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Renewables Integra.on into Power Grid Systems Prof. G.R. Tynan UC San Diego MAE Dept. MAE 119

Integrating Time-variable Renewables into a Power Gridnewmaeweb.ucsd.edu/courses/MAE119/WI_2018/ewExternalFiles... · Short term effects – e.g. wind gusts ... case)of))series)RL)circuit,)resistor)and)inductor)are

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Page 1: Integrating Time-variable Renewables into a Power Gridnewmaeweb.ucsd.edu/courses/MAE119/WI_2018/ewExternalFiles... · Short term effects – e.g. wind gusts ... case)of))series)RL)circuit,)resistor)and)inductor)are

Renewables  Integra.on  into  Power  Grid  Systems  

Prof.  G.R.  Tynan  UC  San  Diego  MAE  Dept.  

 MAE  119  

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Outline:    Hierarchy  of  Issues  to  Consider  •  What  does  a  grid  really  look  like?  •  Instantaneous  Power:    Genera.on  =  Load  •  Characterizing  Renewable  Electricity  Varia.ons:  

–  Time-­‐scales  &  Magnitudes  •  A  (painfully)  simplified  model  to  see  the  physics:    AC  Circuit  

•  Synchronous  Generators  •  Response  to  transient  load-­‐mismatch:    Frequency  Stability,  Reac.ve  Power  Transients  &  Voltage  Stability  

•  Need  for  Storage:    Time-­‐scales  of  response;  Power  &  Energy  Required  

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Outline:    Hierarchy  of  Issues  •  What  does  a  grid  really  look  like?  •  Instantaneous  Power:    Genera.on  =  Load  •  Characterizing  Renewable  Electricity  Varia.ons:  

–  Time-­‐scales  &  Magnitudes  •  A  (painfully)  simplified  model  to  see  the  physics:    AC  Circuit  

•  Synchronous  Generators  •  Response  to  transient  load-­‐mismatch:    Frequency  Stability,  Reac.ve  Power  Transients  &  Voltage  Stability  

•  Need  for  Storage:    Time-­‐scales  of  response;  Power  &  Energy  Required  

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Con.nental  scale  view  of  interconnected  regions  in  N.  America    

Global  Energy  Network  Ins.tute,  NERC  Regions  

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U.S.  Transmission  Grid  

Source:    FEMA  

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Electrical  Power  Genera.on  Sta.ons  

•  Mul.ple  Sources  •  Wide  spa.al  distribu.on  

•  Wide  range  of  sizes  (10’s  MW  up  to  ~1000MW)  

•  Q:    How  does  energy  get  to  load  centers  (i.e.  where  the  people  are  located)?  

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Example:    California  Electrical  Transmission  Network  

•  Tranmission  network  w/  V>115kV  shown  

•  Note  interconnec.ons  across  state  borders  

•  Mul.ple  transmission  line  owners/operators  

•  Power  transferred  over  100-­‐1000  km’s  

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Power  to  the  People:    The  Transmission  &  Distribu.on  System  

Source:    Wikipedia  

“Transmission”  System  

“Distribu.on”  System  

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Distribu.on  System  Schema.c  

Source:    Wikipedia  

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Simplified  AC  Circuit  Models:    Transmission  Line  

Assuming  sinusoidal  Time  varia.ons  of  V(z,t)    And  I(z,t)  then  V  and  I  obey  The  Telegrapher’s  Equa/ons:  

Source:  hep://www.iec.ku.edu/~js.les/723/handouts/  2_1_Lumped_Element_Circuit_Model_package.pdf  

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Simplified  AC  Circuit  Models:    Transmission  Line  (cont’d)  

Can  show  V(z)  and  I(z)  obey:  

Source:  hep://www.iec.ku.edu/~js.les/723/handouts/  2_1_Lumped_Element_Circuit_Model_package.pdf  

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Outline:    Hierarchy  of  Issues  •  What  does  a  grid  really  look  like?  •  Instantaneous  Power:    Genera.on  =  Load  •  Characterizing  Renewable  Electricity  Varia.ons:  

–  Time-­‐scales  &  Magnitudes  •  A  (painfully)  simplified  model  to  see  the  physics:    AC  Circuit  

•  Synchronous  Generators  •  Response  to  transient  load-­‐mismatch:    Frequency  Stability,  Reac.ve  Power  Transients  &  Voltage  Stability  

•  Need  for  Storage:    Time-­‐scales  of  response;  Power  &  Energy  Required  

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Safe  &  Stable  Grid  Opera.on  Requires  Power  Generated  =  Power  Consumed  

Demand  Curve  at  Household  Level:  

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Demand  Curve  at  State  Level  (e.g.  California)  Shows    Significant  Diurnal  and  Seasonal  Varia.on:  

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Demand  &  Supply  Curve  at  Na.onal  Level:  

Source:    The  Energy  Collec.ve  

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Key  Concept:    Capacity  Factor  

•  Capacity  Factor,  CF  defined  as    

CF =

CF =PavePMAX

where

Pave =1T

P(t)dt0

T

∫

PMAX ~ Max.System Design Power

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Typical  Capacity  Factor  Energy  Source   Capacity  Factor  (typ.)  

Baseload  Coal  Plant   >90%  

Baseload  Nuclear/Hydro   >90%  

Solar  PV   15%  

Wind   30-­‐40%  

Natural  Gas  CCGT  (Baseload)  

>90%  

Natural  Gas  (Peaker)   <<90%  

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Capacity  Factor  Impacts  Energy  Produc.on  Over  Extended  Periods  

e.g.    A  1  GWe  Nuclear  Plant  w/  CF=90%    Produces    ~7.9  TW-­‐Hr  of  Electrical  Energy/Year  

e.g.    A  1  GWe  Solar  PV  Plant  w/  CF=15%    Produces  ~1.3  TW-­‐Hr  of  Electrical  Energy/Year  

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Actual  &  Projected  CA  Demand  Curves  

CEC,  2010  

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Outline:    Hierarchy  of  Issues  •  What  does  a  grid  really  look  like?  •  Instantaneous  Power:    Genera.on  =  Load  •  Characterizing  Renewable  Electricity  Varia@ons:  

–  Time-­‐scales  &  Magnitudes  •  A  (painfully)  simplified  model  to  see  the  physics:    AC  Circuit  

•  Synchronous  Generators  •  Response  to  transient  load-­‐mismatch:    Frequency  Stability,  Reac.ve  Power  Transients  &  Voltage  Stability  

•  Need  for  Storage:    Time-­‐scales  of  response;  Power  &  Energy  Required  

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Variety  of  relevant  .me-­‐scales  for  intermieency  

•  Short  term  (seconds-­‐minutes)  – Wind  gusts  – Clouds,  Contrails  for  CSP  Systems  – Clouds  for  PV  Systems  

•  Intermediate  term  (hours  –  days)  – Weather  systems  modify  wind,  DNI,  GHI  

•  Long  term  (Weeks  to  Seasonal  

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Short term effects – e.g. wind gusts

Source: http://en.wikipedia.org/wiki/Image:Lee_Ranch_Wind_Speed_Frequency.png

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Diurnal  &  Seasonal  Variability  CA  Data  &  Projec.ons  

Solar  

CEC,  2010  

Wind  

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Wind Speed Variability Leads to Significant Variation in Wind-generated Power

Source: E.On Netz, “Wind Report 2005

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Can Also Experience Rapid Changes in Rate of Power Feed-In:

“Handling Such Significant Differences in Feed-in Level Poses a Major Challenge to Grid Operators” Source: E.On Netz, “Wind Report 2005

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Another  Example:    UCSD  PV  System  

Pideal

Pdata

P

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Another  Example:    UCSD  PV  System  

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Plot in terms of Capacity v Amount of Time at that production rate.Result: Reduced Capacity Factor

Source: E.On Netz, “Wind Report 2005

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Outline:    Hierarchy  of  Issues  •  What  does  a  grid  really  look  like?  •  Instantaneous  Power:    Genera.on  =  Load  •  Characterizing  Renewable  Electricity  Varia.ons:  

–  Time-­‐scales  &  Magnitudes  •  A  (painfully)  simplified  model  to  isolate  the  physics:      

–  Simple  1st  order  AC  Circuit  •  What  does  voltage  source  really  look  like?  

–  Synchronous  Generators  •  Response  to  transient  source-­‐load  mismatch:    Frequency  

Stability,  Reac.ve  Power  Transients  &  Voltage  Stability  •  Need  for  Storage:    Time-­‐scales  of  response;  Power  &  Energy  

Required  •  Storage  Technologies  

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1st  order  AC  Circuit  Model  to    Iden.fy  Key  Issues:  

Think  of  distribu.on  network  as  an  equivalent  circuit:    Series  LR  Circuit  

heps://www.electrical4u.com/rl-­‐series-­‐circuit/  

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1st  order  AC  Circuit  Model  to    Iden.fy  Key  Issues:  

Recall:    Current  from  an  AC  Voltage  Across  a  Purely  Resis.ve  Load  Ohms  Law    V=IZ  where  Z=R  (purely  real)  for  resis.ve  load:    

Phasor  representa.on  

heps://www.electrical4u.com/rl-­‐series-­‐circuit/  

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1st  order  AC  Circuit  Model  to    Iden.fy  Key  Issues:  

Recall:    Current  from  an  AC  Voltage  Across  a  Purely  Induc.ve  Load  Ohms  Law  with  Impedence,  Z=    jωL  (i.e.  Z  is  purely  Imaginary)  Gives  V=    jωLI(t)  è  phase  shiB  between  V(t)  and  I(t)!     Phasor  

representa.on  

heps://www.electrical4u.com/rl-­‐series-­‐circuit/  

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1st  order  AC  Circuit  Model  to    Iden.fy  Key  Issues:  

What  does  I(t)  and  V(t)  across  the  RL  load  look  like  now?  

heps://www.electrical4u.com/rl-­‐series-­‐circuit/  

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1st  order  AC  Circuit  Model  to    Iden.fy  Key  Issues:  

What  does  I(t)  and  V(t)  look  like  now?  Solu.on:  

Step-­‐  I.  In  case  of    series  RL  circuit,  resistor  and  inductor  are  connected  in  series,  so  current  flowing  in  both  the  elements  are  same  i.e  IR  =  IL  =  I.  So,  take  current  phasor  as  reference  and  draw  it  on  horizontal  axis  as  shown  in  diagram  below.  Step-­‐  II.  In  case  of  resistor,  both  voltage  and  current  are  in  same  phase.  So   draw   the   voltage   phasor,   VR   along   same   axis   or   direc.on   as   that   of  current    phasor.  i.e  VR  is  in  phase  with  I.  Step-­‐  III.  We  know  that  in  inductor,  voltage  leads  current  by  90°,  so  draw  VL  (voltage  drop  across  inductor)  perpendicular  to  current  phasor.  Step-­‐   IV.   Now   we   have   two   voltages   VR   and   VL.   Draw   the   resultant  vector(VG)  of  these  two  voltages.  Such  as,    and  from  right  angle  triangle  we  get,  phase  angle    

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1st  order  AC  Circuit  Model  to    Iden.fy  Key  Issues:  

What  does  I(t)  and  V(t)  look  like  now?  

VL  Phasor  

representa.on  

θ = Tan−1 ωL / R( )

θ

heps://www.electrical4u.com/rl-­‐series-­‐circuit/  

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1st  order  AC  Circuit  Model  to    Iden.fy  Key  Issues:  

How  does  POWER  in  circuit  behave?    Remember,  P(t)=V(t)I(t)…    …So  P(t)  is  COMPLEX:    

Power  in  Resis.ve  Load:  

Power  in  Induc.ve  Load:  

Total  Instantaneous  Power:  

PR(t) = ZRI2 = RI 2 (t)

PL (t) = ZLI2 = jωLI 2 (t)

Ptot (t) = ZR + ZL( ) I 2 = R + jωL( ) I 2 (t)Real  (aka  “True”)  Power  

Dissipated  in  Load  Reac.ve  Power  

(Oscillatory  Energy    Sloshing  Around  in  the  Circuit)  

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1st  order  AC  Circuit  Model  to    Iden.fy  Key  Issues:  

How  does  POWER  in  circuit  behave?    Remember,  P(t)=V(t)I(t)…    …So  P(t)  is  COMPLEX:    

heps://www.electrical4u.com/rl-­‐series-­‐circuit/  

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1st  order  AC  Circuit  Model  to    Iden.fy  Key  Issues:  

P(t)  is  COMPLEX…  Consider  first  the  real  part    

Power  in  Resis.ve  Load:  

Remember  V(t)  and  I(t)  thru  R:  

Q:    What  does  average  power  look  like  (over  one  AC  cycle?)  

PR(t) =VR(t)I(t)

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1st  order  AC  Circuit  Model  to    Iden.fy  Key  Issues:  

P(t)  is  COMPLEX…  Consider  first  the  real  part    

Power  in  Resis.ve  Load:  

Remember  V(t)  and  I(t)  thru  R:  

Q:    What  does  average  power  look  like  (over  one  AC  cycle?)  A:    P(t)>0  always  è  <P(t)>  is  finite  and  posi7ve    è    represents  rate  of  energy  dissipa7on  

PR(t) =VR(t)I(t)

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1st  order  AC  Circuit  Model  to    Iden.fy  Key  Issues:  

P(t)  is  COMPLEX…  Consider  next  the  imaginary  part  

Power  in  Induc.ve  Load:  

Remember  V(t)  and  I(t)  thru  L:  

Q:    What  does  average  power  look  like  (over  one  AC  cycle?)  

PL (t) =VL (t)I(t)

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1st  order  AC  Circuit  Model  to    Iden.fy  Key  Issues:  

P(t)  is  COMPLEX…  Consider  next  the  imaginary  part  

Power  in  Induc.ve  Load:  

Remember  V(t)  and  I(t)  thru  L:  

Q:    What  does  average  power  look  like  (over  one  AC  cycle?)  A:    PL(t)  OSCILLATES  in  7me  so  that  <PL(t)>=0!    è  Energy  is  stored    In  L  for  half-­‐cycle,  then  returned  in  other  half-­‐cycle  

PL (t) =VL (t)I(t)

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So  now  back  to  our  toy  model  of  power  grid:  

Q:  What  actually  determines  V(t)  (which  we  have  assumed  is  sinusoidal?)  A:    This  is  actually  a  real  physical  device:    (usually)  a  “Synchronous  Generator”  

heps://www.electrical4u.com/rl-­‐series-­‐circuit/  

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Basics  of  Synchronous  Generator:      Electromagne.c  Induc.on  

Lenz’s  Law  

V = − ∂ϕ

∂t= − ∂

∂t!B ⋅d!A

C∫

2.  Induced  Voltage:  

Principles  of  Opera.on  of  Sync.  Machines,  Wiley    

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Basics  of  Synchronous  Generator:      Electromagne.c  Induc.on  

Principles  of  Opera.on  of  Sync.  Machines,  Wiley    

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Basics  of  Synchronous  Generator:      Work  &  Energy  Flow  

Principles  of  Opera.on  of  Sync.  Machines,  Wiley    

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Schema.c  of  a  Synchronous  Generator:        

Principles  of  Opera.on  of  Sync.  Machines,  Wiley    

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Schema.c  of  a  Synchronous  Generator:        

Principles  of  Opera.on  of  Sync.  Machines,  Wiley    

External  Torque  Must  be  Applied  To  the  Rotor  to  Keep  in  Spinning!    Q:  Where  does  that  torque  come  from?  A:    Mechanical  Work  from  a  Heat  Engine!  

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Basics  of  Synchronous  Generator:      Power  Balance  Considera.ons  

Synch.  Generator  Driven  by  Torque  Input  from  External  Source  (HEAT  ENGINE!).    Angular  Momentum  Conserva.on  Gives:    

J d2θm

dt 2= Ta = Tm −Te

In  Steady-­‐state  Ta=0    çè  Genera@on  Rate  =  Load  

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Basics  of  Synchronous  Generator:      Power  Balance  Considera.ons  

Re-­‐write  as  POWER  by  mul.plying  through  by  angular  rota.on  

In  Steady-­‐state  Pa=0    çè  Genera@on  Rate  =  Load  

Jω Sd 2θm

dt 2= Pa = Pm − Pe

Where    

 Pa~  change  in  kine.c  energy  of  rota.on  of  the  generator    

 Pm  ~  rate  of  mechanical  work  applied  to  the  generator    

 Pe    ~  rate  of  electrical  work  (i.e.  electrical  power)  produced  by  generator    

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The  rota.on  of  heat  engine  can  store  significant  energy:  

Photo:    General  Electric  

Imagine  this  spinning  at  3600  rpm  

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Now  consider  a  grid  w/  mixture  of  heat  engines  &  renewables  w/o  storage  

Projected  demand  curve  for  CA    In  2020  from  2010  CEC  Study:  

Schema.c  System  Architecture  

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Weather-dependent Systems Can Experience Rapid Changes in Rate of Power Feed-In:

“Handling Such Significant Differences in Feed-in Level Poses a Major Challenge to Grid Operators” Source: E.On Netz, “Wind Report 2005

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How  does  grid  respond  to  a  sudden  loss  of  genera.on  capacity  from  such  a  disturbance?  

Recall  Power  Balance  Eqn:  

In  Steady-­‐state  Pa=0    çè  Genera.on  Rate  =  Load    But  w/  Reduc@on  in  Renewable  Power  Genera@on,  Load  now  shiBs  to  Remainder  of  System    BUT…    Pm=const!    è  Pe    >    Pm      

Jω Sd 2θm

dt 2= Pa = Pm − Pe

Where    

 Pa~  change  in  kine.c  energy  of  rota.on  of  the  generator    

 Pm  ~  rate  of  mechanical  work  applied  to  the  generator    

 Pe    ~  rate  of  electrical  work  (i.e.  electrical  power)  produced  by  generator    

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How  does  grid  respond?  (cont’d)  With  drop  in  renewables  input  we  have  Pe    >    Pm    ….    Now…  Recall  Power  Balance  Eqn  at  Synch.  Generator:  

Jω Sd 2θm

dt 2= Pm − Pe < 0

dθm

dt=ω S

Remember  defini.on:  

So  rota.on  frequency  of  generators  begins  to  change!  

dω S

dt= d

2θm

dt 2< 0

Rota@on  frequency  of  generators  =  Frequency  of  AC  Voltage    è  AC  Freq.  Changes!  

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How  does  grid  respond  (cont’d):  How  does  POWER  in  circuit  behave?    Remember,  P(t)=V(t)I(t)…    …and  P(t)  is  COMPLEX:    

heps://www.electrical4u.com/rl-­‐series-­‐circuit/  

RESULT  OF  LOAD  IMBALANCE:    OSCILLATIONS  IN  MAGNITUDE    OF  REACTIVE  AND  REAL  POWER    

 è  OSCILLATIONS  IN  PEAK-­‐PEAK      VOLTAGE  

 è RISK  OF  DAMAGING  EQUIPMENT  è (ARCING)  

è PROTECTIONS  WILL  DISCONNECT  è CIRCUITS  TO  PREVENT  PERMANENT  è DAMAGE  

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Illustra.on  of  this…  

hep://www.news.com.au/technology/environment/aemos-­‐third-­‐report-­‐highlights-­‐wind-­‐power-­‐link-­‐to-­‐south-­‐australia-­‐blackout/news-­‐story/2bbf105bc613f70966659465043633b0  

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How  to  mi.gate  these  effects?  •  Spa.al  Averaging:    deploy  renewables  over  large  enough  

region  to  “average  out”  temporal  varia.ons  

Wind  Power  Myths  Debunked,  IEEE  2009  

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How  to  mi.gate  these  effects?  •  Reduce  Load  Dynamically  (Demand  Response)  •  Incorporate  Energy  Storage  Into  System  

–  Repurposed  Conven.onal  Hydro  –  Pumped  Hydro  –  Electrochemical  (Baeeries,  Flow  Baeeries)  –  Large  Capacitors  –  Fuel  Produc.on  (e.g.  H  from  water)  w/  storage  for  later  use  –  Flywheels  –  Compressed  Air  –  Thermal  Storage  

•  Q’s  for  storage  system  spec’s:  –  What  is  peak  power  required  from  system?  –  Over  what  dura.on  is  storage  needed?  –  What  is  total  stored  energy  requirement?  –  What  is  op.mum  posi.on  within  grid?  

 

Wind  Power  Myths  Debunked,  IEEE  2009  

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Order-­‐of-­‐Magnitude  es.mates  of  regional  (e.g.  WECC)  storage  requirements  

Transient  Descrip@on  

Magnitude  of  Power  Imbalance  (MW)  

Corresponding  Energy  (MJ)  

Possible  Technology?  

AC  Osc.  Timescales  (0.1-­‐1  sec)  

0.1  –  10’s   0.1  -­‐  100   ???  

Frequency    Transients,  1-­‐10  sec  

1-­‐100   0.1-­‐100   ????  

Short-­‐term  RE  Variability,    10-­‐103  sec  

10  -­‐  1000   102-­‐104    ????  

Diurnal  Varia.on  3-­‐10  hours  

100-­‐10,000   104-­‐107    ????  

Seasonal  10-­‐100  days  

1000-­‐10,000   109-­‐1011   ????  


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