The “duck curve” is a whimsical term to describe a serious challenge in the incorporation of renewable energies into the power grid. Specifically, the duck curve shows the disparity between peak electricity demand and renewable energy production during a single day. A group of researchers at Cornell University recently published a study stating that the US state of New York could experience a higher degree of this supply-demand mismatch in winters due to the growth of solar PV in the region. From a geographical and seasonal perspective, New York has the combination of plentiful sunshine and low electricity demand at midday in the winter. The timing imbalance between the peak PV generation (at midday) and the load peaks (in the morning and evening) is thus much more pronounced. The model analysis undertaken by the Cornell researchers indicates that the state’s power grid may have to increase its ramping requirements up to 151% during those sunny winter days if solar PV accounts for a greater share of the state’s electricity mix. With the state government preparing to massively expand large-scale and distributed PV projects, more attention is now being paid to the issue of maintaining the stability and flexibility of the region’s power grid.
Most renewable energies offer a form of electricity generation that is intermittent, so their daily power output curves often do not align with the load curve. In the case of PV systems, they tend to reach their highest power output at midday when the sunshine is at its maximum intensity. At this time, the grid operator that is receiving electricity from PV systems would curb generation at other power plants (e.g. coal, natural gas, nuclear, etc.) to prevent waste. Later in the evening, when the sun sets and PV systems stop working, the grid operator would immediately ramp up the electricity supply from those same sources in order to avoid shortage. The load curve also generally peaks in the evening due to people spending time at their homes. With intermittent renewable generation becoming mainstream, regional and national grids can expect a more volatile supply-demand situation. Their management and flexibility will be tested to their limits as well.
The chart above shows a duck curve in the load profile of California on 22 October 2016. The orange line, which represents the load of renewable generation, depresses during the middle of the day and forms a trough that looks like the belly of a duck.
(Source: Arnold Reinhold CC BY-SA 4.0 via Wikimedia Commons)
For their model analysis and duck curve projections, Cornell researchers have established three hypothetic scenarios of the total installed PV capacity for the state of New York: 4.5GW, 6GW, and 9GW. Under the 9GW scenario, the model analysis reveals that the state’s peak electricity demand from conventional energy sources in the summer could be cut by around 9%. Furthermore, solar PV could meet 10-74% of the local electricity demand during the peak load period in the summer depending on the location and weather.
On the other hand, the duck curve becomes more of an issue for New York’s power grid in the winter. The load curve of the state is relatively flat during daytime in this season, while the electricity output from PV systems can increase dramatically depending on the weather. According to the model analysis, the regional ramping requirements could go up to 151% on sunny days in the winter.
Jeff Sward, who is a doctoral candidate at Cornell and one of the co-authors of the study, hopes that the work of his team will help improve New York’s electricity transmission system in the future.
The adoption of smart grid technologies for better grid management has become more urgent as governments worldwide pursue green energy projects. The state of New York has been strengthening its renewable energy policies since 2012, when Governor Andrew Cuomo first launched the “NY-Sun” initiative to spur renewable energy transition and sustainable development. The state government has continued to increase its subsidies for PV installations in the recent years. On the whole, New York’s installed PV capacity has been growing annually as a result of policy incentives and advances in PV technologies.
Data provided by the New York State Energy Research and Development Authority (NYSERDA) reveal that PV installations within the state increased by more than 1,000% from December 2011 to December 2017. Furthermore, NYSERDA supported the development of more than 84,000 PV projects in the same period. New York was also third in the ranking of states by PV installations between January and June of 2018. NYSERDA is a public corporation that assists in financing renewable energy projects and implementing energy efficiency measures.
Cuomo has announced that his legislative agenda for 2019 includes a commitment to make New York run on 100% renewable energies by 2040. Solar PV and offshore wind are expected to be instrumental in realizing this ambitious green energy vision. Meanwhile, increasing public discussions on trends in future energy technologies, local electricity demand, and grid management will also lead to the development of more stable and reliable renewable generation systems.
The Cornell study, “Strategic Planning for Utility-Scale Solar Photovoltaic Development – Historical Peak Revisited,” was published on 15 May in Applied Energy.
(This article is an English translation of news content provided by EnergyTrend’s media partner TechNews. Source of the top photo: Eleleleven CC BY-SA 2.0 via Flickr)
