 Solution

Variability reduces firm capacity and creates balancing costs, but does not impose a universal tiny upper limit on the energy fraction from wind power. As an illustrative scale calculation, $10\mathrm{GW}$ installed at capacity factor $0.30$ produces $26.3\mathrm{TWh}$ annually, about $8.8\%$ of an assumed $300\mathrm{TWh}$ annual demand. Larger installations can supply larger fractions if the rest of the system is adapted.

Geographical spread, forecasting, interconnection, flexible generation, demand response and energy storage manage fluctuations on different timescales. They are not interchangeable: a battery that balances seconds does not necessarily cover a week of low wind. Correlated weather, curtailment, network constraints and reserve requirements become more important at high penetration. Backup capacity need not burn fuel continuously at the wind plant's nameplate output; energy and capacity should be accounted for separately. The defensible conclusion is that significant penetration requires system planning and has costs, not that variability alone confines wind to a negligible contribution.^[ref]