Which of the following is NOT a source of power for portable generators?

A portable generator typically relies on readily available energy sources that can directly produce electricity in a compact and mobile format. Diesel engines, solar energy, and small gasoline engines are common sources of power for portable generators. Each of these options converts energy into electrical power in a way that suits portable applications.

When it comes to wind energy, however, utilizing it for a portable generator presents significant challenges. Wind energy generation typically requires specific infrastructure like wind turbines, which cannot be easily transported or set up in various locations like other sources of power. Additionally, the variable nature of wind makes it less reliable for immediate and consistent power generation needed in portable applications.

Therefore, while wind energy can be harnessed for electricity, it does not fit the typical profile of power sources for portable generators, making it the correct answer for this question.