Combined performance gain +8,6%

Starting from the same PERC cell, a benefit of up to 8.6% in kWh/m2 can yearly be expected from all Energyra modules.

This higher module efficiency is enabled by the back contact interconnection system:

• The ability to use full cells (rather than half-cells) while still achieving a high module power
• An optimized low-irradiance performance
• A lower NOCT, due to the increased heat spreading in the conductive backsheet.

Therefore, using a CBS in solar modules enables an improved energy yield,

improved module aesthetics, and improved long-term durability due to reduced thermo-mechanical stresses.

Backcontact combined performance gain: 

•   + 8.6% (STC Lisbon, kWh/m2)
•   + 9.4% (STC Amsterdam, kWh/m2)
  

Increase of Power Density: +5.6%

The comparison considers PERC cells that went through the same manufacturing process, with 2 distinctions:

• Cells for the MBB and CBS module have an efficiency gain of over the 5BB module, due to the reduced front metallization and reduced resistive losses
  
• 5BB/MBB modules are built with M6 format cells (166.0x166.0mm) and CBS modules with a G1 cell (158.75x158.75mm), due to the availability of MWT cells at the time of this research.

Additional gain of up to 8% for CBS is nowadays very relevant, due to the improved availability of larger cell formats such, as M4 and M6 in the daily operation of Energyra

Increased Yield (STC, Amsterdam): +2.5%

The use of half-cells is becoming more common in the PV module industry. After all, reducing resistive losses in increases nameplate power at STC.

Due to the reduced cell current, half-cell modules generally have a lower series resistance than full-cell modules. This improves module peak power, but clearly reduces low-irradiance performance.

CBS modules enable a high module power by using full cells. Furthermore, CBS optimizes low-light performance by tailoring series resistance in the design.

The effect of the low-irradiance behavior on energy yield has been estimated using PVSyst. The table below shows two simulated annual yields (in kWh/kWp):

• Lisbon:          GHI =1758 kWh/m2/year, ~ 35% diffuse
• Amsterdam: GHI =  965 kWh/m2/year, ~ 58% diffuse

Better heat distribution: yield + 3.5%

A module’s power and energy yield is a result of its operating temperature and temperature coefficient, driven by cell technology. The NOCT (Nominal Operating Cell Temperature) for CBS modules was found to be 5-7ºC (41-44.6°F) lower than for conventional modules, resulting in 3.5% yield increase. 

The NOCT is a fine predictor for the operating cell temperature. This is measured at 800W/m2 irradiance, an air temperature of 20°C (68°F), and a wind speed of 1m/s with open backside mounting.

The module power can be expressed as a function of temperature:

𝑃(T)=𝑃(25°C) +𝑐𝑇(𝑇−25°C). In traditional modules, heat is primarily dissipated from the rear of the cells. In a CBS module, the presence of the conductive sheet increases heat spreading.

In section 2, this effect had not yet been included in the simulations (an NOCT of 47°C was assumed for all module). Including the reduced NOCT, see the graph.

In our factory near Amsterdam we assemble solar panels with an extremely high degree of automation (Industry 4.0) and AOC/AI (Auto Optical Inspection/ Artificial Intelligence) control. As a result, our back contact modules are assembled more accurately and continuously monitored for quality.

• Fully-robotized
• AOC/AI vision technology
• HD camera inspection
• Traceability
• Extensive in-house QA lab