Investigation of thermal and electrical performances of a combined semi-transparent PV-vacuum glazing

 

Authors: Aritra Ghosh, Senthilarasu Sundaram & Tapas Okay. Mallick

Source: Applied Energy, Volume 228, 2018 | https://doi.org/10.1016/j.apenergy.2018.07.040
(https://www.sciencedirect.com/science/article/pii/S0306261918310687)

 

Highlights

• Thermal and electrical performances have been measured utilizing indoor take a look at cell for crystalline silicon primarily based PV-vacuum glazing.
• Maximum PV cell temperature was achieved 97 °C below 1 solar publicity (1000 W/m2)
• Overall heat transfer coefficient was 0.8 W/m2 Okay for this glazing.
• Solar issue was calculated for this PV-vacuum glazing.

Abstract

Combined semi-transparent PV-vacuum glazing offers low total warmth switch coefficient, reduces photo voltaic warmth achieve, generates clear electrical energy and admits comfy daylight. In this work, thermal and electrical performances of a multicrystalline silicon primarily based PV-vacuum glazing have been characterised utilizing indoor take a look at cell. For this explicit combined system, PV lined 32% of the glazing space. Two completely different combos of PV-vacuum glazing techniques have been manufactured the place for the primary case vacuum glazing confronted take a look at cell exterior setting (VPS) and for the second case vacuum glazing confronted take a look at cell inside setting (SPV).

SPV kind was discovered to have superior efficiency as PV cell achieved decrease temperature than VPS kind after 125 min publicity below 1000 W/m2 fixed depth from a simulator. For this sort PV-vacuum glazing, total warmth switch coefficient (U-value) was 0.8 W/m2 Okay and the photo voltaic issue was 0.42. U-value of this PV-vacuum glazing was 66% decrease and the photo voltaic issue was 46% decrease than PV double-glazing. Close energy drop from PV attributable to elevated temperature was noticed for each PV-double and PV-vacuum glazing.

1. Introduction

Consumption of world vitality elevated by 40% from 1990 to 2007. Until 2035, one other 8–10% increment is predicted attributable to speedy progress of urbanization [1]. Transport, business and buildings are the most important vitality consuming sectors. Building sector alone accounts 40% of international vitality. To mitigate this excessive constructing vitality demand, zero vitality or low vitality buildings are potential [2]. To obtain environment friendly buildings, vitality environment friendly home windows are important which might management incoming extreme photo voltaic warmth achieve (cut back constructing cooling load), restrict warmth loss (cut back constructing’s heating load), and preserve comfy daylight (possess discomfort glare). However, home windows are essentially the most important constructing envelope by permitting visible connection between indoor house and exterior setting.

Building-integrated photovoltaic (BIPV) glazings are progressive and rising glazing expertise which has functionality to exchange typical low efficiency building facade supplies. In city cities and locations the place rooftop and floor areas are restricted, semi-transparent BIPV glazing or glazed façades are different superior expertise [3]. In a photovoltaic (PV) glazing, PV system is sandwiched between two glass panes [4]. This glass –PV –glass construction is advantageous over conventional PV system as they permit daylight into the indoor house whereas they’re put in as a BIPV. Thus, a semi-transparent BIPV glazing controls getting into photo voltaic warmth achieve and discomfort glare, introduces comfy daylight, and generates electrical energy.

PV system for BIPV glazing consists of first technology silicon, second technology amorphous silicon (a-Si) [5], cadmium telluride (CdTe) [6], CIGS, third technology DSSC [7] and perovskite [8]. Second and third technology PV units have benefits over silicon as tuning the thickness modulation of transparency is feasible. However, DSSC [9], and perovskite [10], [11] each have stability situation which hindrance them to be utilized as sensible glazing below outside environmental situation. Second technology a-Si is essentially the most investigated PV system for PV glazing software as their see by construction enable pure daylight [12]. Second technology a-Si, CdTe and CIGS have presently reached the most effective laboratory effectivity of 11.9%, 21.7% and 21.4% respectively [13]. Crystalline silicon remains to be preferable over all these aforementioned PV because it provides excessive effectivity and excessive stability below outside setting.

Semi-transparent kind PV glazing introduces daylight illuminance into the indoor house, which isn’t attainable to acquire from an opaque silicon primarily based PV glazing. Thus spaced kind PV construction utilizing crystalline silicon primarily based glazing is engaging. These common distributions of small space PV cells block the incident incoming photo voltaic radiation and the hole between cells enable daylight and close to infrared radiation (NIR) [14]. Depends on the PV protection completely different transparency stage is achievable [15]. To get hold of finest PV cell protection, native climatic conditions, buildings orientation and consumptions particulars are important [16].

PV glazing has potential to scale back cooling load however enhance seasonal heating hundreds [17] because it blocks incoming photo voltaic warmth achieve. For chilly local weather constructing, comfy daylighting, excessive photo voltaic good points and low warmth loss are required. Thus, for giant glazed façades, vacuum glazing kind is your best option to offer allowable daylight and enable photo voltaic warmth achieve for discount of the house heating demand throughout day time [2]. Vacuum glazing consists of two low – emissivity (e) coated glass panes, arrays of small pillars between the 2 glasses to maintain the surface atmospheric stress and leak free edge sealing [18], [19].

Vacuum glazing provides low warmth switch as vacuum between two glasses cut back conductive and convective warmth switch and presence of low emission coating reduces the radiative heat transfer [20]. First vacuum glazing was fabricated utilizing excessive temperature melting level solder glass edge sealing which degrades low emission coating [21]. Low temperature indium alloy edge sealing was employed in a while to allow the low-e coating [22]. Cerasolzer kind CS186 was additionally investigated for substitute of expensive indium edge sealant [23]. Metal-based opaque small pillars array was changed by clear pillars to make this glazing extra aesthetic [24].

Vacuum glazing provides related transmittance to a double glazing with 53% low warmth loss in comparison with double glazing [18]. This increased transmittance typically creates discomfort glare. Addition of photo voltaic warmth gain-glare management PV materials can management this extreme glare and possess appropriate daylight. Addition of spaced kind PV and vacuum glazing will kind low warmth loss clear energy producing glazing as proven in Fig. 1. Spaced kind semi-transparent PV-vacuum glazing is actually multifunctional by controlling photo voltaic warmth achieve, warmth loss, glare and introduces allowable daylight. Interesting truth of this glazing is that no distortion of transmitted gentle by the non-PV lined half of the glazing. This signifies that daylight obtainable exterior might be similar to inside after passing by this glazing as gentle passes by solely three silica made glass pane and low emission coating.

a-Si PV primarily based PV-vacuum glazing is the one reported combined PV-vacuum glazing work the place complete 4 glass panes have been employed [25]. We report for the primary time thermal efficiency of multicrystalline silicon primarily based semi-transparent (32% PV cell protection and 33% spectral photo voltaic transmittance by non-cover half) PV-vacuum glazing utilizing indoor take a look at cell characterisation. Total quantity of glass panes for this work was three. In this work,

• two completely different combos have been ready. In the primary case, vacuum glazing confronted exterior laboratory ambient and for the second case, vacuum glazing confronted inside take a look at cell ambient; Results have been in contrast with related space semi-transparent PV-double glazing (32% PV cell protection);
• electrical efficiency of PV system was evaluated for the presence of vacuum glazing;
• total heat transfer coefficient of combined PV-vacuum glazing was investigated;
• photo voltaic issue was decided for this semi-transparent combined glazing.

Results of this work might be helpful for retrofit or low vitality constructing designer.

2. Experiments

2.1. System fabrication

To notice semi-transparent PV-vacuum glazing, vacuum glazing dimension of 0.35 m × 0.2 m from NSG SPACIA, multicrystalline photo voltaic cell dimension of 0.155 m × 0.155 m, and Pilkington ok glass single glazing dimension of 0.35 m × 0.2 m have been combined. Three completely different techniques of which two PV-vacuum glazing and one PV double glazing for comparability have been fabricated for the experiment. For kind 1 PV vacuum glazing, PV cell was positioned on the highest of single glazing, and after pouring sylgard encapsulation vacuum glazing was positioned on the highest of it.

Type 1 PV glazing is referred on this work as VPS PV-Vacuum glazing as proven in Fig. 2. For kind 2 PV-vacuum glazing, PV cell was positioned on the highest of vacuum glazing and after sylgard encapsulation, single glazing was positioned. Type 2 is referred as SPV PV-vacuum glazing for this work. Type 3 was ready by glass PV glass construction to match with the aforementioned two sorts of PV vacuum glazing. This kind of glazing is indicated as SPS or PV-double glazing. For all three sorts of glazings, PV cell lined 32% whereas 68% space was non-covered by PV. Details of these three techniques are talked about in Table 1.

Table 1. Details of differing kinds of techniques.

A small-scale take a look at cell dimension of 0.37 m × 0.22 m × 0.26 m was fabricated utilizing 10 mm thick polystyrene to carry out indoor characterisation. The ratio of take a look at cell and glazing was 1:1. Outdoor characterisation utilizing take a look at cell provides a number of constraints and inside and exterior variables act concurrently. Therefore it’s tough to distinguish a single accountable variable which influences the outcomes [26]. Thus, on this work, indoor characterisation at laboratory setting was most well-liked. Glazing was connected on high of the take a look at cell such that it faces the indoor simulator instantly, which resembles much like a vertical airplane glazing dealing with south.

For VPS kind PV-vacuum glazing, vacuum glazing confronted laboratory room setting and single glazing confronted take a look at cell indoor setting. For SPV kind PV-vacuum glazing single glazing confronted laboratory room setting and vacuum glazing confronted take a look at cell indoor setting as proven in Fig. 3.

2.2. Indoor characterisation arrange

Transmittance and reflectance at photo voltaic spectrum (280 nm -2500 nm) of ready glazing techniques have been measured utilizing an ultraviolet–seen–close to infrared (UV/VIS/NIR) spectrophotometer (PerkinElmer® Lambda 1050) geared up with an integrating sphere (150 mm diameter) with 2 nm interval as proven in Fig. 4.

The indoor characterisation was carried out utilizing steady indoor solar simulator publicity. This simulator is AAA kind and its spectrum matches with photo voltaic spectrum between 250 nm and 3000 nm. Five thermocouples have been employed to measure exterior and inside glass floor, take a look at cell ambient and indoor laboratory ambient and PV cell temperature. Pico knowledge logger recorded 5 min interval temperature knowledge. Photograph of full experimental arrange is proven in Fig. 5.

3. Methodology

Thermal transmission and photo voltaic warmth achieve are the 2 main modes of warmth switch by a glazing expertise [27]. Overall warmth switch coefficient signifies how properly a glazing is insulated by evaluating the quantity of warmth that passes, in regular state, by the central half of the glazing. Evaluation of total warmth switch coefficient is determined by exterior, inside, thermal conductivity and thickness of glazing. Solar warmth achieve coefficient (photo voltaic issue) reveals the admittance of photo voltaic warmth achieve by the glazing into an indoor house [28].

Overall warmth switch coefficient for this PV vacuum glazing was calculated utilizing beneath equation

the place

Qin is the incident radiation on the glazing [29]

Total warmth switch by the glazing is given by [30]

The complete warmth contained in the take a look at cell is given by [31]

The complete warmth losses by the take a look at cell may be represented by equation

Overall warmth switch coefficient of this glazing is given by

Required parameters to seek out out U-value for this combined vacuum glazing is listed beneath Table 2.

Table 2. Parameters particulars for U-value calculation.

Solar issue (g) or photo voltaic warmth achieve coefficient signifies the transmitted photo voltaic vitality by a glazing. Spaced kind PV-vacuum glazing consists clear and opaque portion. Thus g worth for this technique is given by Eq. (7) [32].

the place photo voltaic transmission, reflection and absorption are given by Eqs. (8), (9), (10) respectively. In the Eq. (7), hout and hin are the exterior and inside warmth switch coefficient.

Net vitality flows by a glazing in a constructing may be determined utilizing Eq. (11) [33].

the place α proven in Eq. (12) is the ratio of photo voltaic good points to thermal losses

4. Results and discussions

4.1. Spectral efficiency

Spectral transmission, reflectance, absorption have been measured for combined PV-vacuum and PV double glazing utilizing UV–VIS-NIR spectrophotometer and calculated utilizing Eqs. (8), (9), (10) respectively as proven in Fig. 6. Calculated photo voltaic transmission (Ts), reflection (ρs) and absorption (As) for non-covered half of PV-vacuum glazing have been 33%, 40% and 27% respectively. These parameters qualitatively outline the spectral behaviour of the whole PV-vacuum glazing. Higher transmission was round 550 nm. Obtained low transmission and increased reflection in close to infrared (NIR) area have been attributable to presence of low emission coating within the vacuum glazing. Average photo voltaic transmission was 77% whereas solar reflectance and absorption was 14% and 8% respectively for PV-double glazing.

4.2. Surface thermal efficiency

Fig. 7 reveals the temperature variation of PV vacuum glazing below fixed 1000 W/m2 photo voltaic radiation from an indoor simulator. This construction is SPV kind PV-vacuum glazing the place single glazing confronted laboratory setting and vacuum glazing confronted take a look at cell inside setting. PV cell temperature elevated from 32 °C to 86.4 °C after 125 min of publicity. First 40 min of publicity, cell temperature elevated at 1.25 °C/min whereas laboratory room temperature elevated at 0.025 °C/min.

During the identical interval inside glass floor temperature elevated at 0.625 °C/min. Next 80 min PV cell temperature elevated from 80 °C to 86 °C. Temperature distinction between PV cell and inside glass floor was as a result of heat insulation properties of vacuum glazing. Vacuum glazing reduces conductive and convective warmth circulation whereas the presence of low-e coating restricts radiative warmth circulation. Thus, total warmth circulation from the cell by the vacuum glazing is restricted.

Fig. 8 reveals completely different temperature of VPS kind PV vacuum glazing after 125 min exposure under 1000 W/m2 utilizing an indoor simulator. In this case, vacuum glazing confronted indoor laboratory setting and single glazing confronted take a look at cell inside setting. PV cell temperature elevated from 26 °C to 97 °C with an elevated charge of 1.36° C/min on the first 40 min. Test cell inside temperature elevated at 0.45 °C/min throughout the identical interval. PV cell temperature and inside glass temperature each elevated practically similar charge. This is as a result of presence of single glazing which allowed increased warmth circulation from PV cell by the glass.

Fig. 9 reveals the temperature adjustments for PV double-glazing. PV cell temperature elevated at 1 °C/min at first 40 min of publicity. This increment could be very near the SPV kind PV vacuum glazing. Spectral behaviour of PV-double glazing confirmed (Fig. 6) increased photo voltaic transmission in comparison with PV-vacuum glazing (Fig. 6). Moreover, PV-vacuum glazing’s photo voltaic transmission decreased as a result of presence of low-e coating.

However, in Fig. 9 the take a look at cell inside temperature was low in comparison with each combos of PV-vacuum glazing. The motive for this decrease take a look at cell inside temperature was as a result of low thermal insulation of this double glazing. This double glazing was ready by attaching two 4 mm thick single glazing with minimal (1 mm) air hole between them. Thus this combined glazing behaved much like an 8 mm thick single glazing below indoor simulator publicity. Due to the thermal bridge between two glass panes, warmth loses the place increased in comparison with PV-vacuum glazing.

4.3. PV efficiency

PV cell efficiency for 2 completely different kind combined PV-vacuum glazing was measured utilizing I-V tracer as proven in Fig. 10. PV double glazing measurement was additionally carried out for comparability. Measurements have been carried out for 125 min steady publicity below 1000 W/m2 indoor simulator radiation. PV cell temperature dependent open circuit voltage (Voc) has been proven for 3 differing kinds of glazing techniques in Fig. 10. Voc has dependency on the traits of PV materials.

Thus, variation of Voc is determined by the saturation present and gentle generated present. PV cell temperature dependent Voc is given by Eq. (13) [34]. At excessive cell temperature, energy band gap of PV cell decreases (semiconductor bandgaps lower with temperature [35]) and consequently Voc is decreased. Reduction of Voc for VPS kind glazing was 25% from its preliminary situations whereas for SPV and SPS kind it was 20% and 16% respectively.

FF reveals optimum present/voltage trade-off and the minimal extracting value of photogenerated prices from the cell into the circuit [35]. At increased illumination attributable to enhance of present circulation resistive losses enhance which may be seen from collection resistance (Rs) dependent FF Eq. (14) [36]. In this work discount of FF for SPV, VPS, SPS kind have been 13%, 23%, 19%. Decrease of FF was as a result of enhance in resistive losses for the upper steady illumination.

Maximum energy of PV cell may be expressed by Eq. (15). Thus, discount of most energy (Pm) is instantly proportional to the discount of open circuit voltage, and Fill issue (FF). Reduction of most energy for SPV, VPS, and SPS kind from preliminary situations have been 38%, 44%, 34% respectively. Maximum energy drop of PV cell was not remarkably excessive for the presence of vacuum glazing in comparison with single glazing. Maximum power output decreased in increased order for VPS kind glazing as PV cell temperature elevated from 32.7 °C to 96 °C.

It is seen from Fig. 10 that the open circuit voltage (Voc) and fill issue (FF) and most energy (Pm) decreased with increased PV cell temperature. These outcomes are in settlement with the beforehand revealed literature [37], [38], [39], [40]. The relative change in FF, Voc and Pm for 3 completely different techniques are listed in Table 3. Close energy drop of PV for PV-vacuum and PV-double glazing enhances the likelihood of utilizing PV-vacuum for glazed façade software.

Table 3. Relative change of FF, Voc, Pm for VPS and SPS kind PV vacuum glazing and PV double glazing.

4.4. Thermal transmission and photo voltaic issue (SHGC)

Thermal transmission of PV-vacuum glazing and PV double-glazing was calculated utilizing Eq. (6). Calculation was carried out after floor temperature reached near regular state situation. Fig. 11 reveals the general warmth switch coefficient of PV-vacuum glazing. Calculated common U-value for this glazing was 0.8 W/m2 Okay. Previously, utilizing outside take a look at cell, thermal transmission of vacuum glazing and combined SPD-vacuum glazing have been discovered to be 1.4 W/m2 Okay [18] and 1.0 W/m2 Okay [30] respectively.

Higher exterior wind pace influenced these outcomes. In this work wind pace was negligible and temperature distinction between take a look at cell inside and laboratory setting govern the consequence. Fig. 12 reveals the general warmth switch coefficient of PV double-glazing. Average U–worth for this technique was 2.37 W/m2 Okay. Previously evaluated double glazing U-value for outside situation was 2.98 W/m2 Okay [29]. Thus, thermal transmission outcomes of each PV-vacuum and PV double glazing are in settlement with the previously published work.

Higher temperature distinction between take a look at cell inside and exterior setting was discovered for PV-vacuum combined glazing attributable to decrease U-value than PV double glazing. U-value discount of 66% was attainable utilizing vacuum glazing built-in with PV glazing. Solar issue for these combined glazing was calculated utilizing Eq. (7). For PV vacuum glazing the photo voltaic issue was 0.42 whereas for PV-double glazing photo voltaic issue was 0.79. Net vitality by this PV vacuum glazing was evaluated utilizing Eq. (12). Net vitality increased than 1 signifies this glazing is appropriate for chilly local weather and reveals 46% increased vitality achieve in comparison with PV-double glazing. Table 4 listed the completely different thermal loss and photo voltaic achieve of these two glazings.

Table 4. thermal loss, photo voltaic achieve and ratio of photo voltaic achieve thermal loss for PV-vacuum and PV-double glazing.

5. Conclusions

Experimentally thermal and electrical traits have been carried out for semi-transparent (32% space was lined by PV cell) combined PV- vacuum glazing and PV double glazing utilizing indoor take a look at cell. For PV-vacuum glazing, two completely different combos SPV and VPS sorts have been fabricated. Total three glass panes have been employed to fabricate every kind of PV-vacuum glazing system. Vacuum glazing was dealing with take a look at cell indoor setting and single glazing was dealing with laboratory setting for SPV kind whereas vacuum glazing was dealing with laboratory setting and single glazing was dealing with take a look at cell setting for VPS kind. Two glass panes PV double glazing was manufactured and employed to match outcomes with semi-transparent PV-vacuum glazing.

For all three sorts of glazing, PV cell temperatures have been increased than glass floor and take a look at cell indoor temperature. Maximum PV cell temperature was 97 °C for VPS kind as presence of vacuum glazing on the exterior aspect works as a warmth insulator. Rise of PV cell temperature was decrease for SPV kind attributable to presence of single glazing on the exterior aspect which allowed increased warmth switch from PV cells to setting. Semi-transparent SPV and VPS each supplied equal U-value, photo voltaic issue (g-value) and transmission, nonetheless, PV cell efficiency was superior for SPV kind.

PV cell efficiency for PV-vacuum glazing didn’t outperform in increased order in comparison with PV-double glazing. Moreover, 66% decrease U-value and 42% decrease photo voltaic issue make PV-vacuum glazing a appropriate candidate for low vitality constructing. For chilly climatic condition, PV-vacuum glazing is potential attributable to low U-value. Net energy analysis additionally confirms that this PV-vacuum mixture is helpful for chilly local weather. Lower ambient temperature can alleviate or management the rise of PV cell temperature, which is able to improve the ability output. This is the primary electrical efficiency investigation of PV cell utilizing PV-vacuum mixture.

Acknowledgement

This work has been carried out as half of the analysis undertaking ‘Joint UK-India Clean Energy Centre (JUICE)’ which is funded by the RCUK’s Energy Programme (contract no: EP/P003605/1). The tasks funders weren’t instantly concerned within the writing of this text. In help of open entry analysis, all underlying article supplies (knowledge, fashions) may be accessed upon request by way of e mail to the corresponding writer.

References