Hydrogen produced by solar and other clean energy sources is an essential alternative to fossil fuels. In this paper, a commercial alkaline electrolyzer with different cell numbers and electrode areas are simulated in different pressure, temperature, thermal resistance, and electrical current. This alkaline electrolyzer is considered unsteady in simulations, and different parameters such as temperature are obtained in terms of time. The Obtained results are compared with similar results in the literature, and good agreement is observed. Various characteristics of this alkaline electrolyzer as thermoneutral voltage, faraday efficiency, cell voltage are calculated and displayed. The outlet heat rate and generated heat rate are obtained as well. The pressure and the temperature in the simulations are between 1 and 100 bar and between 300 and 360 Kelvin respectively. The results show that the equilibrium temperature is reached 2-3 hours after the time that the Alkaline electrolyzer starts to work.