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Understanding renewable energy ‘drought’ at solar, wind sites

Source：pv-magazine

A team of researchers has proposed a model for assessing potential renewable energy drought at existing solar and wind sites and has urged developers to consider a “trilemma” of competing factors when planning future deployment.

The research paper “Renewable energy quality trilemma and coincident wind and solar droughts,” available in the journal Communications Earth & Environment, says that while wind and solar are becoming mature and economically competitive, the two sources remain variable and intermittent.

It adds that in some cases, renewable energy droughts, defined as extreme or prolonged reductions in renewable power generation, can coincide across large regions and have impacts on energy systems that sap investor, public, or policy support.

The paper, which says knowledge on renewable energy droughts remains limited, goes on to propose a statistical method to identify and characterize renewable energy droughts using long time-series data at high spatiotemporal resolution. The model uses three categories of droughts – blue, orange and red – to represent the risk to existing power systems.

The methodology is applied to China, the country with the world’s largest electric power sector. It finds there is a high correlation of wind and solar droughts occurring in the provinces of Heilongjiang, Inner Mongolia East, Jilin and Liaoning, which are all connected to the northeast China grid. Meanwhile, a strong presence of solar droughts is highlighted in Tianjin, Beijing, Hebei, Henan, Jiangsu and Shandong, which are all connected to the adjacent north, central and east China grids.

The methodology could be applied to other countries, according to the researchers. “The results could prove essential to inform capacity expansion and operation strategies for a reliable decarbonized energy system insulated from the perils of wind and solar droughts,” the paper says.

The researchers also propose a “trilemma” of indicators to assess the quality of a renewable energy site. The first, resource availability, is the main factor currently considered and is utilized by measuring the site’s annual capacity.

The second, resource variability, refers to the stability of a site and is measured through its standard deviation from the capacity factor. The researchers say this can be managed using short-duration battery storage. 

The third, resource extremeness, refers to resource quality in terms of its propensity to energy droughts. The paper says this metric can guide the development of long-duration energy storage and other backup resources.

The academics say using this triad could “improve existing understanding of renewable energy quality and identify ‘ideal’ sites for renewable energy development.” They add that the importance of each aspect of the trilemma will shift as a country works towards decarbonization, meaning stakeholders must prioritize one of the three areas at different levels of renewable penetration.

“At low penetration levels of variable renewables, resource availability will need to be prioritized; as the penetration of variable renewable energy increases, system planners must prioritize the attribute of resource variability at higher penetration levels; and at deeply decarbonized systems, planners will need to focus on the attribute of resource extremeness,” the research paper notes.

Researchers from Beihang University, Beijing’s Rocky Mountain Institute, University of North Carolina, Stanford’s Carnegie Institution for Science, Duke University and Ottawa’s Carleton University contributed to the research.

 

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