Surely it costs the environment the same, no matter what time it's generated?
Nope. Consider the difference between nukes and gas for example.
A nuke has to run at more or less full bore all the time, whereas gas can be turned up and down at a moment's notice. One of the tradeoffs is therefore environmental impact vs flexibility.
Historically it has been well-nigh impossible to store electricity so we've been constrained to only using nukes to provide baseload. Now we have batteries we can decrease the amount we need to use gas by shifting night generation to use it in the day.
And about the 50% efficiency in 20 years who cares I'll be dead thing....if my current system was working at 50% I (and maybe most of us) woukd find that unusable so would either have to use the grid more (which will have been the case all through as the efficiency decreases) or replace the batteries. Assuming replacement, hasn't that just handed a huge problem to the next but one generation.
Batteries aren't exhausted in the same way that fuel is though, they just need to be recycled
Don't both the above scupper the eco argument and expose the true motives for all this...financial gain?
It's certainly true that a lot of people are only prepared to shift to low-impact energy usage if it's of financial benefit to them, which is pretty depressing really, but I suppose it's better than refusing to do anything.
