sploo
Somewhat extinguished member
I just spoke to a colleague about this; and the answer is indeed that there will be times where there's definitely not enough renewably generated electricity on the grid to support all customers on "100% renewable" tariffs. However, it'll be offset by renewable power being generated at off peak times.Several quite large companies advertise(d) 100% renewable, and on a windless night the amount of renewable electricity drops to a few percent. Where else does the electricity come from?
I.e. if you use X units of electricity per month on a renewable tariff then there should be X units going into the grid from renewable sources (over that month), but at any one particular instant it cannot be guaranteed that there's enough renewable power being generated to cover all the use.
So basically, it's either all fine and definitely renewable; or a complete fudge and a lie - depending on your point of view and personal biases.