Is it? Most marginal power generation (ie what energy source has to increase when you use a bit of power) is gas, even in peak hours. Plus Powerwall has, last real world results that I have seen, around 20% round trip losses. So unless you are topping up with 0 carbon energy and the grid marginal is 0 carbon, then AC coupled Powerwall etc is far from an environmentally friendly option. Powerwall 1 was better as that was DC coupled so much less losses, so your own solar could top it up far more efficiently. But it still does not get away from fact that storing then using one electron, means that somewhere else, more than one electron (be it 1.1 or 1.2 electrons) is going to have to be created elsewhere to offset that and if that means using an extra 20% from energy generation schemes, then that is quite some impact. You cannot justify something like Powerwall on environmental grounds if you are on grid, even if you generate your own electrons, except for a tiny proportion of the year. The solution is to use less energy in the first place and what you do need to use, try and use it when grid marginal has least carbon impact. Its a very complex balancing act, made even more complex by the reduction of many high carbon energy sources - yay to that.By shifting your load you are contributing positively to less "bad" electricity being needed during the peak hours. That's all good.