energy problems

1. The statement given in C is the "coefficient of performance", not the "energy efficiency". Energy efficiency is to achieve the same goal (i.e. cooling) but use less energy.

2. "End-use energy efficiency" measures how efficient energy is delivered to end-users. It is irrelevant to the energy efficiency of an air-conditioner.

3. Halogen lamp enables the filament to reach a much higher temperature than ordinary tungsten lamp, thus producing more light than ordinary tungsten lamp.

4. Renewable enrgy direct from the sun: solar panels or solar cells.
Indirect from the sun: wind power, tidal power etc. The blowing of wind and changing of tides are due to energy from the sun.

5. When the sun is overhead, all light rays from the sun are incident normally onto the ground. After 3 hous, the sun's light rays are inclined at 45 degrees to the horizontal ground. The light-ray component that is incident perpendicular to the ground thus equals to the (overhead light-ray) x cos(45)