Add option to always charge in Spot price mode if below specified minimum price

[pkuehnel]

This should only happen if there is no date set in the future or if the selected date is too far to plan charging slots.

[pkuehnel]

Also charge if below solar price

[andreasfaerber]

A first step into that direction (As C# is not for me):

https://github.com/andreasfaerber/tsc-spotpricecharger

Needs some beta testers, in particular with solar systems as these are not taken into account so far (i have none) to get these respected if anyone is interested in testing.