MANUFACTURINGOUTLOOK
that has to deal with positive as well as negative balances. During peak production, energy storage allows to keep the energy conversion at maximum level and store the output difference for later recovery.
Control and monitoring Accordingly, we will move to smarter control strategies and alternative power electronics topologies that dynamically optimize the yearly production of the smart modules. We foresee the increased use of monitors (such as distributed temperature sensing) as well as real-time controllable parameters (such as the conversion factor of the dc-dc converters). They will allow the plant-level controller to optimize the energy yield, and their use will benefit the lifetime and reduce the maintenance costs of the PV plant. From a technological point of view, this implies that additional power electronic circuits and sensors need to be placed in and around the module.
An embedding technology The question rises where all this additional functionality at module level will be located: in the junction? Or embedded in the module? The latter approach may be necessary for components such as sensors or cell-level active bypass diodes. This will then require an appropriate technology that allows embedding the different components into the modules.
At the same time, we should take into account the evolutions that are taking place in cell manufacturing and module integration processes. Roadmaps for Si PV predict a steady decrease in thickness, eventually down to very thin (40µm) wafers, in order to reach the ultimate cost potential of the Si solar cell. This has some important consequences, such as an enhanced risk for wafer breakage and the need for virtually stress-free processes. This evolution will be accompanied by a transition from the traditional two-sided
contacted cells to back-contacted cells and modules.
Back-contacted cells are also very attractive for integration into buildings, as they have visually disturbing contacts brought fully to the rear, increasing a lot their aesthetic value. We therefore expect a gradual evolution from standard c-Si PV manufacturing to the fabrication of advanced back- contacted cells together with new methods to integrate cells and additional components in the PV modules.
In this context, imec has come up with the i- module (or interconnect-module) approach that allows integrating and interconnecting thin back- contacted solar cells into modules [10]. First experiments have resulted in functional modules with small-area (2x2cm2) 120µm thin back- contacted cells, and preliminary outdoor tests are promising. The technology has the potential to result in modules with a lower production cost, higher peak power, better energy yield and longer lifetime, and is inherently lead-free. The potential advantages, as compared to the conventional approach as used in e.g. the SunPower modules [11], and the ECN approach [12], are summarized in Table 1.
Figure 3: In the smart PV concept, the PV module will offer more features and
functionalities. More components and intelligence will be integrated in and around the module
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Table 1: Benchmarking of the i-module technology to competitive
approaches for BC solar cells
www.solar-pv-management.com Issue IV 2011
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