This question already has an answer here:
- How to trade Power between Cities? 4 answers
- I've built a usual city.
- I've built a new city with redundant power production right near the first one.
- I've initiated a deal to sell power to the first city successfully.
- I've started a new city right near the second one planning to buy electricity from it (I've even built intercity power line connection and taken care to connect the power lines on the both sides).
- But the deal to trade power between the second and the third cities is not available (does not appear in the list).