Feed-in Tolerance for HMKE (Small-Scale Household Power Plants)
Feed-in limitation systems are configured when the utility provider does not permit power export to the grid. However, this does not mean that there is zero tolerance for backfeed!
In this article, we explain how utility providers calculate the allowable amount of return current.
A tolerance range is defined for each system size:
- For HMKE systems (household-scale): 2%
- For 50–500 kW systems: 1%
- For systems above 500 kW: 0.5%
Monthly Nominal Operating Hours
The utility uses a predefined number of nominal operating hours per month to determine the allowable export energy for the approved inverter:
|
Month |
Operating Hours |
|
January |
44 |
|
February |
63 |
|
March |
99 |
|
April |
123 |
|
May |
142 |
|
June |
149 |
|
July |
154 |
|
August |
143 |
|
September |
108 |
|
October |
84 |
|
November |
53 |
|
December |
38 |
Formula for Monthly Maximum Feed-in Energy
kWhMAX=T×P×Ts
Where:
- T = Theoretical maximum monthly operating hours (from the table above)
- P = Rated power of the approved inverter (kW)
- Tₛ = Tolerance band
Example:
For a 10 kW inverter in August:
143×10×0.02=28.6 kWh143 \times 10 \times 0.02 = 28.6 \text{ kWh}143×10×0.02=28.6 kWh
Thus, the maximum allowed feed-in for that month would be 28.6 kWh.