Consequences of dynamic transmission line rating for renewable power

Michael Giberson

I think the implication of this article are good for wind power, but not as good for solar power.

Some of the discussion borders on being over my head, but the main point is that many transmission line capability ratings are static while the actual transmission line capability is dynamic. Dynamic line ratings – ratings which reflect current weather data – can increase the amount of power that can be reliably carried on existing transmission infrastructure.

Generally speaking a transmission line’s carrying capability is limited by the danger of overheating. To be safe, transmission operators will compute a rating for a line under possible adverse conditions.  A line is more likely to overheat during hotter, calmer times and less likely to overheat at colder, windier times, so transmission operators will base ratings on assumptions of high temperature and low wind. The result is that transmission line limits are probably too conservative most of the time.

The consequences for wind power and solar power generation are fairly obvious: Wind power output is higher when it is windy, and so is transmission capability, so use of dynamic line ratings would ease transmission constraints associated with large wind power output.  Wind power also tends to be higher at night and during cooler periods of the year, so again dynamic line rates would allow more transmission capacity to be used. (This approach is already in use in a few places.)  Solar power output, on the other hand, tends to be higher during hotter times of day, when transmission capability is lower. Still, it is likely that dynamic line ratings would benefit solar too, since most of the time transmission lines limits are likely too conservative.

I should also point out that dynamic line ratings should be good for consumers, too, since the more efficient use of transmission capability reduces congestion, meaning it is easier for consumers to reach any available low cost power on the system.