Hitachi Group has developed and operated an integrated construction system for large scale power plants for more than a decade to improve the quality of the construction work. Nowadays, the system has been applied to other business fields with different scales and methods, such as renewable energy plants. This time, we applied human centered design process to improve the system based on user needs, so that it can be upgraded to deliver the best performance. This report explains how we have improved the system for solar plant construction. First, we conducted a field observation research at a solar plant where the unimproved system was introduced. We found that users were entering work records of a dozens of construction sites into the system one by one in their office, and there were gaps between their workflow and the intended workflow of the system. Therefore, we proposed functions that enable users to enter work records on their work sites with a tablet PC. We introduced an interface allowing users to enter multiple records at once. Then, we conducted the second research and confirmed that the new functions have been used and their work efficiency has improved.