Question

The average energy per unit time per unit area that reaches the upper atmosphere of the Earth from the Sun, called the solar constant, is 1.47 kW/m2. Because of absorption and re- flection by the atmosphere, about 0.9 kW/m2 reaches the surface of the earth on a clear day. How much energy is collected during 1 h of daylight by a window that measures 1.1 m by 1.5 m? The window is on a mount that rotates, keeping the window facing the sun so the sun's rays remain perpendicular to the window. Answer in units of MJ.

Answer 1

Answer: 5.34 MJ

Explanation: The window is a rectangle with area:

A = 1.1(1.5)

A = 1.65 m²

We know that only 0.9 kW/m² reaches Earth so:

P = $0.9\frac{kW}{m^{2}}(1.65)m^{2}$

P = 1.485 x 10³ W

Watts is an unit of Power and it can also be written as J/s.

An hour has 3600s or 3.6 x 10³s, so:

E = 1.485 x 10³ $\frac{J}{s}$(3.6 x 10³s)

E = 5.346 x 10⁶ J

Mega is equal to 10⁶, then:

E = 5.35 MJ

A 1.1 m by 1.5 m window collects, during 1 hour of daylight, 5.35 MJ