Deliberately curtailing renewable energy output improves grid performance and lowers total operating costs. More generation, in this regime, produces worse outcomes.
The mechanism is a “unit dispatch transfer effect.” Forecast-based scheduling of high-variability renewables constrains real-time flexibility so badly that the grid spends more on ramping products than it saves from the extra renewable generation. Every additional megawatt-hour of uncertain supply tightens the flexibility constraint, forcing the system to hold more expensive reserves.
Moderately reducing renewable output relaxes the constraint. Fewer ramping requirements. Lower total expenses. The surplus was more expensive than the shortfall.
This is not an argument against renewables — it's an argument about the coupling between generation and flexibility. The cost of power isn't just the cost of producing it. It's the cost of producing it while maintaining the ability to adjust. When the adjustment cost rises faster than the generation cost falls, the surplus becomes a liability.
The general pattern: in any system where components must coordinate, the marginal value of adding more of one component depends on the flexibility cost it imposes on the others. A faster car that requires a wider turning radius may be slower around the track. More renewable capacity with less dispatchable backup may cost more to operate.
The optimization target is the coupled system, not the component.