May has arrived and days are getting longer and warmer. This is good news for baseball fans, barbecue enthusiasts, and grid operators concerned about integrating unprecedented levels of solar energy onto the California grid.
Source: Solar panels at Busch Baseball Stadium
Plugging lots of solar into the power system creates challenges, particularly on days when electricity demand is relatively low and renewable generation is high. Here in California, this happens in March and April when solar intensity is up (relative to the winter months), but air conditioning demand has yet to kick in.
Back in 2013, some California energy analysts with an eye for aesthetics were looking at how projected increases in renewable energy generation might affect power system operations. They plotted actual and projected hourly net load profiles (i.e. electricity demand minus renewable generation) over the years 2012 to 2020, focusing on late March when integration concerns loom large. The result was remarkably duck-like.
The California ISO “duck chart” made a big splash for a number of reasons. For one, a graph that looks like a duck makes an otherwise dry, technical issue more fun to talk about. Conversations about renewable integration become more engaging when sprinkled with fowl word plays.
Perhaps more importantly, the graph highlights two related integration challenges. First, the long duck neck represents the steep evening ramp when the sun sets just as Californians are coming home and turning on their lights and appliances. Accommodating this ramp requires maintaining a fleet of relatively expensive generation resources with high levels of flexibility. Second, the duck’s growing belly highlights the near-term potential for “over-generation”. As solar penetration increases, net load starts to bump up against the minimum generation levels of other grid-connected generators, such as the state’s remaining nuclear power plant. At some point, system operators have to start curtailing solar to balance the grid.
How’s the duck shaping up?
The CAISO duck chart predicts that we should see increasingly duck-like net load profiles in March and April. So I’ve been keeping an eye on the great data that CAISO makes readily accessible. This year, the duck showed up. The graph below plots average net load profiles for late March/early April since 2013 (I averaged across seven days around March 31 to smooth out the variation that comes with random weather, week days versus weekends, etc.).
Note: All data taken from CAISO website. Graph summarizes hourly data, March28-April 3, 2013-2016.
In the 2016 duck season, we saw mid-day net loads at or around predicted levels. Increased solar penetration on both sides of the meter (utility scale and distributed) has been driving net loads down when the sun is up. Fortunately, the ramp from 5 – 8 pm has not been quite as steep as projected because electricity demand in the evening hours has been lower than projected. Perhaps this is due to unanticipated demand-side energy efficiency improvements. I could not easily find hourly curtailment data. The data I could find on plant outages indicate that March 2016 saw the highest forced solar plants outages on record, but these outages could be due to factors other than curtailment.
My after-the-fact duck chart suggests that renewables integration challenges are showing up more or less on schedule (although ramping requirements are somewhat less than projected). So far, these challenges are quite manageable without major changes to grid operations. But the duck of the future – especially given California’s new target of 50% renewables by 2030 – will present a more formidable challenge.
Renewables integration strengthens the case for regional coordination
California is not alone in creating and confronting unprecedented renewable integration complications. Take Hawaii, for example, where a 100% renewables target makes California’s 50% look timid. Our colleagues at University of Hawai’i, Michael Roberts and Mathias Fripp, have been thinking hard about how Hawaii can pull this off at least cost. The charts below illustrate a hypothetical 100% day in Oahu in April (no more duck when all load is served by renewable energy!):
Source: Fripp (2016)
The broken line in the right graph represents the “traditional”, business as usual demand profile. To hit the 100% target, wind and solar generation increases to nearly double current levels of the traditional peak. Differences between the timing of renewable energy production and traditional demand are reconciled primarily by EV charging and other demand-side response programs (although batteries and pumped storage also play a role).
When you’re an island in the middle of the ocean, you’re pretty much on your own when it comes to tackling these grid integration challenges. Thus, Hawaii is preparing to demonstrate how significant renewable energy integration can be achieved with demand response, grid management, and storage. In contrast, California has more options to leverage.
Although California fancies itself a different world, it is physically connected to (but not perfectly integrated with) a larger western power system. From an economic perspective, expansion of the energy imbalance market and improved coordination of the western grid looks like an obvious and important piece of California’s renewable integration puzzle. A regionally coordinated western grid would integrate mandated renewables across a larger area, thus reducing the likelihood of over-generation. Coordination across balancing areas should also provide increased flexibility.
In the past, economists have documented the efficiency gains of improved regional coordination and bemoaned the inefficiencies of the balkanization that persists. Looming renewable integration challenges could provide the needed additional impetus for grid integration. To be sure, there are some important details that need to be better understood. But if done right, a fully coordinated regional grid could help clip the duck’s wings.