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Solar Thermal Dynamic Optimization

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					                                         WHAT STARTS HERE CHANGES THE WORLD




   Dynamic Optimization of Solar
Thermal Energy Systems with Storage
       Kody Powell, The University of Texas at Austin
      Dr. John Hedengren, Brigham Young University
    Dr. Thomas Edgar, The University of Texas at Austin




             TWCCC: September 2011
                             WHAT STARTS HERE CHANGES THE WORLD




Overview of Solar Thermal Power
          • Thermal energy storage → dynamic
            heat integration
          • Solar thermal – case study
          • Storage increases solar share by 80%
          • Systems approach – insight into plant
            design




                                                             2
                                                                                          WHAT STARTS HERE CHANGES THE WORLD




                   Solar Thermal vs Photovoltaic (PV)
                               Solar Thermal                                   Photovoltaic
    Energy                     Sunlight → Heat →                               Sunlight → Electricity
    Conversion                 Mechanical → Electricity
    Cost ($/kWh)               0.121 (0.06 Projected)2                         0.18-0.231
    Efficiency3                ~18%                                            ~12%
    Solar Irradiance           Direct Normal Irradiance (DNI) Global Horizontal (GHI)
    Used
    Scale                      Large Scale                                     Distributed to large scale
    Storage                    Thermal Storage                                 Battery Storage
    Dispatchable on            Yes                                             No
    a large scale
    Impact on grid             Small                                           Large
    stability
1 http://www.window.state.tx.us/specialrpt/energy/exec/solar.html
2 http://www.reuters.com/article/2009/08/24/us-energy-maghreb-desertec-sb-idUSTRE57N01720090824?sp=true                   3
3 http://solarbuzz.com/facts-and-figures/markets-growth/cost-competitiveness
                      WHAT STARTS HERE CHANGES THE WORLD




The Potential of Solar Thermal Power




                                                      4
                                                                                   WHAT STARTS HERE CHANGES THE WORLD



                           How Can Systems Approach Help Solar
                                        Thermal?
                                                                           • Plants operate on diurnal
                                                                             cycle
                                                                           • Forecasting technology
                                                                             advancing
                                                                           • How do we take advantage?


Image from: Marquez, R. and Coimbra, C. F. M., Forecasting of global and
direct solar irradiance using stochastic learning methods, ground
experiments and the NWS database, Solar Energy, Volume 85, 2011


• Look at extreme
  scenarios
• Some information is
  better than none                                                                                                 5
                                                             WHAT STARTS HERE CHANGES THE WORLD




                               Constant Setpoint Approach
 • NMPC approach
 • Measure irradiance,
   use as FF to plant
 • Constant setpoints
   for Temperature/
   Power
 • Relief pipe used
   when hot tank fills

         t T
min
u (t )       x( ), y( ), u( ), d( )  d
         t 0

x  f  x( ), y ( ), u( ), d( )  
                                      
0  g  x( ), y ( ), u( ), d( )    t  0, t  T 
0  h  x( ), y ( ), u( ), d( )  
                                                                                            6
                                  WHAT STARTS HERE CHANGES THE WORLD




             Results: Constant Setpoint Approach
Performance
Improved by:
•Optimal
temperature
•Hybrid Operation
•Storage Bypass

Further
Improvements
Needed:
•Strategy for more
stable operation
•Consider
stochastic
problem
                                    WHAT STARTS HERE CHANGES THE WORLD




                 Dynamic Optimization w/ Forecast
Hypothesis:
• Performance can be
  improved by:
   – Controlling to
     optimal
     temperatures
   – Hybrid operation
   – Ability to bypass
     storage
   – More DOFs
          t T
 min
 u (t )      Po( ) d
          t 0                                                      8
                                        WHAT STARTS HERE CHANGES THE WORLD




               Results: Dynamic Optimization w/ Forecast

Performance
Improved by:
•Optimal
temperature
•Hybrid Operation
•Storage Bypass

Further
Improvements
Needed:
•Strategy for more
stable operation
•Consider
stochastic
problem
                                           WHAT STARTS HERE CHANGES THE WORLD



     Dynamic Optimization Improves
             Performance
                       Solar Energy    Energy
                       Collected (MWh) Collected/
                                       Total Incident
                                       Energy (%)
Sunny Day
Standard Control            18.02             76.8%
Dynamic Optimization        18.59             79.2%
Partly Cloudy Day
Standard Control            14.60             75.8%
Dynamic Optimization        15.83             81.1%
Mostly Cloudy Day
Standard Control            4.75              52.1%
Dynamic Optimization        7.80              85.4%
                                                                          10
                                                   WHAT STARTS HERE CHANGES THE WORLD




          Proposed Dynamic-RTO Formulation

• Supervisory Control                              Forecasted
                                        Weather    Disturbances
• NMPC for stability                    Database
  (run every 2-5                                                      D-RTO
  minutes)
• D-RTO runs every      Disturbances
                                         Plant
  1-2 hours                                               Plant
   – Fewer variables                                      States
     may help solver
     find global min
• Forecast and plant                    NMPCs             Optimal Setpoints
  states updated         Plant Inputs
  regularly

                                                                                  11
                                 WHAT STARTS HERE CHANGES THE WORLD




           Opportunities for Further Improvement

• More DOFs →
  greater benefits
• Consider entire plant
• Include electric grid
  and demand
  forecasts
• Economic
  optimization
• Apply to other
  systems: distributed
  power generation,
  CHP, grid energy
  storage, home
  energy management

                                                                12
                            WHAT STARTS HERE CHANGES THE WORLD



Expanding the Potential of Solar Thermal Power




                                                           13
                                   WHAT STARTS HERE CHANGES THE WORLD




                 Conclusions
• Better utilization of renewable resources
  – Take advantage of low temperature heat
• Systems approach leads to design insights
• Hybridization can greatly expand solar thermal
  utilization
• Similar approach can be applied to other
  systems: CHP, distributed generation, PV with
  storage, etc.
• Thanks to APMonitor, Pecan Street Project,
  National Science Foundation, Cockrell School
  of Engineering, UT-Austin, Edgar Group                          14

				
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posted:10/10/2011
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