A flat daily fee for having access to the grid makes total sense to me. You're using the grid to sell, and you're using it to buy, and you're using it as backup in case your equipment fails or in case it's winter. Even just being connected for backup seems to me like it's worth a few cents a day.
Interesting about the sales tax thing. I presume that's how it works here too. But most people don't register for GST (you don't need to until you have $30k in annual sales), so they won't charge GST on their sales -- they'll just pay it on their purchases.
Question: do you technically sell all your instantaneous production and buy it back, or do you sell just your net production? No difference to you either way, big difference to someone not registered for GST.
Having it reset end of March is presumably for ease of accounting at QEC HQ: that way they don't need to figure out how to price the liability at all, since they aren't carrying it on their annual books! A lot of things are done for ease of accounting here, e.g. internet monthly usage caps reset on the first for everyone in the entire city. Good luck getting any data through the satellites on the 30th.
But also, March is the second-best month for fixed solar panels (April barely edges it out). Afterwards the sun moves around so much your capacity factor falls. Zeroing out at the end of March is particularly annoying. Maybe it'll get changed with time.
Regardless, it's better than zeroing out once a month (which IIUC is how it is in many US jurisdictions), or daily, or, as it is until this policy goes into effect, continuously.