appropriate technologies

7/25/2019 Appropriate Technologies

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APPROPRIATE TECHNOLOGIES

USED IN DEVELOPING COUNTRIESBy Trish Morrow

https://www.linkedin.com/in/trish-morrow-27959988


2/23

What is a solar stove?

Any device which uses heat from the sun to cook food or boil drinking water.

Does not use electrical energy from photovoltaic modules, just uses heat.

http://www.solarcooking.org/gallery1.htmhttp://www.solarcooking.org/gallery1.htm


3/23

Why use solar energy for cooking?In developing countries biomass is burnt as

the primary source of domestic energy for

cooking, heating and boiling contaminated

drinking water. (Kammen, 1991)

About half the population of China boil

their drinking water mostly over biomass

stoves 1% of Jakartas GDP is spent by the residents for

boiling their drinking water (Gadgil, 1998)

With an average cookstove efficiency of 12%,

fuelwood can only boil water three times its own

weighta typical family of five would use 12kg/day 1kg of firewood releases 440g CO2and ~650g C-

equivalent of non CO2greenhouse gases. (Gadgil,

1998)

50-100 acres of forest destroyed/minute(Lovejoy, 1991)

http://www.efn.org/~apro/atstove00.html
http://www.efn.org/~apro/atstove00.htmlhttp://www.efn.org/~apro/atstove00.html


4/23

Why use solar energy for cooking?http://www.webcom.com/bi/images/billboard.gif

Biomass burning in developing countries is firmly linked to acuterespiratory infection,a leading heath hazardto children in

developing nations, resulting in an estimated 4.3 million deaths per

year. (Kammen, 1991)

Other health effects - woodsmoke contributes to: pneumonia,

low birth weights, cataracts, and nervous or muscular fatigue.URL: htt ://www.solarcookin .or /cookin smoke.htm

Mara,D.D., Tropical Public Health Lecture Notes, University of Leeds, 2000.
http://www.webcom.com/bi/images/billboard.gifhttp://www.webcom.com/bi/images/billboard.gifhttp://www.webcom.com/bi/images/billboard.gifhttp://www.webcom.com/bi/images/billboard.gifhttp://www.webcom.com/bi/images/billboard.gif


5/23

How does woodsmoke compare with tobacco

smoke?CONSTITUENTS OF LEVELS FOUND IN LEVELS FOUND IN HEALTH

TOBACCO SMOKE WOOD SMOKE TOBACCO SMOKE EFFECTS

/ WOOD SMOKE (g/kg wood burnt) (ng/cigarette)

Aldehydes 0.6-5.4

Formaldehyde 0.1-0.7 70-100 Carcinogenic

Acetaldehyde 0.03-0.6 18-1400 Carcinogenic

Benzene 0.6-4.0 12-48 Carcinogenic

Benzo(a)anthracene 4x10-4 - 2x10-3 20-70 Carcinogenic

Chrysene 5x104- 1x10-2 40-60mg Carcinogenic

Benzofluoranthenes 6x10-4- 5x10-3 4-22 Carcinogenic

Benzo(a)pyrene 3x104- 5x10-3 20-40 Carcinogenic

Ideno(1,2,3-cd)pyrene 2xl0-4-1.3x10-2 4-20 Carcinogenic

Dibenzo(a,h)pyrene 3x104- lx10-3 1.7-3.2 Carcinogenic

Dibenz(a,h)anthracene 2x10-5 - 2xl0-3 4 Carcinogenic

Ca 9xl0-4-1.8x10-2 41-62 Carcinogenic

Cr 2x10-5 - 3x10-3 4-70 Carcinogenic

Ni lxl0-6 - lx10-3 0-600 Carcinogenic

References:URL: http://www.webcom.com/bi/table2.htmChemical constituents of Wood Smoke

URL: http://www.brown-and-williamson.com/Index_sub2.cfm?ID=18

Approximate Chemical Composition of Whole Mainstream Smoke
http://www.webcom.com/bi/table2.htmhttp://www.brown-and-williamson.com/Index_sub2.cfm?ID=18http://www.brown-and-williamson.com/Index_sub2.cfm?ID=18http://www.brown-and-williamson.com/Index_sub2.cfm?ID=18http://www.brown-and-williamson.com/Index_sub2.cfm?ID=18http://www.brown-and-williamson.com/Index_sub2.cfm?ID=18http://www.brown-and-williamson.com/Index_sub2.cfm?ID=18http://www.webcom.com/bi/table2.htm


6/23

How does a solar oven work?

http://www.solarcooking.org/sbcdes.htm#heat_gain


7/23

How does a solar oven work?

Sunlight enters the oven through the glass lid. It strikes the black

absorber plate in the base and changes in wavelength.

The longer wavelength infrared radiation is trapped by the glass

which is only transparent to shorter wavelengths

Insulation in the walls reduces heat escaping through them.

http://www.solarcooking.org/sbcdes.htm#heat_gain

Consider:

Heat gain into a solar oven

Heat loss from the box

Heat transfer from the oven to the cookingvessel

Effect of materials used for the box

Materials used for reflector and glazing

Volume of the cooking space, compared

with volume of food to be cooked


8/23

Thermodynamics of solar ovensHeat lossesare via

conductionthrough the oven walls andfloor,

convectionthrough any gaps in the lid or

around the glazing, air in the walls, or via

radiation.

http://www.solarcooking.org/fi/petrithe.htmRogers and Mayhew, 1981 Box Temperature as a functionof wall resistance

Thermal resistance due to conductionis defined by

the equation q = T1-T2R

where q is the heat flux (W/m2) and R is the thermal

resistance (m2W/C).

Heat flux due to radiationis given by the equationqr = 1 2K(T1

4-T24) A

1 - 1 2

whereis the emissivity of the wall surfaces and K is

the Stefan-Boltzman constant = 5.67 x 10-8(W/m2K4).


9/23

Thermodynamics of solar ovens

Heat loss from radiation isapproximately three times the loss

from convection.

To be able to reach a cooking

temperature of at least 100C, aresistance of at least 1 unit is needed.

Doubling the wall thickness from

5cm thick to 10 cm thick gives only a

6% increase in resistance.

http://www.solarcooking.org/fi/petrithe.htm

Total wall resistance is given by considering

radiation and convection resistance in parallel,to give the following equation: R = Rrad Rc

Rrad + Rc


10/23


Convection currents can be reduced by

providing a physical barrier to airflow eg. Abaffle or some insulating material.

Insulating materials used to prevent heat loss

include wood shavings, sawdust, rice husks,

peanut shells, newspaper, aluminium foil, andfor those who love wasting money, fibreglass.

Doubling the number of panes of glass (from

one to two) only decreases the heat loss

coefficient by 20%. Four panes instead of one

gives a 40% decrease only.

The most important mechanism of heat

transfer to the pot itself is by conduction from

the absorber plate. Optimum thickness 1mm.



11/23


Painting pots black is helpful but makes little

difference to the emissivity. Conduction is themost important form of heat transfer.

Elevating the absorber plate has no significant

effect overall.

Aluminium foil is the most effective reflector,given its low cost.


Material Durability Cost Specular

Reflectance

Mirrors Breakable Very high 0.88Aluminium Foil Tears easily Moderate 0.86

Aluminium Sheet Good High 0.85

Aluminised polyester Tears Moderate 0.75-0.85

Metal from fuel tins Rusts Moderate N/A


12/23

Other types of Solar Stoves

Parabolic solar stove

A hybrid type of

solar stove with a

sloping front and

multiple reflectors

Solar panel cooker uses reflectors like the

parabolic stove with an oven bag for glazing

http://xahlee.org/SpecialPlaneCurves_dir/Parabola_dir/parabola.html

Its all done with mirrors!

http://www.solarcooking.org/gallery1.htm


13/23

Pasteurisation of drinking water

Women in Nepal testingwaterquality using a Colilert

test kit

A water pasteurisationindicator is used to

indicate whether water

has reached 65C for 6

minutes.

The Colilert Test Kit

http://www.solarcooking.org/gallery2.htm

http://www.idexx.com/Water/Products/prod.cfm?ID=2

http://www.solarcooking.org/solarwat.htm


14/23

Where are solar stoves being used?

Solar radiation in Europe

Tens of thousands in China, hundreds of thousands in India

Projects in Chile, Nicaragua, Tanzania, Sierra Leone, Nepal,

Kenya, and Guatemala, to name but a few

Some used in developed countries, eg. United States

Solar radiation in Australia

We are

here!

URL http://www.bom.gov.au/sat/solrad.shtml: http://www.satellight.net/core.htm
http://www.satellight.net/core.htmhttp://www.satellight.net/core.htm


15/23

How does a composting toilet compare with

any other type of toilet?

They turn excreta into a valuable fertiliser, without contamination with

heavy metals.

They are usually built above ground (no pit to excavate)

They usually dont use any water for flushing (or very very little) .

http://www.compostingtoilet.org


16/23

How does a composting toilet compare with

any other type of toilet?Feachem et al, 1983

RANKING OF EXCRETA DISPOSAL TECHNOLOGIES BY EASE OF

OPERATION & MAINTENANCE, WATER NEEDS & HEALTH BENEFITS

Technology Lack of Effort Requireda WaterNeeds Health Benefitsb

User Municipality Ideal Actual

Flush Toilet/sewers/ 10 4 H 10 9

oxidation pond

Vault/Vacuum truck 8 0 L 8 6

Pit Latrine 8 5 L 8 6

Septic Tank 6 5 H 8 7

Aqua Privy 5 5 M 9 6

Bucket Latrine 3 1 L 5 1Batch Composter 1 10 L 8 5

Continuous Composter 0 10 L 7 3

L = low M = medium H = high

a 0 = maximum effort 10 = minimum effortb 0 = no benefits 10 = maximum benefits


17/23

Why use Composting Toilets?

Reduced use of expensive chemical

fertilisers Suitable for areas with high water table

No need for back-breaking work

digging latrine pits when the ground is too

stony

Water saving (40% of potable treatedwater is used for toilet flushing)

Energy saving (like all forms of on-site

sanitation)

Sale of compost may finance

composting latrine

Save money on water rates and septic

tank pumping

Avoid water and groundwater pollution


18/23

How does a composting toilet work?

True composting toilets provide a controlled environment to enable aerobic

decomposition.

Some toilets which separate urine primarily work by dehydrading the

faeces so that the pathogens die by dessication

May use baffles, mixers or fans to improve airflow, and may use heatingunits

Two types:

Batch(includes Carousel composting)

Continuous

http://www.compostingtoilet.org/3makers/aussie.htm

Wh i il b i


19/23

Where are composting toilets being

used?Mexico, Guatemala and

VietnamSome used in developed

countries, eg. Australia,

United States, United

Kingdom

Composting Toilets sold in the UK

BRAND NAMES COMPANY PRICE

Sun Mar Ecolet, Excel, Centrex Eastwood 1000

Clivus Kingsley Clivus

Dowmus Elemental solutions 2000

Aquatron Elemental solutions

http://www.elementalsolutions.co.uk
http://216.32.240.250/cgi-bin/linkrd?_lang=EN&lah=ccce88da2f4221c4bb581fa9b1b29426&lat=981312927&hm___action=http%3a%2f%2fwww%2eelementalsolutions%2eco%2eukhttp://216.32.240.250/cgi-bin/linkrd?_lang=EN&lah=ccce88da2f4221c4bb581fa9b1b29426&lat=981312927&hm___action=http%3a%2f%2fwww%2eelementalsolutions%2eco%2euk


20/23

Solar photovoltaic energyEnvironmentally sound (42 gCO

2/kWh vs 450g CO

2/kWh

for gas, Greijer et al, 2000)

Solar energy is more labour intensive, creating employment

(Solar thermal power employs 2.14 times more workers than

coal fired power stations, Truax, 1992)

Cost of system for one 30W panel, a battery and 4 x 10wfluorescent light tubes ~$600USD = 400

Appropriate Technologies Used in Developing Countries


21/23

Low Cost

Water Supply

Appropriate Technologies used in Developing Countries


22/23

Biogas for cooking


23/23

Indigenous peoples technical knowledge & skills

appropriate technologies

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