The average price of RTM is lower than that of DAM; moreover, DAM has a lower negative price frequency than RTM. Therefore, the TAC of the third scenario is 12 million USD higher than the TAC of the first scenario. This gap mainly results from the electricity cost. This pattern implies the importance of participating in the proper electricity market, which affects the expected level of system flexibility. Given the relatively high electricity price, the TAC of the last four scenarios is in the range of 160-180 million USD. The electricity cost of the fifth scenario is even higher than the TAC of the first scenario. Being flexible can still lower the overall production cost to some extent in this scenario. For example, the TAC of the fifth scenario is 30 million USD lower than the TAC of the sixth scenario. However, because the negative price frequency of RTM in Houston is almost zero, there is no strong incentive to produce hydrogen via electrolysis.