Solar cooling, desalination

GROUP 9

- S. Prashanth Kumar

- R. Gautam Reddy

- S. Prithvi Raj

Global Stats & Facts

Availability of fresh water supply for agricultural,

industrial and domestic uses is reaching critical

demands.

1.1 billion people around the world have no access to

clean drinking water.

The World Health Organization reports that

contaminated water contributes to 80% of all sickness

and disease worldwide.

The total amount of water available on earth has been

estimated at 1.4 billion cubic kilometres, enough to cover the

planet with a layer of about 3-km deep.

Desalination

Desalination refers to any of several processes that

remove excess salt and other minerals from water for

○ Human Use

○ Irrigation

○ Animal use

Concentration Of Salt

Fresh Water Less than 0.5 ppt

Brackish Water 0.5-30 ppt

Saline Water 30-50 ppt

Brine Greater than 50 ppt

Desalination Techniques

Distillation

– Multi-stage flash distillation

– Multiple effect distillation

Membrane processes

– Reverse osmosis

Solar Humidification (Solar still)

Distillation

Multi-Stage-Flash Distillation:

The leading method

The traditional process used in these operations is

vacuum distillation-essentially the boiling of water at

less than atmospheric pressure and temperature.

Lesser energy requirement

Multi-Effect

Single Effect

Multiple-Effect

Distillation

Reverse Osmosis Reverse osmosis (RO) is a filtration method that removes

many types of large molecules and ions from solutions by

applying pressure to the solution when it is on one side of a

permeable membrane.

The result is that the solute is retained on the pressurized

side of the membrane and the pure solvent is allowed to

pass to the other side.

Overview:

Uses electricity rather than heat

Proven technology

For a typical community level solar powered RO

plant:

PARAMETER VALUE

Capacity (lit/day) 2000

Feed Salinity (ppm) 2000 – 2500

Product Recovery (% ) 70 - 80

Pressure (kPa) 1.1 x 103 – 1.2 x 103

Power Requirement (kW) 1.6 - 1.8

Product Salinity (ppm) 200 - 250

Solar Desalination

The process is based on the use of solar thermal energy to evaporate water, thus separating pure water from brine.

Direct Solar Desalination:

Indirect Solar Desalination

Direct Solar Desalination

Still Humidification-Dehumidification

HD

Single-effect Multi-effect

Direct Solar Desalination

Single-effect Stills

Water production < 6 liters/m2,day

Examples:

Basin stills

Wick stills

Greenhouse integrated stills

basin-type solar still

Basin still with radioactive cooling

Condenser

◦ Packed Bed

◦ Cooled during night

Evaporator

◦ Solar still

◦ Natural Convection

Production

◦ 5-6 litres/m2,day

SOLAR STILL OUTPUT DEPENDS ON MANY

PARAMETERS

Climatic Parameters

Solar Radiation : The still output increased from 1.76 liters/m2 day at 16.74 MJ/m2 day to 5.11 liters/m2 day at 27.08 MJ/m2 day.

Ambient Temperature: An increase in still output was observed with increase in ambient temperature. The increase in output is about 0.87 liters/m2 day for each 10°C rise in ambient temperature.

Operational parameters

Water Depth: Higher distillate output was

observed with lower water depth.

Preheating of Water

Coloring of Water: The effect of dye on water

output was also studied. The output got increased

by colouring the water.

Multiple-effect basin stills

have two or more compartments.

The condensing surface of the lower compartment is

the floor of the upper compartment.

The heat given off by the condensing vapor provides

energy to vaporize the feed water above.

Efficiency is therefore greater than for a single-basin

still typically being 35% or more but the cost and

complexity are correspondingly higher.

Direct Solar Desalination

Humidification - Dehumidification

Water production 1 - 20 litres/m2,day

HD with open-air cycle

HD with open-air cycle

Humidification

◦ Water heating by

solar collector

Dehumidification

◦ Ambient air

Production◦ 6 litres/m2,day

Solar Air Conditioning

Air conditioning is the control of the indoorenvironment by controlling the thermalcharacteristics mainly heating and coolingthe air supplied to the room.

Solar air conditioning refers to the use ofsolar energy to power a cooling appliance.

Days that have the greatest need forcooling are also the very same days thatoffer the maximum possible solar energygain.

There are several basic types of solar

cooling technologies

1. Absorption Cooling

2. Desiccant Cooling

3. Vapor Compression Cooling

4. Photovoltaic Solar Cooling

5. Evaporative Cooling

Absorption Cooling

The basic principle behind solar-thermaldriven cooling is the thermo chemicalprocess of absorption of a liquid or agaseous substance into a liquid or a solidmaterial.

Solar cooling uses the solar collectors toprovide thermal energy to drive thermallydriven coolers.

The usefulness of a given absorbent -refrigerant pair is determined by thetemperature dependence of vaporizationand absorption process.

LiBr – water solar cooling system

Desiccant Cooling

Desiccant cooling is a new and cleantechnology which can be used to cool theinside air of the buildings without using anyharmful refrigerants.

Desiccant cooling systems are basicallyopen cycle systems using water as arefrigerant in direct contact with air.

Desiccants like silica gel or zeolite drawmoisture from the air and they areregenerated by using solar thermal energy.

Desiccant cooling system

Desiccant Cycle

In a vapor compression cooling , the solar

thermal energy is used to operate a Rankine

cycle heat engine

The solar power also converted to electricity

can be used to run the air conditioning

systems.

Evaporative cooling is to spray water into dry

air where the temperature is reduced by

evaporation water into the air.

Zero energy building

Conclusions

Integrating desalination units with renewable energy sources

is important for addressing the issues related to adverse

impacts of climate change.

Also, for remote areas, where scarcity of power and water

co-exist, the one and only solution to produce safe drinking

water is to go in for renewable energy sources.

With improvement in PV efficiencies and the subsidies

available, cost of PV systems is expected to come down,

making the solar PV based desalination systems more cost-

effective.

Reference

http://en.wikipedia.org/wiki

http://www.solarserver.com

http://www.daviddarling.info/encyclopedia

http://www.solarcoolingtypes.com/

http://www.solair-project.eu/146.0.html

Renewable energy conversion transmission and storage – Bent Sorensen

THANK YOU