Renewable Energy Systems Flashcards

What is 'duck curve' and why is it a grid integration challenge for solar energy?

Answer: A net load curve showing steep afternoon ramp-up as solar generation drops near sunset, straining dispatchable resources

The duck curve describes how high midday solar output suppresses net load, followed by a sharp evening ramp when solar drops and demand peaks, requiring rapid ramping from flexible dispatchable generators or storage.

Which resource is typically used to assess long-term wind energy potential at a prospective project site?

Answer: Measure-Correlate-Predict (MCP) analysis combining on-site measurements with long-term reference data

MCP correlates short-term on-site wind measurements (typically 1–2 years) with long-term reference datasets (e.g., ERA5 reanalysis) to produce a reliable multi-decade wind resource estimate for energy yield modeling.

In a concentrated solar power (CSP) plant with thermal energy storage (TES), what is the primary advantage of molten salt as the storage medium?

Answer: It can store large amounts of thermal energy cost-effectively and be used to generate steam for turbines hours after sunset

Molten salt (typically a nitrate blend) is cost-effective, stable at high temperatures (up to ~565°C), and can store gigawatt-hours of thermal energy that dispatch electricity after dark, giving CSP a dispatchability advantage over PV.

What does Renewable Portfolio Standard (RPS) legislation require of electric utilities in states that have enacted it?

Answer: Utilities must source a specified and increasing percentage of retail electricity sales from eligible renewable resources

An RPS (also called Renewable Energy Standard) mandates that utilities gradually increase the share of their retail electricity sales derived from qualifying renewable sources, typically enforced through Renewable Energy Certificates (RECs).

Which environmental consideration is a significant siting constraint for large-scale wind energy projects in the US?

Answer: Bird and bat mortality risks requiring Endangered Species Act consultations

Wind turbines pose collision risks to raptors, migratory birds, and bats; projects in sensitive areas must conduct avian and bat studies and may require mitigation measures or operational curtailment under the ESA and MBTA.

What is 'virtual net metering' (VNM) as it applies to community solar programs?

Answer: A billing mechanism crediting multiple customer accounts with generation from a shared off-site solar facility

VNM allows credits from a single community solar array to be distributed across the utility bills of multiple subscriber accounts, enabling customers who cannot install rooftop solar to benefit from renewable energy.

Which performance ratio (PR) value would indicate a well-performing utility-scale PV system in a sunny US climate?

Answer: 0.75–0.85

Performance ratio measures actual vs. theoretical energy output accounting for all losses; values of 0.75–0.85 are typical for well-designed utility-scale PV systems, with higher values indicating fewer losses from soiling, shading, wiring, and inverter inefficiency.