The phrase "primary fuel source" refers to the main substance or energy that is used to power something. It is the primary or main material used to generate power or fuel an activity. Full definition
Used for centuries by our ancestors as primary fuel sources, it has recently become subject of fierce rejection. (physiqueauthority.com)
They are also primary fuel sources for brown electricity generation, and so brown electricity prices rise and fall with the costs of these raw materials. (zerocarbonista.com)
This is the same core theory behind using high - quality fats as the body's primary fuel source instead of carbohydrates. (besynchro.com)