Can’t buy power from neighboring city

Before answering the question directly, you need to understand a sparsely documented caveat to region play... region hubs.

Excess utility capacity is divided up equally amongst city sites in a region hub. A region hub is defined, for utility purposes, as any city connected by ROAD to a city that wants to provided utilities to other cities.

A typical region hub in the Simcity world has 4 city sites connected to it by road. Some have as many as 7. We will use the example of having 4.

EXAMPLE: City A is in a region with 16 city sites, divided into 4 region hubs.

• City A decides to specialize in coal mining, and power itself with a coal power plant using local resources to keep costs down.
• City A only needs 15Mw to operate, but the power plant constantly produces 75 Mw. Giving it 60Mw in excess capacity. This excess capacity is offered to other cities in the region hub.
• The 3 other city sites are given the choice to buy an equal 20Mw share of the excess power since 60 / 3 = 20
• City C and D do not need the excess power, as they are generating it on their own. However, city B wishes to buy more than their share. They do not have this option. City A would need to increase their capacity in order to give out a larger share to City B.

This is how the game currently operates, and it appears to be working as intended.

The problem appears to have been caused by the orders and positioned I had placed the buildings in, in comparison to the coal mine. This appears to be down to the route that the agents carrying the materials in choose to travel when leaving the Coal Mine.

In the original route, the coal power plant was at the end of the blue route on a backstreet, while it is now located on the yellow route, before the trading port;

When the agents carrying coal leave the coal mine, they always seem to take the easiest route, which in this instance results in them not crossing over the road, thus they always turn right towards the smelting plant.

Each stop along the way has a specific level amount of coal they can store;

• The Smelting Plant has storage for 10 tons of coal
• The Trade Port has storage for 100 tons of coal
• The Coal Mine has storage for 20 tons of coal

Before the agents will start delivering elsewhere, each of these storages need to fill up to maximum, which means the Coal Power Plant wasn't getting coal in the original instance because the output of the Coal Mine wasn't sufficient enough to fill up the storage capacities of all of the buildings before it.