semPower allows for performing compromise, a priori, and post hoc power analyses for structural equation models. The R-package is available from CRAN [https://cran.r-project.org/package=semPower], its source from github [https://github.com/moshagen/semPower]. Alternatively, you can use semPower online at https://sempower.shinyapps.io/sempower/
For more details see the manual [https://github.com/moshagen/semPower/blob/master/vignettes/semPower.pdf], for details on using compromise power analyses in model testing, see:
Moshagen, M., & Erdfelder (2015). A new strategy for testing structural equation models. Structural Equation Modeling, 23(1), 1–7. doi: 10.1080/10705511.2014.950896