The traditional distiller and HSPT distiller are both made of 1.5 mm thick galvanized steel. The saline water basin (tank) is covered with glass cover allowing the solar rays to heat and evaporate the water. This vapor will condensate at the inside side of the glass cover and slide to the collector. Both distillers have similar dimensions including the saline water basin (tank) dimensions and the glass cover dimensions; as shown in Figure 1. The glass cover is 2.0 mm thick and it has a slope angle of 28°. The water level for both tanks is 5.0 cm high. This water level is selected to cover the thermoelectric module since it is 4.0 cm × 4.0 cm. Both distiller basins were painted with black color for increasing solar radiation absorption.

Figure 1.

Traditional solar distiller dimension in (mm)

In addition, each distillers have stainless steel electrical level switch; these switches are normally closed type. There is a make-up tank connected with both basins by solenoid valve. The solenoid valves are wired to the electrical level switches in series, so that the electrical current will pass the solenoid once the water level decreases under the preset value of the level switch.

In the following, the novel design of HSPT is fully presented the HSPT distiller consists of two main tanks: the hot water tank (solar distiller basin that stores the saline water) and the cold-water tank (that collects the purified water). The dimensions of both tanks are shown in Figure 2. The thermoelectric modules are sandwiched between these two tanks, such that the hot side of the thermoelectric is attached to the solar basin and the TEM cold side is attached to the cold tank. On each side of the TEM, 3.0 mm thick aluminum plates are attached. In addition, aluminum plates are used instead of the galvanized steel for the inner side of the tanks. Because aluminum has higher thermal conductivity than the galvanized steel, the galvanized steel walls are replaced by aluminum plates. The cold tank has straight fins to increase condensation of water vapor. The hot tank was covered by wooden pieces insulating it from the surrounding weather conditions. However, the cold tank is not. It is painted in white color.

In the HSPT distiller, condensation takes place in two collectors. The first collector is indicated as number (1), see Figure 2. The vapor condenses at the inner side of the glass cover forming water drops which slides to this collector. The second collector is indicated as number (5), where condensation takes place at the inner side of the cold tank walls; especially at the aluminum plate that is attached to TEMs. Figure 3 and Figure 4 illustrate more HSPT distiller design and fabrication. Figure 3 shows HSPT during manufacturing and Figure 4 shows the hot tank, the cold tank and the glass cover for HSPT.

This novel design is considered an energy efficient system that increases distilled water productivity as will be proved by both the experimental work and simulation. In the HSPT distiller, the saline water in the hot tank is heated by two main sources: the solar radiation and the thermoelectric module. The Thermoelectric modules are sandwiched between the saline and the condensation tanks. The hot side of the thermoelectric module pumps the heat to increase saline water evaporation, and simultaneously it will increase condensation by recovering the latent heat from the vapor around the fins.

Figure 2.

The HSPT dimension in mm: 1- purified water collector, 2- inlet water input, 3- thermoelectric module, 4- purified water output, 5- purified water tank, 6- saline water, 7- glass cover, 8- condensation fins

Figure 3.

HSPT front view during manufacturing

Figure 4.

HSPT side view: 1- the hot tank, 2- the cold tank, 3- the glass cover

The Thermoelectric module used in this paper is shown in eqs. (1), (2) and (3). Q_h and Q_c are the heat flow rate from the hot side (Q_h) and entering the TEM from the cold side (Q_c). is the Seebeck coefficient and is the electric resistance, is the thermal conductance of the thermoelectric module, and ΔT = T_h - T_c is the temperature difference between the hot and cold sides of the TEM presented in eq. (4). These parameters are taken from the module datasheet with number TEC1-19908. Then, these parameters are validated experimentally by applying a simple least square fitting procedure for the collected reading of voltage, current and temperature; where the voltage loop presented in eq. (3) is used. The results are: $\alpha \cong 0.088$ V/K, and $R\cong 2.38$ Ω $k\cong 0.8889$ W/K. The mathematical modelling will be explained more in this section.

$Q_{\text{h}}=n\left[\alpha I{T}_{\text{h}}-k\Delta T+\frac{1}{2}{I}^{2}R\right]$ (1)

$Q_{\text{c}}=n\left[\alpha I{T}_{\text{c}}-k\Delta T-\frac{1}{2}{I}^{2}R\right]$ (2)

$V=n\left(IR+\alpha \Delta T\right)$ (3)

$\Delta T=T_{\text{h}}-T_{\text{c}}$ (4)

In the following, HSPT mathematical model is derived. This model includes energy balance, mass balance and heat transfer equations. HSPT thermal model can be simplified into five main zones: 1) the glass cover model, 2) the water tank (basin) model, 3) the thermoelectric model, 4) the basin wall model, and 5) the cold-water film in the cold tank as shown in Figure 5.

Figure 5.

The thermal model diagram

At zone 1 (glass cover) eq. (5) presents Energy balance equation:

${\dot{E}}_{\text{in1}}-{\dot{E}}_{\text{out1}}=\frac{d{T}_g}{dt}{m}_g{c}_g,$ (5)

where ${\dot{E}}_{\text{in1}}$ is the energy entering the glass cover and it is found by eq. (6):

${\dot{E}}_{{\text{in}}_{\text{1}}}={\alpha }_{\text{g}}S{A}_{\text{g}}+Q_{\text{c,wg}}+Q_{\text{r,wg}}+Q_{\text{ev,wg}}$ (6)

and the solar energy absorbed by the glass is found in the term ${\alpha }_{g}S{A}_g$.

The convection heat transfer from the basin water to the glass cover ${\alpha }_{\text{g}}S{A}_{\text{g}}$ is given by eq. (7):

$Q_{\text{c,wg}}=h_{\text{c,wg}}{A}_{\text{w}}\left(T_w-T_g\right),$ (7)

where $h_{\text{c,wg}}$ is calculated by eq. (8) found in [27]:

$h_{\text{c,wg}}=0.88{\left[T_w-T_g+\frac{\left(p_w-p_g\right)\left(T_w+273\right)}{268.9\times {10}^3-p_w}\right]}^{\frac{1}{3}},$ (8)

and the basin water saturated vapor pressure is $p_w$ at basin water temperature $T_w$ and pressure of the water saturated vapor $p_g$ at glass temperature $T_g$ is given by eqs. (9) and (10):

$p_w=\exp \left(25.317-\left(\frac{5144}{273+T_w}\right)\right);$ (9)

$p_g=\exp \left(25.317-\left(\frac{5144}{273+T_g}\right)\right)$ (10)

The radiation heat transfer rate from the basin water to the glass cover is found using eq. (11), presented by [28]:

$Q_{\text{r,wg}}=h_{\text{r,wg}}{A}_w\left(T_w-T_g\right),$ (11)

where the radiation heat transfer coefficient $h_{\text{r,wg}}$ is calculated using eqs. (12) and (13):

$h_{\text{r,wg}}={\epsilon }_{\text{e}}\sigma \left[{\left(T_w+273\right)}^2+{\left(T_g+273\right)}^2\right]\left[\left(T_w+273\right)+\left(T_g+273\right)\right];$ (12)

${\epsilon }_{\text{e}}=\frac{1}{\left(\frac{1}{{\epsilon }_{\text{g}}}\right)+\left(\frac{1}{{\epsilon }_{\text{w}}}\right)-1}$ (13)

The evaporation heat rate transfer from the water to the glass cover $Q_{\text{ev,wg}}$ is found by eq. (14); this equation was presented by [29]:

$Q_{\text{ev,wg}}=h_{\text{ev,wg}}{A}_w\left(T_w-T_g\right),$ (14)

where the evaporation heat transfer coefficient is found by eq. (15) and is given by [30]:

$h_{\text{ev,wg}}=16.273\times {10}^{-3}\times h_{\text{c,wg}}\times \left[\frac{p_w-p_g}{T_w-T_g}\right],$ (15)

and the glass cover zone energy out is found in eq. (16):

${\dot{E}}_{{\text{out}}_1}=Q_{\text{c,ga}}+Q_{\text{r,ga}}+\frac{d{m}_1}{dt}{h}_{\text{gout}}$ (16)

$\frac{d{m}_1}{dt}$ is the glass cover collected purified water production rate.

$Q_{\text{c,ga}}$ is the convective and radiation heat transfer rate from the glass cover to the surrounding ambient air and it is found by eq. (17), see reference [29]:

$Q_{\text{c,ga}}=h_{\text{r,ga}}\left(T_{\text{g}}-T_{\text{a}}\right),$ (17)

where the radiation heat coefficient $h_{\text{r,ga}}$ is found by eq. (18), see reference [31]:

$h_{\text{r,ga}}={\epsilon }_{\text{e}}\sigma \left[\frac{{\left(T_{\text{g}}+273\right)}^4-{\left(T_{\text{sky}}+273\right)}^4}{T_g-T_a}\right]$ (18)

The sky temperature is found by eq. (18), see reference [32]:

$T_{\text{sky}}=\left[0.0552\times {\left(T_{\text{a}}+273\right)}^{1.5}-273\right]$ (19)

At zone 2: Salty Water Energy balance, eq. (20):

${\dot{E}}_{{\text{in}}_2}-{\dot{E}}_{{\text{out}}_2}=\frac{d{T}_w}{dt}{m}_w{c}_p,$ (20)

where the energy entering the zone is found by eq. (21):

${\dot{E}}_{{\text{in}}_2}=Q_{\text{sw}}+Q_{\text{c,bw}}+\frac{d{m}_{\text{in}}}{dt}{h}_{\text{in}}+Q_h.$ (21)

$Q_{\text{sw}}$ is the solar energy absorbed by the water, and found by eq. (22):

$Q_{\text{Sw}}\text{=}\zeta {\alpha }_{w}S{A}_w,$ (22)

where ζ is the glass transmittivity. $Q_{\text{c,bw}}$ is the rate of heat transfer from the basin wall to the water and found by eqs. (23) and (24):

$Q_{\text{c,bw}}=h_{\text{c,bw}}{A}_{\text{b}}\left(T_{\text{b}}-T_{\text{w}}\right);$ (23)

${\dot{E}}_{{\text{out}}_2}=Q_{\text{c,wg}}+Q_{\text{r,wg}}+Q_{\text{ev,wg}}+Q_{\text{ev,wwc}},$ (24)

where the $Q_{\text{ev,wwc}}$ is the evaporation heat transfer from the hot water inside the basin to the water film on inner side of the cold tank wall and the related heat transfer coefficient $h_{\text{ev,wwc}}$ is found by eq. (25),

$Q_{\text{ev\_wwc}}=h_{\text{ev,wwc}}{A}_b\left(T_w-T_{wc}\right)$ (25)

$T_{wc}$ is the cold tank wall temperature, while the heat evaporation transfer coefficient between the water in the basin to the water film on the inner side of the cold tank is found by eq. (26):

$h_{\text{ev,wwc}}=16.273\times {10}^{-3}\times h_{\text{c,wwc}}\times \left[\frac{p_w-p_{\text{bc}}}{T_w-T_{wc}}\right]$ (26)

The convection heat coefficient between the water in the basin to the water film on the inner side of the cold tank is found by eq. (27):

$h_{\text{c,wwc}}=0.88{\left[T_w-T_{wc}+\frac{\left(p_w-p_{\text{b}}\right)\left(T_w+273\right)}{268.9\times {10}^3-p_{wc}}\right]}^{\frac{1}{3}};$ (27)

and the evaporation pressure near the water film inside the cold tank $p_{wc}$ is found by eq. (28):

$p_{wc}=\exp \left(25.317-\left(\frac{5144}{273+T_{wc}}\right)\right)$ (28)

At zone 3: Thermoelectric Module energy balance is found by eq. (29):

${\dot{E}}_{{\text{in}}_{\text{a}}}-{\dot{E}}_{{\text{out}}_3}=0$ (29)

The input energy is found by eq. (30):

${\dot{E}}_{{\text{in}}_{\text{a}}}=Q_c+P$ (30)

The output energy is found by eq. (31):

${\dot{E}}_{{\text{out}}_{\text{a}}}=Q_{\text{h}}$ (31)

where $Q_{\text{c}}$ and $Q_{\text{h}}$ are given in eqs. (1) and (2), while the thermoelectric input energy is found by eq. (32):

$P=V\times I$ (32)

At zone 4: Distiller Walls energy balance and the energy balance are found by eqs. (33), (34) and (35), where $T_{\text{b}}$ is the basin temperature:

${\dot{E}}_{{\text{in}}_{\text{4}}}-{\dot{E}}_{{\text{out}}_{\text{4}}}=\frac{d{T}_{\text{b}}}{dt}{m}_{\text{b}}{C}_{\text{b}};$ (33)

${\dot{E}}_{{\text{in}}_{\text{4}}}=Q_{\text{Sb}};$ (34)

${\dot{E}}_{{\text{in}}_{\text{4}}}=Q_{\text{c,bw}}+U_b{A}_b\left(T_{\text{b}}-T_{\text{a}}\right)+U_{\text{b2}}{A}_{\text{b2}}\left(T_{\text{b}}-T_{\text{wc}}\right),$ (35)

where $A_b$ is the basin wall area, and the $A_{b2}$ is the cold tank wall area. The basin outer wall is insulated by wooden cover to minimize the energy loss.

At zone 5: Cold Water film energy balance is found by eqs. (36), (37) and (38):

${\dot{E}}_{{\text{in}}_5}-{\dot{E}}_{{\text{out}}_5}=\frac{d{T}_{\text{wc}}}{dt}{m}_{\text{wc}}{c}_{\text{p}};$ (36)

${\dot{E}}_{{\text{in}}_5}=Q_{\text{ev,wwc}}+U_{b2}{A}_{b2}\left(T_{\text{wc}}-T_{\text{b}}\right),$ (37)

where:

${\dot{E}}_{{\text{out}}_5}=Q_c+\frac{d{m}_{\text{2}}}{dt}{h}_{\text{out2}}$ (38)

Note that the evaporation of the basin water is divided in three types; the evaporation from the basin water to the glass $Q_{\text{ev,wg}}$, the evaporation from the basin water to the basin wall $Q_{\text{ev,wb}}$ and the evaporation from the basin water to the cold water film inside the cold tank $Q_{\text{ev,wwc}}$. The total evaporation is found by eq. (39):

$Q_{\text{ev}}=Q_{\text{ev,wg}}+Q_{\text{ev,wwc}}$ (39)

The experiment was conducted during the summer of 2022, on the 16th of June. It took place at the Applied Science Private University, Renewable Energy Center in Amman, Jordan. In this experiment both the traditional solar distiller and the HSPT distiller were tested at the same conditions, as shown in Figure 6. In this section, the experimental results for both distillers are presented. These results are fully analyzed and discussed.

Figure 6.

The experiment setup: 1- the HSPT, 2- the traditional solar distiller, and 3- the solar panel

Experimental results.

Table 2 shows the symbols used to describe the readings recorded for both distillers during the experiment. They are required to test the distillers’ performance and to validate their capabilities.

Table 2.

Symbols used to describe the readings recorded for both distillers

Symbol	Description
A	Current value (A)
Sol-Rad	Solar radiation (W/m2)
Ta	Temperature of the surrounded environment
Tb	Temperature of the basin tank (hot tank) wall
Tc	TEM cold side temperature
Th	TEM hot side temperature
Tg	Temperature of the glass cover
Tw	Temperature of the hot water in the basin
Twc	Temperature of the water in the cold tank
TDS	Total dissolved solids (ppm)
V	Voltage value (V)

Table 3 shows the readings recorded for the HSPT distiller. As shown in the table, the photovoltaic solar panel starts producing current at 7:00 am. During the experiment both voltage and current are measured and used to calculate the power produced by the PV panel. The PV panel used has a maximum current is 8.0 A with approximately 30.0 V output without load. The maximum power measured in the experiment is reached at 11:00 am, when the current and voltage reach their maximum values. Since the solar panel converts sunlight to electricity, during this period of the day, the solar radiation reaches its maximum value; as shown in Figure 7.

Table 3.

Readings recorded for the HSPT distiller on the 16th of June, 2022

Time	Th(°C)	Tc (°C)	Tw (°C)	Tg (°C)	Twc (°C)	Tb (°C)	V (volts)	A (Amp)	TDS (ppm)	Glass (mL/hour)	Tank (ml/hour)	Power (W)	Ta (°C)	Solar radiation W/m2
7:00	30	22	19	22	24	22	9.6	1.3	0	0	0	12.5	23.9	342
8:00	40.5	26	27	34	31	31	11	1.45	0	0	0	16	25.2	533
9:00	58	30	31	34	34	39	20.7	2.5	0	0	0	51.8	25.1	718
10:00	77	37	41	47	34	51	29.5	3.22	0	5	0	95	27.4	882
11:00	85	39	49	54	38	58	29.5	3.67	0	14	0	108.3	29.9	980
12:00	90	43	56	55	44	60	29.5	2.98	90	25	0	87.9	31.2	1000
13:00	94	53	63	57	47	62	28.8	2.85	85	35	55	82.1	32.3	952
14:00	95	50	63	58	48	64	28.6	2.8	73	55	80	80.1	32.8	897
15:00	96	52	65	58	50	67	29	2.84	69	55	88	82.4	32.9	765
16:00	93	49	63	57	48	65	28.8	2.87	67	58	92	82.7	33	590
17:00	84	45	60	52	45	60	25.2	2.56	39	37	62	64.5	32.2	376
18:00	54	40	52	45	39	50	7.7	0.85	32	38	73	6.5	30.6	159

Figure 7.

The Solar radiation on the 16^th of June, 2022

The water temperature (T_w) at the beginning of the experiment was 19 °C at 7:00am; it reached its maximum value of 65 °C at 15:00. Figure 8 shows that the purified water is collected from two drains: the glass cover collector and the cold water tank. The purified water starts accumulating in the glass cover collector at 10:00; while it starts accumulating in the cold-water tank at 13:00. The delay in productivity of the cold water tank is due to the following three reasons. First, the humidity inside the distiller increases with the evaporation process. The evaporation process starts to accelerate after 12:00. Second, the vapor should travel longer distance to reach the cold side of the thermoelectric. This delayed the condensation of the vapor inside the cold water tank. Third, the cold water tank collector is design unproperly. Some water should be filled in this tank before it starts sliding through the valve; delaying the start of the readings.

The results shows that even though the surface area of TEM is much smaller than that of the glass, and even though the start point of distillation on glass was earlier than that of the TEM by 3 hours, the TEM productivity (ml/hour) is 1.4 times greater than that of the glass; as shown in Figure 8.

Figure 8.

The purified water productivity using the HSPT showing both the glass collector and the cold tank productivity

Experimental results for traditional distiller compared to the Hybrid single slope Solar distiller with PV powered Thermoelectric.

This section presents, analyzes, compare and discuss the experimental results for both distillers. Table 4 shows the experimental results when using the traditional distiller. The novel design of the HSPT uses TEM as a secondary actuation element in HSPT distillers for increasing both evaporation and condensation enhances the distiller productivity. The experimental work involving both traditional distiller and the HSPT proves this statement The results are displayed in Figure 9 which shows that the effect of the TEM as a source of heat starts approximately at 10:00. At 10: 00, both the glass cover temperature (T_g), see Figure 9a, and the basin tank (hot tank) wall temperature (T_b), see Figure 9b, of the HSPT distiller is higher than that of the traditional one. This is true, even though they are both in the same location; similar weather temperature and similar solar radiation. In addition, they have the same power source where the two PV panels attached to the two distillers have the same properties.

Table 4.

Readings recorded for the traditional distiller on the 16th of June, 2022

Time	Tw (°C)	Tg (°C)	Tb (°C)	Productivity mL/hour	Tatm (°C)	Solar Radiation (w/m2)
7:00	20	34	30	0	23.9	342
8:00	21	35	31	0	25.2	533
9:00	23	36	32	0	25.1	718
10:00	24	40	35	0	27.4	882
11:00	26	48	37	0	29.9	980
12:00	28	53	53	4	31.2	1000
13:00	44	58	54	3.5	32.3	952
14:00	46	56	62	14	32.8	897
15:00	46	55	57	15	32.9	765
16:00	52	50	53	19	33	590
17:00	52	41	41	23	32.2	376
18:00	48	41	43	21	30.6	159

Figure 9.

A comparison between the HSPT and the traditional distiller: a) temperature of the glass cover, b) temperature of the basin tank (hot tank) wall

In addition, comparing the water temperature in the hot tank for both distillers assure the effect of TEM as a heating source. The water temperature is very close to the wall temperature in the HSPT while it is different for the traditional one; as shown in Figure 10. Since the walls are made from metal, they heat up and then have high temperature compared to the water stored inside the hot tank. This is true in case that there is no energy source except the solar radiation; as in the case of the traditional distiller. Figure 10a shows this behavior for the traditional distiller. T_w and T_b are different, this is because the walls heat up faster and gain higher temperature compared to water. In addition, for points 16:00 to 18:00 on the x-axis, the water inside the traditional distiller keeps its energy for a longer time than the does the metal walls.

On the other hand, in case of HSPT, the difference between T_w and T_b is much smaller. This proves that the water is heated up by the energy harvested in the cold tank by the TEM, which is pumped back to the saline water basin for reuse. In addition, Figure 10b shows that, both basin wall and the water inside the basin have the same temperature for points 16:00 to 18:00 on the x-axis. This is again because of the heating effect of the TEM.

Figure 10.

A comparison between T_b the wall temperature (a), and T_w the water temperature (b) for both HSPT and the traditional distiller

Figure 11 shows the increase in water temperature (T_w) for both distillers. For the traditional distiller, the water temperature is 20 °C at 7:00 and reach its maximum value of 52 °C at 16:00. For the HSPT distiller, the water temperature is 19 °C at 7:00 am and reach its maximum value of 65 °C at 15:00. The difference of 13 °C (65 °C – 52 °C) degrees between the maximum values of water temperature for both distillers highlights the contribution of the thermoelectric module in the heating process. This difference in water temperature directedly affects the productivity. Thus, the use of the TEM in the HSPT distiller hugely increases its productivity compared to the traditional one; as shown in Figure 12.

Figure 11.

A comparison between the water temperature of HSPT distiller with the traditional solar distiller

In addition, Figure 12 shows that the traditional distiller starts producing water at 12:00 compared to the HSPT distiller which starts producing purified water at 10:00. The max productivity of the traditional solar distiller is found 23 ml/hour and the max productivity of the HSPT solar distiller is 150 mL/hour; which emphases the huge increase in productivity as a result of utilizing the TEM. In addition, this increase in productivity per day can be calculated as follows: the total production per day for HSTP (772 mL/day) minus that for traditional distiller (99.5 mL/day) divided by (99.5 mL/day) equals 672%. This 672% increase in productivity is achieved by the following factors:

1) the thermoelectric module adds more heat in the case of HSPT distiller compared to the heat generated by the solar radiation alone in case of the traditional distiller.

2) the thermoelectric module absorbs heat from the vapor causing water to condensate on the cold side of the TEM modules.

3) the energy harvested in the cold tank is pumped back to the saline water basin for reuse it in evaporating process resulting in enhanced productivity.

4) the thermoelectric cold side temperature is less than glass cover temperature for both HSPT and the traditional solar distiller; this will increase the condensation in the cold tank compared to the glass cover in both distillers.

Figure 12.

A comparison between the HSPT productivity with the traditional solar distiller productivity at the same conditions on the 16^th of June, 2022

Increase the production of HSPT by 672% is considered promising compared to the increase in productivity addressed by previous design enhancements suggested by the journal papers published by the authors of this paper. These authors, in cooperation with others, has published a number of publications presenting the results of novel designs of the solar distiller. These novel designs are implemented and experimented in the same location as the novel design discussed in this paper. Table 5 presents these publications and their contribution to the increase of productivity compared to the novel design presented in this paper.

In addition to the increase of productivity the efficiency of the HSPT distiller is 33% much more efficient compared to the traditional solar still that has 8% efficiency considering the solar power gained from PV and directly through the distiller class cover, and a night production for HSBT equals 300 ml, and for the traditional still equals 100 ml.

In this section the simulation model is validated by comparing the simulation results to the experimental results achieved in by the HSPT distiller. The simulation is based on the proposed mathematical model explained in section 1.2, and it is built using MATLAB Simulink software. The simulation model uses the parameters listed in Table 1. It consists of a set of differential equations which took 6 hours to be simulated and solved using MATLAB.

The simulation model shows an acceptable matching between experimental and simulation results as depicted in Figure 13. But there are a number of reasons why there are some mismatches. First, the variable heat losses in the distiller. Second, the cold-water tank collector is design unproperly. Some water should be filled in this tank before it starts sliding through the valve, delaying the start of the readings. other expected enhancement by considering the shading from still side walls.

Figure 13.

A comparison between the HSPT results with simulation results