Suggestion - Option to calculate cost saving against another plan

[kernow]

Currently the cost savings are calculated against our current price plan minus PV and predbat. For some people this won't give the true cost saving against not having a PV system as they would be on a different plan if they didn't have a PV system e.g. octopus agile with PV system vs fixed rate without.

It would be good if we could provide our own cost for comparison to calculate the savings. This could be done my adding a setting and providing a fixed cost per KWh that would override the current plan cost.

We would then be able to see the true cost saving of having a PV system vs not having one.