From the NYT article about Germany:
> At the same time, other mainstays of the country’s electricity supply, especially some coal and nuclear power plants, are unable to dial back quickly enough, leading to negative prices on electricity trading markets.
From the Forbes article about the Columbia river (Oregon / Washington):
> issue is what happens when too much electricity is on offer. The enormous supply of hydroelectricity during spring runoff can push electricity prices to zero—the BPA gives away electricity to local utilities for free when it’s forced to produce more than it wants to. Since wind producers enjoy production subsidies, they can push rates below zero, effectively paying other utilities to switch off their generators. Last winter, the BPA told wind producers under its balancing authority that it wouldn’t pay negative rates to them during high-water events.
This gets more complicated when you also take into account the non-power constraints on hydro generation. Environmental concerns limit how much water can go over the spillway (which hyper-aerates the water and increases turbidity... which is bad for the fish. http://www.oregon.gov/deq/FilterDocs/Coltmdlwqmp.pdf gets into this including the water standards act.
> The concentration of total dissolved gas relative to atmospheric pressure at the point of sample collection shall not exceed 110 percent of saturation, except when stream flow exceeds the ten-year, seven-day average flood. However, for Hatchery receiving waters and waters of less than two feet in depth, the concentration of total dissolved gas relative to atmospheric pressure at the point of sample collection shall not exceed 105 percent of saturation;
The interconnectivity of all of these factors is quite interesting to me and one of those things that is much deeper than a simple management of the power market.