The 2017 solar eclipse – a surprising use case for demand flexibility
On 21st August 2017 thousands of people were stepping out of their offices, schools and homes to turn their eyes to the sky. For the first time in the smartphone era, a total solar eclipse occurred in mainland United States. But as people were pointing their phones upwards to capture the historic moment, months of planning and preparation were coming together for the energy industry.
The solar eclipse problem
Not only was this the first total solar eclipse to occur in the USA in the social media era, but it was also the first to significantly effect solar panels across the country. The state of California, from which the eclipse was visible, has around 12 % of capacity which comes from large scale solar PV.
For several hours during the solar eclipse a large portion of solar power was knocked off the grid by the moon’s shadow: around 4GW, roughly equivalent to the power demand of Los Angeles.
Planning, preparation, and flexibility
Grid operators had been planning for this day for months. Along with planned increased generation from hydro and gas power plants, customers were also asked to change their demand. As the eclipse passed across California the moon’s shadow reduced the output of PV cells. The system operator for the state of California - California ISO - issued flex alerts to enrolled customers, asking them to reduce their demand. On top of this, smart thermostat manufacturer, Nest, automatically altered the temperature of customers enrolled in their Rush Hour scheme across the country to help reduce demand. Nest estimated that they alone reduce demand by around 700 MW during the eclipse through adjusting around 750,000 thermostats.
This demand response was not only useful to replace the power that would have been available from solar PV generation, but also because it helped generators which otherwise would have needed to change their rate of generation much more quickly than usual. A typical generator in California can change its output capacity by 29 MW/min. California ISO calculated that to match the change in output from solar PV the rate of generation would have had to increase at a rate of 70MW/min as the eclipse crossed the state. This would have had to decrease at a rate of 90 MW/min as the sun came back from behind the moon.
An even bigger challenge next time
Rather than a once-in-a-lifetime occurrence, the next solar eclipse in the USA will occur in April 2024. The path of totality will trace across Texas, Oklahoma, Arkansas, Missouri, Indiana, Ohio, and New York State. Their neighbouring states will also experience significant shadow.
The EIA project a solar capacity of around 140 MW across the USA by 2024, which would represent a 75% increase of capacity. Thus, the need for flexibility will be even greater in 2024 than it was in 2017.
Dealing with the issues that arise from the solar eclipse might seem like a niche application, but it actually serves as a good analogy for the fluctuations that the modern grid experiences.
As the sun sets and generation from solar farms fall, people arrive home from work and turn on their lights and TVs. This fall in generation twinned with a rise in demand serves as a parallel to the issues seen during the eclipse, and it can be solved in a similar way.
By building a network of flexibility, demand can be shifted away from these high demand times, relieving stress on the grid. Times of high demand are also times of high prices and high carbon – if we can automatically shift customer use out of these periods we are saving money and reducing carbon intensity. Read more about the benefits of demand flexibility here.