into the grid. See the link a couple posts ago. Hybrid inverter is not required.

[Mike90250]

Again, Solaredge inverters can be set to limit the feed into the grid. See the link a couple posts ago. Hybrid inverter is not required.

I was not aware they actually could do that, saves a bundle on batteries !

[donald]

I was not aware they actually could do that, saves a bundle on batteries !

But your are missing a lot of the functionality of a hybrid inverter. It's just load deflection, I think? No voltage source inverter function. No charge controller.

[inetdog]

But your are missing a lot of the functionality of a hybrid inverter. It's just load deflection, I think? No voltage source inverter function. No charge controller.

Not sure what you mean by load deflection. It is reducing the DC input power to the GTI to prevent the AC output from exceeding what the local loads are absorbing.
It is true that it does not provide any backup in case the grid goes down and does not allow any local time shifting of power. It just keeps the GTI from treating the grid as an unlimited virtual energy storage device.

[lamagra]

Back to the OP actual Question

The OP wants to Load Shave. No backfeed to the grid. That means the normal GT inverter will not do the job, it requires a Hybrid Inverter, with outboard Charge Controller and 100ah of battery for every Kw of inverter load.

I know they can work, but I don't know if they are 100% no backfeed. There may be a few inconsequential watts here and there as the control circuits throttle the inverter with varying loads. I know the XW series does Load Shave (or Grid Support, AC1) pretty well, the control circuits are all there for the Gen Support (AC2) and it's not ever blown up my genset from backfeeding.

And yes, in Load Shave/Grid Support more, idle losses are over 100w, and it's tricky to get the battery cut-in/out points set properly. It's all in their manual and appendixes.

Actually that's not what I'm saying; I wasn't talking about peak shaving. I was asking about how load is shared between the PV system and the grid but I think I compiled a little from each member's input and this is how I see it now:
Since the grid tie inverter acts as a current source, this means it will output all the energy produced by the solar modules. The grid will just "follow" by supplying the deficit (if PV output < load) or absorbing the excess (if PV output > load) according to Kirchhoff's current law. I think the gap in the analysis was considering that the grid tie inverter "coordinates" with the grid to only supply a certain share of the load while what it really does is outputting the entire PV production, offsetting grid consumption or exporting the excess to it.

Anyone could confirm that? Anything else to add?

[foo1bar]

The grid will just "follow" by supplying the deficit (if PV output < load) or absorbing the excess (if PV output > load) according to Kirchhoff's current law. I think the gap in the analysis was considering that the grid tie inverter "coordinates" with the grid to only supply a certain share of the load while what it really does is outputting the entire PV production, offsetting grid consumption or exporting the excess to it.

Anyone could confirm that? Anything else to add?

That's pretty much it.
The only caveat is that the assumption is "the grid" is something which essentially absorbs (or supplies) pretty much whatever current is needed.
That is effectively true for any decent sized power company... Because a larger power company has many many many customers, the output from one customer's PV is basically in the noise (it's probably less difference than if a laundromat starts up a dozen washers simultaneously.)
If "the grid" were something smaller (like a generator supplying one house or even 2 or 3 houses) then it would be a more complicated analysis since the power from the PV is no longer much much much smaller than the power produced/consumed by "the grid"

[sun_fan]

I was actually looking for an answer to how a GTI (no batteries in the system) would behave when a connected inductive load is started up. This post appeared to be a good starting point. Can anyone throw some light on this? Will the grid would provide the surge current demand of the load? Will the GTI trip in such an event? Is it required to size the inverter for the surge current?

[sensij]

Will the grid would provide the surge current demand of the load?

Yes. In a grid-tie installation, the grid supplies any needed power over what the inverter is supplying. Inverter sizing is strictly based on the power that it needs to handle from the PV array.

[ButchDeal]

I was actually looking for an answer to how a GTI (no batteries in the system) would behave when a connected inductive load is started up. This post appeared to be a good starting point. Can anyone throw some light on this? Will the grid would provide the surge current demand of the load? Will the GTI trip in such an event? Is it required to size the inverter for the surge current?

people seem to think that there is some disconnection or something from the grid when the inverter is running . There is not. The grid is still attached and the inverter is just pumping as much power as it can (based on the array and light) into the grid. The grid is still providing power to the home. If the inverter is providing MORE power then the home is using then the extra power flows naturally from the source to the grid.
Turn on a big surge load in the home and it comes from the grid just like it would if the inverter wasn't there.

The only time you need to size the inverter to the load or surge current is if it is a battery based system that would need to handle the load / surge on its own.

[ButchDeal]

Actually that's not what I'm saying; I wasn't talking about peak shaving. I was asking about how load is shared between the PV system and the grid but I think I compiled a little from each member's input and this is how I see it now:
Since the grid tie inverter acts as a current source, this means it will output all the energy produced by the solar modules. The grid will just "follow" by supplying the deficit (if PV output < load) or absorbing the excess (if PV output > load) according to Kirchhoff's current law. I think the gap in the analysis was considering that the grid tie inverter "coordinates" with the grid to only supply a certain share of the load while what it really does is outputting the entire PV production, offsetting grid consumption or exporting the excess to it.

Anyone could confirm that? Anything else to add?

The Grid tie inverter follows the grid in frequency and wave form. Other than that you can think of it as a pipe feeding the house of water. The pipe comes from the grid and the house on the other end. You cut into the pipe and add a "T" with a new small water source (inverter) on it. it puts water into the line. You don't care which way the water flows when it hits the "T", either into the house or back into the grid. If your new water source is not enough at any time extra water comes form the grid....

[sun_fan]

ButchDeal : Thanks for making it clear...