solar energy (thermal, pv) - Åbo akademiusers.abo.fi/rzevenho/apt17-2b-sol.pdfsolar energy...

Solar energy (thermal, PV)

Ron ZevenhovenÅbo Akademi University

Thermal and Flow Engineering Laboratory / Värme- och strömningstekniktel. 3223 ; [email protected]

Advanced Process Thermodynamicscourse # 424520.0 (5 sp) v. 2017

ÅA 424520

28.3.2017Åbo Akademi Univ - Thermal and Flow Engineering Piispankatu 8, 20500 Turku 2/58

2b.1 Solar energy


Potential Solar energy could within one hour provide the energy that

is used in all human acitivities in a year. Drawbacks are

– relatively low energy(exergy) density,

– limited to certain sites– potential effect on local

environment– intermittency– expensive technology

(PV .... is getting cheaper!)

Options are– heat supply (or cooling!)

for housing or industry,– electricity generation– fuel (H2!) production, metals

Pic: IEA08

Note: 40% of the worlds energy demand is in the form of heat.


Earth surface temperature Solar energy irradiation can be used to estimate planet

surface temperature T; (neglecting significant geothermal heat!)

for Earth with radius Re and irradiation Sc ~ 1355 W/m2

(solar constant) an energy balance Ein = Eout givesπ·R2

e·Sc= 4·π· R2e·σ·T4

e Te ~ 278 K which is too low !

A better result is obtained when including albedo factorρp and greenhouse gas coefficient γp, which for earth are ~ 0.3 and ~ 0.4 , respectively:(1- ρp)·π·R2

e·Sc= (1- γp)·4·π·R2e·σ·T4

e Te ~ 289 K

Experimental: Te ~ 288 K for earth ( value for T°). For Venus Tv ~ 327 K, corrected with γp ~ 0.999 (atmosphere > 95%

CO2!) and ρp ~ 0.7 Tv ~ 765 K (experimental Tv ~ 733 K )


Incoming solar irradiation

The solar radiation received at ground (sea) level consists ofdirect and indirect (scattered, reflected, diffuse) radiation.

At ground (sea) level, the solar energy content is ~ 3% UV, 44% visible and 53% IR

Clouds can reflect < 20% .. > 80%, absorb < 10%.

Table: K08Pic: TDDGP12


Solar energy, renewable energy: 2015

Solar thermal heat recovery compared to other ”minor” renewableenergy sources used pic: IEA-SHC16

Note: of all energy used worldwide ~19 % is renewable energy, being9 + 4 % biomass and 6% other (REN21, 2016) (fossil ~78.3 %, nuclear ~ 2.5 %)

January 31, 2017300GW Of Solar PV Installed Globally

http://www.energymatters.com.au/renewable-news/global-solar-capacity-em5881/


Solar energy, renewable energy: 2006

Solar thermal heat recovery ↔ other ”minor” renewable energysources pic: IEA-SHC08

Note: of all energy used worldwide in 2005, 11% was renewableenergy (IEA08)

For comparison with data for 2015/16

ÅA 424520


2b.2 Solar thermal energy


Solar heat conversion /1

A light-absorbing material, a collector, is used the absorbthe incident solar radiation energy while minimisingreflection and transmission.

At the same time losses should be avoided temperatures~ ambient air temperature are preferable.

The heat is transferred to a fluid (air, water, oil, ..). In active systems, energy must be added;

for passive systems naturalcirculation is made use of.

An example of a passive system is a house with ordinary glass windows, or a greenhouse, or a solar pond.

Solar pond

Pic: Se04


Solar heat conversion /2

Solar thermal energy includes residential heating, process heating, or power generation. This relates to different temperature ranges and scales/sizes.

Five important ranges are– Cooling / refrigeration (absorption process) *– Up to 100°C domestic / industrial water, space heating

(50-60% of European energy use, solar supply ~ 0.1%)– 100 - 250°C industrial heat (~8% of European energy use)– 250 - 800°C thermal power

plants ( electricity)– 800 – (>)1200°C thermo-

chemical splitting of water H2.

Pic

: http

://w

ww

.uk-

ener

gy-s

avin

g.co

m/s

olar

_sw

imm

ing_

pool

_hea

ting.

htm

l

See also MS08and * course 424519 Refrigeration


Solar heat conversion /3 Higher temperatures can be obtained by blocking for long-

wavelength radiation (using glazing), and more effectively by concentrating the radiation, using curved, focussingsurfaces, mirrors and lenses, incl. Fresnel lenses

Important: insulation from conductive & convective heat transfer (losses)

Pic: Se04

Fresnel lens(left)conventionallens (right)


Solar thermal collectors in use end 2014

~ 94% of the solar thermal energy capacity is for the supply of hot water in buildings, of ~410 GW (end of 2010: 196 GW), mainlyas flat-plate and vacuum (evacuated) tube collectors (ETC)

pics: IEA-SHC16Finland end of 2014: ~39 MWth, 2008: ~25 MWth, 2006: ~10 MWth


Pic: Se04

Flat plate collectors /1

Pic: Se04

Pic: MS08


Flat plate collectors /2

Table: Se04 Pic

ture

: http

://w

ww

.insu

rgen

t49.

com

/Fla

tPla

teS

olar

Col

lect

ors.

jpg

Of prime importance are– 100 % of short wave radiation is absorbed, while only a few %

of long wave radiation is emitted. Earlier, Cr-oxide coatingswere used, nowadays several other materials can be used.

– The orientation / tilting towards the sun. This can be mechanically and automatically controlled.


Vacuum tube collectors have lower thermal losses and hence reach higher outlet temperatures

Pic: SWE-4/2008

Evacuated (vacuum) tubes

Slightly different and (often) better: so-called Sydney tubes


Domestic hot water, combi systems

Pics: MS08

Option:combinationwith a heat pump !


Focussing (concentrating) collectors /1

Pics: K04,Se04


Focussing (concentrating) collectors /2

Pics: K04Heliostat field collector Optimising for reflector spacing

Pic

: http

://w

ww

.trec

-uk.

org.

uk/im

ages

/pow

er_t

ower

_alm

eria

_spa

in.jp

g

ÅA 424520


2b.3 Solar-thermal energyconversion to work/power

ÅA 424520

Solar radiation: dilution

28.3.2017Åbo Akademi Univ - Thermal and Flow Engineering Piispankatu 8, 20500 Turku 20

Sky / atmosphere

Sun

51016.246300

1

sky theof area

sun by the covered""sky theof area

f


Solar-thermal conversion (bb’s) /1

Radiation from an effective sky temperature Tsonto a blackbody (bb) surface at Tb can be used in a Carnot engine E that rejects heat at environmenttemperature Te =T° and generates work W.

For a solar collector directed ┴ to the sun, incoming radiation flux (W/m2) ~ Ssun(solar constant) = ƒ·σT4

sun (dilution ƒ~2.16×10-5)

And, the collector absorbs bb radiationfrom the surroundings at T° = Te ~ 288 K

Also, the collector emits bb radiation

net influx = σ·(ƒ·T4sun + (1-ƒ)·T°4 –T4

b) = σ·(T4

s –T4b); T4

s = ƒ·T4sun + (1-ƒ)·T°4

Ts

Tb

T°

WE

Müserengine

28.3.2017 Åbo Akademi Univ - Thermal and Flow Engineering Piispankatu 8, 20500 Turku

22/58


net influx = σ·(ƒ·T4sun + (1-ƒ)·T°4 –T4

b) = σ·(T4

s –T4b); T4

s = ƒ·T4sun + (1-ƒ)·T°4

With T°= 288 K Ts ~ 432 K.where Ts is an ”effective sky tempeature”

For the endoreversible engine, the max. power Wmax is achieved with

- see also section 1.5 (Exergy)

This gives engine efficiency η = W/ Qin = 0.1835, and solar energy conversion efficiency ω = W/ƒσT4

sun = 0.13

Ts

Tb

T°

WE

s

o

H

o

optimum

HC

optimum

LC

T

T

T

T

T

Tη

Qin

Qout

THc

TLc

TH

T°

Qin

Qout

THc

TLc

TH

T°

Müserengine

Qin



The performance can be improved by concentratingthe incident solar radiation, compensating for the dilution ƒ = (Rearth orbit / Rsun)2.

Maximum concentration factor Cmax = 1/ƒ = 46300, which increases the net influx to net influx = σ·(C·ƒ·T4

sun + (1-C·ƒ)· T°4 –T4b),

giving higher effective sky temperature Ts

With C ~ 400, solar energy conversion efficiency ω canbe improved to > 60%.

Another way to improve ω is a selective coating on the collector surface that reduce emission. Combined with concentrators, ω > 70% is possible.

Stefan – Boltzmann engine

Source: W08, see also dV08


Heat conduction or convectionto low temperature reservoir not possible (extra-terrestial applications)

Stefan – Boltzmann enginewith conductive/convective heat rejection

Source: W08, see also dV08


ÅA 424520


2b.4 Photo-voltaic (PV) energyconversion

Solar energy: capacity for PV kWh/m2/yr

Source pic: Sun and Wind Energy, 6-2011, p 100

28.3.2017Åbo Akademi University | Domkyrkotorget 3 | 20500 Åbo | Finland 27


Photo-voltaic energy is based on radiation creating electricpotential differences, ΔV, to generate electric current, i, makinguse of semi-conductors (electrons can occupy ranges (”bands”) of energy levels).

This gives a power outputs up to several 100 W/m2 Typical panel size 0.1 - 0.25 kW; largest plant ~ 850 MW (China)

Most units are still based on crystalline silicon(c-Si) but other materials are ”taking over”?

In 2005, ~ 3 TWh (3×106 kWh) solar electricity was generated, increasing to 253TWh during 2015* (104.5 TWh in 2012)

This covers ~ 1% of global 24100 TWh generated*

Total installed capacity 2010 2012/132015/16: 25 100 300 GW (REN21, EnergyMatters)

Note: trackers can improve efficiency with 20-50%* https://blogs.shell.com/2016/08/30/solardeploy/ (17.2.2017) P

ic: h

ttp://

ww

w.m

apro

yalty

.com

/sol

ar.h

tml

Photo-voltaic energy conversion /1

Instead of using the thermal radiation from the sun and convert the heat to power (= electricity), a photovoltaic device can be applied directly. This technology uses the ability of a (metal or) semi-conductor to convert an incident flow of photons to an electric current: the electrons in the valence band absorb energy from the photons and jump to the conduction band and become free, generating an electro-motive force (EMF). Connecting this to an external circuit with a resistance, an electrical current is established.




Solar energy efficiency η, defined as the ratio electric power out/solar energyabsorbed: η = ΔV∙i/Qin

with ΔV ~ 0.5 V, i ~ 3 A per cell was found to be ≤ 33.7% for non-concentrated sunlight (Si: 1.1 eV ~29 %)

With concentration factors C ~ 400 values up to η ~ 35% are reached with bandgap voltages ~1.1 – 1.3 eV. In practice η > ~ 0.15 is difficult.

Pic

: http

://w

ww

.geo

citie

s.co

m/E

urek

a/19

05/_

pvF

inla

nd.g

if

Pic

: http

://w

ww

.gre

ente

chno

log.

com

/200

7/12

/la

rges

t_so

lar_

phot

ovol

taic

_arr

ay_i

s_ac

tive_

at_a

ir.ht

ml

Shockley–Queisser limitfor p-n junction PV power


Solar PV: Voltage, current and power


The relation between the voltage and current for a typical solar panel at different insolation is depicted in the left figure, giving the power curves with maxima (peak power points) at about U = 17 V.

(U,I)-relations for different load resistances on the outer circuit are indicated in the right figure (SH14) for a 1 m2 solar panel.

Solar PV: Performance Examples


PV cell performance for power density P=J·V can be quantified by different variables.A central factor is the efficiency, defined as

where Ps is the power density of the incidentlight. FF, a fill factor, is a measure of the“squareness” of the voltage-current-curve given by

Performance indicesof some solar PV cells are reported in the table(W10).

s

mm

P

VJ

ocsc

mm

VJ

VJFF



Source: https://www.nrel.gov/pv/ and https://www.nrel.gov/pv/assets/images/efficiency-chart.png

Status March 2017

PV systems can be combined with waste heat recovery in hybrid systems, at the sametime cooling the PV unit.


Source: Sun and Wind Energy 4/2008, 9-2010& http://solarwall.com/en/products/pvthermal.php& Charalambous et al., Appl. Thermal Eng. 27(2-3) 2007, 275



.

Solar PV: technology comparison (IEA 2010)

Source: http://www.geni.org/globalenergy/research/review-and-comparison-of-solar-technologies/Review-and-Comparison-of-Different-Solar-Technologies.pdf

Pic: IEA08


Photo-voltaic enery: capacity Contrary to the mid-1990’s, more than 90% of the PV

systems are now used in grid-connected systems (integrated in buildings.)

In 2009 three countries (DE, ES, JP), account for ~75% of installed PV capacity, today the spread is more diverse: CN, DE, JP, US, IT - but per capita: DE, IT, BE, JP, GR.

Pic: REN21

300 GW Of Solar PV Installed Globally

http://www.energymatters.com.au/renewable-news/global-solar-capacity-em5881/

January 31, 2017

PV energy in Germany, June 2011


Sun & Wind Energy2012/02 p. 90

ÅA 424520


2b.5 Concentrated solar power (CSP)


Concentrated solar power (CSP) /1

As solar radiation and energy demandvary, a heat storageis typically used

Several units are runningat several 100 MW

Investments: from 4 to > 10 US$/W, electricity price150-300 US$/MWh (2012)

In CSP units direct sunlight is concentrated to higher energydensities, giving high temperatures; the heat is used in e.g. a steam cycle or Stirling engine, driving an electricitygenerator.

This can be applied in several areas – see Figure below. Preferably 2000 kWh/m2/year ( ~ 500 W/m2) is available

Pic: IEA08


Concentrated solar power (CSP) /2

CSP collectors are either troughs, dishes or towers, achieving concentration factors of 30-100, 1000-10000 and 500-1000, respectively.

~ 100 plants operating and > 45 planned worldwide, see for a list: http://www.nrel.gov/csp/solarpaces/

Total global operating ~ 4.8 GW: ~50% Spain, ~33% USA Troughs > 90%, besided dishes, towers or Fresnel lenses Several trough-based plants are combined with fossil fuel

energy: Integrated Solar Combined Cycle plants

pic:

http

://w

ww

.inha

bita

t.com

/wp-

cont

ent/u

ploa

ds/a

zsol

arpl

ant3

.jpg

pic:

http

://w

ww

.inte

rnat

iona

lrive

rs.o

rg/f

iles/

imag

es/s

olar

_the

rmal

_web

.jpg

pic:

http

://w

ww

.thai

sola

rpow

er.c

om/s

u/si

mul

atio

n/so

lar_

tow

er.g

if


Integrated Solar Combined Cycles

The SEGS (Solar Energy Generating Systems)project (CA, USA): SEGS-V 5th of 9 units picture: Modern Power Systems, 2/2007

304 390°C Pic: K04


Integrated Solar Combined Cycles

System with heat storage using molten salt (NaNO3/KNO3) for 50 MW at Guadix, Andalusia, on-line 2008, Andasol 1, 624 collectors, 0.5 km2, followed by same size Andasol 2 (2009) and 3 (2011)

PTPP = parabolic trough power plant

picture: MPS 2/2007; see also SWE 5/2008, .....

ÅA 424520

CSP: the best way to go for power?


Stirling dish engine. ”These beautiful concentrators deliver power per unit land area of 14W/m2.” (M08)

www.stirlingenergy.com

Solar Energy: (thermal, PV, …): Challenges

Even though the sun constitutes a huge energy reserve and the radiation that enters earth could easily supply mankind with all the required energy (in fact, about 10,000 times more), there are many challenges, besides decisions by politicians (e.g. feed-in tariffs):• Large area are needed, and large investments• Weather conditions have a strong effect • Influx mainly limited to daylight hours• Large fluctuations occur• Stability of materials• Availability of special materials

Possible remedies would be• Cheaper “collector” materials• Cheaper short-term and long-term

energy storages• Massive integration of units


https://www.scientificamerican.com/article/energy-costs-at-record-lows-thanks-to-natural-gas-and-clean-energy/

7 Feb. 2017 (accessed 17.2.2017)


”Hidden costs” of renewableenergy

ÅA 424520


2b.6 Other solar energy applications


Solar hydrogen production Four important thermochemical routes for solar hydrogen

production, all involving endothermic reactions Hydrogen can come from water, from fossil fuels, or both of

these. With fossil fuels, CO2 is produced It may require special (high temperature) materials

Pic: IEA08


Other use of solar energy, CSP CSP or other forms of solar

energy could be used for – metals production, – energy carriers production– methane reforming– chemicals production– all sorts of endothermic chemistry

– water desalination(”AQUA-CSP” and similar efforts)

for example running a steam cycle with outlet steam of 70°C (instead of 35°C) as to get heat for desalination at somewhat reduced electricity production efficiency

Pics: AQUACSP07

Solar chimney, solar tower

November 2010:


50 kWe demo in Spain 1982-1989(height 195 m)

for 200 MWe unit in NSW, Australia, later downscaled to 50 MWe

http://www.enviromission.com.au/EVM/content/technology_technologyover.html

power densityonly ~ 0.1 W/m2

M08

NOdevelopments forquite some time

January 2014: see National Geographic : NG14

ÅA 424520


2b.7 Exergy analysis (an example)


Exergy analysis – solar power /1

Schematic of a solar power system (pic: KSM03)


Exergy analysis – solar power /2

Pic: KSM03

Note [5] =RenewableEnergy 19 (2000) 135


Exergy analysis– solar power

/3

Pics: KSM03

ÅA 424520


2b.8 Passive coolingsee R&D at ÅA Thermal and Flow Engineering: 2a.8 & 2a.9

Solar coolingsee ÅA course 424519 Refrigeration, #9

ÅA 424520


2b.9 Desertec....

Desertec..... Source: MPS, Dec. 2012 p. 61



Sources 2b AQUACSP07: ”Concentrating solar power for sea water desalination”, German Aerospace Centre

(DLR), Nov. 2007. http://www.trec-uk.org.uk/reports/AQUA-CSP-Full-Report-Final.pdf B97: A. Bejan “Advanced engineering thermodynamics” 2nd ed. Wiley (1997) HR08: Y. Hwang, R. Rademacher. ”Review of solar cooling technologies”. HVAC&R Research 14(3)

(2008) 507-528 IEA08: “Energy technology perspectives - Scenarios and strategies to 2050”, IEA, Paris IEA-SHC08: “Solar heat worldwide, Markets and Contributions to the Energy Supply 2006”, Edition

2008, IEA-Solar Heatiing and Cooling Programme, May 2008, AEE INTEC, Austria IEA-SHC16: “Solar heat worldwide, Markets and Contributions to the Energy Supply 2014”, Edition

2016, IEA-Solar Heating and Cooling Programme, May 2016, AEE INTEC, Austria http://www.iea-shc.org/data/sites/1/publications/Solar-Heat-Worldwide-2016.pdf

K03: Kryza, F.T. “The power of light” New York: McGraw-Hill, 2003 K04: Kalogirou, S.A. “Solar thermal collectors and applications.” Progr. Energy & Comb. Sci. 30

(2004) 231-295 K08: Khalil, S. “Parameterization models for solar radiation and solar technology applications”. Energy

Conv. & Manage. 49 (2008) 2384-2391 KSM03: Koroneos, C., Spachos, T., Moussiopoulos, N. “Exergy analysis of renewable energy sources”

Renew. Energy 28 (2003) 295-310 L08: Lior, N. “Energy resources and use: The present situation and possible paths to the future”

Energy 33 (2008) 842-857 MM77: A.B. Meinel, M.P. Meinel “Applied solar energy” 2nd ed., Addison-Wesley (1977)


Sources 2b (cont’d)

M08: MacKay, D.J.C, ”Sustainable energy – without the hot air” v. 3.5.2. UIT Cambridge, UKhttp://www.withouthotair.com/

MPS = magazine Modern Power Systems http://www.modernpowersystems.com MS08: Müller-Steinhagen, H. ”Applications of solar heat for temperatures ranging from 50-1000°C”,

Proc of Eurotherm 2008, Eindhoven (the Netherlands) May 2008 NG14: http://news.nationalgeographic.com/news/energy/2014/04/140416-solar-updraft-towers-convert-

hot-air-to-energy

REN21: Renewables 2016 Global Status Report (GSR 2016) http://www.ren21.net/wp-content/uploads/2016/10/REN21_GSR2016_FullReport_en_11.pdf

SAKS04: de Swaan Arons, J., van der Kooi, H., Sankarana-rayanan, K. Efficiency and sustainability in the efficiency and chemical industries. Marcel Dekker, New York 2004. Chapter 15.

Se04: Șen. Z. “Solar energy in progress and future research trends.” Progr. Energy & Comb. Sci. 30 (2004) 367-416

SH14: Stine, W.B., Harrigan, R.W. Power from the Sun. (2014) http://www.powerfromthesun.net/ Sö04: Sörensen, B. Renewable energy 3rd ed. Elsevier Academic Press, Burlington (MA) 2004 SWE = magazine Sun & Wind Energy http://www.sunwindenergy.com TDDGP12 J.W. Tester, E.M. Drake, M.J. Driscoll, M.W. Golay, W.A. Peters ”Sustainable Energy -

Choosing Among Options” MIT Press, Second edition 2012 dV08: A. De Vos ”Thermodynamics of solar energy conversion”, Wiley-VCH, 2008 W08: S.E. Wright ”Endoreversible terrestial solar energy conversion”, Renew. Energy 33 (2008) 2631-

2636 W10: Wang, Q. Photovoltaic Physics and Materials, Lecture notes, University of Singapore, 2019/10

solar energy (thermal, pv) - Åbo akademiusers.abo.fi/rzevenho/apt17-2b-sol.pdfsolar energy...

Documents