# Biomass Energy Questions and Answers – Solar Radiation on Inclined Plane Surface

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This set of Biomass Energy Problems focuses on “Solar Radiation on Inclined Plane Surface”.

1. When is the power density of the absorbing surface equal to the incident sunlight?
a) Absorbing surface and incident sunlight are perpendicular to each other
b) Absorbing surface and incident sunlight are parallel to each other
c) Absorbing surface and incident sunlight are inclined at an acute angle to each other
d) Absorbing surface and incident sunlight are inclined at an obtuse angle to each other

Explanation: Net power received from incident sunlight depends on two things – the power contained in the sunlight and the angle of the receiver with respect to the incident sunlight. Incident power equals the received power when the receiver is perpendicular to the incident sunlight.

2. For a fixed receiver, incident power density and received power density are always equal.
a) True
b) False

Explanation: For a fixed receiver, incident power density and received power density are not equal always. In fact, the net received power is often less than the incident power as the angle between the sun and the receiver changes continuously.

3. What is direct solar radiation?
b) Radiation reflected from an obstacle
c) Radiation traveling on a straight line from sun to earth
d) Sum of diffused and reflected radiation energies

Explanation: Direct solar radiation is that radiation which travels in a straight line from the sun. It travels to the earth without deviating from its path due to obstacles.

4. What is diffused solar radiation?
a) Sum of direct and reflected radiation energies
b) Radiation reflected from an obstacle
c) Radiation traveling on a straight line from sun to earth

Explanation: Diffused solar radiation is that radiation which has been scattered by molecules and particles in atmosphere. Though it deviates from its initial path, it does travel down to the earth.

5. Which of the following is tried to maximized in tilted receivers (panels)?

Explanation: Receivers are tilted to maximize the collection of direct solar radiation from the sun. The tilt tries to ensure that the receivers are perpendicular to the direct radiation. It accounts for the continuous change in angle between the sun and the receiver.

6. When receivers (panels) are laid horizontally, they usually collect _______
d) Heat

Explanation: When solar receivers (panels) are laid horizontally, they usually collect diffused radiation. This is because diffused radiation is equally distributed throughout the sky and hence can easily be gathered.

7. More the tilt in receivers (panels), larger amounts of diffused radiation is collected.
a) False
b) True

Explanation: More the tilt in receivers, larger amounts of direct radiation is collected. As the tilt increases, the amount of diffused radiation received considerably reduces.

8. What is reflected solar radiation?
a) Sum of direct and reflected radiation energies
b) Radiation reflected from an atmospheric obstacle
c) Radiation traveling on a straight line from sun to earth
d) Radiation reflected from a non-atmospheric obstacle

Explanation: Reflected solar radiation is that sunlight/radiation that is reflected from a non-atmospheric obstacle. The obstacles could be trees, ground, light poles, cars, etc. They do not contribute significantly towards electricity generation from solar panels.

9. Reflected solar radiation is used in _______
a) Snowy regions
b) Temperate region
c) Equatorial region
d) Tropical region

Explanation: Generally, reflected solar radiation does contribute significantly towards electricity generation. However, energy from reflected radiation is harvested in snowy regions as fresh snow reflects about 80-90% of the incident radiation.

10. What is global insolation?

Explanation: Global insolation or total insolation is the sum of the radiation received by earth from sun. It is nothing but the sum of direct radiation, diffused radiation and reflected radiation. This is used as a reference for the insolation at some tilt.

b) Sun’s radiation and striking surface are perpendicular to each other
c) Incident solar radiation and striking surface are perpendicular to each other
d) Global insolation – direct radiation

Explanation: Normal radiation describes the radiation that strikes a surface that is perpendicular to the sun’s radiation. It is not same as direct radiation as the it does not talk about the incident radiation. It may so happen that normal radiation and direct radiation may be the same at some tilt.

12. What is hour angle of the sun?
a) Angle of radiation with earth’s surface
b) Angle between the hands of sun dial
c) Angle made by the sun’s rays with moon’s surface
d) Orientation of earth with respect to sun

Explanation: Hour angle of sun is defined as the actual orientation of earth with respect to the sun. Mathematically, it is calculated by converting earth’s one rotation in degrees and dividing it by the time taken – 360/24 = 15 degrees/h.

13. What is solar intensity?
a) Amount of outgoing solar energy
b) Amount of incoming solar energy on a plane surface
c) Amount of outgoing solar energy on a plane surface per unit time
d) Amount of incoming solar energy on a plane surface per unit time per unit area

Explanation: Solar intensity is defined as the amount of incoming solar energy on a plane surface per unit time per unit area. It is a weighted average of the full radiation and is equal to 1367 Watt/square meter.

14. What is solar azimuth angle?
a) Orientation of earth with respect to sun
b) Orientation of moon with respect to sun
c) Angle of radiation with earth’s surface
d) Angular distance between zero azimuth and sun’s projection on ground

Explanation: Solar azimuth angle is defined as the angular distance between zero azimuth and the projection of the line of sight to sun on the ground. Zero azimuth is a line due north or due south. Azimuth angle is measured clockwise from zero azimuth.

15. Diffuse radiation models can be classified into ________ and __________
a) direct and reflective
c) isotropic and anisotropic 