There are two sorts of questions at play here. You use the term 'free will' which is largely subject to philosophical methods, and you use the term 'evolution' which is largely subject to scientific methods. It is important to establish some presumptions, to wit:
1) If you are presuming evolution is a sound scientific theory, then you are conceding the importance of empiricism and scientific methods for establishing certainty.
2) Let us presume that 'free will' whatever that may be doesn't exist. As you haven't defined what 'free will', it might be difficult to draw conclusions from inference regarding that.
My question is: If we don't have free will, why was the quality of being conscious selected for? What advantage is there for being conscious of our environment if the conscious part of us has no way of affecting our physics/biology?
Now, let's set aside any word games that might be played and restate your question as such: why did natural selection select for consciousness?
This is a good question, and may be more scientific than philosophy despite your invocation of the terms 'consciousness' and 'free will'.
Remember, in natural selection which affects descent with modification, the question can be refined to how does consciousness add to extra fitness in reproduction?
Remember, that in evolution, the concept of adaptation has a very central role in understanding evolutionary fitness, and it might be easy to see the extra evolutionary fitness granted by consciousness through example.
If one has two organisms, let us say the mushroom and the mushroom hunter, we can compare their roles in the ecosystem. A mushroom merely grows. It is stationary, does not react to sudden changes in the environment. And largely exists passively. Spores are spread through the wind, and probability dictates if a spore carries on.
A mushroom hunter also grows, but consciousness grants some extra behaviors in the literal sense. A conscious human is not stationary, but can move about the environment in an attempt to fill goals aware of changes around herself. She exhibits intelligent behavior related to awareness. A mushroom hunter can distinguish between safe and poisonous mushrooms, and consume safe mushrooms to ensure survival. Consciousness allows her to move through environment over great distances, and avoid death by other animals, particularly predators. Consciousness allows a female mushroom hunter to pick a fit male mushroom hunter, perhaps against her own impulses based on reason.
So, what advantage? Natural selection favors adaptability, and consciousness (which occurs at speeds less than 500ms) influences behavior by increasing the capacities of intelligence, particularly in a competition with other intelligent agents.