I had solar panels installed in March last year and qualified for the FIT grant just in time. This means I have a full 12 months of usage figures, and have set my monthly payments to close to my annual use, which should not vary very much. The automatic usage estimate still appears to be using average usage from before the panels were installed. This means my estimated usage is more than double what it is in practise. It should be possible for Bulb’s system to note the installation date and only use figures after this date, your personal website setup is modified if you have the FIT grant. The current setup forces me to supply meter reading every month, if I want to avoid estimated bills that would be nearly 100% out.
Even with solar being installed, you still need to submit monthly meter readings, I’m not sure based on your post if you’ve been doing this. Without doing so there is no way for Bulb to track your now declining import usage and therefore correctly adjust their estimated monthly and annual usage for your account. However, with that said, surely you would have a smart meter if you had solar installed a year ago?
Further, depending on the size of your PV array, and your usage patterns, you might find that you’re exporting a sizable portion of your solar during the afternoon and drawing from the grid during the evening, at least this is what we were experience.
I have been giving monthly readings since I joined Bulb more than two years ago. Since I have the FIT and a small set of panels (only six), it’s not in my interest to have a smart meter as I will actually pay more - with FIT assumed export is 50%. I export less than this because I also have a box that dumps excess power to my hot water tank.