The Duck Curve Explained

If you’ve heard of the Duck Curve, then you may be aware of the impact that Solar PV is having on California’s electrical grid.  However, if you’re not familiar with the term, you will be soon. Solar PV is a tremendous alternative and sustainable resource for electricity and already produces gigawatts of power every day. That’s fantastic, except, the production of solar energy happens when the sun shines. Which doesn’t necessarily coincide with our power consumption profile during the day.

the duck curve is a continuous issue in CaliforniaIn fact, Solar PV already generates more power than we can consume during certain times of day, especially during the spring time. Although solar irradiance is high, temperatures would be well below summertime peaks.  This mismatch in production vs consumption does an abrupt reversal as the sun sets, effectively shutting off our power supply while our demand for electricity is still high and rising.  If you visualize a graphical plot of the power required from the California Independent System Operator (CAISO) you see a shape resembling a duck’s back and head, the “Duck Curve”.

The power required from power generation plants balances against solar energy on the electrical grid. But, that can vary dramatically throughout the course of the day.  This forces CAISO to reduce power plant output and sometimes give power away to other states to keep things in check.  Then, as the sun sets, the pendulum swings the other direction and CAISO must scramble to bring power plant outputs up to maximum quickly as the solar energy drops rapidly with the setting sun. What aggravates the situation is the timing of people using their appliances and increasing power demand from the utilities.  As more solar is added to the grid, the situation worsens.

Energy Efficient Solutions

The solutions are apparent but elusive:

  1. Manage load on the grid by utilizing energy during peak hours and less at night.
  2. Install energy storage when we have excess power available, then discharge as needed later in the day.

Changing our load requires careful evaluation and deployment of energy analytics which help large energy users adjust business processes to bias energy consumption to meet grid needs, a la, “Smart Grid” technology.

Advanced analytics that can guide operations, at manufacturing plants and water districts, are undergoing rapid growth and application.  Energy storage using various technologies is not new but hasn’t developed to support energy requirements on this scale.  The CAISO must quickly ramp up power output by as much as 36,000 MW to balance grid requirements.  Storage comes in many forms.  Some of the more common technologies are currently battery storage, hydro pumping to elevated reservoirs and ice storage. Ice storage is when ice is made at night and used for space cooling during peak demand periods.

The Duck Curve will continue to be a growing problem with the installation of additional Solar PV. However, storage and energy demand analytics look to be promising solutions for the future.