Influence of the State-of-Charge Control on the Size of the Energy Storage Systems to be introduced in PV Power Plants

Abstract

The  usefulness  of  introducing  energy  storage (ES) systems (ESS) into PV power plants to make the production less  stochastic  and  even  predictable  is  a  fact.  Its  economic viability  is  not  so  clear  though, what  makes  essential  the  use  of an  optimally  sized  ESS.  This  paper  analyses  how  much  the energy ratings required by these ESS can be reduced by varying the  values  of  a  control  parameter:  the  ESS  reference  state-of-charge  (SOC)  recovery  time  (τSOC).  This  control  parameter  is introduced  to  force  the  plant  to  recover  a  given  SOC  within  a certain  period  of  time,  thus  reducing  the  SOC  variability  and allowing  the  use  of  smaller  ESS.  To  do  the  analysis,  a  generic PV  plant  with  ES  is  first  introduced  its  main  control  equations. Then,  two  energy  management  strategies  are  defined  to  operate it. The analysis shows the τSOC impact on the plant performance and  also  on  the  change  in  the  ESS  ratings  obtained  by  varying the τSOC value for each of the strategies is presented. The results obtained  in  this  paper  are  based  on  one  year  long  simulations which used actual irradiance data sampled every two minutes.