Baseload resources describe the portion of the power generation stack that optimally produces a steady flow of MWs across all hours of the day. The most cut and dry example would be nuclear resources. Apart from a few weeks every year (refueling maintenance), these plants will run at full capacity regardless of intraday shifts in supply and demand. Thermal and hydro are not considered baseload as they have the ability to ramp their production depending on what is going on in the market. With the growth of solar generation, price signals increasingly push resources to “flex” their output, with the aim of dropping non-solar generation in the midday and pushing it up after the sun sets. Batteries have been introducted over the past few years as another resource that provides flexibility to the enriched solar system within California.

Figure 1 | CAISO Generation Stack (MW)

All this said, baseload resources are far from obsolete. In addition to serving as important bastions of grid reliability, Mother Nature can still create conditions conducive to all-hours generation. The figure above represents CAISO’s generation stack, with resources distinguished by color. In recent days, California has been hit with stormy weather that delivered cloudy skies that resulted in a lack of solar generation hitting the grid. Looking at the supply shape of thermal, hydro and imports the hourly values took on more of a baseload look. Resulting from this type of shaping, SP15's day-ahead auction clears increased as the marginal megawatt needed to move into the lower end of the natural gas stack to get the units and/or imports to respond to the demand needs.

The figure below compares day ahead LMP for SP15 (left) and NP15 (right) across the 10^th and 11^th, where the second day saw a drop in solar production and the rise in thermal generation from different parts of California and the adjacent regions tethered to the Golden State via the transmission highway.

Figure 2 | NP15 (right) and SP15 (left) Day ahead LMP Comparison ($/MWh)

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