Must-Run Status

Imagine a wedding hall that promises one particular guest they will always be seated first, no matter how full the hall gets, because that guest cannot simply come back another day if turned away. Must-Run status gives solar and wind generators almost exactly that guarantee inside India's power grid.

A thermal or hydro plant can usually be ramped up or down on request, so if the grid has more supply than demand at a given moment, a grid operator can simply ask a flexible plant to generate less. Solar and wind cannot be stored or rescheduled the same way, their output depends entirely on whether the sun is shining or the wind is blowing right now, and if that power is not used the instant it is generated, it is lost for good. Must-Run status is a regulatory rule that grid operators must accept whatever power solar and wind generators are producing at any given moment, and cannot curtail, or reduce, that output except in genuine grid security emergencies.

The reason this rule exists is investment certainty. A renewable developer's entire financial model depends on selling essentially all the power it generates. If curtailment were routine and unpredictable, as it is for some thermal plants during low-demand periods, lenders would price renewable projects as riskier and more expensive to finance, undermining exactly the kind of investment India has been trying to attract.

The cost of this guarantee falls on the rest of the grid. When renewable output surges, especially around midday for solar, and there is not enough flexible, non-Must-Run capacity available to scale back, grid operators can face genuine balancing challenges keeping supply and demand, and therefore grid frequency, in line.

Whenever a grid operator discusses renewable integration challenges or the need for more flexible thermal and storage capacity, Must-Run status is the underlying reason solar and wind cannot simply be asked to ease off the way a coal plant can.