This document summarizes research on a membrane distillation system powered by solar energy for seawater desalination. The system was tested under fluctuating solar conditions to analyze its performance. Results showed that while the distillate yield decreased with reductions in solar input as expected, due to thermal mass the response was delayed. Additionally, distillate quality remained within safe drinking guidelines even during fluctuations, demonstrating the viability of a solar-powered membrane distillation system for producing clean water from seawater.

1. Effects of Solar Energy Intermittency on
a PV/Thermal Powered Membrane
Distillation System
Amanda J Hughes, Tapas K. Mallick and Tadhg S O’Donovan
4th ICAER
10-12th December 2013
IIT Bomday, Mumbai, India

2. Motivations and Aims
0.9 billion
people
without
clean
drinking
water
0.8 billion
without
water and
electricity
1.5 billion
people
without
access to
electricity
- Provide a reliable and competitive means of water
desalination that can be implemented in developing
countries.
- Development of a membrane distillation system with
concentrating photovoltaic/thermal energy source for
seawater desalination
.

3. “Water, water, everywhere, Not any drop to drink.” –S. T.
Coleridge

4. Solar based solutions are particularly suitable for desalination
purposes, given the availability of such source in most of
the water stressed areas
(i.e. the more the water scarcity, the more the solar radiation)

5. Desalination Processes
Thermal
Membrane
Electro Dialysis
Reverse Osmosis
Membrane distillation
Solar stills
MED
MVC
MSF

6. Membrane Distillation
 What it is?
 Thermally driven membrane
separation process
 Hydrophobic membranes allow
pure water vapor to pass
through, whilst salt is retained

7. Membrane Distillation
Advantages
 100% theoretical salt retention
 Low operating temperature, 30-800c, when compared with
conventional distillation
 Reduced vapour space compared to conventional thermal
processes, thus reduced plant volume.
 Low operating pressure when compared with conventional
pressure driven membrane processes
 The membranes used in MD are tested against fouling and
scaling.
 Chemical feed water pre-treatment is not necessary.
 System efficiency and high product water quality are almost
independent from the salinity of the feed water.

8. Membrane Distillation
• Problems
• Membrane wetting
• High thermal energy consumption
• Low permeate flux capacity when compared with established
membrane technologies. (MD capacity 1-10 m3/d compared with
100-1000 m3 for Wind-RO)
This is still an emerging technology….

9. Developing a membrane module

10. Developing a membrane module
Condensing plate
Stainless steel end
plate
Distillate stream
Membrane
Cold
Channel
SEM
Image of
membrane
Spacers
Stainless steel end
plate
Hot
Channel

11. Energy system
Parabolic dish with a PV/thermal receiver
Aperture area of 1m2 and a receiver area
0.002m2,
giving a concentration ratio approximately 500×.
 The photovoltaic cells have an efficiency of
36%
 2 axis tracking required

Evacuated tube collectors
• The evacuated tube collectors have an area of
5.7m2 and an efficiency of 65%

12. PV/T receiver – Temperature effect
 PV absorbs a section of the solar
spectrum, the rest is converted to
heat
 PV cells have a nominal operating
temperature, usually around 250C
 Any increase in temperature above
this cause a decrease in efficiency
of the PV.
 0.4% per degree for silicon
Heat collected from the PV cells will
provide the driving force for
membrane distillation

13. System overview

14. How does the membrane cope
with a fluctuating power supply?
• Solar intensity is
known to fluctuate
throughout the day,
subsequently so will
the inlet seawater
temperature of the MD
unit.
• Transient operation
will affect the quantity
and quality of the
distillate produced.

15. Temperatures from energy system
Output
temperatures
from the energy
system,
calculated via a
mathematical
model

16. Geometry & Boundary Conditions of 3D
Densely Packed Receiver
Results from the distillate yield
No
Region
Boundary condition
1
On top of cells
Inflow heat flux as found from numerical model
2
Ambient
Ambient temperature of 20-45oC
The distillate surface
3
Cell’s flow
4
Sides of
rate showed a cell
time
5
Heat Sink
delayed response to
the solar
PV receiver components
1: Frame
fluctuations, due to
2: Cover glass
3: Al O ceramic
the thermal mass of
4: Solar cells
1
5: Copper MD unit
the plate
2
3
Surface to ambient radiation and natural convection
Heat is conducted through the layers
Surface to ambient radiation and convection
2
3
1
2
6: Aluminium heat sink
4
4
5
3
5
6

17. Conductivity of the distillate yield
The distillate quality
varied, but always
remained well within the
guidelines set by the
World Health
Organisation.
The result show that
there is nothing to rule
out transient operation
of the MD module

18. Discussion & Conclusions
 A Membrane distillation module was developed at Heriot Watt
 The system was tested under fluctuating operating conditions, as
would be the case were it powered by a solar energy system.
 The quantity of drinking water produced was greatly reduced
when the power supply reduced, as is to be expected. A delay
was seen in this effect due to thermal mass of the system.
 The quality of the drinking water produced, its conductivity,
remained within the safe drinking guidelines set by World Health
Organisation, even during fluctuating operation… something not
seen in a renewable energy powered membrane system to date!

19. Thank you for
your attention !
Any Questions?