Grid tied solar PV

[greenstar power]

A 50kWp grid tied solar PV system has been installed in our factory (we actually require about 400kW for normal operation). The final AC output from the inverters are connected directly onto the main bus-bars of the Main DB. Can someone please explain how the power from the solar yield is first used up completely, before power is drawn from the grid? In other words, whatever yield is produced by the solar PV is consumed before mains power is used. There is no changeover switch or device that senses the output form the solar PV.
How does this work? Please help!! Thanks very much

[SeanB]

The grid tie simply feeds power into the bus bar. If there is a meter between the incoming mains and the bus bar, a meter on the solar input and a meter showing the draw of the factory then you will see that the power drawn from the mains is less than the power used by the factory by an amount equal to the panel output.

The solar inverter simply provides voltage in phase with the mains with a slightly higher voltage so that current flows into the grid, exactly like a power station does. the grid supply is made up of hundreds of small power plants ( solar ones are generally the smallest) each contributing to the overall power pool much like a team pulling on a rope, each adding a little more power to supply a massive pull to the end of the rope.

[greenstar power]

Thanks very much for this response. What puzzles me is, if you have a load, and connect 2 batteries in parallel to supply this load, both of the batteries will contribute to the needs of the load (obviously, in varying proportions depending on numerous parameters). In our example, the solar energy  is first used completely before the grid power is used. Why does no power get consumed from the grid whilst sufficient energy is available from the PV? Power ONLY gets consumed from the grid when the solar energy is either depleted or insufficient. There is no monitoring device that changes over from PV to grid, both sources are simply connected in parallel onto the mains bus-bars.

[SeanB]

Solar array feeds power into the grid. Usage is whatever load there is. If you have a load that is more than the panel power then they supply up to their rated maximum then any extra power has to come from the grid. If there is less load than the amount the panels supply then it goes back to the grid to be used elsewhere, and your main meter will turn backwards as power is now flowing the other way. The grid is merely a system that moves power from producers to users, it has no real direction, just moves power from one to another.  You are simply adding power to it at a point inside the factory, so the usage from the rest of it is lowered by the amount the panels produce.

[greenstar power]

Thanks again for this. So, to summarise: if my factory requires approximately 1,75MWh per annum and I introduce a solar array which provides, on average 1MWh per annum, I will only pay for  0,75MWh (which comes from the utility) and all the energy I produce from the solar array will be used before I start to receive power from the grid? Obviously, in my case I will never produce energy enough to make the meter turn backwards, but I can rest assured that all the energy produced by the array will be used BEFORE I get power from the grid?

[SeanB]

Correct, but you must look at the saving of 1MWh as a return from the panel, as it represents power that you otherwise would have had to buy at prevailing rates.

[greenstar power]

Thanks for all your advice