Ad 1: If electricity goes from Germany to a foreign power company, then German private consumers cannot be billed for the use of the grid. Instead the foreign power company will pay the contract price which was originally set for cheaper baseload power, while it will actually cost more, coming from an expensive peaker plant. Someone will have to foot that bill (probably TenneT, but I'm not sure, see below).

Ad 2: From what I understand, the relationship of grid operators and power plant operators in Germany is still rather messy. The EU forced a separation only recently (TenneT bought E.ON's part of the grid). However, Gundremmingen is on the part of the grid operated by TransnetBW, the one of the four still fully owned by the power plant operator parent company (EnBW), so TenneT apparently comes into the picture as direct neighbour and provider of transit. So I'm not sure who pays whom in this setup.

_{*Lunatic*, n.
One whose delusions are out of fashion.}