Construction of a 100 kWp solar power system on top of carports built for a parking lot with 60 parking spaces on company premises

Ermittlung des elektrischen Energieertrages von 12 PV-Modultypen, im Vergleich

Supervision of project: S. Hock – electrical engineering technician
Author: E. Zentgraf – degreed engineer (University of applied science)
Courtesy translation: M. Moore

Table Of Contents:

1. Introduction

2. Dimension
2.1. Circuit diagram
2.2. Power Inverter
2.3. Schematic wiring diagram / Calculated Yield
2.4. Connection diagram to alternating current grid

3. Lightning arrester / Overload protection / Grounding / Potential Equalization
3.1. Exterior lightning arrester
3.1.1. Earth loop electrode
3.1.2. Decreasing of induction effects
3.2. Indirect lightning effects and internal lightning protection
3.2.1. Combination lightning arrestor

4. Construction and Implementing of pv-system
4.1. Building of supporting basic frame and installation of PV panels
4.2. Grid Feed-in
4.3. Completion and Initiation

5. Technical Data of photovoltaic systems on top of carports

6. Acknowledgements

 

1. Introduction
By mid 2010 the TEC Institut was assigned a cooperation to design and implement constructions for carports with a photovoltaic system of 100 kWp on its roofs. Awarding authority was ANTARIS Solar GmbH & Co. KG, who proposed to arm new carports for 60 parking spaces with a solar power system.

2. Dimensions
The three carports occupy a total of 775 m² of roof space. (See Photo number 1)
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Maintaining a mandatory separation distance towards the roof edges and the necessary expansion joints implies a total of 447 solar panels, type ANTARIS ASP 215 W with acapacity of 215 Wp per panel. This results in a total output of 96.1 kWp.
All roofs are oriented fairly southwest (south +20°). PV modules are installed at an angle of inclination of 7°. Maximum voltage and reverse current are taken in account as well. The frames of the carports are of a solid wooden construction, covered with trapezoidal sheet metal.
The photovoltaic modules are mounted onto a 6 mm sectional rail, which is attached to the
trapezoidal sheet metal.

2.1 Circuit diagrams
Circuit diagram on photos number 2 to 4 show the installation and relaying of photovoltaic modules on top of the 3 carport roofs.

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Img. 2: circuit diagram for carport 1

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Img. 3: circuit diagram for carport 2
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Img. 4: circuit diagram for carport 3
The photovoltaic modules are interconnected with a wire cross-section of 4 mm². The wiring
of strings proceeding from the individual roof to the inverters inside the technical room are
laid with a wire cross-section of 6 mm².


2.2 Inverters
As you can learn from the circuit diagram (img. 2 to img.4), not only one inverter vendor
was predefined, but instead we used different inverters from two renowned manufacturers.
The intention behind this was to use the technical room, which is a part of the solar power
system, for future presentations and to show our visitors a wider range of products.
Otherwise the construction could have been arranged much easier.
The 9 Inverters are as such:
• Danfoss, TLX 12,5 3 each
• Danfoss, TLX 10 K 2 each
• Danfoss, TLX 15 1 each
• SMA, SMC 9000TL-10 2 each
• SMA, SB 5000-20 1 each
2.3 Functional circuit diagram
Photo number 5 shows a complete functional circuit diagram of the solar power system.

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Img. 5: Schematic of entire solar power system

Calculation of proceeds for the complete solar power system, done with the conservative
calculation software ‘PV Sol’ resulted in an annual yield of 834 kWh/kWp.


2.4 Wiring diagram to the AC main power supply

Photo number 6 shows the inverters connecting into the power grid.
Note: For the single phase inverters (right side of image) from SMA a phase monitoring (not
shown on the picture) was installed.

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Img. 6: connecting diagram to DC-Grid

3. Lightning protection / protective attachment / grounding / potential equalization
Lightning protection is mandatory for solar power systems of this kind. This is subdivided into an external and an internal lightning protection.

3.1 External lightning protection

The external lightning protection includes all utilities and measures of collecting and diverting of lightning. A lightning protection system consists of a lightning rod, lightning cable (minimum 16 mm² copper wire) and an earth electrode. This must be installed according to VDE 0185-305 part 3.

3.1.1 Earth loop electrode
The earth loop electrode is not only a part of the lightning protection system, but also manages grounding and potential equalization.
The earth electrode must be laid at a minimum depth of 0,5 m and a minimum distance of 1 m away from the protected object.
Routing of earth electrode – see img. 7, 8, 9. In the course of grounding and potential equalization all conductive parts of the roof, for
instance the frames of the solar panels, sectional rails and trapezoidal metal sheets must be connected with the earth loop electrode.

 

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Img. 11: Three of a total of 10 lightning rods

3.1.2 Reduction of induction effects

A decrease of induction effects of direct and nearby lightning strikes is granted by a nonplanar wire arrangement. Shielding them with metal conduits decreases the magnetic effects as well. (see imgs 11a and 11b)

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Img. 11b: Circuit wires are laid in bundle to decrease induction area.


3.2 Indirect effects of lightning and internal lightning protection

Every strike of lightning produces indirect effects in the vicinity of about 1 km.
The probability of lightning striking a building indirectly is thus much higher than lightning striking directly. The term of ‘building’ refers to the technical room of the solar power system.
Indirect lightning strikes are primarily inductive, capacitive and galvanic couplings. These couplings produce surge voltages, which electrical installations in buildings should be protected from. The internal lightning protection describes all measures and utilities inside a building that deal with the protection of electronic equipment from indirect lightning strikes, as well as the effects of switching actions within the common power grid. Requirement for functionality is an uninterrupted potential equalization according to VDE 0100, part 540 / IEC 364-5-54. With this equalization all conductive systems (for example water-, heating- and gas pipes) are connected with the ground electrode.

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Img. 12: A primary potential equalization bar within the technical building. The earth loop electrode is connected
in the centre.

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Img. 13: Two more busbars connected with the primary potential equalization
3.2.1 Combined lightning current and surge arrester
One more method of protection against lightning strikes, a so called combined lightning
current and surge arrester was installed on the DC side of every inverter. It is important to
use a combined lightning current and surge arrester for every tracker – see img. 14.

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Img. 14: Example of combined current and surge arrester

4. Construction and implementing of solar power system

4.1 Construction of frames and installation of solar panels

Photo number 15 was captured during necessary groundwork

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4.2 Feed-in

Photos number 21 and 22 display the inside of the technical room shortly before initial
operation


Photo number 23 displays the voltage transformer cabinet necessary for feed-in

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Img 23: Inside view of voltage transformer cabinet

4.3 Completion and implementation
On December 22nd, 2010 the solar power system was completed and initialized by an
associate of E.ON-Bayern. At about 11:30 a.m. there was a fully operational feed-in. The
system is being monitored remotely.
All further outdoor work like paving the drive ways and parking lot as well as planting grassy
areas had to be postponed to next spring season due to a heavy onset of winter.

5. Technical data of carport solar power system:
Overall performance: 96.1 kWp
Gross photovoltaic area: 730 m²
Panel alignment: southwest (20°)
Panel inclination: 7°
Predicted, specific annual yield: 834 kWh/kWp (acc. PV-Sol)
Panel type: ANTARIS ASP 215 polycrystalline
Panel nominal power: 215 Wp
Amount of panels: 447 pcs

Amount of inverters: 9 pcs
– Danfoss TLX 15 k: 1 ea
– Danfoss TLX 12,5 k: 3 ea
– Danfoss TLX 10 k: 2 ea
– SMA SMC 9000 TL-10: 2 ea
– SMA SB 5000-20: 1 ea


6. Acknowledgment
We would like to express our thanks for technical assistance and relevant words of advice to:
– Fa. Ulltech AG, 63741 Aschaffenburg, Herrn Brehm
– Fa. Boxit, 63322 Rödermark, Herrn Rittinghaus
– Fa. GP Blitzschutz, 64850 Schaafheim, Herrn Pavlovic
Waldaschaff, February 8th, 2011
Eberhard Zentgraf
Qualified Electrical Engineer