grid parity for solar is actually simple: it is indeed linked to self-consumption and, as most installations are individual ones, the price that matters is the retail tariff (currently at 28c/kWh in Germany, ie rather high and certainly higher than solar costs).

For producers who deliver power on the wholesale markets (most wind farms and the industrial solar plants), it's the spot market that matters.

There are indeed industrial companies that like interruptible power (in France, the cheapest tariff for industrial users is one where EDF has the right to switch off these consumers with limited notice) - either because they have non-time sensitive processes, or because they have back up capacity of their own.

Wind power