Most field crop spraying happens exactly where you don't have a power socket — out in open farmland, sometimes a good distance from the shed or homestead. The HTP Engine Set is built around that reality: the high-pressure pump is driven by a petrol or diesel engine, so the whole unit is self-contained and can be carried or wheeled to wherever the field is, with fuel as the only input it needs to run.
The trade-off against our electric HTP model is running cost and noise — an engine burns fuel and runs louder than an electric motor. But for farms with unreliable grid power, fields at a distance from any power connection, or simply a preference not to run extension cords across open land, that trade-off is usually worth it for the freedom to spray anywhere the field needs it.