Energy Analyst Discusses the Future of California's Energy Grid

      Every evening between 5 and 6 PM in California, the sun sets, office workers head home, ovens are turned on, and the electricity grid faces one of its most intense periods of demand. During this time, electricity prices increase, natural gas plants quickly ramp up operations, and utilities strive to balance supply and demand in real-time.

      This evening period increasingly influences how consumers utilize connected devices, from smart thermostats adjusting temperatures to electric vehicles scheduling their charging times to avoid peak rates.

      Energy researchers often refer to this moment as a daily stress test for a power system that now significantly relies on renewable energy sources.

      California's grid operates under a distinctive combination of technologies and market regulations. Solar power contributes a substantial portion of daytime electricity, while natural gas plants continue to help balance supply during demand peaks after sunset.

      According to energy market analysts, the grid's behavior is often dictated as much by economic factors as by energy policies. These dynamics are becoming more apparent at the household level as utility pricing models and consumer-facing applications provide users with better insights into when electricity is cheapest or most expensive.

      Why Solar Is a Double-Edged Asset

      Unlike New England, California's grid does not depend on coal or oil. The fuel mix is cleaner but also more complex.

      Solar power enters the grid at a very low marginal cost, which means it is usually dispatched first when available. Natural gas plants then meet any remaining demand as necessary.

      Energy market researcher Neel Somani indicates that this setup creates a unique pricing dynamic: the cost of electricity is often set by the last generator needed to meet the demand. “There’s renewables and natural gas units, but in California, you don’t have the more polluting sources, like coal," explains Somani. "When there’s a demand, it’s first met with renewables, which have nearly zero marginal costs, and then less efficient natural gas units are activated to fulfill any remaining demand.”

      This system, overseen by the California Independent System Operator (CAISO), means that electricity pricing on any given day largely hinges on one question: How inefficient does a natural gas plant need to be before the grid can’t meet demand without it? When solar energy is plentiful, the answer is significantly inefficient, keeping prices low. However, this answer shifts quickly after sundown.

      Solar generation peaks during midday, delivering inexpensive electricity when residential and commercial demand is at its lowest. But as the sun sets, this flow of low-cost energy vanishes just as people return home and turn on multiple household devices. This creates what grid operators term the "duck curve," which visually illustrates net electricity demand that dips sharply at midday and then rises dramatically in the evening.

      For consumers, this trend is increasingly evident in time-of-use pricing, where operating appliances like dishwashers, laundry machines, or electric vehicle chargers during midday can lead to noticeably lower energy expenses.

      The 5 PM Problem

      “When individuals arrive home at 5 PM, they turn on their lights, TVs, and ovens all at once, causing a demand spike,” Somani explains. “Therefore, if you look at the power price chart, you’ll notice a spike around 5 PM, which then stabilizes in the late evening.”

      This spike is exacerbated—not alleviated—by solar energy. The challenge lies in system design. To meet the sudden increase in demand that occurs after sunset, grid operators must dispatch gas turbines. However, the quickest gas turbines available, known as simple cycle gas turbines, are also the least efficient. Combined cycle gas turbines are more efficient but take longer to activate. “There are essentially two types of gas turbines,” Somani states. “Combined cycle gas turbines and simple cycle gas turbines. The fast-activating ones are simple cycle gas turbines, but they are less efficient. Consequently, we end up seeing even higher evening prices than we would without renewables.”

      The irony is striking. The same solar expansion that has positioned California as a national leader in clean energy has, in certain respects, increased the volatility of its evening prices. The more solar energy saturates the system during the day, the more abrupt the ramp that conventional generators must manage when solar drops off.

      The U.S. Energy Information Administration has closely monitored this trend, noting that as California's solar capacity rises, the midday decrease in net load continues to diminish, creating a steeper climb back to evening demand levels. Grid operators must navigate a ramp ranging from 10 to 17 gigawatts within a three-hour time frame, demanding accurate coordination among numerous generating assets.

      The Geography of the Problem: NP15 and SP15

      The challenges faced by California's grid are not uniformly distributed. The state's transmission infrastructure separates it into two major pricing areas: Northern California, known as NP15 (North Path 15), and Southern California, termed SP15 (South Path 15). These two zones are linked by a transmission corridor called Path 15, and when that line experiences congestion, wholesale prices in the