Magnesium oxide (MgO) is an essential material for producing solid oxide fuel cells (SOFC) sealant. It can be derived from bittern waste. The common approach uses membrane electrolysis, which requires complex equipment and high energy costs. Alternatively, direct electrolysis can be taken using proper parameters to maximize the production rate. This work analyzes the process according to the input voltage, which varies between 10 and 16 Volts. The designed working voltage is suitable for direct conversion from renewable sources such as photovoltaic. The evaluation shows that the working voltage notably affects the reaction rate of the bittern solution. The working voltage of 16 Volts has the lowest power factor (2.58), while the working voltage of 10 Volts indicates the highest power factor of 3.56. It makes the reaction rate for the working voltage of 10 Volts extremely low, causing the lowest production rate of MgO with only 4.27 Grams. Oppositely, the suitable working voltage improves the production of MgO up to 75%. Microscope evaluation indicates that the produced MgO from the process has a lower agglomeration concentration after heat treatment at 700 °C, which is desirable to ensure effective fuel transfer in fuel cell apparatus.