I signed up to AGL on the basis of a fixed rate (all day - peak and non-peak) but as soon as my account was setup it was changed unilaterally by AGL to a Time of Use plan with vastly different rates. Notification of the change was provided prior to 6am in the morning on a Sunday which appears to be deliberate to avoid me noticing. I wouldn't have signed up if I knew this was going to happen.
You have to be sure if changing from another retailer, or updating plans, changing to solar etc, that you are explicit in saying you wish to remain on a single or flat tariff, not go to a TOU tariff.
I changed to solar not long ago, wasn't told by anyone about this, that I could have requested when going to the digital meter(s) that I wanted to stay on a single tariff.
So I was put on TOU (with CL) and once you are on TOU it is very hard to go back (if not impossible).
I probably COULD have argued the point, as an AGL rep on the phone told me there is no choice (wrong apparently) in going to TOU tariff with solar.
It's possible I could have followed up and got this changed, but in reality with solar in particular we are able to work through the times and use ok to keep it down.
I was told by numerous solar and battery folk, that pretty much everyone will be made to go onto TOU type tariffs on digital meters in the coming year or two.
If you choose the right plan, and use your power at the best times for your plan, it can work out better anyway.