Air emissions due to wind and solar power

Area of Science:

• Environmental science
• Energy systems engineering
• Climate change mitigation

Background:

• Renewables portfolio standards (RPS) drive wind and solar energy adoption.
• Intermittency of renewables necessitates flexible power generation, often natural gas.
• Rapid cycling of natural gas plants affects emissions and operational efficiency.

Purpose of the Study:

• To model the emissions impact of natural gas generators supporting variable renewable energy.
• To quantify CO2 and NOx emissions under different renewable penetration levels.
• To assess the economic implications for NOx emissions under RPS policies.

Main Methods:

• Utilized 1-minute time-resolved emissions and heat rate data from natural gas generators.
• Incorporated power output data from multiple wind and solar photovoltaic plants.
• Modeled integrated renewable-plus-gas power systems to analyze operational impacts.

Main Results:

• CO2 emissions reductions were approximately 80% of ideal scenarios, even with high renewable penetration.
• NOx emissions reductions were limited to 30-50% with steam injection; dry control increased NOx.
• Significant upward pressure on NOx permit prices is anticipated in states with high RPS.

Conclusions:

• The integration of variable renewables via RPS leads to suboptimal emissions reductions for CO2 and potential increases in NOx.
• Operational constraints of natural gas plants significantly diminish the environmental benefits of renewable energy deployment.
• RPS policies may lead to increased costs associated with NOx emissions compliance for power generation.