The BFIRST “VF01”ventilated façade module is a BIPV construction and energy multifunctional element, whose design allows an easy and quick installation based on a hanger system.
VF01 contributes to reduce the power consumption of buildings through its PV power generation capability. Passive thermal features are also available, thanks to the air flowing behind the module promoted by its special shape. This property also increases the efficiency of the PV modules, due to the reduction of the operating temperature of the cells.
VF01 module is made up of the connection of 60 mono-crystalline PV cells in series, embedded in a fibre-reinforced matrix of glass-fibre and resin. Main electrical parameters are gather in the table below, additional data are exposed throughout this Electrical Design Guideline.
SYSTEM PERFOMANCE ESTIMATIONS
|ESTIMATION OF POWER PRODUCTION INPUTS|
|Annual global irradiation||Orient E||Orient SE||Orient S||Orient SW||Orient W||Unit|
|Demo-site: Pikermi, Greece||–||1065||–||–||–||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||11.88 kWp.|
|Nominal power of system||10 kWp.|
|Inclination of modules||90º.|
|Inverter||“Sunny Tripower 10000 TL” three-phase PV inverter by SMA.|
|Nominal power of PV field||2.16 kWp|
|Nominal power of system||1.95 kWp.|
|Inclination of modules||90º.|
|Inverter||“Sunny Boy SB 2100TL” mono-phase PV inverter 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|
|Demo-site: Pikermi, Greece||–||1642||–||–||–||kWh|
|Production per BIPV unit||Orient E||Orient SE||Orient S||Orient SW||Orient W||Unit|
|Demo-site: Pikermi, Greece||–||205||–||–||–||kWh|
|Specific production per area||Orient E||Orient SE||Orient S||Orient SW||Orient W||Unit|
|Demo-site: Pikermi, Greece||–||103||–||–||–||kWh/m2|
|Specific production/ power||Orient E||Orient SE||Orient S||Orient SW||Orient W||Unit|
|Demo-site: Pikermi, Greece||–||760||–||–||–||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.
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.
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
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 shading elements for window and balconies: SE02-D1 and SE02-D2, respectively.
Micro-inverters distribution at grid phases
Layout and equipment
The Greek demo-system based on VF01 modules is formed by 9 modules managed by a “Sunny Boy 240-10” micro-inverter with MPPT per module. Micro-inverters are connected in parallel. Power is transferred to a three-phase grid connection.
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
BIPV connection diagram
Electrical installation and monitoring system
VF01 BIPV modules include 2 diodes 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.
VF01 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.