Control strategies to use the minimum energy storage requirement for PV power ramp-rate control

• Ramp-rate control is simulated for smoothing PV power fluctuations.
• Two new strategies in order to use the minimum storage requirements.
• These strategies allow halving the energy storage state of the art capacity.
• Strategies are validated with real operational data.

Over the last few years, the considerable increase in the number of multi-MW PV plants has led transmission system operators (TSO) to express concern over potential PV power fluctuations caused by transient clouds. As a result, new grid codes are being issued in order to include new criteria that make it easier for the TSO to react appropriately to harmful short-term power fluctuations. Faced with this situation, some type of energy storage system (ESS) is required in order to smooth out these fluctuations and comply with the regulations. Previous studies dealt with the ESS capacity required to comply with the maximum allowable ramp-rates stated in the grid code regulations, for any PV plant size for the worst fluctuation model. As the sign of the first fluctuation is unknown, a double capacity battery is required to absorb both the upward and downward fluctuations. In this paper we propose two innovative management strategies which make it possible to half the size of the ESS state of the art. The general validity of both strategies has been confirmed through simulations carried out with real operational PV power output data taken every 5 s in the course of one year at the 38.5 MW PV power plant of Moura (Portugal).