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This overview discusses the optimization of combining wind and hydrogen systems, including the use of batteries and fuel cells for electricity storage. The analysis explores different system configurations and their efficiency, cost, and performance.
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Overview of Wind-H2 Configuration & Control Model (WindSTORM) September 9, 2003 Lee Jay Fingersh National Renewable Energy Laboratory
Introduction • Wind is intermittent • Hydrogen production, storage and fuel cells can be used to store electricity • Batteries can also store electricity • Hydrogen can also be produced from wind to be used as a fuel • What is the best approach to combine hydrogen systems with wind?
Wind-hydrogen interface optimization Wind turbine power converter Generator Interface DC Bus Grid Interface Multi-Pole Switch or Switches Electrolyzer Fuel Cell or Combustion Device Battery
Classical wind-hydrogen storage system Storage system efficiency: 25% to 35% e- Power Grid Variable-speed drive e- Wind turbine e- Rectifier e- Inverter e- e- e- Electrolyzer Fuel-cell H2 H2 H2 Fuel H2 Storage Compressor
Storage system with shared power converter Storage system efficiency: 30% to 40% e- Power Grid Variable-speed drive e- Wind turbine e- e- e- e- e- Electrolyzer Fuel-cell H2 H2 H2 Fuel H2 Storage Compressor
“H2 only” system Power Grid Variable-speed drive Wind turbine In-tower low-pressure Storage Electrolyzer Fuel-cell Storage system efficiency: 30% to 40% e- e- e- e- e- e- e- H2 H2 H2 Fuel H2
“Battery and H2” system Storage system efficiency: 80% to 85% e- Power Grid Variable-speed drive e- Wind turbine e- e- e- In-tower low-pressure Storage e- e- e- H2 Electrolyzer Nickel-hydrogen battery Fuel-cell H2 H2 Fuel H2
“Battery only” system Storage system efficiency: 85% to 90% e- Power Grid Variable-speed drive e- Wind turbine In-tower low-pressure Storage e- e- e- H2 Nickel-hydrogen battery
Battery technology discussion • Batteries for grid interconnect will be subjected to an enormous number of cycles in a 20 year lifetime • One of the only battery chemistries that can withstand repeated daily cycles for 20 years is Nickel-Hydrogen • Used in space applications for the same reason • Uses the same reaction as nickel-metal-hydride • Uses separate hydrogen storage rather than storing hydrogen in the electrode • Cycle life reported to be 10,000 to 500,000 cycles • 2 cycles per day for 20 years is 15,000 cycles
Analysis Approach (WindSTORM) • Analysis is needed to answer “What is the best approach to combine hydrogen systems with wind?” • Simulate calendar year 2002 • California ISO load data • Windfarm data from Lake Benton, MN • Requirement: Power must balance hourly • Seek to reduce necessary traditional generation capacity (windpower capacity credit) • Determine optimal control methodology • Calculate system size and cost
Analysis parameter assumptions • Wind has 50% capacity credit • 100 MW wind farm reduces peak requirements on traditional generation by 50 MW • Equivalent to 50 MW “firm” power from 100 MW windfarm • Wind has 12% energy penetration • Wind has 20% capacity penetration • No net hydrogen production • Battery charge efficiency 95% • Battery discharge efficiency 90% • Electrolyzer efficiency 75% • Fuel cell efficiency 50%
Cost assumptions • Cost of Wind: $1,000/kW • Cost of battery: $70/kWh • Cost of electrolyzer: $600/kW (2010) • Cost of fuel cell: $600/kW (2010) • Cost of H2 storage (in-tower): $3/kWh ($100/kg) • FCR: 11.58% • O&M: fixed at $0.008/kWh
Important notes • The battery hours of storage required and cost of energy can vary dramatically with changes in the system: • Windfarm location • Windfarm size • Control methodology • Forecasting method
Alternate approach – produce hydrogen • Utilize slightly larger electrolyzer and more aggressive control strategy to produce some net hydrogen • All other requirements remain in effect • Electricity price: $0.04/kWh • Hydrogen price: $0.10/kWh • Capacity credit: $18/kW/year
Analysis of hydrogen production scenarios • Battery and H2 system with hydrogen production • 5% of windfarm output turned into hydrogen • Enough to support about 2,250 vehicles • 10.7% of windfarm revenue from hydrogen • 5.8% of windfarm revenue from capacity credit • Cost of H2 production: $0.072/kWh ($2.40/kg) • Cost of H2 production is low because electrolyzer capacity factor is greater than 58%. • Cost drops to $0.062/kWh ($2.06/kg) if electrolyzer cost drops to $300/kW • H2 only system – no electricity • Cost of H2 production: $0.081/kWh ($2.70/kg) • Cost of H2 production is higher because of lower electrolyzer capacity factor (38%)
Conclusions • It is possible to “firm up” wind power for a roughly 10% increase in COE. • Using batteries is cost effective • Using hydrogen systems alone is not cost effective because the closed-cycle efficiency is too low • Hydrogen production can be simultaneously accomplished and is cost effective • Hydrogen production alone Is less cost effective • Control strategy and proper system sizing are very important • With further investigation, it may be possible to do much better