I have an RV and I plan to buy a pure sine wave inverter to convert 12V DC to 120V AC. The larger watt inverters cost more but they give me more flexibility to run more powerful things (although perhaps not very long). However, most of the time, I'll be using low watt things.
Are there any downsides to larger watt inverters other than cost (assuming the two inverters pull the same current at no load for the lights, etc.)?
Efficiency. If the inverter operates at no load it still consumes the energy. Larger inverter -> more energy loss, even if efficiency of the inverter is the same. There is a loss in a transitor switching and loss in the magnetics, like transformer, inductor/choke. Transitors need gate driver circuit, when more transistors are paralleled the gate capacitance increases, this charge/discharge energy is wasted. If transformer is involved there is a loss due to magnetization characteristics, more iron, more loss. Same is about ferrite chokes, larger chokes -> more ferrite -> more losses.