c04 - Electrical design SL02


The BFIRST “SL02” skylight module is a BIPV construction and energy multifunctional element, designed for generating electricity and partially enabling the passage of natural light.
SL02 is a skylight unit of fibre-reinforced composite with photovoltaic cells encapsulated. It also might be used as façade unit. SL02 module can be installed together with a closed conventional double glass skylight. The outside PV skylight would be a fixed structure, with the modules orientated with the optimal inclination. It would provide electricity and shading.

Real prototype of “SL02” skylight module

SL02 skylight module and building integrating procedure





Annual global irradiation Orient E Orient SE Orient S Orient SW Orient W Unit
Demo-site: Zamudio, Spain 1975  – kW/m2
Seville 1691 1887 1960 1877 1674 kW/m2
Bucharest 1274 1422 14780 1424 1277 kW/m2
Berlin 972 1077 1117 1075 968 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


EU climatic zone locations Descriptive value
Nominal power of PV field 12.94 kWp.
Nominal power of system 10 kWp.
Inclination of modules 23º.
No. modules 152.
Inverter “Sunny Tripower 10000 TL” three-phase PV inverter by SMA.
Demo-site: Zamudio, Spain Descriptive value
Nominal power of PV field 1.53 kWp.
Nominal power of system 1.30 kWp.
Inclination of modules 23º.
No modules 18.
Inverter “IG 15 (outdoor)” by FRONIUS INTERNATIONAL.


Production of BIPV system Orient E Orient SE Orient S Orient SW Orient W Unit
Demo-site: Zamudio, Spain 2238 kWh
Seville 16903 18948 19621 18682 16502 kWh
Bucharest 12911 14532 15125 14469 12834 kWh
Berlin 9800 10969 11389 10900 9689 kWh
Production per BIPV unit Orient E Orient SE Orient S Orient SW Orient W Unit
Demo-site: Zamudio, Spain 124 kWh
Seville 111 125 129 123 109 kWh
Bucharest 85 96 100 95 84 kWh
Berlin 64 72 75 72 64 kWh
Specific production per area Orient E Orient SE Orient S Orient SW Orient W Unit
Demo-site: Zamudio, Spain 67 kWh/m2
Seville 60 67 69 66 58 kWh/m2
Bucharest 46 51 53 51 45 kWh/m2
Berlin 35 39 40 38 34 kWh/m2
Specific production per power Orient E Orient SE Orient S Orient SW Orient W Unit
Demo-site: Zamudio, Spain 1461 kWh/kWp
Seville 1307 1465 1517 1444 1276 kWh/kWp
Bucharest 998 1123 1169 1119 992 kWh/kWp
Berlin 758 848 880 843 749 kWh/kWp



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.


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


SL02 demo-system building integrated in Spain

The electrical connection strategy of the BFIRST demo-system in Zamudio (Spain) has been decided according to the recommendations provided in this guideline.

Layout and equipment

The “SL02” system of the Spanish demo is formed by 18 series connected modules. The working conditions for all the modules are similar; thus, no mismatching losses are foreseen. The total installed power is 1602 Wp.
It has been used one 3kW inverter “Ingecon Sun 3TL-M”, by INGETEAM, with to power inputs and MPPT systems. The skylight system is connected to one of this inputs, the other one is used by the VF-AL system, also installed in the Spanish demo-building.

PV solar fields of the BIPV systems (SL02 & VF-AL) in the Spanish demo

“Ingecon Sun 3TL-M” inverter, by INGETEAM

Single-line diagram of the Spanish BIPV demo-systems



SL02 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.
SL02 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.