Power/radiated energy/emissivity/tempera... (stefan's law) problem?


Question:
A solar heating system has a 25% conversion efficiency; the solar radiation incident on the panels is 500 W/m^2. What is the increase in temperature of 30 kg of water in a 1.0 h period by a 4.0 m^2 area collector?

Answer:
25% of 500 W/m^2 is 125 W/m^2.

In 4m^2 area the power received is 4m^2 x 125W/m^2
=500 W = 500 J/s.

In one hour i.e., in 3600s the energy received is
3600 x 500 = 1800 k J.

The energy required to raise the temperature of 1kg water through 1 degree centigrade is 4.190 k J.

The energy required to raise the temperature of 30 kg water through 1 degree centigrade is
30 x 4.19 = 125.7 k J.

Increase in temperature when 1800 kJ is given to 30 kg of water is {1800 kJ / 125.7kJ} 14.32 degree centigrade.
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