My assumption is the return of money to the shares is as a result of the Palmerston North CC litigation finally being put to bed. The market was pricing in a 60%+ possibility that PNCC would win in some manner and so a loss of investment for share holders.
On a global basis, Governments seem to be getting more serious about global warming and this should drive the price of power higher in the medium term. That would leave these guys looking pretty.
Let's see what the agm brings