Sure, 30kW storage is fine, but it implies you use all the energy every day (or night). In the summer months my current set up uses basically 0 grid hours (as I already have some storage for night time). The 30% really is an excess after storage, running home appliance, charging batteries etc.
If you store 30% for 3 hours, that's 90% of peak generation. It seems, by law, you could then finish selling that excess power for the next ~1.3 hours at your maximum rate (less storage inefficiencies).
You could figure out what time of day rates are highest, because that would imply you're releasing the most pressure on fossil fuel generators.
