Very often people do get big increases in bills . . . it all really depends on what sort of tariff you are on, how it relates to how / when you use power, and even the state / region you are in.
Even with solar, it can be a shock when you get your first bill, for example if you are put onto a time of use (TOU) plan, work all day, and use power in peak times before and after work.
Did you get a battery too @Jie_Zhang ?
That will make a big difference to plan choices, and be the way to avoid high peak charges.
Yes, there are options out there, but you should look at what AGL has to offer, (if there is a choice) whether you are better off on a single tariff or go onto a TOU tariff, or if there is a demand tariff attached to any tariff type you choose.
Then there are the local feed in tariffs (FITs) offered, possibly a VPP plan.
Solar options can be hard to work through with people's own usage patterns etc, I found it's just as important after all that to get the retailer and plan right after getting through that.