The electricity provider Tibber offers a dynamic electricity tariff in which the average spot price on the electricity exchange is charged either on an hourly or monthly basis. For monthly billing, you enter the meter reading into the app at the end of the month; for hourly billing, you currently either need a smart meter gateway (which unfortunately are still not being rolled out in Germany), an intermediate meter from Discovery or the so-called Tibber Pulse (cf. here).
@Christian Butterweck has already developed a script to charge ESS based on the spot price, thanks for that! With hourly billing based on spot market prices and a smartly responding ESS, electricity costs can potentially be saved and the power grid stabilized.
I would love to see a cooperation between Victron Energy and Tibber so that the GX device is able to report hourly consumption values to Tibber and thus no additional meter is necessary. After a first inquiry from me, the Tibber team seems to be quite open to this and they already offer some open interfaces in their system. So it looks like there is a similar philosophy for dealing with interfaces.