A hot-water heater is operated by solar power. If the solar collector has an area of 6.0 m2 and the power delivered by sunlight is 550 W/m2, how long will it take to increase the temperature of 1 m3 of water from 23°C to 61°C?
Rate of heat supply = 550 J/s x 6.0m² = 3300 J/s
Heat energy required H = m.s.∆θ
H = (1000kg)(4200 J/kg.ºC)(38ºC) = 1.60^8 J
t = 1.60^8 J / 3300 J/s .. .. ►t = 4.84^4 s .. (13.4 hr)