Inverter Generation, Local Use and Export to grid confusion (Electrical)

[rustyk00]

Hi all,

My first post so please be kind! And sorry this is so long winded, I've been reading and reading but I can't find any straight answers.

We own an agricultural/light industrial estate with about 20 units. Electricity comes from the grid into one main building (which is ours), then splits out in a few 'chains' that feed all the other units over our own electrical infrastructure.

A 3kw solar system was installed a few years ago, it uses Trina 295W panels and a Solis 4G single phase inverter.
It was installed by an electrician and we do not get any payments for the electricity we generate, as it was not installed by a 'registered' installer.
The Solar system is installed on one of the units at the 'far end' of farm, so at the end of one of the 'chains'.

Basically I'm trying to ascertain if excess power that we generate will be used by other units on the farm.
My logic is that all the power has to go somewhere and if we installed a generator (solar) at one end of a chain and we have a grid feed at the other end, then anything in the middle will 'draw' power from both the solar system and the grid?

The inverter is grid tied and I notice that the export limit is set to 0. But, when I look at the Interter panel when generating energy, the Watts shown is often a much higher number than we could possibly be consuming just within the unit it is installed in.
I thought that if excess power was being generated but not 'exported', then the inverter would automatically reduce the power generation to match the local load?
My understanding it that it would change the voltage to a less efficient point on the curve, to reduce generation.

In this scenario, since the incoming grid power is being distributed along various nodes within one chain, I'm inclined to think that the inverter sees any load on the farm as a local load.

Thanks if you've had the patience to read this! I can produce a diagram if it makes it clearer?
I suppose basically I'm unsure as to how the system knows what power goes where and where it comes from! I understand quite a few of the basic principles of AC, but in this practical situation I'm at a loss.

[bcroe]

If you have just one meter, I would expect everything fed by the meter would be
able to consume your solar generated power. With multiple meters, only stuff on
your string and meter would be involved, for no export. Bruce Roe

[Mike90250]

Somebody is running a big freezer !!!!

[rustyk00]

If you have just one meter, I would expect everything fed by the meter would be
able to consume your solar generated power. With multiple meters, only stuff on
your string and meter would be involved, for no export. Bruce Roe

Hi Bruce, thank you for the reply.

We only have one meter which is provided by the electric company and is installed where the main power feed comes into our farm from the grid. So, all the power used on our land is one (very expensive) bill.
We have installed our own meters on each unit so that we can charge our tenants for the power that they use.

The unit containing the solar installation is about 3 'hops' along from the main grid feed. When I say 'hop' I mean each hop being a standalone building/unit, which has its own meter supplied by us.
In effect we have a 'public' grid, which is the incoming feed from the utility company, then we have a 'private grid' which is our own overhead cabling which feeds the industrial units.

What I don't understand is how the 'export' limiter on the inverter works (if at all).
On a given day, say the inverter states generating 2KW but I know we're only using 500W in the building that the solar installation is in. To me, that must mean that 1.5KW is going out of the unit where the solar is installed, and either being used elsewhere on the farm (ideal) or being fed back to the public grid.

If the export limiter was working, I'd expect us to be generating 500Watts to match the load in the unit, not 2Kw? The fact this we're generating more, suggests that is in in fact 'exporting' power, albeit to our local grid.

Thanks for you time.

[rustyk00]

Somebody is running a big freezer !!!!

Actually, knowing the people around here it's much more likely to be a gigantic beer fridge

[oregon_phil]

Do you have an export power manager box located by your main power panel? See attached. If it is attached anywhere else, could you draw a picture of your power layout?

[rustyk00]

Do you have an export power manager box located by your main power panel? See attached. If it is attached anywhere else, could you draw a picture of your power layout?

Hi,

Thanks for the reply.

We have no EPM, we also have no current sensor or CT connected.
Export power set is "OFF" and backflow power is set to 0 Watts.

[oregon_phil]

You need the export power manager box mounted at your electrical panel with RS485 communication cable back to your inverter. The inverter settings are just settings with no place to go.

[rustyk00]

So it sounds like without the external EPM, the export settings on the inverter don't do anything?

In which case, generation is not being limited and we are sending excess power back to the grid?

[oregon_phil]

So it sounds like without the external EPM, the export settings on the inverter don't do anything?

In which case, generation is not being limited and we are sending excess power back to the grid?

Without the EPM, I don't see how export can be controlled. Those are just inverter settings.

Whether or not your power is going back to the grid at any point in time is unknown since you don't have equipment to measure power direction at your meter. One thing to determine: Which does your power meter do when you are only generating solar (Meter goes Up, down, or stays the same)?

Just like the power company, you could take meter readings at certain intervals to determine kWh power use for all of your power meters, and you know solar generated for that same time interval, but you need to know what your main power meter does when energy is being pushed onto the grid. This method would tell you whether or not you were pushing power back onto the grid OVER THAT PERIOD OF TIME.

On average, you could be a net user of power during that period of time, but within that period of time, there could be many many instances where power is pushed back onto the grid.