Basically the overall efficiency of the solar cell refers to the sunlight-to-electricity conversion process. On the other hand, the solar cell is better modeled as a current source since for the largest loads the current drawn is independent of load. In this respect the paper defines solar cell efficiency related only to the electrical parameters, as a ratio between the output power and the power generated by current source. Numerical algorithm is implemented in order to obtain the electrical parameters and to calculate the efficiency of the solar cell for different environmental conditions. Also the solar cell sensitivity of efficiency is calculated when the temperature and irradiance levels are changed separately and/or simultaneously. The examples presented prove the correctness and the accuracy of the proposed method.