Is efficiency the only important aspect to solar energy?

Transcription

1 Is efficiency the only important aspect to solar energy? Michael G. Debije Chemical Engineering and Chemistry Functional Materials and Devices (SFD) Eindhoven University of Technology April 21, 2012 Alumni Dag 1

2 Meeting the solar challenge Transportation 28% Buildings residential 21% Heating Cooling Lights 10% 12% 32% Buildings use 40% of our energy Industry 33% Buildings commercial 18% Heating Cooling Lights Ventilat 16% 13% 7% 28% Our inability to control sunlight costs ~16% of worldwide energy consumption!! Why has this not been addressed before? large areas need be covered with inexpensive systems that look pleasing, work in shaded conditions and can take a beating 2

3 State-of-the-art in solar cells Silicon blue Type III-V Silicon black Organic Dye-sensitized CIGS 3

4 Race for efficiency 4

5 Even higher efficiency using concentrators: focusing Decrease solar cell size Use high-efficiency cells 5

6 Even higher efficiency using concentrators: reflecting Decrease solar cell size Use high-efficiency cells 6

7 Difficult to integrate into the built environment 7

8 Another solution? replace expensive semi-conductor materials with inexpensive, colorful plastics that provide aesthetic advantage and adaptability which can be employed where standard panels cannot Bringing the light to the cell. 8

9 The basic function of the luminescent solar concentrator Plastic waveguide Solar Cell Luminescent dye Bringing the light to the cell. 9

10 Mostly inexpensive materials The waveguides may be of any color The waveguides may be cut to (almost) any shape The device can be made flexible The waveguides could be transparent The devices could be lower in weight Work in both direct and indirect sunlight Advantages 10

11 Increased options Photo courtesy Eduardo Sentchordi Photo courtesy Harry Harkema 11

12 Great flexibility 12

13 Responsive signs that generate own power Solar Cell Solar Cell Waveguide Dye pattern LEDs Battery storage 13

14 to light themselves at night LEDs 14

15 Application 15

16 How could we employ liquid crystals to improve LSC function? Photo: Oleg Lavrentovich, Liquid Crystal Institute 16

17 A bit about liquid crystals Liquid Crystalline Monomers & Polymers planar homeotropic splay twisted crystal mesophase liquid (liquid crystal) reactive mesogen hν UV liquid crystalline polymer A variety of conformations possible 17

18 Taking advantage of anisotropy of light emission from organic fluorescent dyes 18

19 Emission from fluorescent dyes A dye molecule does not emit isotropically 19

20 Liquid crystal alignment of dyes Alignment layer Host liquid crystal + guest dye Dye oriented by liquid crystal (homeotropic) Dye oriented by liquid crystal (planar) 20

21 Directed emission 1.6 Output Ratio (E /E ) Dichroism Parameter, R a Perfect alignment: R a = 1 Totally random: R a = 0 Get 55% more light from one edge than the other! Verbunt et al, Advanced Functional Materials, 2009,

22 Another challenge Around 50% of absorbed energy is lost through the top and bottom surfaces! 22

23 Reducing surface losses with liquid crystals Selective reflector 23

24 Copying ideas from nature 24

25 Cholesterics + Chiral dopant = Nematic LC Chiral nematic (Cholesteric) 2µm 25

26 What the cholesteric does * A right-handed cholesteric helix reflects a bandwidth of right-circularly polarized light of specific wavelength. * The reflected wavelengths depends on the pitch of the helix * Left-circularly polarized light will pass through this cholesteric 26

27 Reflection of the cholesterics Absorption Emission Transmission (%) Wavelength (nm) 0 dgr 20 dgr 30 dgr dgr Wavelength (nm) 27

28 Results of using cholesterics Lumogen With normal cholesterics, Red 305 we are able to convert 35% of surface losses into useful emission With new broadband cholesterics, we could be able to convert > 60% of losses into useful emission! with interesting visual effects 28

29 A typical office: blinds drawn, lights on 29

30 Existing solutions Photo- and electro-chromic windows: Control light entrance but generates no electricity 30

31 Transparent electrical generation Organic and thin-film solar cells Generate electricity but cannot change transparency 31

32 Using LCs: Tunable smart windows Light Dark Privacy Can be automatic or manual Unique design simultaneously generates electricity as well as controlling light influx, lessening air conditioning needs MG Debije, Adv. Funct. Mater. 20, 1498 (2010) Pictures courtesy Peer+ 32

33 Switchable windows, dark state Host LC 0V Glass PV I Dye 33

34 Switchable windows, light state 10V Glass PV I Dye 34

35 Anisotropy in absorption/ emission Absorbance Incident light parallel to alignment direction Incident light perpendicular to alignment direction Emission (mw) Wavelength (nm) 35

36 Window goals Switch between 10% and 70% transmission The coloration should be neutral 36

37 Record efficiencies (ECN): What value is adaptability? Type III-V cells: 7.1% Silicon cells: 4.3% 37

38 Our challenge Improve the light-to-electricity efficiency Match the design to the architect s needs 38

39 Ubiquitous to the built environment? Is there room for a large-area, lower efficiency system? Does the ability to add color and shape, or retrofit interest anyone besides designers? Is the Netherlands going to take the lead? 39

40 Acknowledgements At the TU Eindhoven Paul Verbunt Industrial partners: Ties de Jong - Theo Hoeks Albert Schenning Sabic IP Dick Broer - Casper v. Oosten Cees Bastiaansen Peer+ Dick de Boer Shufen Tsoi Funding STW Vidi grant