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In this paper, the lightning protection requirements of a typical residential building have been discussed and techniques have been provided to protect the building from both direct and indirect damages of lightning, with special attention to the protection of PV panels placed on the roof. These techniques include the designing challenges and also the type of devices which can be used to reduce the surge current flow and magnetic field. It has been shown that for buildings with roof top PV systems only the avoidance of lightning attachment to unprotected parts of the building is not sufficient. Lightning currents passing through the lightning protection system may still affect the PV power system through inductive coupling. Hence strategic placement of PV systems and shielding of conducting systems wherever possible has been recommended. It has also been envisaged that the impact of lightning on PV systems is directly related to the isokeraunic level of the region and elevation of the building. Several recommendations have been proposed in designing the air termination system for a roof with PV panels in high isokeraunic regions. Finally the building integrated photo voltaic (BIPV) projects which are conducted in Malaysia have been evaluated..
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Lightning Protection Techniques for Roof-Top PV
Systems
Narjes Fallah#1, Chandima Gomes*#2, Mohd Zainal Abidin Ab Kadir#3,
Ghasem Nourirad#4, Mina Baojahmadi#5, Rebaz j.Ahmed#6
#Centre for Electromagnetic and Lightning Protection Research (CELP),
Electrical & Electronic Engineering Dept, Universiti Putra Malaysia, Malaysia
1s.narjes.f@gmail.com, 2chandima@eng.upm.edu.my
3mzainal@eng.upm.edu.my,4gh.raad@gmail.com,5baojina@gmail.com,6 rebardilyun@gmail.com
AbstractIn this paper, the lightning protection requirements of a typical
residential building have been discussed and techniques have been provided
to protect the building from both direct and indirect damages of lightning,
with special attention to the protection of PV panels placed on the roof.
These techniques include the designing challenges and also the type of
devices which can be used to reduce the surge current flow and magnetic
field. It has been shown that for buildings with roof top PV systems only the
avoidance of lightning attachment to unprotected parts of the building is
not sufficient. Lightning currents passing through the lightning protection
system may still affect the PV power system through inductive coupling.
Hence strategic placement of PV systems and shielding of conducting
systems wherever possible has been recommended. It has also been
envisaged that the impact of lightning on PV systems is directly related to
the isokeraunic level of the region and elevation of the building. Several
recommendations have been proposed in designing the air termination
system for a roof with PV panels in high isokeraunic regions. Finally the
building integrated photo voltaic (BIPV) projects which are conducted in
Malaysia have been evaluated..
Keywords-Lightning protection system, roof-top PV system, BIPV
I. INTRODUCTION
At present, photo voltaic cells have a growing demand as a
renewable energy source. One of the common type of
implementing photo voltaic system is roof-top installation
where the PV panels are integrated to the new buildings and
new constructions. This integration raise challenges in
designing the building and also the PV system. A major issue
arises in this case is the lightning protection of the building
and PV system. Available protection techniques for
safeguarding the buildings against direct strikes are necessary
to be evaluated to provide a safe location to install the PV
system. The general strategies in installing the PV system
components and location design for optimized efficiency of
power production should be compatible with strategies of
lightning protection design. Hence, a comprehensive revision
and analysis of information is essential at present for better
optimization of the lightning protection of PV systems.
This research, which is done in the above background, has
been conducted to propose maximum protection for a
building-integrated PV system, by the analysis of protection
techniques available so far. The emphasis is given on
structural protection of the building against direct strikes
while protection against induced effects is also discussed.
II. LIGHTNING PROTECTION SYSTEMS
Lightning protection system of a building is defined in
standards [1] as a “complete system to diminish physical
damage due to lightning flashes to a structure”. These physical
damages happen either by attachment of stepped leader to the
structure or a nearby object from which side flash may
emanate. In the case of direct strike or side flash, due to the
rapid rise time of impulse current of lightning, arcing may take
place into conductive parts of the building interior (and exterior
as well). Such arcing may trigger fires and even explosion in
the event of explosive storages in the vicinity. On the contrary,
if lightning strikes nearby, a strong electromagnetic field will
be created in the structure which may induce over voltages in
electrical and electronic equipment inside the building. Both of
these effects should be taken into account to offer a complete
protection system for buildings; therefore, lightning protection
techniques provided for buildings are divided into two groups:
external Lightning Protection System (LPS) and internal
Lightning Protection System.
A. EXTERNAL LPS
External protection system of a building intercepts the
direct lightning strikes by air termination system, conducts the
lightning current through a low impedance path to the earth
termination system, and disperses this high current to a low
resistance earth. In following the challenges in designing these
three components are discussed.
1) Air termination system:
Different types of the air termination systems can be
installed on the roof depending on the shape and materials of
the roof and usage of the building. Also, the type of protection
and the area which is critical to be protected influence the
selection of air termination system. Considering these factors,
finials, meshed conductors, and catenary wires (isolated or
non-isolated) can be installed as the air termination system.
Implementation of each of these air termination systems on a
building needs the methods that provide total protection against
a lightning stepped leader. Three methods have been
introduced in standards for designing the air termination
system: the rolling sphere method (RSM), the protection angle
method (PAM), and the mesh method (MM) [2]. These three
methods can be applied depending on the class of the LPS. In
the protective angle method the height of the building is an
exclusive factor in determining the protection scenario (angle
978-1-4673-5074-7/13/$31.00 ©2013 IEEE
2013 IEEE 7th International Power Engineering and Optimization Conference (PEOCO2013), Langkawi, Malaysia. 3-4 June
2013
417
of protection). In designing finials as the air termination
system, either the protective angle method or the rolling sphere
method can be used to verify the protected area. The method
adopted determines the number of rods and location of them.
However, depending on the class of protection, application of
protective angle method is restricted based on the height of the
building. For an example for buildings taller than 30 m the air
termination system cannot be designed under protective angle
method if the required level of protection is I or II. For
structures taller than 60 m, strikes to vertical walls of the
structure below the roof-level air terminations should also be
taken into account. This is achieved by protecting the upper
20% of the building (by height) with mesh-type air
terminations [2].
Tapes or wires also can be installed as mesh conductors
on the building edges or as catenary wires in either isolated or
non-isolated systems by which the structure below the wire
up to a specified distance is protected, this distance should be
calculated by RSM or PAM. The air termination system
applied by any of the above methods must either be
electrically connected to all other conducting parts of the
vicinity or be kept at a minimum separation, s, from such
parts. The value of s can be determined by equation 1. The
values of km, kc, and kiare given in Tables I, II, and III. L is
the length in meter, along the air-termination or down
conductor, from the point where the separation distance is to
be considered, to the nearest equipotential bonding point [2].
  
(1)
Table I: Isolation of External LPS: Values of Coefficient ki
Class of LPS
ki
I
0.08
II
0.06
III and IV
0.04
Table II: Isolation of External LPS: Coefficient kc
Number of down
conductors (n)
kc
1
1
2
1…0.5
4 and more
1…1/n
Table III: Isolation of External LPS: Coefficient km
Material
km
air
1
Concrete, bricks
0.5
2) Down conductor: In the LPS of a building, down
conductors which provide safe passage to lightning current
towards the earth, can be implemented by separate conducting
tapes/wires or natural components of the building such as
reinforcing rods of walls or concrete columns and steel
structured frames. Unless at least two down conductors are
installed possibly in exposed corners of the building for non-
isolated LPS; the down conductors must be distributed around
the structure equally while keeping the minimum separation
(s) with doors, window frames, railings etc. that would be
subjected to human touch during thunderstorms periods. The
typical values of the distance between down conductors are
shown in Table IV. In case of tall structures bonding all down
conductors at regular vertical intervals (say 20 m) may keep
the system at equipotential. In isolated LPS for rod air
termination, one down conductor is required for each mast,
also, for catenary wires, at least one down conductor is
necessary per support. It should be noted that, down
conductors must be installed straight and vertical, and they
should not be installed in loops or as over hangs. If loops
cannot be avoided, the separation distance across the gap must
be greater than minimum separation, s, which can be
calculated as equation 1 [2].
Table IV: Typical Values of Distances between Down Conductors and
between Ring Conductors
Class of LPS
I
II
III
IV
3) Earth termination system: The surge current flows
through the down conductors will be dispersed to the soil by
the earth termination system. The earth termination system
for a building can be in the shape of vertical or horizontal
conductors or a combination of them. Such system is called
type Aearthing systems. The second system is termed type B
earth termination which is a closed ring conductor laid
around the building at a distance of about 1 meter from the
structure walls. In a given ring conductor 80% of its length
should be in contact with soil. Depending on the class of the
LPS, aspecified length of horizontal or vertical electrodes in
configuration of two electrodes must be connected at each
down conductor in the type A system; in type B earthing
systems with ring conductor, if the radius of the ring
electrode is less than the length specified in the type A
earthing system, additional horizontal or vertical electrodes
can be added to the ring conductors where the down
conductors connect to the ring electrode. Earth electrodes are
permitted to be installed inside the structure through the
basement, or by using natural elements inside the structure as
the ring conductors for the type B earthing systems as well
[3]. However there are several criteria to be satisfied for such
usage [2].Earthing under pathological soil conditions has
been addressed in [4-6]
B. INTERNAL LPS:
In the event of lightning, the danger of direct strikes to the
protected building is reduced by external lightning protection
2013 IEEE 7th International Power Engineering and Optimization Conference (PEOCO2013), Langkawi, Malaysia. 3-4 June
2013
418
system which facilitate the high inrush current to flow
through multiple down conductor system and then disperse to
the soil through the earth termination system. Apart from the
direct strikes, nearby strikes of lightning can also affect the
electrical systems inside the building due to surges that are
generated by inductive coupling (rarely capacitive coupling
as well). To assess the effect of electromagnetic field of
lightning, according to the standards, a different lightning
electromagnetic environment is defined with different
protection measures; this definition segments the building
and its surrounding into the zones which are known as
Lightning Protection Zones (LPZ). The occurrence of
lightning flashes, the lightning current or induced current and
the electromagnetic field are varied in these different LPZs.
Dangerous sparking may take place for external services
entering the building such as power lines, data lines and
water and gas pipes. Also electrical and electronic
equipments inside the building may be affected by induced
voltages due to magnetic coupling. Employing equipotential
bonding through transient protection devices (TPD) or Surge
Protective Device (SPD) and spatial shielding or using
shielding cables lightning threats can be minimized. Bonding
conductive services at the boundary of each LPZ directly
(earth connection) or through of SPDs (live/neutral systems)
will prevent conducting of lightning surges to the following
LPZ. All electronic and electrical equipments inside the LPZ
can be equipotentialized through SPDs. The spatial shielding
or three dimensional meshed structures may decrease the
effects of magnetic fields inside the LPZ. The coordinated
SPD and the cascade spatial shielding shall drop the partial
lightning induced current and partial magnetic field inside the
inner LPZ. The magnetic shield also has to be bonded to the
bonding bar as well as all conductive services entering to the
LPZ. The bonding bar which is installed to bond all
conductive services entering a LPZ, the metal component of
internal system, the magnetic shield of the LPZ and
protective earth conductors shall be as close as possible to the
LPZ boundary. It is recommended for services to enter the
LPZ at one location and connect to bonding bar at one point,
if it is not possible there should be different bonding bars
which finally interconnected together. Moreover, by
shielding of internal lines, the mutual induction effect would
be minimized, also routing electrical and signal lines together
will minimize the induction loop and passing them close to
the natural components of the structure that is earthed as well
[4-7], [5-8].
III. LIGHTNING PROTECTION TECHNIQUES
FOR ROOFTOP PV SYSTEMS
Building Integrated Photo Voltaic (BIPV) system as a type
of implementation of solar energy has a high demand at
present. The assessment of risk of damage due to lightning for
these systems is necessary as the systems are installed at
significantly large heights and extended surface at such
heights make these systems vulnerable to be intercepted with
lightning stepped leaders. Therefore, the external LPS of
BIPV systems must be designed by considering the PV panel
on the roof top as well.
To design suitable air termination system which is capable
of protecting PV panels from direct strikes and induced effects
several extra precautions should be taken by the designer. The
roof should be protected considering the PV panel as an
isolated system from the LPS. In this case extra care should be
taken regarding the shape, height, and total configuration of
panels. In addition, the separation distance of panels to the
LPS is another specified issue. In designing the air termination
system which consists of rods on the flat surface roofs by the
protection angle method can be seen in Figure 1, the angle of
the PV panels or the maximum angle of the moving panels
should be taken into consideration; the protected area by the
rod must cover the panel when the panel surface is rotated. In
Figure 1, it can be observed that by the rolling sphere method
the distance between each two rods in a row, also the distance
between the rods in one row to the other row can be obtained.
Further, in designing LPS, care should be taken to minimize
the shadow effect of finials on panels which may reduce the
efficiency of system.
As shown in Figure 2, at least the minimum separation s
should be kept between LPS and the panel’s frame (isolated
LPS). Separation s should also be kept between the bonding
conductor and PV panel’s mounting structure unless the LPS
is bonded to the frames (non-isolated LPS) to be protected.
The requirement of an isolated or non-isolated LPS depends
on the sensitivity of the PV system for the stray lightning
currents that will be diverted into the metal framework of the
panel. Depending on the requirement of isolation or non-
isolation of external LPS, other necessary components of the
LPS (such as SPD) may be determined.
An important aspect of external LPS in the presence of
roof top PV system that has not been properly addressed in the
LP standards is the mechanical stability of the vertical air-
terminations. In the event of a mechanical failure of vertical
air-termination (such as the whole rod being enrooted from
the base or part of the upper segment detached from the main
rod), the cost of damage may be highly enhanced if the fallen
part lands on the PV system. Damage may be even worse in
the case of mechanical failure of early streamer emission
(ESE) type air terminations (recommended in French
Standards NF C 17-102 and Spanish Standards UNE-21186)
where a heavy metal part is most often connected at the
pinnacle of the rod. Authors have observed such damage to
the roof of buildings in several countries including Malaysia
and India.
Hence, more stringent conditions should be introduced
into the standards (or guidelines) on the mechanical strength
of vertical air-terminations of LPS for buildings with roof top
PV systems. These recommendations should cover the fixing
strength of the base plate, material strength, weight of the rod
etc. On the other hand, mesh type (horizontal tapes or wires)
air-termination systems can strongly be recommended for
such structures instead of vertical metal rods. Such design will
also reduce the shadow-effect problem as well.
2013 IEEE 7th International Power Engineering and Optimization Conference (PEOCO2013), Langkawi, Malaysia. 3-4 June
2013
419
Figure 1: protection of PV panels applying rolling sphere method and
protection angle method [10]
Figure 2 :Applying protection angle method for PV panels[10]
The selection of SPDs for roof-top PV systems depends on
the selected class of LPS for building and the isolation of PV
panels’ frames from LPS, unless bonding the frames to the
LPS makes the system non-isolated which diversifies the SPD
type applicable for that PV system and sizes of earthing
conductors that carry the lightning induced currents.
Protection of DC wires which connect the output of PV panels
to the inverter inside the LPZ1 is performed by SPDs that are
connected before the inverter in DC side; although, if the
separation distance between panels on the roof and inverter is
more than 10 m, two sets of SPDs are required, one close to
the PV modules and another one close to the inverter.
Furthermore, one set of SPD is essential in the AC side, but in
case, the distance between the inverter and load center is more
than 10 m, one SPD is also needed in the load center. Figure 3
shows a roof top PV system with all components, the internal
and external LPS.
As mentioned above the types of SPDs applicable for the
PV system can be selected according to the situation between
the panels and LPS. For a roof-top PV system in a building
without the external LPS, two sets of SPD type 2 are needed
in the DC side and two sets of SPD type 2 in the AC side and
load center (distance more than 10 m). In the roof-top PV
system with external LPS, if the distances between air
terminations and bonding conductors on the roof to the
panels’ frame and mounting system are more than the
separation distance S in equation 1, the PV system can be kept
isolated, in this case, two sets of SPD type 2 are required in
the DC side and one SPD type two in the AC side close to the
inverter, but the SPD in the AC load center should be selected
from type 1. For the non-isolated PV system where the LPS is
connected to the panels’ frames due of restriction in keeping
the distance S, two sets of SPDs type 2 are required in the DC
side, but in the AC side of inverter one SPD type 1 must be
installed close to the inverter and one SPD type 1 is also
needed in the AC load center. Designer-friendly guidance for
planning and implementing SPDs for low voltage power
systems has been given in [9-11].
In order to reduce the dangerous sparking between the PV
system components and to make the PV system
equipotentialized, all SPDs and inverter equipment grounding
must be bonded to the Equipotential bonding bar, this bonding
bar should be connected to the main earthing bar close to the
earth termination system, and also the panels’ frame must be
connected directly to both the equipotential bonding bar and
the main earth bonding bar. The sizes of earthing conductors
which connect the components to the bonding bar are different
depending on the volume of the induced current that may be
carried through the conductor. Indeed, Different dimensions
of conductors are employed when the LPS is connected to the
panel [12-16].
Figure 3: SPD connection for roof top PV system[10]
IV. BIPV CASE STUDIES IN MALAYSIA
Malaysia with a tropical climate with sunny weather
condition is a suitable area for installing PV systems. Also
great numbers of bungalows constructed in the country side
provide opportunities to install the rooftop PV systems. The
preference of bungalows instead of tall buildings normally
with flat surface roofs are the lower height of the building and
slopped roof. By installing PV panels on the bungalows’
roofs, the danger of lightning strikes shall be much less than
tall apartments, also the shading effects in most cases can be
reduced because the panels are mounted above a height that is
taller than trees or any other equipment on the ground.
Furthermore, in the rooftop PV systems most of the wirings
and all other equipments except panels can be imbedded
inside the building with the separation distance to the LPS
which can be protected against lightning.
In comparison of the slopped roofs with the flat roofs from
the protection view, the panels on the slopped roof are
mounted directly on the roof without any mounting structure
while in flat surfaced roofs the panels are mounted on rebars
with certain height fixed to structure; therefore, the height of
the structure to be protected in the flat surface is higher and
also, needs higher rods to be protected. Hence, in most such
2013 IEEE 7th International Power Engineering and Optimization Conference (PEOCO2013), Langkawi, Malaysia. 3-4 June
2013
420
cases mesh type air-terminations may not be possible and
vertical type air-terminations become a must. Figure 4 and 5
show two BIPV projects in Malaysia, the slopped roof and the
flat roof respectively [17].
Figure 4: BIPV bungalow, Bangsar, Malaysia. 5.5 KWP[17]
Figure 5: BIPV bungalow, BKT Damansara, Malaysia. 4.2 KWP [17]
V. CONCLUSION
An efficient design of the LPS with a well-located PV panel
provides high efficiency of power generation with minimized
lightning risk. To design the external LPS, the type of PV
system and the configuration of PV panel should be taken into
account. The shape of the roof and location of the panel are
also important factors in optimizing the LPS. It is
recommended to design the required LPS for the PV system
during the construction or pre-construction stage of the
building, so that the efficiency of the protection system could
be maximized. Wherever it is possible, mesh type air
terminations are preferred over vertical rods to minimize
mechanical damage in the case of air-termination failure and
also to avoid shadow effect.
Acknowledgement: The Department of Electrical and
Electronics Engineering and Centre for Electromagnetic and
Lightning Protection Research, Universiti Putra Malaysia are
acknowledged for the facilities provided in completing this
work successfully.
REFERENCES
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[2] “IEC 62305-3 :  : Protection agaist Lightning-Part 3- Physical damage
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2013 IEEE 7th International Power Engineering and Optimization Conference (PEOCO2013), Langkawi, Malaysia. 3-4 June
2013
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... In this way the high current disappears in the ground having low resistance. In the internal LPS lightning protection zone (LPZ) is created to protect the building from the electromagnetic field of the side flashes [2]. ...
... The down scaled model is connected to the ground inside the experimental lab. Similarly the rods arrangement is diagonal as (1, 3) and (2,4). ...
... Frequent occurrence of these problems may reduce the utilization rate and interrupt the power supply, thereby increasing power generation costs [11]. Various studies have been conducted on lightning effects on PV and WT systems either theoretically [12][13][14][15][16][17][18][19][20][21][22] or experimentally [23][24][25][26][27][28][29][30] Reference [12] developed a computer program to evaluate the risks of lightning effects on PV systems and decide whether lightning protection systems (LPSs) need to be installed or not. Reference [13] performed a sensitivity analysis of PV panels placed on the roof for lightning overvoltage. ...
... Various studies have been conducted on lightning effects on PV and WT systems either theoretically [12][13][14][15][16][17][18][19][20][21][22] or experimentally [23][24][25][26][27][28][29][30] Reference [12] developed a computer program to evaluate the risks of lightning effects on PV systems and decide whether lightning protection systems (LPSs) need to be installed or not. Reference [13] performed a sensitivity analysis of PV panels placed on the roof for lightning overvoltage. The authors considered the effects of lightning strike spot, lightning current amplitude, soil resistivity, building height, and distance between solar arrays and external LPSs. ...
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Abstract—Lightning strike causes large transient current injection into hybrid systems at the point of contact. The generated transient overvoltage due to lightning current is a high concern on various expensive electrical equipment of the hybrid system and is meant to be studied in depth to reduce damages caused by this overvoltage. Analysis of lightning transient effects on a hybrid PV–wind system has been carried out in this study. The complete model of the system has been simulated by PSCAD/EMTDC software. The system consists of 2 MW PV farm, 2.1 MW wind farm, energy storage system and load. The entire system is integrated with the utility grid. Lightning current is generated by Heidler function with the help of same software. In this work, two points are selected from hybrid system to inject lightning current. The first point is the DC side of the PV modules whereas the other is the wind turbine tower. In the second case, the partial lightning current is assumed to be injected into the electrical part in the form of arcing. Transient overvoltage has been observed at different locations of the hybrid system by injecting lightning currents; the simulation results are obtained for 50% waveform of negative first stroke and negative subsequent stroke.
... To protect the building structure lightning rod is placed on a preferred place which can protect the building structure and the surrounding. In this, lightning rod is also connected with down conductor and earth terminal [22]. Position of lightning air terminal (LAT) on any building structures is very important. ...
... As far as the grounding resistance of the PV installation is concerned, values lower than 10Ω are recommended, in order to restrain the developed overvoltages. Internal LPS includes equipotential bonding and electrical insulation between the parts of the PV system [7,8,9,10], in order to avoid sparking within the PV system, due to lightning current flowing in the external LPS or in other conductive parts. SPDs are connected between each line conductor and earth and behave as insulators in case of normal operation of the system and as conductors in case of incoming surges, diverting the lightning current to earth. ...
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