If you have grid power then you will struggle to even compete with wind power. The biggest factor is the battery cost. Unless you can get cheap batteries I doubt that you will break even. Probably best to use a small battery bank and revert to grid power when there is not much wind about. Large battery banks only make sense when you are off grid and even there is a maximum useful size and in low wind times you need back up ( even if it is solar).
Again much depends on your site, I suspect your 400W turbine may average about 60W if you steer clear of periods with days of no wind. If your load is intermittent at 140W you may be able to supply it most of the time with a modest battery bank.
Regarding 1500kWh monthly then your best option is to conserve, you will never supply that sort of thing cost effectively with anything requiring batteries. Power saving when on grid can only be effective with grid tie ( long pay back period) or something like water heating that doesn't have the cost of batteries and their frequent replacement. if you want to do it for fun or if you can get near free batteries then that is a different matter.
A large battery bank will cost a fortune. Small ones will be cycled more and have a shorter life. Batteries wear out if you use them and they die if you don't use them, the best compromise is just enough to do what you want with a modest cycling under normal conditions. If you must have back up for long windless periods expect to pay the earth.
Flux
