Physics of Renewable Energies

O.Bie be lLM U M ünche n1 7 .0 7 .2 0 1 4

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Germany´ s Master Plan t ill 2050

o) Nuclear power plants: term inate by 2022

o) Coal power plants: term inate by 2050 or Carbon-Capture&Storage (CCS)

o) Renewable energies: 50% of total elect r ical power by 2035

o) Status quo 2013: 634 TWh

Power maximum: 44 GW (Summer) 77 GW (Winter)

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Wind Energy

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Wind energy: Origin, vert ical profile

geost rophical wind: | pressure gradient

Prandt l layer wind profile:

ln(z/z0)v(z) = v(h ref) * -------------------- ln(h ref/z0)

z0: surface roughness

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Wind speed profile:

NB: also depending on tem perature gradient : a stable < neut ral 0.98K/100m < instable = = > Hellm ann power law: v (z) = v(href) * (z/href) w ith a= 0.40, 0.16, 0.11 (@open coast )

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Wind energy converter dEkin P= --------- ~ A * v³ dt max. efficiency @ v2 = (1/3) v1

etam ax = 16/27 ~ 59% (A.Betz 1920)

Converter principle: Buoyancy rotor

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Converter eff iciency: Tip speed rat io

downstream wind: angular momentum = = > efficiency loss (G.Schmitz 1955)

= = > t ip speed rat io = v rot / vwind determ ines efficiency

= = > rotor blades opt im ized for default wind speed

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Wind speed frequency

Weibull dist ribut ion

k k-1 kF(v) = ---- * (v/a) * exp( -(v/a) ) a

k: form factor (t yp. k= 1.5 - 2)a: scale parameter, e.g. k= 2 = = > < v> = a * /2

Rayleigh dist rib. = Weibull@k= 2

NB: o) Most Probable Value < Mean

3 o) P(v) ~ v

= = > rotor blade opt imizat ion !

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Elect rical Power vs. Wind Speed

= = > max. power @ default wind speed

turn on @ ~ 4 m/s

safety turn off @ ~ 25 m/s

line entry at 50Hz < = = > r.p.m. = = >

direct AC line connect ion:synch./asynch. elect ric generator: fixed r.p.m. for 50Hz= = > gearing required

alternat ively: AC(generator@arb.frequency) --> DC --> AC(50Hz)

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DWD: 5 yr. average product ion: < 1555, 2591, > 4320 kWh/m² rotor area

Wind Energy Potent ial vs. Wind Power Plants1 0

Wind Power Turbines in Germ any = = >

< = = Development of Wind Power Turbines

situat ion in April 2014:

Total Wind Power: 33.6 GW(on-shore 33GW, off-shore 0.6GW)

Wind Power Turbines: ca. 25000

--> Repowering opt ion: Smaller old = = > larger new plants

t ypical plant l ifet ime 20 yr.

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Wind Farm s

down st ream wind disturbed by turbulences

= = > m in. distance between wind turbines: 6 - 15 t imes rotor diameter

---> avg. power per base area: 2 - 15 W/m²

preferred wind direct ion ---> opt im ize arragement of wind turbines

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Wind Turbine Alignm ent Effects

o0

o7.6

o11.3

o18.4

= = > 10 - 40% power loss

---> Alignment mat ters !

(or: small changes of wind direct ion significant ly affect power output )

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Wind to AC Elect ric Power Efficiency

29-51%

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Photovoltaic Energy

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Solar Energy: Radiat ion Balance 24Total Insolat ion: 5.6 * 10 J/yr (2-3% converted into wind)

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Solar Energy: Im pact of Atm osphere

Air Mass Rat io:

AM0 = outer spaceAM1 = vert ical penet rat ionAM1.5 = 1.5 * AM1 (solar cells specs. ref.)in generalAMx = x*AM1 = 1/sin(azenith)

azenith

3.1 1.5 1.0 0.7 0.6 0.5 0.44 0.39 eV

spectral sensit ivity cryst.Si

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Principle of Solar Cells (Reminder)

+ -

cryst .Si: indirect semiconductor ---> addit ional phonon needed ---> smaller l ight absorpt ion

= = > thicker Si layer needed (~ 300 µm) ----> cost

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Solar Cells: Maxim um Efficiency

required: h m in = Egap

but h > h m in: E = h - Egap lost ---> heat

convolut ion with Planck spectrum and

account ing for phonons

= = > Shockley-Queisser efficiency (1961)

= = > crystalline Si (Egap= 1.1eV)

max. efficiency:

ca. 29% ------------- -->

NB: o) overall m ax. 31% for Egap= 1.35eV

o) C: light concentrat ion enhances efficiency

h okay h too small

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Achieved Efficiencies

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Solar Cells: Maxim um Power Point (MPP)

module size 10x10cm²

1000 W/m²

@ T= 298K

---> open circut voltage: Voc~ 0.6V

short circut current : Isc~ 3A

---> Voc * Isc = 1.8 W

with load:---> max.power point (MPP) about 20% less

PMPP = 0.5V * 2.8A = 1.4W

MPP depends on: Insolat ion & Temperature

= = > MPP t racking

MPP

MPP

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Solar Module

many solar cells in series (---> voltage)

several st r ings in parallel (---> current)

care for cell shading:shaded cells: source ---> load = = > bypass diodes

examples ofbroken cells = = > < = = thermal image

solar module 3 cells part ially shaded

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Photovoltaic Potent ialDWD: Integral insolat ion per year

average for 1981-2010

min: 951 kWh/m²

max: 1261 kWh/m²

mean: 1055 kWh/m²

Photovoltaic efficiency typ. 15%

= = > 160 kW h/m ² + 3 1 - 1 6

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Photovoltaic to AC Elect rical Power Efficiency ~ 11-15%

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Solar Therm al Energy

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Solar Therm al Power - a few remarks

perferred techology:

parabolic t rough power plants

heat storage for evening hours

example: Andasol/Spain, 50 MWhel

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Parabolic Trough Power Plants - typical specificat ions North Afr ica

< -- 6h storage

< --100 kWhel/m² yr

< -- m irror cleaning steam circuit but air cooling (= 0.5-2M city)

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Solar Therm al Energy to AC Elect rical Power Efficiency

~ 16%

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Biom ass Energy

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Biom ass - on a single slide

very low efficiency: 0.1 - 5 %

< 2.5 kWhel/m²/yr

634 TWh/yr

---> 254000 km²

= 71% of Germany

Indust ry project ion: 54.3 TWhel/yr in 2020

NB: Elect ric power only

addit ional needs: + heat ing + fuel + agricultural products

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Transm ission of Energy

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Volat ility of Renewable Energies - Requirements for stable Power Grid

?< = = >

current ly (according to power gradient )

basic load: brown coal+ nuclear power (a few MWh/min) mid load: b lack coal (a few 10 MWh/min)peak load: gas+ pump storage (~ 100 MWh/min)

= = > Use or Store !

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Transport of Elect rical Power

Wind energy: Northern Germany

Photovoltaic: Southern Germany

Pumping Storage: average and high mountains

= = > need to t ransport power over long distances across country

techniques: high voltage three- phase AC (HVAC)

high voltage DC (HVDC)

physics: PLoss= (Pt ransp/U)² * R

NB:~ 6% t ransmission loss (GER)

Status quo 4Q 2013: Plan t ill 2023

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Transport of Elect rical Power - Physics and Electr ical Engineering

Target : max. effect ive power t ransmission, lim it losses

HVAC < --> long t ransmission line Line reactance: X = L'/C'

Line resistance: R = R' · x

Load resistance: RE

Load reactance: XE = i LE

= = > max.effect ive power t ransmission: X = -XE and R = RE (i.e. properly term inated)

= = > natural effect ive power: Pnat = U² / X (i.e. opt im al operat ion point )

over/under natural eff. power point ---> enhanced resist ive losses

Overhead t ransmission line vs. Underground cable Xline > Xcable Pnat ,line < Pnat ,cable max.80°C line temp. vs. max.90°C cable temp. operate@ nat .eff.power vs. operate@ under natural eff.power power loss okay vs. enhanced power loss long distances (typ.> 100km ) vs. short distances only (typ. < 30 km )

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Transport of Elect rical Power - Overhead vs. Underground

Cable --> + invisible, less space enhanced losses lim ited overload capacity d ifficult maintenance short distance

Line --> + natural eff. power, losses okay + high overload capacity (air cooling) + easy maintenance + long distance (< 1000km, HVDC (cable) t ransmission > 1000km) more space, unat t ract ive look

= = > long distance t ransmission needed: Northern < --> Southern GER, inter-EU for storage

380kV, 190km2 x 1100 MW

line vs. cable

est im at . losses124 GWh/yr vs.169 GWh/yr

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Storage of Energy

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Elect rical Power StorageOpt ions

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Pum ping Storage Power Stat ion

Epot = m g h

for 1 kWh: m = 1800 kg, h = 200 m (Olympic Tower) m = 1000 kg, h = 360 m

typ. efficiency: 80%

e.g.: 8.7 TWh (power consumpt ion of 5 days) h = 300m, level oscillat ion 20 m:

= = > 535 km² upper reservoir area i.e. area of Lake Constance (Bodensee)

energy density: 16 kWh/m²

Status quo: 33 pumped storage stat ions

38 GWh storage capacity (i.e. 2.2% of daily power consumpt ion)

NB: Full supply with wind+ solar power requires > 10 TWh storage capacit y

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Power to Gas to Power

Electr ical Power --> Electrolysis --> Hydrogen

opt ionally: Hydrogen + CO2 --> Methane CH4

employ Methane storage capacity (current ly 21.4 Mio m³ = 214 TWh = 20% of annual need)

Overall efficiency 36%(cp. lead bat tery efficiency: 80%)

NB: 1.0 kWhel from storage requires ~ 2.8 kWhel to storage

--> 2.8 higher cost per kWhel

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Storage Needs (or stand-by power plants)

exploit long term average effects, e.g.:Fall-> Spring: Wind power highSpring-> Fall: Solar power high

= = > combine

NB: 1TL= 1.74 TWh Tagesladung LAb= Ladungsabweichung (actual mean consumpt ion) real data:1996-2008, Hesse

short term (minutes to hours): Pumping storage, Gas & Steam power plants

mid term (hours to days): Pumping storage, Gas & Steam power plants

long term (days to months): Pumping storage, (opt ionally Power-to-Gas)

= = > reduct ion of storage needs (best : 80% Wind + 20% Solar, current ly: 64% : 36%)

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Opt im izat ion of Storage Needs (Dissertat ion M.Popp, TU Braunschweig, 2010)

= = > 6 TL = 10 .4 TW h storage capacity

available: 0.038 TWh

(for: 30% standby power, i.e. ~ 25 GW plants in standby, opt im ized 80%Wind+ 20%Solar com binat ion, 50% ut ilizat ion of Wind turbines = 1/2 yr full load, 160% storage loading power cp. to avg. consum pt ion im port /export as needed without lim itat ion)

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Som e Final Nota Bene

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A brief Word on Cost (M.Kaltschm it t et al.: Erneuerbare Energien, Springer 2013)

cost est imate includes: construct ion, operat ion, maintenance, loan, etc. does not include: t ransmission cost , EEG cost apport ionment , taxescurrent cost (SWM): ca. 0.26 €/kWh (includes ca.52% public charges, apport ionm ents, taxes)paid product ion cost : ca. 0.13 €/kWh

= = > cost will/must r ise for profitability of renewable energies

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Space Requirem ents

Wind 2 - 15 W/m² --> 3.5 - 26.3 kWhel/m² yr (on-shore)

7.0 - 52.6 kWhel/m² yr (off-shore)

Photovoltaic 160 W/m² --> 152 kWhel/m² yr

Solar Thermal 28 - 48 W/m² --> 100 kWhel/m² yr (Spain, Northern Africa) (w ith, w/o storage)

Biomass 0.3 W/m² --> 2.5 kWhel/m² yr

Geothermal 0.05 Wtherm /m² --> 0.4 kWh therm /m² yr

Pumping Storage 16 kWhel/m²

634 kWhel = 464TWhel (Wind, 80%) --> 17650 km² (on-shore only)

+ 116 TWhel (Photovoltaic, 20%) --> 800 km²

+ 54 TWhel (Biomass) --> 21600 km²

10.4 TWhel (Pumping Storage) --> 1300 km² (upper + lower reservoir)

41350 km² (Germany: 357167 km²) = = > Renewable Energies need space

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Quotat ion from Report ordered by Germ an Governm ent 2010

= = > Report : Depend significant ly on elect r ical power import Even more if expected 30% power savings not achieved t ill 2050

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Figure Referencesp.0 segelreporter .comp.1 www.stat ist isches-bundesam t.dep.4 de.wikipedia.org: geostrophischer Wind V.Wesselak et al.: Regenerat ive Energietechnik, Spr inger Viewegp.5 V.Wesselak et al.: Regenerat ive Energietechnik, Spr inger Viewegp.6 M.Kaltschm it t et al.: Erneuerbare Energien, Spr inger Vieweg 2x V.Quaschning: Regenerat ive Energiesystem e, Hanserp.7 M.Kaltschm it t et al.: Erneuerbare Energien, Spr inger Viewegp.8 M.Kaltschm it t et al.: Erneuerbare Energien, Spr inger Viewegp.9 M.Kaltschm it t et al.: Erneuerbare Energien, Spr inger Viewegp.10 www.dwd.de www.windm onitor .dep.11 www.windm onitor .de M.Kaltschm it t et al.: Erneuerbare Energien, Spr inger Viewegp.12 M.Kaltschm it t et al.: Erneuerbare Energien, Spr inger Vieweg segelreporter .comp.13 R.J.A.MStevens et al.: Effect of turbine alignm ent on the average power output of wind-farm s, ICOWES2013p.14 M.Kaltschm it t et al.: Erneuerbare Energien, Spr inger Viewegp.16 V.Wesselak et al.: Regenerat ive Energietechnik, Spr inger Viewegp.17 M.Kaltschm it t et al.: Erneuerbare Energien, Spr inger Viewegp.18 2x M.Kaltschm it t et al.: Erneuerbare Energien, Spr inger Vieweg V.Wesselak et al.: Regenerat ive Energietechnik, Spr inger Viewegp.19 2x M.Kaltschm it t et al.: Erneuerbare Energien, Spr inger Viewegp.20 M.Kaltschm it t et al.: Erneuerbare Energien, Spr inger Viewegp.21 2x V.Wesselak et al.: Regenerat ive Energietechnik, Spr inger Viewegp.22 M.Kaltschm it t et al.: Erneuerbare Energien, Spr inger Vieweg V.Quaschning: Regenerat ive Energiesystem e, Hanserp.23 www.dwd.de M.Kaltschm it t et al.: Erneuerbare Energien, Spr inger Viewegp.24 M.Kaltschm it t et al.: Erneuerbare Energien, Spr inger Viewegp.26 M.Kaltschm it t et al.: Erneuerbare Energien, Spr inger Vieweg V.Quaschning: Regenerat ive Energiesystem e, Hanserp.27 M.Kaltschm it t et al.: Erneuerbare Energien, Spr inger Viewegp.28 M.Kaltschm it t et al.: Erneuerbare Energien, Spr inger Viewegp.30 www.energieinfo.dep.32 M.Kaltschm it t et al.: Erneuerbare Energien, Spr inger Vieweg eike-klim a-energie.eu p.33 www.bundesnetzagentur .dep.34 A.J.Schwab: Elektroenergiesystem e: Erzeugung, Transport , Übertragung und Verteilung elektr ischer Energie, Spr ingerp.33 www.50hertz.com B.R.Oswald: Ver lust- und Ver lustenergieabschätzung (www.netzausbau-niedersachsen.de)p.37 M.Sterner, Hochschule Regensburgp.38 www.diebrennstoffzelle.de

p.39 Fraunhofer IWES, 2009p.40 M.Popp, Speicherbedarf bei einer Strom versorgung m it erneuerbaren Energien, Spr ingerp.41 M.Popp, Speicherbedarf bei einer Strom versorgung m it erneuerbaren Energien, Spr ingerp.43 M.Kaltschm it t et al.: Erneuerbare Energien, Spr inger Viewegp.45 EWI, GWS, Prognos: Energieszenar ien für ein Energiekonzept der Bundesregierung, Projekt Nr. 12/10, 2010

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