Supplemental Information. Storage and Recycling of Interfacial. Solar Steam Enthalpy

Transcription

1 JOUL, Volume 2 Supplemental Information Storage and Recycling of Interfacial Solar Steam Enthalpy Xiuqiang Li, Xinzhe Min, Jinlei Li, Ning Xu, Pengchen Zhu, Bin Zhu, Shining Zhu, and Jia Zhu

2 Supplemental Information Figure S1. Photos of the real setup Figure S1. Photos of the real setup. (A) Optical image of steam generation device. (B) Optical image of electricity and water generations. (Inset) The optical of aluminum chamber without top plate. The aluminum chamber (Length: 11 cm, Width: 5.5 cm, Height: 1 cm) was selected as condensed chamber. Some yellow copper wire was filled in the inside of aluminum chamber to increase steam condensation. T 1, T 2 and T 3 represent the position of thermocouples. 1

3 Figure S2. Optical images of folded and unfolded graphite/nonwovens films Figure S2. Optical images of folded and unfolded graphite/nonwovens film. (A) Optical image of a folded graphite/nonwovens film. (B) Optical image of an unfolded graphite/nonwovens film after folding over 50 times. 2

4 Figure S3. Comparison of interfacial heating and bulk heating Figure S3. Comparison of interfacial heating and bulk heating. (A) The mass change over time at bulk heating and interfacial heating under 30 kw/m 2. (B) Steam temperature over time at bulk heating and interfacial heating under 30 kw/m 2. 3

5 Figure S4. The influence of thermal storage part on performance of solar steam generation Figure S4. Mass change over time of interfacial solar steam generator with thermal storage part under different solar irradiations. 4

6 Figure S5. The temperature distribution in thermoelectric device Figure S5. The temperature distribution in thermoelectric device. (A), (B), (C) and (D) temperature distribution in thermoelectric device under 8, 17, 22 and 30 kw/m 2 respectively. (Hot (in) represents the temperature of hot side near steam; Hot (out) represents the temperature of hot side near water outside; Cool represents the cool side of thermoelectric device. 5

7 Supplemental Note 1.Comparison of open system and semi-closed system Interfacial solar steam was proposed and achieved high efficiency ( ~ 80%) under one sun with advanced structure and material designs, photon and thermal management, including our group 1,2. However, this efficiency is achieved in open system that is different from all the previous systems, which is a semiclosed system. Here, a set of comparative tests were made to support this point. As shown in Fig. S6, the efficiency of our solar steam generator can reach around 75% under one sun if we remove sealed cap, but only about 18% efficiency in semi-closed system under one sun. The possible reason is that the vapor diffusion is suppressed that resulted in the decrease of evaporation rate in semi-closed system. Figure S6. The difference of open system and semi-closed system. (A) The schematic of open system and semi-closed system. (B) The evaporation rate (Note: The evaporation rate represents the rate, which subtract dark evaporation rate) of open system and semi-closed system over time under 1 kw/m 2. 6

8 Supplemental Note 2. The analysis of energy loss The heat loss by the solar steam generator consist of three losses: radiation, convection and conduction. Here, the radiation loss was calculated by Stefan- Boltzmann. Φ =εa σ(t 1 4 -T 2 4 ) (1) Where Φ denotes heat flux, ε is emissivty (assuming the absorber has maximum emissivity of 1), A is surface area (about 20 cm 2 ), σ is Stefan- Boltzmann constant, T 1 is the average temperature of absorber (The temperature of absorber are 100, 100, 100 and 100 under 8, 17, 22 and 30 kw/m 2, respectively) and T 2 is an environmental temperature (~25 ) in the experiment. Therefore, based on equations (1), the radiation heat losses of solar steam generator have account for 8%, 4%, 3% and 2% under 8, 17, 22 and 30 kw/m 2, respectively. The convection loss was calculated by Newton' law of cooling. Q= h A (T 1-T 2) (2) Where Q denotes the heat, h is convection heat transfer coefficient (10 W/m 2 K). A is surface area (The area of glass sealed cap is about 50 cm 2 ) and T 1 is the temperature of glass sealed cap. ( The temperature of glass sealed cap are 98, 122, 144 and 157 under 8, 17, 22 and 30 kw/m 2, respectively) and T 2 is an environmental temperature (~25 ) in the experiment. Therefore, based on equations (2), the convection heat losses of solar steam generator have account for 19%, 14%, 13% and 11% under 8, 17, 22 and 30 kw/m 2, respectively. The conduction loss was calculated by Fourier's law. Φ = -ka T (3) Where Φ denotes the heat flux, k is the thermal conductivity of material (0.04 W/mK), A is the area 7

9 (about 20 cm 2 ) and T is temperature gradient. The temperature of absorber are 100, 100, 100 and 100 under 8, 17, 22 and 30 kw/m 2 respectively, and T 2 is an environmental temperature (~25 ) in the experiment. The thickness of material is about 1.3 cm. Therefore, based on equations (3), the conduction losses of solar steam generator have account for 3%, 1%, 1% and 1% under 8, 17, 22 and 30 kw/m 2, respectively. It is note that the optical losses are 10% (5% come from absorber and the other 5% come from glass sealed cap). We noted that the heat losses and efficiency have a big discrepancy under 8 kw/m 2. The possible reason is that there are some condensed water on the glass sealed cap (as shown in Fig. S7) that increase the optical reflection 3. Obviously, the ratio of heat losses is decreasing under higher illumination (The heat losses are 14%,17%, 19% and 30% under 30, 22, 17 and 8 kw/m 2, respectively). Figure S7. The phenomenon of condensation on the sealed cap. (A) The phenomenon of condensation on the sealed cap under 8 kw/m 2. (B) The phenomenon of condensation on the sealed cap under 17 kw/m 2. It can be found that about 25% energy has lost in the process of solar energy to steam generation under 30 kw/m 2. In other words, about 75% energy was used for power generation. Obviously, most energy as heat loss was wasted instead of using for power generation. Here, the thermal conductivity of insulation foam and thermoelectric materials are about 0.04 and 1.5 W/mK. The thickness of insulation foam and 8

10 thermoelectric materials are about 1.6 cm and 0.4 cm. The area of insulation foam and thermoelectric materials are about 122 cm 2 and 32 cm 2. Based on Fourier's law, we can calculate the ratio of heat losses through the insulation foam and thermoelectric materials are about 1.9% and 72.1%. 9

11 Supplemental Note 3. The superheated steam for simultaneous generations of clean water and electricity In order to further enhance the performance of simultaneous generations of clean water and electricity, the superheated steam method was selected to increase the steam temperature. As shown in Figure S8-1A, a black Cu tube (diameter 5 mm), which was placed between absorber and sealed glass, was selected as heating body to further heat the steam to achieve the superheated steam. The schematic diagram of superheated steam generation device is showed in Figure S8-1B. The black Cu tube can reach high temperature (>100 ) under illumination of the sun. Then, the black Cu tube can heat the steam to superheated steam when the steam flow through the black Cu tube. Figure S8-1. The schematic diagram of superheated steam generation device. (A) Optical image of superheated steam generation device. (B) The schematic of superheated steam generation device. The mass change over time under 30 kw/m 2 is shown in Figure S8-2A. The efficiency of superheated steam generation device is about 72.2% (obtained from the slope of the mass change curves at steady state). More strikingly, the temperature of steam is larger than 100, and can reach 146 at steady state under 30 kw/m 2 (as shown in Figure S8-2B). It can be seen that the open-circuit voltage and shortcircuit current can reach to 4.15 V and 0.61 A, and the maximum efficiency can reach 1.23% under 30 kw/m 2 (as shown in Figure S8-2C and D). In the future, it is expected that advanced thermal control and 10

12 management can be used to further increase the steam temperature, and therefore to further improve the power generation performance. Figure S8-2. The performance of superheated steam generation device. (A) Mass change over time of superheated steam generation device under illumination of 30 kw/m 2. (B) Temperature of output steam over time under illumination of 30 kw/m 2. (C) Voltage and current over time under illumination of 30 kw/m 2. (D) Output power over resistance under illumination of 30 kw/m 2. 11

13 Supplemental Note 4. Comparison with solar cell based technology Let s use solar cell (20% solar to electricity efficiency) and solar desalination membrane (95% solar to vapor efficiency). As shown in Fig. S9, for one square meter of light, the total conversion efficiency should range from 20% (if one square meter area is covered with solar cell) to 95% (if one square meter area is used only for solar desalination membrane). For example, if we use 0.5 sqm for solar cell and 0.5 sqm for solar desalination, the total efficiency is 57.5% ( = 57.5%) or equivalent to the efficiency of 10% for solar to electricity and 47.5% for solar to vapor. If we use 0.1 sqm for solar cell and 0.9 sqm for solar desalination, the total efficiency is 87.5% ( = 87.5%) or equivalent to the efficiency of 2% for solar to electricity and 85.5% for solar to vapor. Figure S9. The comparison of efficiency between solar cell + solar still and our device. For comparison, as shown in Fig. S9, for the same one square meter of light, our device can generate ~72.2% for solar to steam and ~1.23% for solar to electricity, as the electricity is generated by recycling the internal energy of steam from solar steam process. With quantitative explanations above, it clear that in terms of efficiency, our device is comparable to PV powered approach while it is still at infancy. 12

14 Supplemental Note 5. Future improvement The device can be further developed and optimized, with the advances in the field of solar steam generations and thermoelectrics. For example, we are pleased to see 95% solar-to-steam conversion efficiency was achieved through the design of hydrogels recently 4, which can be used to further improve the efficiency of our concept. Tremendous progress has also been made in the field of thermoelectrics. The thermoelectric device efficiency can be expressed as: T T h 1 ZT 1 ZT avg avg 1 (1) T T c h Where η is thermoelectric device efficiency. A theoretical quantitative analysis reveals that with solar to steam efficiency of 95% and ZT=2 at 400 K, we can expect ~95% solar to steam and 7.9% solar to electricity. With solar to vapor efficiency of 95% and ZT=2.5 at 400 K, we can expect ~95% solar to vapor and 8.9% solar to electricity, which will then be much higher compared to what you can achieve with solar cell powered approach (as in Fig. S9). 13

15 Supplemental Note 6. Analysis of the integrated thermal storage The relationship between thermal storage ability and time evolution of output is analyzed. In our experiment system, the heat flow is assumed to travel just through thermoelectric module because the chapter is wrapped by thermal insulation materials. Meanwhile, the conversion efficiency of thermoelectric module is assumed to be a constant. We can obtain the following formulas: T0 - Tt P( t) P0 T T 0 P( t) Qf (t) Q (t)dt -cmdt f e (1) (2) (3) Temperature and output power can be produced as following, T (t) T e ( T P(t) P e 0 0 T e ) e P0 t - ( T0 Te ) cm P0 t - ( T0 Te ) cm (4) (5) P is output power. T 0 and T e are steady temperatures under irradiation and temperature of environment, respectively. P 0 is the initial output power. Q f is the heat flux through the thermoelectric module. η is the conversion efficiency of thermoelectric module. c and m are thermal capacity and mass of chapter. In the experiment, T 0=100, T e=25, P 0=0.208 W, Q f=37 W, c=0.88 J/g, m=75 g. Hence, t ( P t) e (6) The relationship between thermal storage ability and performance of output power is shown in Fig. S10. 14

16 Figure S10. The relationship between output power (P) and thermal storage of the chamber. (A) P/P 0 over C/C 0 (where P 0 represents steady output power under irradiation, and P represents output power of 1 min after tuning off the light. C 0=cm, where c and m are thermal capacity and mass of chapter in this experiment). (B) P/P 0 over time at different thermal storage capabilities. 15

17 Supplemental Note 7. Power generation performance of device under discontinuous irradiation The duration of the extended period can be used to reduce the influence of intermittent illumination such as rolling cloud cover. As shown in Fig. S11A and B, discontinuous irradiation (in each cycle, the interval is 1 min between on and off) was used to simulate changing cloud cover in real applications. It can be seen that the device with thermal storage can continually output electricity. That speciality is determined by thermal storage ability of chapter and can be promoted by tuning thermal capacity or mass of chapter materials. As shown in Fig. S10A, the reduction of output power is only about 10 % decrease when the thermal storage increase 5x. Figure S11. Power generation performance of device under discontinuous irradiation. (A) The change of open-circuit voltage with/without solar irradiation under 30 kw/m 2. (B) The change of short-circuit current with/without solar irradiation under 30 kw/m 2. 16

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