office (+352) 88 81 12-1  
fax (+352) 88 91 83         
E-mail info@erg.lu  

 

Where to install? Yield? Technologies?

In order to generate a good yield, the foreseen surface should be

  • well exposed to the sun: Best yields for facing south, losses of about 5% for an orientation south-west or south-east. An orientation towards east or west is also possible, but with reduced yield by 15 to 20%. The inclination of the modules influence further the yield. Best exposure occurs when the rays of the sun fall vertically on the module. For a operation over the entire year, an inclination of about 30 degrees is optimal in Luxembourg

  • and not shadded by trees, buildings, chimneys, pylons, etc. These shadows are increased or reduced due to the different altitude of the sun over the day and over the year. Best is to avoid the areas with shadow.

(A design software with shadow simulation may give a good assistance).

The photovoltaic system may be built on

  • single- or multi-family houses, annexed garages or car ports

  • office, industrial, public and agricultural buildings or shopping centers

  • a free surface on the ground (Attention: No financial state support)

The photovoltaic modules may be

  • installed parallel to the roof (common installation). A distance is required between the module and the roof surface depending on the type of module in order to allow a natural ventilation (yield depends on the temperature). The modules are available with a rigid frame - requiring support rails for mounting - or in flexible stripes that can be glued directly to the roof surface

  • integrated in the roof in order to benefit from electrical production in addition to the insulation (for new buildings or roof renovations)

  • installed on or in a façade, but with less yield (30 to 50% depending of the orientation)

  • installed on a support on flat roofs or roofs with low slope for better module alignment and inclination

  • installed on a one-or two-axis sun tracker with best results in yield (+30%), but requiring a regularly maintenance

The yield of the installation depends on several factors: Geographical location, orientation and inclination, behaviour of modules with low sunlight, operating and ambient temperature, temporal degradation, shadowing, cabling and inverter efficiency.

But clouds mainly act as a filter and influence the direct insolation:

      

nearly cloudless sky                    partially cloudy                         cloudy  

Direct insolation: 80-100%                30-80%                                      0-30%

The installation even produces under indirect sunlight (through diffuse and reflected light), but without significative yield!

Module technologies

According to the cell manufacturing process, the module technology may be

  • monocrystalline: Module yield 14-16%; uniform optical surface; little roof area required; needs enough distance to the roof for good natural ventilation (yield loss at higher ambient temperatures in the summer); manufacturing process very energy-consuming

                 for small roofs, high prices

  • polycrystalline: Module yield 12-14%; characteristic blue glittering apperance- similar to ice crystals; require larger roof area and also a certain distance to the roof (ventilation); manufacturing less energy-consuming

average module prices

  • amorphous (Thin-film): Lowest module yield 8-10%; requires much more roof surface compared to crystalline modules; less susceptible to shading, wind and temperature; better utilization of indirect light; modules can be mounted on the roof (without ventilation distance) or even glued as laminates; manufacuting process very cheap due to less use of material

        Ideal for big roof surfaces with unfavourable orientation and inclination

  • hybrid (combination of the advantages of crystalline and amorphous technology): Higest module yields up to 18%; least roof surface required; not so vulnerable against temperature compared to crystalline modules

Ideal to get maximum yield on small surfaces with good orientation and inclination; most expensive modules

The most common modules on the market (95%) are made of crystalline and amorphous silicon; there are also meanwhile thin-film technologies available based on copper indium gallium diselenide (GIGS), copper indium disulfide (CIS) and cadmium telluride (CdTe). Gallium arsenide applications are still limited to space travel due to high production costs, despite of highest levels of efficiency.

There are also transclucent modules available that combine power generation with ideal sun protection:

  Source: PVT Austria

Attention

  1. An investment in a photovoltaic installation is made for a long return period. The foreseen roof surface should be in good condition to ensure not only the weight of the installation but also to avoid additional waste and construction costs if a roof renovation is later due. Furthermore, a scaffolding may represent additional costs as it is required during installation for safety reasons. These costs may be reduced if the photovoltaic installation is combined with other construction works (new construction, new façade, installation of a solar thermal system,...)

  2. It should be ensured already at the planning stage that no growing trees or adjacent land for future construction will create a shadow in the future. Better to clarify this with the neighbor or the competent authority in advance.

 

The visit of a representative of Reiter&Grethen and a free offer may give you further information for the best -to your situation adapted- installation.