Submerged and Floating Photovoltaic Systems: Modelling, Design and Case Studies

243 Pages·2017·32.616 MB·English

by  Marco Rosa-Clot, Giuseppe Marco Tina

SUBMERGED AND
FLOATING
PHOTOVOLTAIC
SYSTEMS
“we must not force nature but persuade her” (Epicurus 300 B.C.)
SUBMERGED AND
FLOATING
PHOTOVOLTAIC
SYSTEMS
Modelling, Design and
Case Studies
MARCO ROSA-CLOT
ScientificDirector, KMM (Koin(cid:1)e
Multimedia), Italy
GIUSEPPE MARCO TINA
Electric, Electronics and ComputerEngineering
Department, University of Catania, Italy
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ix
CHAPTER 1
Introduction
1 RENEWABLE ENERGY PENETRATION
Energydemandiscontinuouslyincreasingworldwideandtheelectricsector
isbecomingprogressivelyimportant.Theelectricsectorrepresented42%of
energy demands in 2015 and this percentage will rise to 47% in the next
20years[1].Atthesametime,thereisadramaticparallelenvironmentalcri-
sis due to the burning of fossil fuels and, in particular, due to the electric
energy production.
Thiscrisismustbetackledandthemostpromisingprospectisconstituted
bytheexpansionofrenewableenergysources(RES).Thisiswhy,inthelast
fewyears,investmentsinRES(excludingthelargeandmorestablehydro-
electricsector)haveregistereda12%yearlyincreaseintheinstalledpowerin
thelast20years.Thistrendislikelytocontinueinthenext20yearsatalevel
of 7.1% [1].
Two main competing technologies have emerged in the course of the
last two decades: wind farms and solar plants. Photovoltaic (PV) fields and
largewindturbineshaveagreatvisibleimpact,andtodayhavebecomevery
popular, flanking the more important, if less showy, hydroelectric sector.
The penetration of these two technologies in most industrialized countries
andthedumpingoftheircostsareprocesseswhichsuggestthat,withinthe
next few years, the scenario of the energy world will undergo a structural
change.
But how long will this process last? Can RES completely replace fossil
(and nuclear) energy plants? What will the time scale be?
The answers to these questions must face a two-pronged problem:
(cid:129) Power density. While traditional thermal energy plants, powered with
fossil or nuclear fuels, are highly concentrated structures with a typical
sizeof1GWormore,bothsolarplantsandwindfarmsneedverylarge
areas for energy harvesting, and therefore entail a problem of land
occupancy.
(cid:129) Energyavailability.Theenergyproducedwiththermalplantsisproduced
continuouslyandhas,therefore,twofundamentaladvantages:itiscon-
stantlyavailableandcanbemodulatedaccordingtotheneedsoftheend
SubmergedandFloatingPhotovoltaicSystems ©2018ElsevierInc.
https://doi.org/10.1016/B978-0-12-812149-8.00001-6 Allrightsreserved. 1
2 SubmergedandFloatingPhotovoltaicSystems
user. Biomass and geothermal energy are also constantly available
whereassolarenergy,wind,andevenhydroelectricsourceshaveintrinsic
limitations due to the intermittency of their energy yield.
Becauseofthestructuralneedforlargesurfacesandbecauseoftheintermit-
tencyoftheenergyoutput,solarenergystillrepresentsonlyasmallpercent-
ageofenergyproduction,asshowninFig.1,whichcaptureselectricenergy
production at the end of 2015 [2].
If we wish to tilt the balance in favor of RES and fully develop solar
potentialitiessothattheyarecompetitivewithfossilfuels,twodistinctprob-
lems need to be solved: the availability of large surfaces and the issue of
energy storage.
The wind energy sector has partially solved the problem of land occu-
pancy. The production of huge wind turbines triggered a great expansion
in this sector, which reached 3.7% of the total worldwide production in
2015. The availability of off-shore technology contributed to this trend,
and 24% of wind power installed in Europe in 2015 was constituted by
off-shore wind turbines [3].
The PV sector could adopt a strategy similar to that used in the wind
sectorbyfindinglargeareasforhugePVinstallations.However,thisismore
complex.Largesurfaceswithintensesolarradiationcanbefoundbut,ifused
for PV, they would be not available for other purposes, and land in indus-
trialized zones is very expensive. Notwithstanding these problems, a great
efforthasbeenmadeinthisdirection,withplantsofupto500MWhaving
been installed so far, and further efforts will be made in the future [4].
Nonrenewables
76.3%
3.7%
Wind
Hydropower
16.6%
2.0%
Bio-power
Renewable
electricity
23.7% Solar PV 1.2%
Geothermal,
CSP, and
0.4%
ocean
Based on renewable generating capacity at year-end 2015.
Percentages do not add up internally due to rounding.
Fig.1 RESintheelectricsector(worldwidedata,end2015)[2].
Introduction 3
Inthisperspective,thefloatingphotovoltaic(FPV)solutionisaperfectly
viableandfeasiblestrategy.ItsextensiontosubmergedPVplantswillbealso
discussed. The two technologies are different but the basic principle is the
same:exploitlargeexistingwatersurfacesandprofitfromthewaterasause-
fulmediumformanagingalargeplantofPVmodules.Weshowtwoexam-
ples of floating plants in Figs. 2 and 3: one fixed and one with a tracking
system. In Fig. 4 the rendering of a large submerged plant is shown.
Fig.2 FloatingPVplant:fixedplant,100kWpSingapore.
Fig.3 FloatingPVplant:plantwithtracking,200kWpSuvereto(Italy).
4 SubmergedandFloatingPhotovoltaicSystems
Fig.4 RenderingofsubmergedPVplant.
2 FLOATING AND SUBMERGED PV PLANTS: WHERE?
As mentioned above, the large-scale deployment of PV energy entails the
use of a significant amount of land. According to the data reported in
Ref. [5] for the United States, the capacity-weighted average land use for
large PV plants ranges from 0.42 (fixed) to 0.27 (1-axis)MWp/ha, while
morerecentresearchonlanduseandtheso-calledgeographicPVpotential
suggeststhatthepowerinstallableforafixedplantis0.5–0.7MWp/ha[6].
The concept of geographic potential can be extended to water surfaces.
Inthiscase,however,wewouldbeworkingwithtechnicalproblemswhich
areverydifferentfromland-basedPVplantsandwewouldbeabletoarrange
themodulesmorecompactly.Infloatingplantsvaluesincreasetomorethan
1MWp/ha (see Chapter 8).
It should be noted that land hunger, land cost, and land management
heavilyaffectthePVsector.Largeareasoffreelandarenotnormallyavail-
ableindevelopedcountries,andthegrowthofhumansettlementsinindus-
trializedcountriesgeneratesthedemandforstrongpowerunitsconcentrated
in a limited space, which pollute very large areas and trigger issues of air
quality and CO emissions.
2
However, it must be observed that wherever human settlements are
built,waterisalsopresent.Itcanbefoundinavarietyofformssuchaslakes,
Introduction 5
sea,largeartificialbasinsbuiltforvariouspurposes(waterstorage,irrigation,
orciviluse),wastewatertreatment,hydroelectricbasins,abandonedmines,
etc. These very large existing surfaces suggest a very simple solution to the
problem of power/surface limitations: they could be used to install FPV
plants.
Furthermore, in most cases, around or next to basins or lakes, there are
humansettlementswhicharealreadyequippedwithanelectricitygrid,ifnot
withelectricpowerplants.IntheUnitedStates,78%oftheelectricityisused
in states bordering an ocean or a Great Lake [7].
But how large are these surfaces? Can they account for a substantial
expansion of the PV sector and increase its contribution to RES?
Asimpleanalysisoftheavailablewatersurfacesshowsthatverylargefresh-
waterbasinsareavailableeverywhere.Forexample,inSicily,oneofthedri-
estregionsinItaly,thereareover75km2oflargefreshwaterbasins[8].Even
morecanbefoundbytakingintoaccountsmallirrigationbasinsandwater
reservoirssuitableforFPVplants,becausePVinstallationsfavorwatersaving
and water quality control.
2.1 Freshwater Surfaces
Table 1 shows the values of freshwater surfaces, the installable FPV power
(the so-called technical power potential, PVPP) if only α ¼1% of
SW
these surfacesare used, and thecorresponding potential energy production
(technicalenergypotential,PVEP)forextendedregionsworldwide:tropic,
temperate, and cold zones [9] (see Chapter 8).
It should be noted that, notwithstanding this conservative estimate, the
potentialenergywhichcouldbeinstalledonfreshwaterbasinsis6069TWh
and which would cover about the 25% of the entire world production of
electric energy, which in 2015 was 24,215TWh [1].
Table1 TechnicalPVpotentialforclimatezones
Surface PVPP(α 51%) PVEP
sw
km2 GWp TWh
Tropicalzone 1,254,831 1,526 1,851
Temperate zone 1,506,256 1,832 2,064
Cold zone 1,789,819 2,176 2,155
Total 4,550,906 5,534 6,069