If your data centre uses less energy than your renewable energy source, then you can push the excess out onto the grid. Similarly, if you use more than you can

If your data centre uses less energy than your renewable energy source, then you can push the excess out onto the grid. Similarly, if you use more than you can produce, you have to pull the deficit from the grid. Either way, the less energy you use, the more energy has to be generated elsewhere. So energy efficiency still matters. Against that, there are transmission losses. If your data centre in a cold dark place is powered by a solar array in a hot sunny place, you need less energy to spend on cooling, but you have less energy to spend because more energy will be lost in transmission. I don't know how they balance out. (And if you have enough clients in the hot place who want low latency, it makes sense to put the data centre in the hot place even if it's less energy efficient.)