Integration Cost Curve

The first 10% of solar on a grid is nearly free to integrate. The next 10% costs more. By 40-50%, integration costs can rival the generation savings. The curve is nonlinear, and ignoring it produces misleading projections.

The integration cost curve plots the system cost of accommodating variable renewables as a function of their share of total generation. At low penetration, renewables displace the most expensive generators (gas peakers), curtailment is near zero, and backup requirements barely change. As penetration rises, each additional increment displaces cheaper generators (baseload gas, even nuclear), curtailment increases, backup requirements grow, and transmission constraints bind.

The curve's shape comes from three compounding effects. Curtailment increases nonlinearly as generation exceeds absorption capacity during peak output hours. Profile costs rise because all solar (or wind) produces at the same hours, depressing the market value of each MWh. Backup costs increase because dispatchable capacity must be maintained for hours or days when renewable output is low.

California's trajectory. Studies of variable renewable integration put costs near $3-5/MWh at mid-2010s penetration levels and $10-15/MWh as solar's share approached 30%, driven by rising curtailment and evening ramp costs.

At what penetration does integration cost exceed the LCOE savings from solar?

Estimates vary, but typically 40-60% without storage. Beyond that range, additional solar capacity may cost more to integrate than it saves in fuel displacement. Storage, demand flexibility, and regional transmission push this breakpoint higher, which is why they are not optional additions but economic prerequisites for deep decarbonization.

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