I asked SatoshiGPT same question, here is the answer:

The lowest density energy source used in Bitcoin mining includes a variety of methods, with some of the most innovative being the flaring of methane gas from oil fields and waste incineration plants. These methods produce energy at a scale significantly greater than the current consumption of the Bitcoin network. For instance, methane gas flaring alone generates around ten times more energy than what the Bitcoin network consumes.

However, it's important to note that the Bitcoin mining industry is highly competitive and constantly evolving, with a focus on increasing efficiency and reducing energy consumption. The industry operates in a range of energy costs significantly lower than standard residential or industrial consumption, proving the efficiency of Bitcoin in creating a global incentive to develop cheap and sustainable sources of energy.

Bitcoin mining has a profound impact on global energy markets by enabling the extension of physical infrastructure over the internet, which brings significant changes in market dynamics. The profitability of mining equipment depends more on technological factors, such as efficiency measured in joules per terahash, than on the type of energy source used.

As the industry progresses, it's expected that energy consumption per exahash will decrease substantially, reflecting the pursuit of greater efficiency within the industry. This trend is a testament to the value people place on the Bitcoin network, as most of the electricity consumed by Bitcoin is cheap and would otherwise have been wasted.