OPGrid is a flexible power flow toolbox based on Matlab tools able to simulate balanced electrical networks with embedded flexible AC transmission devices (FACTS).The solver is used to investigate the steady state of electric network under different cases of demand variation. The solver is designed to be flexible and able to handle standard data format for exchanging input and output with other software tools. The active power dispatch can be solved based on three mode Conventional , Optimal and Droop Control. The solver setting and case parameters are organised in single structure to be flexible for configuration and easy for exchange. New data file format is proposed to encapsulate all cases information in single file. The solver is implemented to solve multiple cases of demand variation by single call. This can be used to automate the analysis process and minimise the iteration time. The mathematical model can be selected to be based on admittance matrix or incident matrix methods which can be used to compare the performance of the two models. The IEEE test cases have been used to verify the solver accuracy and performance relative to alternative commercial and scientific tools. The solver is released as open source project to support additional functionality and full customisation for scientific research.OPGrid was developed by Bassam Mohamed under the supervision of Prof. Pablo Arboleya, Prof Jorge Garcia, Prof. Pablo Garcia and Prof. Cristina Gonzalez and is distributed under GPL license.