As GPUs da AMD que começam com o HD 7XXX têm um recurso chamado ZeroCore
que reduz o consumo de energia quando o monitor está desligado pelo Windows (não quando você o desliga manualmente)
With Southern Islands AMD is introducing ZeroCore Power, their long idle power saving technology. By implementing power islands on their GPUs AMD can now outright shut off most of the functional units of a GPU when the GPU is going unused, leaving only the PCIe bus interface and a couple other components active. By doing this AMD is able to reduce their power consumption from 15W at idle to under 3W in long idle, a power level low enough that in a desktop the power consumption of the video card becomes trivial. So trivial in fact that with under 3W of heat generation AMD doesn’t even need to run the fan – ZeroCore Power shuts off the fan as it’s rendered an unnecessary device that’s consuming power. (Source)