Spread Sheet showing how to calculate eficiency.
Edit
It is not based on any actual data.
It shows calculations for two solar cookers of areas of 2.5 Sq Mts and 10 Sq Mts.
| Physical constants
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| Specific Heat of water
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| 1
| Calories/gm
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| Specific Heat of Aluminium
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| 0.21
| Calories/gm
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| Solar Constant
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| 1.94
| cal per min per sq cm
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| Latent heat of Vaporisation of water
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| 540
| Calories/gm
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| Constants Assumed
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| Ambient Temperature
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| 20
| 20
| 20
| Centigrade
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| Area of Reflector Sq Meters
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| 2.5
| 2.5
| 10
| Sq. Mts.
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| Variables Assumed
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| Weight of Water
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| 1000
| 10000
| 50000
| gms
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| Weight of Al. Vessel
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| 250
| 2000
| 5000
| gms
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| Time required to evaporate above quantity of water
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| 45
| 480
| 540
| minutes
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| Input Given
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| Energy received from Sun in time required to evaporate
| Area * Solar Constant* Time
| 2182500
| 23280000
| 104760000
| Calories
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| Or in Kilo Calories
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| 2182.5
| 23280
| 104760
| K Cal
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| Output Obtained
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| Calories required to:
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| Raise Water to Boiling point
| 'Weight of Water * Specific heat * Temp Difference
| 80000
| 800000
| 4000000
| Calories
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| For Evaporation
| Weight of Water * Latent Heat of Evaporation
| 540000
| 5400000
| 27000000
| Calories
| Notice that Latent Heat of Evaporation is about 7 times the Heat required to reach the boiling point
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| Sub Total ( Water)
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| 620000
| 6200000
| 31000000
| Calories
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| Raise Aluminium to 100 C
| Weight of Aluminium * Specific Heat of Aluminium * Temp Difference
| 4200
| 33600
| 84000
| Calories
| This is usually an insignificant amount
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| Sub Total ( Al)
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| 4200
| 33600
| 84000
| Calories
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| Grand Total (Water + Al)
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| 624200
| 6233600
| 31084000
| Calories
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| Or in Kilo Calories
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| 624.2
| 6233.6
| 31084
| K Cal
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| Efficiency (GT( Water+Al) / Input %
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| 28.60%
| 26.78%
| 29.67%
| Percent
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| Efficiency (GT( Water+Al) / Input %
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