Exergy, energy, and economic analyses of pyramid solar still integrated with solar water heater

ABSTRACT

One of the top priorities in the development of solar stills is productivity enhancement. The present study experimentally investigates both passive and active pyramid solar stills. In active mode, the pyramid solar still is integrated with a solar water heater. The tests were carried out with conventional pyramid solar still (CPSS) and active pyramid solar still (APSS) at 1, 2, and 3 cm of water depth, respectively. The experimentation has been carried out in Nagpur (Longitude 21.124042, Latitude 79.002211) from April – May 2022. The finding shows that the pyramid solar still coupled with a solar water heater at a water depth of 1 cm produces the highest productivity of 7.99 L/m².The hourly thermal efficiency is to be inversely related to the absorber area and the exergy efficiency is inversely related to the absorber area and directly proportional to the still output. Hence exergy and thermal efficiency of CPSS at 1 cm water depth is enhanced by (107.59%) and (49.36%) as compared to APSS, respectively. The cost per liter of fresh water obtained from conventional pyramid solar still and active pyramid solar still are 0.0139$/L and 0.00751$/L respectively. Based on the study, lower basin water depths and secondary heating enhance the solar still’s productivity.

KEYWORDS:

• Pyramid solar still
• Solar water heater
• Convectional solar still
• Productivity enhancement
• Thermal analysis
• Exergy analysis
• Economic analysis

Nomenclature

Aabs	=	Absorber Area (m2)
AIR	=	Annual interest rate (%)
APSS	=	Active pyramid solar still
Cpw	=	Specific heat of water (J/kg oC)
CPSS	=	Conventional pyramid solar still
DLS	=	Device life span (yrs)
Gror Gb	=	Solar radiation in W/m2
M	=	Mass of water (Kg)
mdp	=	Distillate Productivity (L/m2)
OD	=	Operating Days
PSS	=	Pyramid solar still
QIN	=	Heat Energy input (J)
QOUT	=	Heat Energy output (J)
Qswh	=	Heat energy of solar water heater
SWH	=	Solar water heater
t	=	Time (hrs)
Tbwt	=	Basin water temperature (oC)
Tamt	=	Ambient temperature (oC)
Tswout	=	Solar heater outlet water temperature (oC)
Tswin	=	Solar heater inlet water temperature (oC)
W	=	Operational working days (days/yr)
Subscripts	=
abs	=	Absorber
amt	=	Ambient
bwt	=	Basin water temperature
d	=	daily
dp	=	Distillate Productivity
exg	=	Exergy
IN	=	Inlet
OUT	=	Outlet
r	=	Radiation
swout	=	Solar water outlet
swin	=	Solar water inlet
swh	=	Solar water heater
th	=	Thermal
Greek symbols	=
η	=	Efficiency
∆T	=	Temperature Difference
Q	=	Heat Energy
hfg	=	Latent heat of vaporization

Highlights of the experimentations & results

Major highlights of the experimentation during all days of experimentations are as follows

• The productivity of the PSS will be increase while utilizing solar water heater as an external source of heating.

• During analyses or calculations (as per Eq. 7(7) ${\eta }_{\mathit{exg}}=\left(\frac{(\frac{{\mathit{m}}_{\mathit{dp}}\times h_{\mathit{fg}}}{3600})\times [1-(\frac{{\mathit{T}}_{\mathit{amt}}+273.15}{T_b+273.15})]}{(A_{\mathit{abs}}\times G_b)\times [1-(\frac{4}{3})\times (\frac{{\mathit{T}}_{\mathit{amt}}+273.15}{6000})+(\frac{1}{3})\times {(\frac{{\mathit{T}}_{\mathit{amt}}+273.15}{6000})}^4}\times 100\right)$(7) & 8(8) ${\eta }_{\mathit{exg}}=\left(\frac{(\frac{{\mathit{m}}_{\mathit{dp}}\times h_{\mathit{fg}}}{3600})\times [1-(\frac{{\mathit{T}}_{\mathit{amt}}+273.15}{T_w+273.15})]}{(A_{\mathit{abs}}\times G_b)\times [1-(\frac{4}{3})\times (\frac{{\mathit{T}}_{\mathit{amt}}+273.15}{6000})+(\frac{1}{3})\times {(\frac{{\mathit{T}}_{\mathit{amt}}+273.15}{6000})}^4+Q_{\mathit{swh}}(\frac{{\mathit{T}}_{\mathit{amt}}+273.15}{T_w+273.15})}\times 100\right)$(8) ) of APSS, area of SWH affects the performance of thermal and exergy efficiency which reduces the performance of APSS as compared with CPSS.

• The initial cost of solar water heater increases the production cost per liter of the fresh water.

• The material of PSS should be of good thermal property.

Disclosure statement

The authors confirm that there are no known conflicts of interest associated with this publication and there has been no financial support for this work that could have influenced its outcome.

Additional information

Notes on contributors

Nilesh C Kanojiya

Mr. Nilesh C. Kanojiya is working as research scholar at Department of Mechanical Engineering at G H Raisoni University, Amravati, India. He has more than 9 years of academic & research experience. His research area includes solar energy and heat transfer applications.

Achal S Shahare

Dr. Achal S. Shahare is working as Professor at Department of Mechanical Engineering at G H Raisoni University, Amravati, India. He has more than 20 years of academic & research experience. His research area includes computer aided design and modelling analysis.

Ritesh K Sambare

Dr. Ritesh K. Sambare is working as Assistant Professor at Department of Mechanical Engineering at G H Raisoni Institute of Engineering and Technology Nagpur, India. He has more than 9 years of academic & research experience. His research area includes solar energy and heat transfer applications.