In my country (Poland, so not much renewable energy unfortunately) night-time (and weekend) rates are significantly lower (in some cases over 50% lower). You may choose uniform rate but it's not worth it (just remember to do your washing at night).

I worked in a company that sold energy-trading systems for many countries in Europe, and it was similar there (usually individual customers may choose uniform average rate, or much better offpeak rate and slightly worse peak rate, while the big energy market participants trade with different peak and off-peak rates almost always).