estimating solar energy production potential of urban

6th International Symposium on Mobile Mapping Technology, Presidente Prudente, São Paulo, Brazil, July 21-24, 2009
ESTIMATING SOLAR ENERGY PRODUCTION POTENTIAL OF URBAN REGION
USING LASER SCANNER DATA AND HIGH RESOLUTION IMAGES
G. V. Souza a*, J. A. S. Centeno b, A. M. L. Machado c
a, b, c
Departamento de Geomática, Universidade Federal de Paraná - UFPR.
Caixa Postal 19001, CEP 81531-990, Curitiba, PR, Brasil.
a
regan.gra@gmail.com
b
centeno@ufpr.br
c
alvaroml@ufpr.br
Commission VI, WG V/I
KEY WORDS: Photovoltaic energy, Laser Scanner, high resolution image.
ABSTRACT:
Currently, the use of alternative energies, aiming at the reduction of carbon emission, has become a necessity, mainly in urban
regions, where the use of energy is high. For the production of electric energy from solar radiation, a clean energy source, it is
necessary to know the photovoltaic potential and solar resource of a region. In urban environments, a great amount of flat surfaces
is to capture solar energy in the form of roofs. In order to use the buildings to collect solar energy, it is necessary to know if the
available roofs are viable, in economic terms, in comparison to other alternative sources. This research uses airborne laser scanner
data together with a Quickbird panchromatic imagery to estimate the photovoltaic potential of the roofs within an urban region of
Curitiba, in Brazil. The spatial limits and form of the roof is derived from the integrated dataset, combining laser scanner altitude
data with the multispectral image. Both data sources are complementary and allow the estimate of the form, orientation, slope and
size of the roof. The result is the used to compute the photovoltaic potential for different dates, considering the seasonal variations
of the incident solar energy. The results show that the method can be used to estimate the potential of the use of roofs as solar
collector, and then the size of the roofs is big enough in relation to the resolution of the scanner and the images. A data set with
low density on the roof can lead to an inaccurate estimation of the slope, size and orientation of the planes that form the roof,
causing errors in the estimation of the photovoltaic potential. Nevertheless, the method is valid for the choice of the best places to
use of solar energy as complementary energy source in an urban environment.
1.INTRODUCTION
The percentage of domiciles supplied with electricity comes
gradual increasing each year, making with that the demand
grows in short term. This world-wide demand if has expanded
quickly, had to world-wide the economic growth and the
increase of the population. Ally to other causes, this generated
the necessity of energy rationing.
Advances in science and technology have provided some
alternatives with production of energy to a sustainable level.
One of the technologies you renewed more promising of energy
generation is the photovoltaic generation that comes more
being each time used by the industrialized countries. It has left
of the beginning of being a quiet, static, non-polluting source
and without any depletion of materials that directly converts
the energy of the sun into electric energy.
The photovoltaic solar energy has provided electric energy for
any application and in any localization in the land and the
space, having been that the urban way started if to detach as a
great absorber of this ecological technology.
As characteristic main, the photovoltaic generation shows an
excellent capacity of work with other power plants. Its
installations can be found working with nuclear central offices,
hydroelectric plants and of all the types.
* Corresponding author.
With the objective to get a bigger income of the solar panel, it
is necessary to have a direction that goes following the
trajectory of the sun during the day.
However in the majority of the simple installations, the
localization is fixed, and for this, its positioning must possess
some characteristics in accordance with the orientation and
inclination (Quadri, 1991).
The excellent orientation of the solar panel is guided to the
north, to use to advantage the biggest number of hours of the
sun, independent of the station of the year and the latitude of
the place. In the case of that it is not possible this positioning,
the localization does not have deviation of the North more than
20º (Quadri, 1991).
The inclination depends on two factors:
• Latitude of the place;
• Period of use during the year.
For this work the inclinations had been calculated ideas for use
only in the summer, only in the winter and for all the year.
The extracted variable of the integration of data laser with the
high resolution image that influence in the estimate of the
energy generated in a residence in one day, they had been
given of altitude of the lower point highest and of the residence
in order to know the inclination of the water, and with the
perpendicular the line of the top of the roof, has if the azimuth
of the roof.
This identifies the best part of the roof to locate the
photovoltaic panel, and through the inclination it is calculated
incidence of solar energy in one day. This technique allows
evaluating the photovoltaic potential of some residences with
an only survey. To know the potential photovoltaic of a
residence, as well as its correct positioning, is decisive factor
for use of this clean power plant.
3.1.2
Quickbird image
2.STUDY AREA AND MATERIALS
2.1 Study area
The study area is located in the state of the Paraná, in the city
of Curitiba, quarter Jardim das Americas.
2.2 Materials
For this work they had been used a high resolution image
gotten by the Quickbird sensor, dated of March of 2002, with
0,70m of space resolution (hybrid image), and spectral
resolution of 4 bands. Together, given rude gotten for Laser
sweepings Scanner, dated of April of 2005.
3.METHODOLOGY
3.1 Treatment of the rude data
3.1.1
Laser Scanner
The rude data of the laser to scanner had been used for the
generation of a Digital Terrain Model (DTM), and a Digital
Elevation Model (DEM), for this, used a regular grating with
20 cm of spaced for the generation of both models.
Later, in the ENVI, these models had been deducted, giving
origin to a Digital Model of Normalized Surface (DMNS).
Figure 2. Quickbird image composition 4,3,2.
The Quickbird image was corrected geometrically, and a fusing
for main components was carried through for the attainment of
the image with 4 bands and space resolution of 0,70m.
Later, a clipping of this image was carried through to locate the
same area gotten with the data laser to scanner.
3.2 Data integration
The Quickbird image and the DMNS had been overlapped in
software ENVI, generating a hybrid image, with altitude data.
The gotten data of the Quickbird image had allowed evaluating
the azimuths of waters of the roofs, together with the distances
between the top of the roof and the part lowest, for the
calculation of the inclination. Already the happened data of the
DMNS had allowed calculating the inclination of the roof.
3.3 Choosing edifications
For the analysis of the photovoltaic potential, residences had
been chosen that possess waters in ideal conditions, that is, its
water is in an azimuth of until + 20º in relation to the north.
For verification, some samples had been gotten with distinct
azimuths, in order to evaluate the differences of gotten
potential.
3.4 Calculating inclination
Figure 1. Digital Model of Normalized Surface.
For this work, 23 residences had been chosen, with distinct
characteristics between itself, in order to evaluate its
photovoltaic potential. Distinct the hybrid image was chore in
two software, in order to get the data for the calculation of the
inclination:
• In the ENVI, the heights of the points highest and lower of
the roof of the construction had been chores;
• In the AutoCAD the horizontal distances between the top and
the edge of the constructions had been chores.
For the calculation of the inclination the formula was used (1):
 A − A2 
I = tg − 1  1

 d 
(1)
Where
I = Roof inclination;
A1 = height of the roof’s top;
A2 = height of the roof1s bottom;
D = distance between the top and the bottom of
Where
Ht = touch angle;
M = auxiliary angle;
δ = sun’s declination of the season;
φ = latitude.
the roof.
Now, it is gotten insolation of the water of the roof for the
winter and summer, following the equation (7):
3.5 Azimuth
For the attainment of the azimuth of the water, in the
AutoCAD a perpendicular to the line of the top of the house
was traced, in the chosen direction, and later read its angle in
relation to the north.
3.6 Calculating the duration of the day

H n = cos 


H o = cos − 1 

Where
(2)
)

)
(3)
Hn = clockwise angle of the sunrise;
H0 = clockwise angle of the sunset;
φ = latitude;
δ = sun’s declination.
D = | Hn | + | H0 |
(4)
3.7 Calculating the insolation
The calculation of the insolation of the chosen water of the
house is made in parts.
First with the equation (5), angle auxiliary M is calculated:
Where



(5)
Az = roof’s azimuth;
φ = latitude
For the calculation of insolation, it will use the value of
declination of the sun of 0,409173051 for winter and
-0,409173051 for the summer, having remembered that this
value is given for the city of Curitiba.
The angle of touch of the sun for the winter and the summer is
calculated then, using the above-mentioned values of
declination, through the equation (6):
 cos( M ) * tg (δ
Ht = cos − 1 
tg ( ϕ )

)


Where
(8)
Pf Photovoltaic potential;
Is = insolation.
The values are gotten in Wh/m2 per day, that is, for a solar
panel of 1 m2 per one day.
4.1 Inclination and Azimuth
D = duration of the day;
 tg ( Az )
M = tg − 1 
 sen ( ϕ )
For the calculation of the photovoltaic potential, the value was
used 5000Wh/m2, gotten of Atlases of Solar Irradiation of
Brazil, for the South region.
The value approached for the generation of energy for one day
is gotten by the equation (8):
4.RESULTS
Finally, the duration of the day is given by (4):
Where
Is = insolation;
H0 = clockwise angle of the sunset;
Ht = touch angle.
Pf = 5000* Is
− tg (ϕ ) 

tg (δ ) 
tg (ϕ
tg (δ
Where
(7)
3.8 Calculating the photovoltaic potential
For the city of Curitiba, the declination of the Sun uses it
following declination of the sun:
• Summer = -23º;
• Winter = 23º.
From this data, the hourly angle of the rising is calculated and
to occult of the sun, being used formulas (2) and (3):
−1
Is = H 0 + H t
(6)
House
1
2
3
4
5
6
7
8
9
10
11
12
13
Az.
25
25
26
24
25
66
24
22
24
23
22
22
24
Inclination House Az. Inclination
21,03751103
14 24 10,54877659
25,78480669
15 22 26,62246176
26,91299698
16 24 18,75535909
25,7307056
16 24 21,80140949
14,34613348
16 24 22,32685869
22,12194197
17 23 14,24135875
26,45091631
17 66 14,48820323
28,19989916
18 48 13,86968644
20,46227152
19 25 38,43730149
14,93141718
20 24 21,84099206
9,104600865
21 25 30,76271953
26,28141102
22 25 13,42330525
18,20848447
23 26 13,80414378
Table 1: Azimuth and inclination
4.2 Insolation
The gotten values of the insolation had been for the winter and
summer (extreme situations). The gotten values meet in table 2
to follow:
house
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
16
16
17
17
18
19
20
21
22
23
W/day winter
25534,26
25534,26
25547,17
25520,45
25534,26
11929,29
25520,45
25489,66
25520,45
25505,62
25489,66
25489,66
25520,45
25520,45
25489,66
25520,45
25520,45
25520,45
25505,62
11929,29
13638,7
25534,26
25520,45
25534,26
25534,26
25547,17
W/day summer
45642,66
45642,66
45852,71
45425,86
45642,66
37054,47
45425,86
44971,3
45425,86
45202,13
44971,3
44971,3
45425,86
45425,86
44971,3
45425,86
45425,86
45425,86
45202,13
37054,47
37121,26
45642,66
45425,86
45642,66
45642,66
45852,71
To weigh of this type of problem, the value of the photovoltaic
potential did not suffer a significant alteration.
5.2 Photovoltaic potential
As we saw previously, for the locality, it is ideal that the
photovoltaic panel has its directed face northward. In case that
this is not possible, that it has a variation of + 20°. This factor
is verified clearly, when we use constructions 6, 17 and 18,
that 66° (6 and a water of the 17) and 48° possess azimuths
(18).
The photovoltaic potential falls of 45 kWh/m2 for 37 kWh/m2.
All the other constructions possess values seemed, due to the
order square of them in the place.
6.CONCLUSIONS
This work carried through a estimate of the photovoltaic
potential for residences through data gotten through high
resolution image and laser sweepings to scanner. The
methodology showed that, it is possible to extract this
information in fast way and with a significant speed due to
possibility to verify some constructions in an only survey.
One also revealed that, for constructions that possess the
inclination of its roofs with bigger azimuths that 20°, has a
significant reduction in the photovoltaic potential.
The attainment of data through laser to scanner is efficient for
this type of estimate, therefore, possible problems in the
calculation of the inclination of the roofs do not influence of
significant form in the attainment of the estimate of the
photovoltaic potential. This method proved to be practical,
simple and very efficient.
Table 2 - Photovoltaic potential in wh/m2 per day.
7.BIBLIOGRAPHY
5.DISCUSSING
5.1 Roof’s inclination
For this work, the data had been extracted of a high resolution
image Quickbird pan-sharpened, together with laser sweepings
to scanner. It did not have much variation in the inclinations of
the roofs. This fact occurs for the difficulty of the laser to
always find the top and the edge of the construction, finding an
approach value.
To weigh of the regular grating to have been generated with 20
cm, the amount of points for square meter in the sweepings is
basic for the extraction of this type of information.
At the same time one verifies that this lack of variation does
not influence in the results of the photovoltaic potential,
therefore the constructions possess an average inclination of
25°, being the ones that present discrepancy in relation to these
inclinations, to occur due to the fact of that with the data laser
it is not obtained to detect the edges of the construction.
When reading the height in the edge of these constructions,
many times appeared value zero, (therefore a DMNS was
used), having in the distance to find the value of the height of
the edge of the construction in a more internal point in the
polygon roof, diminishing between the top and the base, then
increasing the inclination, case of construction 19.
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http://www.lepten.ufsc.br/pesquisa/solar/atlas_de_irradiacao.p
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Quadri, N. P. Energía Solar. Librería y Editorial Alsina.
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