Solar irradiance is power per area received from the sun. Solar irradiance is an important variable that affects the solar panel output. Monitoring of solar irradiance can use a pyranometer sensor. However, the drawbacks of the sensor are expensive and less efficient if that is applied to solar power generation systems requiring a lot of sensors. The problem can be solved by soft sensors which can be designed using multiple linear regression models. The model is developed using training data from solar cell output. The variations given is the type of input to build the model. The model input comprises solar cell output voltage, solar cell output current, and a combination of both. Data testing is done by using multiple correlation tests, multiple linear regression significance tests, and multiple linear regression coefficient significance tests. The best design of the soft sensor is a combination of current and voltage as input models. It has the smallest mean square error value of 7.887 × 10-24 for training data and 3.876 for test data.