Energy consumptionWe measured the energy consumption of the different cards, keeping in mind that there’s often a variation between two sample of a given model, due, among other things, to leaks in current and GPU voltages. Moreover, some run at higher clocks as they are factory overclocked.
We measured the graphics card energy consumption at idle on the Windows desktop and in load in Anno 2700 at 1920x1080 with all graphics options pushed to a max.
At idle, the energy consumption of the Radeon HD 7900s varies between 15 and 19W, except for the MSI Radeon HD 7970 Lightning which draws more power. Note that with the screen in standby, they all draw 2W except the Lightning (4W) and turn their fans off.
In load, the Radeon HD 7970s understandably consume more energy than the Radeon HD 7950s with an additional +/- 50W registered.
We also wanted to group all the energy consumption readings in terms of undervolting and overclocking, not so we can judge a particular product (as the results vary from one sample to another) but to give you an overall idea of the difference you can expect:
Hold the mouse over the graph to display energy consumption in watts
Lowering the GPU voltage allows you to reduce the energy consumption of the card by between 4 and 29%, with a lot of variation from one model to another and the models with a significant factory overclocking having less undervolting capacity.
Without any alteration in GPU voltage, overclocking increases energy consumption by between 7 and 24% across all cards tested. When the GPU voltage is changed this goes up to an increase of between 21 and 78%, which is enough to put the power stages of these cards under stress.