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Excess Solar generation - not grid connected (G-59)

Aneysha Minocha
Hi All,


We are working with commercial premises that installed Solar PV in the days of the Feed-in-Tarriff. These sites have excess solar generation being measured through a channel, but there is no export from site (not G-59 connected) and the customer is on a deemed Feed-in-Tariff. From the data, there seems to be a high proportion of "excess" / "export" energy from sites.


Question - if the sites are not consuming the excess energy and thet are not set up for grid export - where is this excess energy going?


Would appreciate your valuable input please.

Thank you!
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  • 0
    Grid tie inverters can be configured in two ways;


    1. Without Export Limitation: Here, whatever power the Solar PV panels generate, is converted to synchronised AC and fed into the power system of the building, irregardless of the building load. Therefore the building load is NOT monitored, and thus the inverter system operates in OPEN LOOP. Therefore any power generated by the inverters is either fed partially into the building load (if building load is more than generated Ac Power), or partially fed into the grid (If building load is less than the generated AC Power). In other words, the building load sees a mix of Grid power and PV power (When load demand exceeds PV generation), and the excess balance is fed into the grid (When load demand is below PV power generation). This happens dynamically with changes in irradiance, and building load. Its here that one earns from a FIT arrangement by earning from exported Energy.


    2. With Export Limitation: Here, the building load is monitored, and Solar PV power generation is monitored. If export is to be curtailed to zer0, then the controller processes the Building AC load, and Inverter AC output, and thus controls the inverter output not to exceed the building load. If there is generation potential from the PV modules (full irradiance), and there is little or no load demand from the building, then the DC side of the inverter (Internal Power Electronics connected to the AC side of the inverter internally) will use the MPPT to control the PV array output dc current, and pull just exactly what's required (There is no really wasted power, its just not converted to begin with, otherwise if this was allowed, the panels would heat up unnecessarily and this would cause other problems as you can imagine). Therefore in this mode, the Inverter operates in CLOSED LOOP. With this technique, no power is exported to the grid, and all generated power is consumed by the building load. Therefore this method is used when there is no FIT contract and you are not allowed to feed into the grid for whatever the reason (Weak grid, no FIT etc).


    How fast the control loop reacts to changes in load current, such as to maintain zer0 grid export, is a story for another day....
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  • 0
    Grid tie inverters can be configured in two ways;


    1. Without Export Limitation: Here, whatever power the Solar PV panels generate, is converted to synchronised AC and fed into the power system of the building, irregardless of the building load. Therefore the building load is NOT monitored, and thus the inverter system operates in OPEN LOOP. Therefore any power generated by the inverters is either fed partially into the building load (if building load is more than generated Ac Power), or partially fed into the grid (If building load is less than the generated AC Power). In other words, the building load sees a mix of Grid power and PV power (When load demand exceeds PV generation), and the excess balance is fed into the grid (When load demand is below PV power generation). This happens dynamically with changes in irradiance, and building load. Its here that one earns from a FIT arrangement by earning from exported Energy.


    2. With Export Limitation: Here, the building load is monitored, and Solar PV power generation is monitored. If export is to be curtailed to zer0, then the controller processes the Building AC load, and Inverter AC output, and thus controls the inverter output not to exceed the building load. If there is generation potential from the PV modules (full irradiance), and there is little or no load demand from the building, then the DC side of the inverter (Internal Power Electronics connected to the AC side of the inverter internally) will use the MPPT to control the PV array output dc current, and pull just exactly what's required (There is no really wasted power, its just not converted to begin with, otherwise if this was allowed, the panels would heat up unnecessarily and this would cause other problems as you can imagine). Therefore in this mode, the Inverter operates in CLOSED LOOP. With this technique, no power is exported to the grid, and all generated power is consumed by the building load. Therefore this method is used when there is no FIT contract and you are not allowed to feed into the grid for whatever the reason (Weak grid, no FIT etc).


    How fast the control loop reacts to changes in load current, such as to maintain zer0 grid export, is a story for another day....
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