Convective cover: Will prevent the heat from

radiating away from the system.

Copper sheet: Coated with a spectrally

selective absorber: Will optimize the solar

energy absorbed (Cao et al., 2014).

Insulating polystyrene foam: Will serve as a

floating material to prevent water-copper sheet

contact thus sustaining copper sheet

temperature.

The key aspect of this technology is

heat loss prevention, which is achieved

by the convective

cover and the

bottom

insulating

material via

thermal

concentration

and heat

localization

Comparative study of innovative solar still modifications: A step

towards water crises mitigation and a sustainable campus

Abstract

References(1) Manikandan, V., K. Shanmugasundaram, S. Shanmugan, B. Janarthanan, and J. Chandrasekaran. (2) Ni, G., Li, G., Boriskina,

S., Li, H., Yand, W., Zhang, T., & Chen, G. (2016). Steam generation under one sun enabled by a floating structure with thermal.

Nature Energy, 7. (3) Kaviti, Ajay Kumar, Akhilesh Yadav, and Amit Shukla. “Inclined Solar Still Designs: A Review.” Renewable

and Sustainable `Energy Reviews 54 (2016): 429–451

Catalina Island entered stage 3 water rationing (50% water

reduction) as of September 6, 2016, placing strain on the USC

Wrigley Marine Science Center’s (WMSC) ability to host tens of

thousands of annual visitors (23,481 in 2015). Despite implementation of water conservation efforts and recent rain events,

freshwater remains a chronically scarce natural resource, especially

during summer months. In May 2016, the WMSC launched a pilot

study to consider solar distillation for passive generation of

freshwater using seawater. Here, we present investigations on

design improvements to enhance freshwater generation in a

conventional solar still: (1), a hybrid design containing a stepped

landscape, internal and external reflectors to direct solar irradiation

and minimize the distance water vapor needs to travel; (2), a multi-

effect basin and wicking material hybrid with external reflectors to

concentrate solar radiation, reuse the latent heat and increase

surface area. (3), One-sun Ambient Steam generator (OAS)

application to concentrate and localize heat, at the same time

prevent heat loss using a convective cover placed on top of a metal

plate and bottom insulating/floating material. The 3 design concepts

were constructed and set up at the WMSC on Mar 17, 2017.

Freshwater generation, irradiation, and temperature will be

monitored for at least 10 days. Results from this study will be used toimplement the most efficient, simple and cost-effective technological

application for passive freshwater generation on Catalina Island.

Results

*Abuyen, K.1, *Holahan, K.2, *White, M.1, Kim, D.1 Close, A.1 and Heidelberg, J.11 University of Southern California, Environmental Studies 2 University of Southern California, Viterbi, School of Engineering

1

2

3

1 Solar irradiation

2 Water evaporation

3 Condensation

Solar powered generatorWater pump

Salt Water Reservoir

Field set up

Seawater

Fresh

water

vessel

Methods

Figure 6: Solar still field set up. Flow through system was applied to the MEB and

Stepped system to reduce brine formation inside the solar still. The reservoir is a

black barrel which aids in preheating the water that enters the solar still basin. The

pump is powered by a Goal Zero solar generator.

pH of the water collected are measured overtime using YSI 85 salinity probe, and

volume of water collected is being measured using a graduated cyclinder. The

temperature of the copper sheet for OAS system and inside the solar still for all the

system, are being measured via Etekcity laser grip 1080 non-contact digital laser

infrared thermometer along with HOBO logger which measures light intensity and

temperature inside the systems. Extech RF20, portable salinity refractometer is

being used to measure the salinity of the reservoir.

Convective cover

Metal plate

Hydrophilic cloth

Floating material

Wicking material

Solar

irradiation

Water

evaporation

Capillary

action

Figure 3: One-sun Ambient

Steam Generator (OAS)

Seawater

Solar still modifications

Figure 5: Multi-effect basin with

wicking material and reflective

mirrors (MEB)

Multi-effect: Increases the thermal efficiency.

Available energy in the form of latent heat, (the

energy required to turn the liquid water into

vapor) is captured from the lower chamber and

reused to heat up water in the upper chamber.

Reflectors: Increased temperature yields higher

evaporation rates; therefore reflecting mirrors are

placed on the top (north side) and bottom (south

side) of the still to direct solar radiation into the

basin.

Wicking material: Instead of a flat plate, a

material with fabric made of cylindrical polyester

will increase the surface area of the water,

allowing more to be absorbed in the base and

susceptible to evaporation to be evaporated.

OAS

SIER

MEB

Reflectors

Top chamber

Bottom

chamber

Wicking

material

Stepped: Decreases the distance the water

vapor travels before being collected via the

collection glass, thus producing more

condensate at a faster rate.

Internal and External Reflectors: Aims to

increase the amount of sun rays exposed to

the system to heat the water effectively and

efficiently. The addition of this feature is said

to increase freshwater yields by 100 to 120%

per square meter, which would, under ideal

conditions, increase the freshwater collected

to approximately 9 liters per day3.

Flow Through System: Contributes more

work to the water, creating more heat. A

black, external reservoir holds the water,

allowing for optimal UV radiation to heat the

seawater accordingly.

Figure 4: Stepped with Internal and

External Reflectors (SIER)

Rainmaker 550 Solar

Water Distiller

SIER Discussion

A primary goal of the stepped and reflector

design was to obtain optimal heating, which

would contribute to a higher freshwater yield.

While data collection is still in process, some

preliminary conclusions could be made.

Primarily, insulation of the interior is of optimal

importance for the function of the system.

Ensuring that the correct materials and

waterproof lining are used, has large effects on

the heating of the system and containing the

water in the system. Additionally, obtaining the

correct flow rate for the system is important, as

the amount of flow contributes to the amount

evaporated – a flow of about 15 gallons per

hour is suspected to produce optimal yeild1. It

was also observed that starting the flow

through system would be best after the black

reservoir has the opportunity to heat up. This

gives the water in subjected to the reflectors

and large surface area the opportunity to

evaporate while the reservoir is heating up as

well. Therefore, the water pump should not be

used until a certain water temperature is

obtained.

MEB Discussion

Volume (mL)Average Still

Temperature (◦C)

Average Cu sheet

Temperature (◦C)Salinity

3/20/2017 - 4/1/2017 2350 NA NA 0.94

4/2/2017 - 4/5/2017 2730 30.9 33.85 ~0

4/6/2017 (overcast) 840 24.7 31.45 ~0

4/7/2017 460 23.3 36.9 ~0

Time (day) 1 2 3 4 5 6 7

H2O Volume collected

(L)20 2.95 2.25 3.2 3.28 3.53 3.23

pH 8.02 7.03 5.67 6.24 6.11 6.54 6.89

EC (ppm) 32 0 0.1 0 0 0.2 0.2

Table 1: Experimental data gathered by McBryan et al using SolAqua Rainmaker 550.

Table 2: Experimental data generated from OAS-solar still system.

The multi-effect basin is meant to increase the

thermal efficiency in the solar still. Available energy

in the form of latent heat, (latent heat being the

energy required to turn liquid water into vapor) is

captured from the lower chamber; thus reusing the

latent heat in the lower chamber to heat up water in

the upper chamber.

I decided to use reflectors to direct solar radiation

into the still because increased temperature yields

higher evaporation rates. Ideally the reflecting mirror

would be as long as the base on the basin is to

maximize the surface area for reflecting potential,

but due to complications, I could only hinge the 1’ x

3’ onto the still.

The wicking material is placed inside the still

because instead of using the flat base of the still to

hold the seawater, the fabric made of cylindrical

polyester will increase the surface area that will be

able to absorb the seawater, increasing susceptibility

to evaporation.

practice. In an effort to

respond to the water

crisis on Catalina

Island, by studying and

applying 3 feasible and

cost-effective hybrid

modifications, this

study aims to increase

the water production of

a solar still, a solar

USC Wrigley Marine Science

Center’s (WMSC)

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20000

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60000

80000

100000

120000

140000

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July

Au

gust

Septem…

Oct

ob

er

Novem…

Decem

…

Jan

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y

Feb

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Mar

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Ap

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May

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Lab/Housing Combined Water Use

25% Reduction50% ReductionFY 15/16FY 16/17

As the most plentiful

water source near the

island is, without a

doubt, the Pacific

Ocean, desalination is

an attractive option to

mitigate the water

crisis at the WMSC.

Desalination is most

commonly considered

to be an energy

intensive and

expensive procedure,

which deters most

from investing in the

driven distillation unit that produces fresh water upon salt water

evaporation and condensation. In this passive system, seawater in

a wedged shaped basin with glass placed on top to seal, is

evaporated. Water vapor is then captured by the glass cover. As the

water vapor condensates onto the glass, via gravity the water

captured drips down the slope into a freshwater collection trough,

then to a collection vessel. Again, here we aim to increase the

water production of a conventional solar still by applying simple

and feasible technological improvements.

Figure 1 (Wrigley Institute Water Bill): The orange

and blue lines indicate the water mandates while the

purple and yellow represent the amount of water

used by the Wrigley Institute in 2016 and 2017.

Introduction

Engineering aspects for the MEB solar still and SIER are still being

modified and improved, therefore, the data is currently underway.

OAS Discussion

One of the important aspects of OAS is the

capillary system which is determined by the water

interactions that occurs between the phases at

which the water is traveling: the basin, through

the wicking material, absorbed by the hydrophilic

cloth then evaporated via convection by the

copper plate. Salt buildup was observed in the

OAS. Increase in salt concentration increases the

surface tension of the water thus reducing the

evaporation rate. This is due to the fact that

surface tension corresponds to intermolecular

forces, which leads to an inverse relationship

between surface tension and evaporation.

Second rusting was observed on the copper

plate. Rusting is basically the degradation of a

metallic material. Upon degradation this reduces

the surface area for kinetic energy. In addition to

that, rust can also act as an insulator which

prevents optimal heat transfer from the copper

sheet onto the hydrophilic cloth which then

reduces evaporation. A theoretical yield of 6

L/day during the summer months is expected

using the SolAqua Rainmaker 550. However, the

experimental set up and data gathering for this

study was conducted during Spring with

precipitation. This occurrence then added to the

reduced fresh water production since the system

was not running at optimal conditions.

AcknowledgementsThis research was supported in part by the Wrigley Institute for Environmental Studies. Thank you

to the USC Wrigley Marine Science Center’s (WMSC) staff: Kellie Spafford, Chris Rodgers, Josh

Jensen, and Randy Phelps for their assistance during the field set up of the solar stills. . Special

thanks to Bryan Tufts Ralph Bolam and Maurice Roper for constructing the solar stills. Lastly, thank

you to the alternative Spring break participants.

** presented a the 2017 USC Undergraduate Research Symposium and City of LA Spring Green EXPO