Renewable Energy Technologies-ME659

Lecture -1

Dr. K.S.REDDY Heat Transfer &Thermal Power Lab.

Department of Mechanical Engineering INDIAN INSTITUTE OF TECHNOLOGY MADRAS,CHENNAI-600 036

Energy Conversion Device

Use

D

E

F

Environment

Finite Source of energy potential

Fossil Fuel - Energy System

Renewable Energy Systems

Environment

Energy Conversion Device

Use

Environment

Current Source of continuous energy flow A

B

C

D

E

F

Renewable Energy System

Environmental Energy

Total solar flux incident at sea level is about 1.2X1017W

Solar Radiation

Tides

Heat

Photosynthesis

KE

Latent Heat, PE

Sensible Heating

Geothermal

Gravitation Orbital motion

From Sun

From Earth

3

30

120,000

Reflected to space 50,000

30

300

40,000

80,000

Tidal power

Geothermal installation

Biofuels

Wind and Wave Conversion

Hydro Power

Solar Power OTEC

The alternative energy sources include: Solar power - Wind power - Biomass fuels Ocean power - Geothermal power - Hydroelectric power

Renewable Energy Technologies

Reference Book: 1. John Twidell and Tone Wier, Renewable Energy Resources 2nd Edn.,

Taylor & Francis (2007) 2. G N Tiwari and M K Ghosal, Renewable Energy Resources- Basic

Principles & Applications , Narosa Publishing House (2005) 3. D Yogi Goswami & Frank Kreith, Edt. Energy Conversion, CRC Press,

Taylor & Francis Group. (2008)

Solar Thermal Power Generation Energy From Sun (Source for REs) Solar technologies have shown greatest potential for cost effective energy

generation. The estimated power released by the sun is of the order of 3.8x1026W The Earth intercepts 1.78 x 1017 W.

(20,000 times the present energy Demand) Approximately 1 % of the world's desert area utilized by solar thermal power plants

would be sufficient to generate the world's entire electricity demand.

Suitable Regions for Solar Thermal Power Plants

Direct radiation 5kWh/md

Solar Energy Utilization

Direct Conversion Indirect Conversion

Thermal Photovoltaic

Water Power Wind Energy Bio - Mass

Ocean Energy

Wave Tidal OTEC

Water Heating Drying of Food

Cooking Distillation

Refrigeration Green Houses Power Generation

Power Generation

Abundantly available, Environment friendly. Economically viable in remote areas.

Solar Energy Conversion System

Solar Thermal Power Technologies

Mirror Systems Air Moving Systems Non-Mirror Systems

Solar Pond (CR=1, T

Power Cycles for Solar Energy Conversion

Rankine Cycle - water or organic fluid Brayton Cycle - helium or air Hybrid Cycles Stirling Cycle - helium or air

Based on Temperature : Low Temperature : < 100 oC Medium Temperature: 100-400 oC High Temperature :>400 oC

Cycles may classified as

Optimum Operating Temperature

Low Temperature Solar Power Systems Flat Plate Collector- Day &Night Generator 1904

The hot water at temperatures close to 100 oC is stored in a well-insulated thermal storage tank

( ) ( )w c R R L fi aQ A F S F U T T =

( )( )L fi a

th R

U T TF

S

=

Thermal efficiency of the system is given by

Heat collected

1 expp L cRL c p

mC F U AFU A mC

=

&&

Where

ORC is used to produce power from low temperature heat. Working fluids :Methyl Chloride, Toluene, SO2 and Refrigerants R11,R113 and R114 The overall efficiency (2%) is rather low, because of low T~50 oC

Collector efficiency = 25% ORC efficiency = 7-8% A 10 kW plant installed at IITM during 1979-80 under Indo-German collaboration Cost :

Rs. 3,00,000/- kW for 6-8 hours of operation.

Temperature inversions have been observed in natural lakes and high concentration of dissolved salts in the bottom layers.

This phenomenon suggested the possibility using ponds as large scale horizontal solar collector.

Solar Ponds

Solar Ponds

Shallow Solar Ponds Salt-Gradient Solar Ponds

Solar radiation absorbed by the pond liner and can attain temperatures of up to 60C .

The Collector Modules are : 4m wide X 200m long

Sometime honeycombs also used as cover

Pond Lining: Butyl Rubber, Black Polyethylene and Hipalon reinforced with nylon mesh For leak proof: Embankments and membrane liners Clay over the liners to make to protect them and and improve their durability.

Salts(brine): MgCl2, NaCl and Sodium nitride

Salt-Gradient Solar Pond

The heat storage zone , or Lower Convective Zone (LCZ): Ideally, this is a near saturated saline solution.

This is best achieved by direct injection of concentrated brine into the LCZ.

A salt-gradient non-convective solar pond can be considered to have three layers:

The top, or Upper Convective Zone (UCZ). : This is relatively fresh water, about 30 cm thick.

Increasing the thickness of this layer decreases the ponds ability to store heat.

It is difficult to keep this less than 0.4 m in thickness if pond size is greater than 10 hectares.

The gradient, or Non-Convective Zone (NCZ).

The insulating zone can be 0.5 to 1.5m thick, depending on the application.

x

D

C1 C2

1

T1 T2

2

A

B

Let T,, C are Temp., Density and Concentrations of the solar pond.

No convection occurs so long as the curve AB is positive. The condition that the lower layer remain denser than

those above is given by d/dx>0; Since = (C,T)

Solar Pond Concentration

The condition for stability is

x

D

C1 C2

1

T1 T2

2

A

B

0T C

dC dTC dx T dx + >

C

T

dTdC T dxdx

C

>

or

Considering effect of small perturbations

C

T

dTdC T dxdx D

C

+ > +

Where kinematic viscosity, Thermal diffusivity, D Diffusivity of salt in water

Where k = thermal conductivity of the solution in NCZ

x = thickness of the gradient zone Ug = ground loss coefficient P = Perimeter of a pond area of A kg = effective thermal conductivity of the ground

under the pond xg = distance from bottom of the pond down to the

water table a,b = constants for a particular pond

( )( )u eff g LCZ UCZkQ A S U T Tx

= +

g gg

a bPU kx A

= + The Steady-state energy equation can be

written as: Heat collected

Solar Pond Power Plant

India: First solar pond was built at Bhavnagar with 1200 m2 Other ponds Pondicherry : 100 m2

IISc Bangalore: 240 m2 Hubli : 300 m2 Bhuj : 6000 m2 largest 1993 Process heat needs of dairy

The first experimental solar ponds were constructed in Israel in early 60s.

Capacities: 6kW and 150kW Worlds largest solar pond: 5MW

with 2,50,000 m2 was constructed in 1984.

Solar Chimney(Up Draft) Green House Effect, Chimney Effect Wind Turbine (Kaplan type)

Thermal Model of Solar Chimney Solar Collector The energy balance for air is give

as (for steady state) Qu = ()eff AC S UL AC TCA = m Cp TChA = C AC S

The mass flow rate of hot air passing through the solar chimney,

m = a ACh VC Where a air density, ACh chimney area

S

AC ()eff

TA

TC

TCh

UL

TCA = TC-TA

where TChA = TCh-TA ACh Hch

The efficiency of collector is given by

( ) C L C CAeffC

a Ch p ChA

A U A TV

A C T

=

( ) L CAC effC

U TQA S S

= = The air velocity at outlet of the solar collector is expressed by

If the air temperature flowing in the solar collector increases linearly along with flow direction, TCA could be estimated as

( )2 1CAC L R

QT FA U F

=

F! is the efficiency factor of solar collector Flow factor is given by F!! = FR/F!

11

2

R

C L

F

A UFmCp

=

+

Where the heat removal factor, FR can be estimated by

Furthermore TCA can be expressed as TCA =1/2 TChA

Solar Chimney The chimney is a pressure tube with friction

loss because of its optimal surface plume ratio.

The chimney efficiency is expressed as: FW Ch

SChp a

P gHQ C T

= =

PFW Power contained in the flow

Where Hch height of the chimney

ChFW C a C ChA Ch

a

gHP Q V T AT

= =

The pressure difference, p, which produced between the chimney base and the surroundings is given by

ChAa Ch

a

Tp gHT

=

Thermal Model of Solar Chimney

Turbine: Static pressure is converted to rotate energy using a cased turbine.

Max. mechanical power taken up the turbine

max2 23 3W C Ch C Ch Cp a

gP V A p H A SC T

= =

23We C TG Ch Cp a

gP H A SC T

=

Electrical power: Pwe =Pwmax X TG

Prototype Plant at Manzanares

Tower height 200 m,

Collector Collector 240m

7 years test phase years test phase successfully completed

100 MW Solar Chimney Height: 1000m, Diameter: 130m Wall thickness at base: 1m, at top : 0,25m Collector: Radius: 3500m, Height outside: 3,5m Height at chimney: 35m, Output: 700 GWhel

Down Draft System- Sneh Aero-electric Power(SNAP) System

SNAP technology uses hot dry air and water to produce electricity.

When a passing cloud sheds rain into hot air, a strong downward draft called WIND SHEAR is generated.

The sprayed water evaporates, making the air at the top of the flue cooler and heavier than the surroundings.

If air is cooled by 12oC, it becomes approx. 4% heavier than previous state. The heavier air can reach a speed of 80kmph.

Besides power production, desalinated water from seawater can be obtained.

SNeh Burning Bush (Hebrew lang.) refers bush burned not consumed Natural Phenomenon-rain on to dry air-create strong

sustained wind drive wind turbines Power plant-hollow tower-openings at bottom-wind

turbines in opening-water spray over hot dry air-heavier air sinks down the tower-meets turbine-exit at the bottom