1. The problem statement, all variables and given/known data A solar heater is used to warm 150 kg of water by 30 K. The intensity of solar radiation is 6000 Wm-2 and the area of the panels is 4.0 m2. The specific heat capacity of the water is 4.2 * 103 J/kg/K. Estimate the time this will take, assuming a solar panel efficiency of 60%. 2. Relevant equations E=mcΔT 3. The attempt at a solution Since there are 4 metres squared of solar panel and an efficiency of 60%: 6000 x 0.6 x 4 = 14400 W The amount of energy needed to heat the water is: E = mcΔT = 150 x 4.2 x 10^3 x 30 = 1.89 x 10^7 J Therefore the time it will take is (1.89 x 10^7 J) / 14400 W = 1312.5 s = about 22 minutes. In the answer sheet it says 3.6 hours, so I'm not sure where I went wrong. Any help is appreciated!