Coal plants are like the baby boomers of the energy sector: A whole bunch are reaching retirement age all at once.

One of them, Hawaii’s AES Corp. power plant in Kalaeloa, marked its impending shutdown on Sept. 1 at a ceremony on Thursday. Companies nationally are switching from coal-fired generation, prodded by stiffer climate-change regulations.

State law barring coal plants after 2022 means an early close here — and higher electricity bills. But company-wide, AES will be coal-free by 2025.