What is a primary disadvantage of using alternating current (AC) systems in long-distance power transmission compared to HVDC?

The primary disadvantage of using alternating current (AC) systems for long-distance power transmission is indeed the increased losses over long distances. This occurs due to the phenomenon of reactive power losses and resistive heating in the transmission lines. In an AC system, as the current travels along the conductor, some energy is lost as heat, primarily due to the resistance of the wires. Additionally, in AC systems, the reactive power can create further inefficiencies, especially over long distances, since the voltage may fluctuate and contribute to energy loss.

In contrast, High Voltage Direct Current (HVDC) systems transmit power with lower losses over long distances because they do not have reactive power losses. HVDC systems maintain consistent power transmission without the need to convert AC to DC and back, which helps in reducing energy losses.

Other options may point to factors like operational costs or grid design complexity, but they do not capture the essence of power loss specifically related to long-distance transmission efficiency the way increased losses do. Additionally, compatibility with renewable energy sources is not inherently a disadvantage of AC systems, as they can integrate well with various energy sources, including renewables.