c01 - Electrical design RS02

Introduction

The BFIRST “RS02” roofing shingle module is a BIPV construction and energy multifunctional element, whose design allows an easy and quick installation based on a plug & play system. RS02 is a roofing unit of fibre-reinforced composite with photovoltaic cells encapsulated and an appearance similar to slate shingles. It also might be used as façade unit.

The design allows an easy and quick setting-up in the roof. It contributes to reduce the thermal load of the building and the power consumption thanks to the electrical generation capability. The sloping surface of the roof optimises the power production of the PV cells. The system permit to reserve an air chamber under the roofing shingles, where can flow the air through to dissipate the extra heat generated by the PV cells and to increase besides the PV performance. The overlapping of the units and the use of intermediate gutters reduce significantly the entrance of rain water.

RS basic unit

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
Belgium (Demo site) 1079 kW/m2
Seville 1577 1856 1950 1842 1553 kW/m2
Bucharest 1190 1402 1482 1407 1195 kW/m2
Berlin 918 1069 1125 1066 911 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 11.52 kWp.
Nominal power of system 10 kWp.
Inclination of modules 40º.
No modules 80.
Inverter “Sunny Tripower 10000 TL” three-phase PV inverter by SMA.
Demo-system Descriptive value
Nominal power of PV field 8.21 kWp
Nominal power of system 6.00 kWp.
Inclination of modules 40º.
No modules 57.
Inverter 2 x “Sunny Boy SB 3300 TL HC” inverters by SMA.
 

ESTIMATION OF POWER PRODUCTION RESULTS

YEARLY PHOTOVOLTAIC PRODUCTION
Production of BIPV system Orient E Orient SE Orient S Orient SW Orient W Unit
Belgium (Demo site) 6934 kWh
Seville 14365 17032 17866 16712 13884 kWh
Bucharest 10941 13049 13803 12999 10860 kWh
Berlin 8371 9896 10435 9813 8231 kWh
Production per BIPV unit Orient E Orient SE Orient S Orient SW Orient W Unit
Belgium (Demo site) 122 kWh
Seville 180 213 223 209 174 kWh
Bucharest 137 163 173 162 136 kWh
Berlin 105 124 130 123 103 kWh
Specific production per area Orient E Orient SE Orient S Orient SW Orient W Unit
Belgium (Demo site) 96 kWh/m2
Seville 142 169 177 165 137 kWh/m2
Bucharest 108 129 137 129 108 kWh/m2
Berlin 83 98 103 97 81 kWh/m2
Specific production per power Orient E Orient SE Orient S Orient SW Orient W Unit
Belgium (Demo site) 845 kWh/kWp
Seville 1247 1478 1551 1451 1205 kWh/kWp
Bucharest 950 1133 1198 1128 943 kWh/kWp
Berlin 727 859 906 852 714 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 system
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

RS02-system integrated in the Belgium demo building.
The electrical connection strategy of the BFIRST demo-system in Mons (Belgium) has been decided according to the recommendations provided in this guideline.
Layout and equipment
The Belgian residential house is connected to the electric grid by means of a three-phases 230 V connection of 12.7 KVA (30 A). The solar field is formed by 57 RS02 modules, distributed in 2 strings of modules connected in series. The “STP 7000TL-20” inverter has 2 power inputs, each one with its own MPPT system, which control the operating voltage of each string. The system performance is controlled by the “RS” monitored system.

Power connection diagram 

“STP 7000TL-20” inverter and “RS” system monitoring

BIPV connection diagram

Electrical Installation and monitoring system
RS02 BIPV modules include 1 diode incorporated, within the connection box, in order to cancel out part of the module if some cell brakes or a persistent punctual shadow damages some cell because the hot-spot heating effect. RS02 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.