OK, I have now run the numbers on our downloaded Octopus data from mid summer when PV was installed to mid winter and simply doubled the answers to get figures for a year. For us Octopus Intelligent would be cheaper by around £150/yr, but when the better rate for solar export is factored in, Octopus Cosy is cheaper by around £450/year but 'your mileage may vary'. [Octopus pay 4.1p/kWh on Intelligent/GO and 15p/kWh on Cosy].
In order to enable some comparisons - we have a south facing PV array, and we use around 4500 kWh/yr and export around 6000 kWh/yr, work from home using around 6000 kWh/yr in the house, have a heat pump using around 8500 kWh/yr and an ev using around 4500 kWh/year. We do not have a battery or solar diverter.
Hope this helps.