Transform PV to Load Capacity Status by Coupling PV Plants to CAES Plants James Mason Renewable Energy Research Institute ASES Forum on Solar and the Grid Buffalo, NY – 13 May 2009

Problem: PV Electricity Supply Is Intermittent * PV Electricity Supply Is Intermittent - Does Do Not Meet Load Capacity Requirements * Load Capacity = Dispatchable Power ¤ Dispatchable = Available on Demand - PV Cannot Replace Load Capacity Plants * PV Is Only Supplemental Electricity * A Large Increase in PV Capacity Without Energy Storage Increases System Variability, the Need for Additional Reserve Capacity, and System Costs, which Translate Into Higher Electric Bills

Insolation Variability: Diurnal and Annual Average Southwest US Insolation

The Solution to PVs Intermittency: Compressed Air Energy Storage (CAES) Alabama Electric Cooperatives McIntosh, Alabama 110 MW CAES Power Plant in Operation Since 1991

PV Power Plants CAES Power Plants HVDC Power Lines CAES Power Plants DC-AC Converter Stations CAES Power Plants

Underground Natural Gas Storage Sites

CAES Power Plant

Supply of PV and CAES Electricity to Local Grid in a Coupled PV-CAES Plant Design for Load Capacity

Next CAES Plant Will Be Similar In Design to the Schematic Adiabatic CAES (No NG) Will Not Be Available Until Post-2020 * PV Electricity for Air Compression Conventional CAES = 0.8 kWh In / kWh Out Adiabatic CAES = 1.43 kWh In / kWh Out * CAES Plant Natural Gas Consumption Conventional CAES = 4,800 Btu (HHV) / kWh Out * Fuel Efficiency of a Coupled PV-CAES Peak Power Plant CAES Only Fuel Efficiency = 71% (3412/4800) Aggregate Electricity Supplied to Grid = 64% PV and 36% CAES Aggregate PV-CAES Fuel Efficiency = 191% (3412/1786) * Conclusion: Coupled PV-CAES Provides Load Capacity, and Significantly Reduces Fuel Consumption and CO2 Emissions

NG Cost for PV-CAES to Achieve Breakeven Peak Electricity Price 1. PV-CAES = Natural Gas Combined-Cycle with CCS A. $2/W Installed PV Cost -Natural Gas Electric Utility Price = $15.17/MMBtu * 117% higher than current natural gas price. B. $1.50/W Installed PV Cost -Natural Gas Electric Utility Price = $11.63/MMBtu * 66% higher than current natural gas price. 2. PV-Adiabatic CAES = Natural Gas Combined-Cycle with CCS A. $2/W Installed PV Cost -Natural Gas Electric Utility Price = $15.83/MMBtu * 126% higher than current natural gas price. B. $1.50/W Installed PV Cost -Natural Gas Electric Utility Price = $12.34/MMBtu * 76% higher than current natural gas price.

Reference Succar and Williams, 2008 EPRI, 2003 Mason et al, 2008 (2010) Capital Cost of CAES surface equipment ($/KWe) (800) Cost of underground storage capacity ($/kWh) Storage hrs Total Capital Cost (1100) Number cycles per year328 Levelized Cost ($/KWh)0.039 (0.044) Cost of CAES Power Plant The levelized cost estimates are calculated by the net present value cash flow method. Financial assumptions: capital structure 80% debt – 20% equity; cost of debt 6.5%; cost of equity 10%; ; 30-year capital recovery period; 38.2% tax rate, MACRS depreciation; 2% annual inflation rate.

Underground Natural Gas Storage Sites

Sizing PV and Air Storage Capacity 1.Size of Air Storage Reservoir Must Account for Solar Variability to Insure Sufficient Air Supply 2.The Optimized Peak PV-CAES Plant Model Indicates That Air Storage Capacity Must Be Sufficient to Enable 110 hours of CAES Operation Independent of Air Storage Recharging (40-60 million cubic feet) 3.Our Optimization Is Based on Insuring Peak Load Capacity Electricity Supply 99.5% of the Planned Operation of the CAES Plant 4.The Optimized Ratio of PV Capacity to CAES Peak Load Capacity Is 1.45:1

Sizing of Air Storage Reservoir and PV Capacity Assigned to Air Compression Has to Account for Insolation Variability

Number of Days per Year Air Storage Reservoir Is Depleted An Important Factor in Selecting the Size of Storage Reservoir

Air Storage Balances of the CAES Underground Reservoir To Insure CAES Plant Availability 99.5% of Planned Operation

Effect of Distributed PV Plants Coupled to Distributed CAES Plants on Levelized Electricity Price Compared to SW PV

Immediate Needs 1.Define CAES in Renewable Energy Incentives - Legislatures and Regulatory Agencies 2.Federal Plan for a HVDC Grid from Southwest to Electricity Markets in Southeast and Along Eastern Seaboard 3.Federal Adiabatic-CAES R&D Program

Acknowledgements Ken Zweibel – George Washington University Vasilis Fthenakis – Columbia University and Brookhaven Natl Lab Tom Hansen – Tucson Electric Power Thomas Nikolakakis – Engineering Grad