The surface area of a concentrator type solar heater is 5 $m^{2}$. It can reflect 80% of solar radiation incident on it while it absorbs the rest. Calculate the energy concentrated by the heater at its focus in 2 hours, if solar energy was delivered to it at the rate of 0.4 kJ/$m^{2}$s.

Energy concentrated = Reflecting percentage of energy x Surface area x Time x Rate of solar energy delivered

= $\frac{8}{{100}}$ x 5 x (2 x 60 x 60) x 0.4 x $10^{3}$

= 11520 x $10^{3}$J

=11.52 x $10^{6}$ J

= 11.52 MJ [ $10^{3}$ J = 1MJ]