# Thermodynamics question?

1. Oct 17, 2011

### Ishida52134

1. The problem statement, all variables and given/known data

In a solar water heater, energy from the Sun is gathered by rooftop collectors, which circulate water through tubes in the collector. The solar radiation enters the collector through a transparent cover and warms the water in the tubes. Assuming that 80% of the incident solar energy gets lost (i.e; it does not go into heating the water), what collector area is necessary to take water from a 200-L tank and raise its temperature from 20 C to 40 C in 1.0 h? The intensity of incident sunlight is 700 W/m^2.

2. Relevant equations

Q = mcdelta t

delta t = iR

3. The attempt at a solution

2. Oct 17, 2011

### SammyS

Staff Emeritus
Welcome to PF.

What have you tried?

Where are you stuck?

3. Oct 18, 2011

### Ishida52134

I've tried applying those formulas and combinations of them. I don't really understand the problem.

4. Oct 18, 2011

### SammyS

Staff Emeritus
What is the definition of power?

How much energy does it take to raise the temperature of 1 kg of H2O by 1°C