Polar Bear Applying TRIZ Methodology for PV Module Development

Size: px

Start display at page:

Download "Polar Bear Applying TRIZ Methodology for PV Module Development"

Jocelin Daniel
5 years ago
Views:

Polar Bear Applying TRIZ Methodology for PV Module Development Oliver Mayer, Marcus Zettl GE Global Research, Freisinger Landstraße 50, 85748 Garching, Germany Tel: +49-89-5528-3412, oliver.

General / Motivation Germany is the worldwide leader in photovoltaic installation.

1 Polar Bear Applying TRIZ Methodology for PV Module Development Oliver Mayer, Marcus Zettl GE Global Research, Freisinger Landstraße 50, Garching, Germany Tel: , Key words: Photovoltaic, solar energy, 3D shape PV, low concentrator, free shape PV, TRIZ, Six Sigma 1. General / Motivation Germany is the worldwide leader in photovoltaic installation. Until GW (Rated power) are operational and connected to the electric grid (in comparison: 1 nuclear power plant block has a rated power of ~ 1 GW). Looking at PV modules they look the same way since 2 decades (Fig. 1): - Flat plate - Either a blue or dark gray/black surface - Aluminum frame Fig. 1: left crystalline PV module, right thin-film CIGS module (source: web) 2. Root Cause of disatisfaction Analyzing the current installations of PV in NEW CONSTRUCTED BUILDINGS it can be found that PV systems are usually not planned and taken into consideration by architects. Looking at the amount of new constructed building and the upgrading with PV right after the building was realized, marketing raised the question: Why isn t PV taken into consideration by architects already during planning and construction? We ran SixSigma tools like Voice of Customer (VoC) and Prioritisation to identify the root cause for the non application of PV by architects. The major reason was found to be: Architects want 3D building elements with flexible size and shape. This lead to the decision to look for a novel solution. As method of choice TRIZ shall be applied. 3. Ideal System and DFR Starting from the ideal system, we were looking for a possibility to turn photon (the relevant external source of energy) into material bound valence-electrons (electric current as we like to have it). Photons have energy but are lacking mass; electrons carry a charge and have mass. The only physical effect that might be able to convert the mass problem is, according to the quantum 1

2 theory, the Higgs-boson, which unfortunately has only been postulated theoretically today and maybe was confirmed by CERN in Therefore we looked into the desirable final result (DFR) that was defined, according to the marketing, sales, research, design, time and customer requirements as follows: - Develop (request to research) a novel module - with the size of ~ 1m x 0,6 m (size requirement from sales), - that converts light into electrons with the help of crystalline c-si cells (material requirement from marketing), - that can be formed in 3D (shape requirement from sales) and - that can be used as façade element as well (multi-functionality requirement from customer) 4. 9-Windows Analysis We started with the 9-windows analysis according to Tab. 1. SuperSys. Individual hooks Frame clamping Past Today Future Mounting structures (alu / wood) Wires Velcro Sail glued Flexible structure System PMMA/glass encapsulation Glue as sealing Sandwich structure Combines light guiding & power conversion EVA for embedding Glass-glass or glass-tedlar for protection Alu-frame or frameless for stability Sandwich structure Combines light guiding & power conversion Embedded module Separated light guiding & power conversion SubSy s. Thick mono c-si cell Thin mono/poly c-si/a-si cell, 3D cell CdTe, CIGS cell OPV cell Tab. 1: 9-windows analysis We concentrated on the two aspects of generating an embedded module and on the separation of light guidance & power conversion. Today s structure of a PV module is a sandwich construction as shown in Fig. 2. The cells are embedded in an EVA foil on the front and on the back side. The EVA compensates the different temperature expansion coefficients of the cell & the glass / Tedlar encapsulation and fixes the cell between the glass and Tedlar foil (or another glass plate). The glass / Tedlar foil protects the EVA / cells against environmental impact like dirt, moisture, etc. On the edges a sealing mass is applied that is connecting the sandwich with the aluminum frame. The module is constructed in a way that the light (photons) are passing the glass and transparent EVA, hitting the PV cell and then being right away converted into electricity (electrons). The route the photons are travelling is not influenced. 2

Fig. 2: Sandwich structure of a PV module (source: DGS) 5. Trend Analysis When looking at the PV modules we found that they are all constructed in a 2D manner: flat and uncolored.

cell surface) and can we reduce the material needed to make a PV cell? For the second question we looked at the market and found thin-film modules to be developed by multiple companies.

3 Fig. 2: Sandwich structure of a PV module (source: DGS) 5. Trend Analysis When looking at the PV modules we found that they are all constructed in a 2D manner: flat and uncolored. As the irradiance per m² is a fixed value and the material needed for power conversion is rare, two questions arose: Can we guide (concentrate) the light in an improved way to the cell (reduction of cell surface) and can we reduce the material needed to make a PV cell? For the second question we looked at the market and found thin-film modules to be developed by multiple companies. This is a trend from 3D 2D (Fig. 3). The question on what could be a 1D or even 0D solution was found in quantum wires and quantum dots (yet under research at universities). For that reason we didn t follow the development of cells. Fig. 3: Trend 3D 2D for cell material (source: DGS) For the module itself as a 2D item the natural development was to go for a 3D shape as desired by the architects as well. 6. Functional Analysis For the existing module a functional analysis was made (Fig. 4). The irradiance sends photons to the module. The frame absorbs the photons and turns them into heat (self-heating). The glass of the module partly reflects the photons to the environment in a scattering way (~5%), partly absorbs and turns them into heat (self-heating ~ 2%) and mainly transmits the light to the next layer (EVA). The main function of the glass is to stop environmental impact to the next layers 3

4 (moisture, dirt, dust, etc.) but at the same time to let pass irradiance the best way possible. The EVA has to join the glass and the PV cells in a dynamic way so that the different thermal expansion coefficients are compensated. Furthermore the cells and the glass cover / Tedlar back sheet are fixed to each other. As the EVA is not 100% transparent as well part of the photons are absorbed and turned into heat. As the PV cells are hotter than the EVA the heat dissipation is moving to the glass. The PV cells convert the photons to electrons and move them to the junction box, where cables transport the electric current. Due to the PV cell technology (which is not part of this consideration) ~ 85% of the photon energy is turned into heat. This heat dissipates thru to EVA to the front glass or to the Tedlar back sheet to the environment. The frame holds the glass and Tedlar foil and thus gives stability to the module. The photons hitting the frame are converted to heat and dissipated to the environment. In this setup the conversion system and the light trapping are geometrically connected. There is no degree of freedom between both. Light transportation cannot be influenced. Irradiance Absorbs irradiance -> heat Frame Sends photons Holds Sends photons Impacts Glass Absorbs irradiance -> heat Reflects irradiance Transmits Photons Stops environment (moisture, dust, etc.) Fixes & thermal expansion compensation Environment EVA Absorbs irradiance -> heat Transmits Photons Fixes & thermal expansion compensation Absorbs irradiance -> heat Cells Generates electricity Junctionbox Holds Impacts Fixes & thermal expansion compensation EVA Stops environment (moisture, dust, etc.) Fixes & thermal expansion compensation Holds Tedlar Fig. 4: Functional breakdown of a current PV module 4

5 7. Contradictions In order to meet the desired result under Tab. 1 we would need to shape the glass in a 3D way and the PV cells as well (EVA and Tedlar as foils are flexible anyway). Via forms glass can be put into any forms (see e.g. drinking glasses). For cells the following contradiction appears: If the cell is made thinner Then it can be bended But the cells get much more brittle and break easier due to thermal and mechanical impact If the cell is made thicker Then it is strong and stable against thermal and mechanical impact But the cells cannot be bended This contradiction translates into the following generic parameters: Improve: shape of the object Not worsening: stability of the object; reliability of the object Using Altshuller s 40 Principles we get the following suggestion / thinking triggers: Preliminary action Spheroidality Curvature Partial or excessive action Flexible shells and thin films Composite materials These 5 triggers have been used to generate ideas on how to get to a 3D shaped module. Preliminary action Can the light guiding and photon conversion be separated in space? First guide the light and then in a second step convert it? Who else needs to guide light -> laser, endoscopes, light manufacturers, telecommunication with light fibers, traffic signs, light detectors in physical experiments Spheroidality Curvature The goal is a 3D shape. Partial or excessive action Thinking of partial or excessive action, concentration of irradiance was suggested as idea. In fact CPV (Concentrated PV) with ratios of up to 1:2000 are realized already today. The idea is to use cheaper reflective or refractive mirrors to redirect and concentrate the irradiance on a smaller area of expensive cell material. By this cost shall be driven down. Flexible shells and thin films The idea or sputtering thin film PV, e.g. CdTe or CIGS onto a 3D shaped glass was already evaluated but is out of scope for business reasons (see desired final result9. This would be an option to follow if that restriction was not given. Composite materials Upon this trigger ideas like combining different semiconductor material or combination of materials for light guidance came to our minds. 5

8. Conceptual Design By going thru the different ideas we found that in security system often technologies are used to spread out light from a single source into all spherical directions.

5: left: Fluorescence sheets with different dyes.

5): Organic molecules (dyes) are distributed in a matrix (e.g. polycarbonate or PMMA). Sun irradiance is absorbed by the dye and reemitted spherically with a red shift.

On the edges PV cells are attached. Here the light is converted into electricity. Looking in nature for a similar principle we found that polar bear are using light guidance as well.

6 8. Conceptual Design By going thru the different ideas we found that in security system often technologies are used to spread out light from a single source into all spherical directions. As physics of light define that the path is reversible we decided to use this for collecting light from all directions and direct it to one direction: a fluorescence collector (Fig. 5). Fig. 5: left: Fluorescence sheets with different dyes. Right: Working principle of a fluorescence collector with dye and solar cells (source: FhG-ISE) The working principle of a fluorescence collector is as follows (Fig. 5): Organic molecules (dyes) are distributed in a matrix (e.g. polycarbonate or PMMA). Sun irradiance is absorbed by the dye and reemitted spherically with a red shift. The color of the transported and concentrated light depends on the dye type (Fig. 5 left side). By this part of the light is kept within the matrix by total internal reflexion and guided to the edges. On the edges PV cells are attached. Here the light is converted into electricity. Looking in nature for a similar principle we found that polar bear are using light guidance as well. They have a black skin, covered with a white, light guiding fur. By this light is guided to the skin and converted into heat as it is black. For this similar technology we called our project Polar Bear. Fig. 6: Fluorescence collector left: drawing in SolidWoks, right: Collector on the test field at GRC Munich (source: private) With this application we have combined the different principle suggested by Altshuller s matrix. We concentrate the light and guide it then to the PV cell (preliminary action), we can bring the 6

plastic into nearly any curvature (spheroidality curvature), we concentrate the irradiance by a factor of ~ 4 (partial or excessive action) and we combined plastics with active dyes (composite

7 plastic into nearly any curvature (spheroidality curvature), we concentrate the irradiance by a factor of ~ 4 (partial or excessive action) and we combined plastics with active dyes (composite materials). Fig. 6 shows the CAD layout of the module and its demo realization in real. It was patented under US Patent US in Optimization of Polar Bear As the demo system was operational, the next step was the optimization of the system. For this purpose we used the TRIZ tool: flow analysis. We looked at the energy flow thru the system in order to find out where the maximum losses occur and where then to start improvement. Fig. 7 shows the graphical representation of the energy flow analysis: Incident light = 100%; transmission = 95%, therefore 100% * 95% = 95 is the entered light. 95% entered light; absorption rate by dye = 35%, therefore 95% * 35% = 33% is the emitted light by the dye. 33% emitted light; transportation efficiency in the plastics = 30%, therefore 33% * 30% = 10% is the collected light at the edge. 10% light at the edge; transmission to PV cell = 95%, therefore 10% * 95% = 9,5% light at the cell. 9.5% light at the cell, conversion efficiency of the PV cell = 35%, therefore 9.5% * 35% = 3.5% electric output of PV cell. The energy flow chart (Fig. 7) shows that losses due to not absorbed irradiance by the dyes, transport losses within the material and PV cell losses are the main drivers for low efficiency. Fig. 7: Flow analysis of Polar Bear In Table 2 we depicted the flows and allocated their types (FluCo = Polar Bear fluorescence collector: Polycarbonate plate with organic dyes, collecting the light and guiding it towards the edges by means of TIR Total Internal Reflexion): 7

The light is collected. This is a productive function, we want this. 95% of the light is collected. 5% of the total light is reflected. This is a harmful function, we don t want this.

8 The light is collected. This is a productive function, we want this. 95% of the light is collected. 5% of the total light is reflected. This is a harmful function, we don t want this. The light is transported internally: 70% is absorbed and thus harmful, 30% reach the edge. There is no value added to the light. It doesn t change its quality. It is just moved supportive function: transportation. The absorption however is harmful. At the edge mirrors are located: They reflect 98% of the light 2% is lost. The reflexion is again supportive (no change in characteristics of the light), the absorption is harmful. Mounting of the cell to the FluCo: The light transmission is 90%, rest is absorption losses (5%). Due to place this is not represented in the table. The light transmission is again supportive. As we need to connect the PV cell to the FluCo the gluing is productive, we need that. The PV cell is handled in this analysis on a high level as it is not object of consideration (see DFR). Tab. 2: Polar Bear Flow analysis The flow analysis tool resembles to the CTQ flow down in the SixSigma approach, the classification into useful, harmful, supportive, etc. functions however is new. Based on the two flows we decided to concentrate on the improvement of the light transportation / reduction of light absorption in the plastic. Going back to the 40 principles, where one of them was Composite Materials we looked for combining different types of dyes into the Polycarbonate Matrix. This showed improvement, but lead as well to novel challenges like material clustering. To solve these problem solid engineering work has to be done. 10. Conclusions This paper reports on a project starting from customer requirements down to a technical solution. A mixture of SixSigma and TRIZ tools like Voice of Customer, Ideal Desired Result, 9- Windows Method, Trends Analysis, Flow Analysis, Functional Analysis, Conceptual Design and Optimization have been used according to the project state. TRIZ showed to be a focused method for solution generation. The combination of TRIZ with the Six Sigma approach coming from quality, engineering or marketing is a powerful way to design a novel, innovative product. 8

9 11. Bibliography Mayer O., Zettl M., Stern O., Bittmann E.: "Solarzellenverkapselung für Polycarbonatmodule", 23. Symposium Photovoltaische Solarenergie, OTTI, Staffelstein Mayer O., Zettl M., Stromberger J., Stern O., Becker G., Hurst J., Hoeks T.: "Solare Niederkonzentratoren aus Polykarbonat", 21. Symposium Photovoltaische Solarenergie, OTTI, Staffelstein Mayer O.: "Installation Concept and Future Applications", High-Efficient Low-Cost Photovoltaics, Springer Verlag, Series in Optical Sciences 140, Hrsg.: Petrova-Koch, Hezel, Goetzberger; ISBN ,

Laser Applications for Photovoltaics Crystalline and Thin Film Technologies

LASERS & MATERIAL PROCESSING I OPTICAL SYSTEMS I INDUSTRIAL METROLOGY I TRAFFIC SOLUTIONS I DEFENSE & CIVIL SYSTEMS Laser Applications for Photovoltaics Crystalline and Thin Film Technologies Back contact