That's such as simplified analysis. Perhaps there's no shortage (unlikely given Texas' power needs), perhaps there's transportation bottlenecks creating local oversupply? That price has to lower to send the price signal that the arb is there and firms can make money building that transmission, at which point, just like the other energy products in West Texas (crude), the relative price will begin to rise again relative to the benchmark. (See: West Texas / Midland grades of crude being priced at steep discounts that are now shrinking due to increased pipeline capacity coming online.) It's not that Midland crudes were "oversupplied" it's that demand was being "artificially" lowered by transportation bottlenecks. (Economists / econometricians may argue definitions with me on that, but from the energy trader perspective, that's how I would approach it.)