c02 - Electrical design SE02-D1

Introduction

The BFIRST “SE02-D1” shading element is a BIPV construction and energy multifunctional element, formed by assembling “SE02 basic units” and specially designed to be installed, as a canopy, on the windows.

SE02-D1 basic unit

“SE02” basic unit consist of a single PV cells string encapsulated within a fibre-reinforced matrix. The mechanical joining of the basic units through a hinges system enables to set up a wide range of geometrical configurations adapting the PV modules to different shapes (flat, wedge, canopy, folding screen, etc.) in order to facilitate and extend the building integrated integration.
In the same way, the most suitable orientation of the modules might be achieved if the building orientation is not optimal.

Assembly procedure of SE02 basic units and electrical layout.

MODULE DATASHEET

 

SYSTEM PERFORMANCE ESTIMATIONS

ESTIMATION OF POWER PRODUCTION INPUTS
METEOROLOGICAL CONDITIONS
Annual global irradiation Orient E Orient SE Orient S Orient SW Orient W Unit
Demo-site: Pikermi, Greece 1662 kW/m2
Seville 1643 1887 1972 1872 1623 kW/m2
Bucharest 1238 1423 1493 1425 1243 kW/m2
Berlin 949 1080 1129 1078 943 kW/m2
Ambient temperature Demo-site Seville Bucharest Berlin Value 3 Unit 3
Average ambient temp (ºC) 7.4 18.7 11.0 9.0
 

PHOTOVOLTAIC SYSTEMS

EU climatic zone locations Descriptive value
Nominal power of PV field 11.97 kWp.
Nominal power of system 10 kWp.
Inclination of modules 31º.
No modules 126.
Inverter “Sunny Tripower 10000 TL” three-phase PV inverter by SMA.
Demo-system Descriptive value
Nominal power of PV field 0.284 kWp
Nominal power of system 0.250 kWp.
Inclination of modules 25º.
No modules 3.
Inverter “M250-60-240-S22/S23” PV micro-inverter by ENPHASE.
 

ESTIMATION OF POWER PRODUCTION RESULTS

YEARLY PHOTOVOLTAIC PRODUCTION
Production of BIPV system Orient E Orient SE Orient S Orient SW Orient W Unit
Demo-site: Pikermi, Greece 364 kWh
Seville 15394 17816 18560 17509 14978 kWh
Bucharest 11722 13622 14300 13549 11653 kWh
Berlin 8926 10291 10769 10211 8800 kWh
Production per BIPV unit Orient E Orient SE Orient S Orient SW Orient W Unit
Demo-site: Pikermi, Greece 121 kWh
Seville 122 141 147 139 119 kWh
Bucharest 93 108 113 108 92 kWh
Berlin 71 82 85 81 70 kWh
Specific production per area Orient E Orient SE Orient S Orient SW Orient W Unit
Demo-site: Pikermi, Greece 104 kWh/m2
Seville 105 121 126 119 102 kWh/m2
Bucharest 80 93 97 92 79 kWh/m2
Berlin 61 70 73 70 60 kWh/m2
Specific production per power Orient E Orient SE Orient S Orient SW Orient W Unit
Demo-site: Pikermi, Greece 1284 kWh/kWp
Seville 1293 1496 1559 1470 1258 kWh/kWp
Bucharest 984 1144 1201 1138 979 kWh/kWp
Berlin 750 864 904 858 739 kWh/kWp

 

DC ARRAY CONFIGURATION

The solar PV fields will be configured by connecting the BIPV modules in series-parallel arrays.
The number of modules connected in series forming a string, and the number of string connected in parallel forming the complete DC array must be decided in accordance with the DC input characteristics of the chosen inverter.
A minimum DC input voltage has to be reached and a maximum input current value not exceeded, under real operating conditions. In this regards, it is essential for the system design to apply the suitable corrections for temperature, based on the correspondent voltage and current temperature coefficients expressed in the module’s datasheet.

PV array configuration

On the other hand, it is advisable to oversizing between a 15-25% the nominal power of the PV array with respect to the nominal power of the inverter, in order to optimize the potential possibilities of the inverter, which performs at the maximum of its capacity at high operating power values.
The BIPV solar fields have to be installed according to the architectural and building requirements exposed in the related Mounting and Construction Design Guidelines and the Mounting and Construction Guidelines.
Special attention has to be paid about the positioning of modules in the building: orientation and inclination should be as optimal as possible to guarantee the maximum performance.
In the same way, possible shadows should be avoided in order to loss production and preserve the health of the modules.

 

POWER CONDITIONING SYTEMS

DC power coming from the PV field must be conditioned in order to enable the use of the generated energy. Depending of the final use of the electricity (AC or DC supplies) and the type of connection to the electric network or load (grid-connected or stand-alone systems) a specific power system must be chosen.

Grid-connected systems

For grid-connected systems, the more common ones, a power system based on inverters, which convert direct current (DC) to alternating current (AC), is required. The type, size, efficiency and operational condition of the inverters should be chosen according to the size and characteristics of the PV field and the grid-connection requirements. All these factors will have a great influence in the system performance.

Inverters should include one or several maximum power point tracker systems, which make possible the adoption of the operating voltage which maximizes the power generation. If modules are located in the building with different operating conditions (orientation, inclination and shading) between them, a distributed power managing based on the use of micro-inverters with individualized MPPT systems is highly advisable. Otherwise, if these modules were connected to the same MPPT the system would see drastically reduced its performance. The use of DC micro-converters, with individualized MPPT, together with a suitable central inverter is other option, regarding the available solutions with distributed power architecture.

On the other hand: for small sized PV systems inverters (or micro-inverters) can be connected to the low voltage panel of the building (single phase connection). In case of large systems, power should be distributed between the electrical network phases (three phase connection); this could be done by using a single inverter per phase or a three phase inverter.

For all above mentioned cases local standards and regulations have to be considered, overall in grid-connection matters, which might reduce the set of products available to carry out the power conditioning of a BIPV system.

Stand-alone systems

For stand-alone (or of-grid-connected) systems with a demand load working with AC, the criteria explained in the last point are also valid. For stand-alone systems with a demand load working with DC, a DC/DC converter use to be needed to adapt the PV field voltage to the load voltage. In both cases, battery systems and auxiliary fuel equipment are commonly included.

Single phase layout example

 

SE02-D1 DEMO-SYSTEM

The electrical connection strategy of the BFIRST demo-system in Pikermi (Greece) has been decided according to the recommendations provided in this guideline. The electrical design of the Greek demo-system also includes prototypes of BIPV ventilated façade and shading elements for balconies: VF01 and SE02-D2, respectively.

Micro-inverters distribution at grid phases

Layout and equipment

The Greek demo-system based on SE02-D1 modules is formed by 3 modules, on the windows, connected in series and managed by a single “Sunny Boy 240-10” micro-inverter with MPPT. Because the basic units lack a diode, the interposition of a diode box between adjacent modules is needed. The micro-inverter is connected to one of the phases of the low-voltage panel located in the building.

The “Sunny multigate” data collector enables the control of the system in real time.

“Sunny Boy 240-10” micro-inverter and “Sunny multigate” data collector

Connection diagram

 

ELECTRICAL INSTALLATION AND MONITORING SYSTEM

SE02-D1 BIPV modules have plug and play connectors, which provides a secure, durable and effective electrical contact and increase the safety and simplicity of the connections during the installation works.

DC cabling transmit power from the PV field to the inverters (or micro-inverters) and AC cabling from the inverters to the grid. Both of them can be totally or partially exposed to the environment; so, they must be resistant to heat, rain, hail, ozone and UV solar light, among others. The design of the cabling layout should reduce, as much as possible, the losses associated to the internal resistance, which depends on cable length and cross-section, without incurring excessive costs.

String boxes for installing string connections and protections could be needed for large systems. Cables connecting in series the modules within a single string and cables connecting different strings in parallel give the suitable values of current and voltage required as input for the central inverters. If the system has a distributed architecture, cables coming from the micro-inverters transmit power to a bus cable, which sends the current directly to the grid connection.

String fuses or blocking diodes should be used for large PV fields, in accordance to the requirements included in the local or national regulation for electrical installations.

Switches should be also installed in order to guaranty the possibility of manually electrically isolating the PV strings or array, during the system installation, maintenance and reparation works.