From the 'Duck' to the (dachshund) 'Dog' Curve

In sunny areas like Cyprus and California, the installed capacity of PV systems has increased dramatically. As a result, the net load (the load satisfied only by conventional generation) has been reduced to extremely low levels during mid-day, creating the well-known 'duck curve'.

However, Cyprus's isolated low-inertia power system has a?total?minimum stable generation requirement of approximately 200MW?due to the inertia requirements. This means that at all times at least 200MW?must?be generated from conventional generators to guarantee?enough inertia in the system.?Thus,?in periods of?low load conditions (<500MW) combined with large energy generated from PVs, the system operators perform RES energy curtailments to maintain system stability.

Curtailing energy from RES due to minimum stable generation requirements has as a result the stabilization of the active power output of the conventional generators. Therefore, the net load of the system during curtailments remains constant, irrespectively from the load demand. In these cases, in low load conditions with massive RES penetration, the 'duck' curve is transformed into a 'dog' curve as shown in the above figure.

More specifically, the curve can be represented by a dachshund dog. This dog breed has a very long main body and very short legs. The latter represents the system's low load demand and the former the duration of the RES curtailments. It should be noted that the duration of the curtailments is proportional to the RES installed capacity and the daylight hours. A similar net load curve will be created if energy storage systems are charging, instead of RES curtailments.

Therefore it can be easily predicted that the net load curve of the future power systems with massive RES penetration, will inevitably be a (dachshund) dog curve.

P.S The figure represents the real net load demand of the power system of Cyprus in 19/02/2023, and the dog is not mine.