Thats why I'm not a fan of the grid tie systems. Here every time there is a little rain the power goes out or when someone cuts an underground line or when someone else connectes a new branch circuit and overloads the transformer. Were without power once a month on average, and twice in the last three years I've had to go back home upon arriving at work to find no power.
It seems pointless to me to have invested all the $ in generating your own power if your going to just put it back into the grid then when you need it most not have it avaulable because the grid went down.