Hi @Simone6334 , there isn’t a ‘solar’ tariff as far as I’m aware. 
With solar PV you will use less electricity from the grid during the sunnier months (during daylight hours) but it won’t help much during winter. 
Your choice of tariff is therefore not straightforward as the E7 tariff costs more during peak and less off peak (overnight).

If you have a smart meter, recording usage every 30 mins, that will give you a guide as to how much energy is used during peak and off peak hours. That might be a useful starting point. 
The electric storage heaters usually take power to ‘charge up’ overnight and then release the heat during the day but you still need to understand if that will last for a full day during those winter months, otherwise you will need to use extra electricity for heat at what might be an expensive time

Hey @Simone6334 

BPLightlog has left some really helpful advice here on this for you already, I just wanted to add that you can view all our available tariffs online. The topic below may also be helpful to you: