Storage slays "The Duck"

The Duck

There is a "Duck" in the solar hen-house!

In 2013 the California Independent System Operator (CAISO) that manages bulk of the state’s wholesale transmission grid, published a graph that shows the difference in electricity demand and the amount of available solar energy throughout the day. When the sun is shining, solar energy floods the market and then drops off as electricity demand peaks in the evening. The result is a funny looking "Duck" curve - the dip in whose belly (1.p.m.) represents the mid-day lull of energy consumption, the back of its neck (6p.m.) indicates the swift ramping up of energy consumption in the evening hours, and its beak represents a tapering off in consumption around bed time (10p.m.). The trouble for the utility is the midday chunk of time where the potential of over generation meets a severe dip in demand. The days of power shortage are definitely over for the US but the 'duck' indicates a greater challenge for utilities - to match supply and demand, ensuring that the system is not overburdened.

“The grid has been called the most complex machine humans have ever built,” said Daniel Kammen, Professor of energy at the University of California, Berkeley. “It is the largest, the most extensive and has the most parts, and it also has a beautiful simplicity. It’s driven by this very simple energy-in must equal energy-out at every moment in time.”

Why Storage?

  • Intermittent production: The major limiting feature of renewable energy is its intermittent supply - depending on the time of the day and season. The production is at its peak between mid morning and afternoon and reduced to 1/5th in the winter. Solar generation follows daily and seasonal sunlight patterns, peaking during the long summer days and reaching its annual minimum during the winter.
  • Demand variability: The peak demand for electricity is usually in the early evening hours, when solar production has clearly dwindled. Demand variability also dictates the load stress and price.  

These alternating hours of usage and production make energy storage an absolute necessity in order to make renewable energy a viable alternative to fossil fuel generated electricity. Energy "ramping" during hours of peak usage require additional gas to be burned or water released from dams in order to match the energy generation with actual usage. If clean energy is to compete with coal and gasoline on the electric grid, energy storage is the only way forward. For all the considerable advancements in photovoltaic (PV) systems in the last 30 years there has been surprisingly little advancement in the field of energy storage on the grid scale.

In 1991, Sony commercialized the first lithium-ion rechargeable battery, forever changing the history of mobile devices. Today, the search is on for the next generation of rechargeable super batteries capable of storing renewable energy on the national electric grid - technologies that are cheaper, more efficient, more powerful, safer and cleaner.

Positive Initiatives 

Policy shifts at the state level have reflected the states' growing fear of relying on carbon heavy energy sources. California, Massachusets, Arizona, Florida have all expanded their incorporation of renewable energy by forming think-tanks and working with both engineers and regulators to focus on the issues facing energy storage in an effort to flatten the 'Duck'. Companies like NextEra are working to close the gap on affordable solar storage by building two new storage systems beside already existent solar farms in Florida just this year. In Massachusets, $20 million is being disbursed in grants to 26 companies for specifically expanding the states storage market by requiring all retail energy suppliers to provide a minimum percentage of sales from clean peak energy sources, including energy storage systems."  

With constant innovation through research and development and legislators in some states closely looking at addressing the problems of the duck curve, it is quite possible in the  near future to develop city scale storage systems for renewable energy, reducing our reliance on carbon-based energy.