# Solar Energy Questions and Answers – Hourly Global, Diffuse and Beam Radiations on Horizontal Surface Under Cloudless Skies

This set of Solar Energy Questions and Answers for Experienced people focuses on “Hourly Global, Diffuse and Beam Radiations on Horizontal
Surface Under Cloudless Skies”.

1. Hourly radiation values can be used to evaluate the performance of ________
a) flat plate collectors
b) curved collectors
c) parabolic collectors
d) metallic collectors

Explanation: Hourly values of solar radiation provides very precise information about performance of solar energy systems. For example, hourly radiation values can be used to evaluate the performance of flat plate collectors.

2. Why are global and diffuse radiation values not measured?
a) Because of sophisticated measuring instruments
b) Because measuring instruments are not available everywhere
c) Because of unavailability of skilled labour to operate measuring instruments
d) Because measuring instruments are not available everywhere

Explanation: Global and diffuse radiation values are not measured mainly because measuring instruments are not available at all locations, in every lab or institute. The major problem is not unavailability of funds or skilled labour.

3. Which of the following is generally used to compute global and diffuse radiation values?
a) Parabolic dish
b) Flat plate collector
c) Theoretical models
d) Pyranometer

Explanation: Global and diffuse radiation values are generally computed from theoretical models. This is because of unavailability of measuring instruments at all locations. Pyranometer is used wherever and whenever possible.

4. Which of the following can be used to estimate beam radiation?
a) Photoelectric effect
b) Solar insolation constant
c) Time taken by sun’s rays to reach earth
d) Zenith angle and altitude

Explanation: Zenith angle and altitude of the location can be used to estimate beam radiation transmitted through a clear atmosphere. Though solar insolation constant is used, it is either just a scaling factor or a constant and not a variable. Photoelectric effect is not related to beam radiation.

5. What is zenith angle?
a) Angle between sun and vertical
b) Angle between the line joining the location on earth’s surface and the equatorial plane
c) Angle between extended sun’s rays to earth’s center and equatorial plane
d) Angle between projection of sun’s rays on horizontal surface and equatorial plane

Explanation: Zenith angle is the angle between sun’s ray and the vertical. Latitude is angle between the line joining the location on earth’s surface and the equatorial plane. Sun’s declination angle is angle between extended sun’s rays to earth’s center and equatorial plane.

6. Which of the following is not used to calculate hourly radiation?
a) Sun’s declination angle
b) Material of parabolic dish
c) Solar constant
d) Hour angle

Explanation: Material of the collector is not used to calculate hourly radiation. The material of the collector affects the values being measured and not theoretically computed values. Sun’s declination, hour angle and solar constant play their part in the computation.

7. Solar radiation on a horizontal surface is the summation of _______
a) direct and active solar radiation
b) active and diffuse solar radiation
c) diffuse and direct solar radiation
d) electrons and photons

Explanation: Solar radiation on a horizontal surface is the summation of diffuse and direct solar radiation. It is not just a summation of electrons and photons as the option does not specify the source of electrons and photons.

8. What are the two models used to determine diffuse radiation?
a) Rayleigh scattering and Hybrid pi model
b) Parametric model and Rayleigh scattering
c) Decomposition model and Hybrid pi model
d) Parametric and decomposition models

Explanation: The two models used to determine diffuse radiation are parametric and decomposition models. Rayleigh scattering is the scattering of light by suspended particles in a medium. Hybrid pi model is used to model a transistor and is not related to radiation.

9. Which of the following is required as a parameter in a parametric model?
a) Cloud cover
b) Solar insolation constant
c) Material of measuring instrument
d) Type of measuring instrument

Explanation: Cloud cover, atmospheric turbidity, fractional sunshine and perceptible water content are necessities of a parametric model. Though solar insolation constant may be required, it is not a parameter. In any theoretical mode, material and type of measuring instrument is irrelevant.

10. Which of the following is an example of parametric model used to compute diffuse radiation?
a) Chandrasekaran and Kumar’s model
b) ASHRAE model
c) Erb’s model
d) T-model

Explanation: ASHRAE model is an example of parametric model used to compute diffuse radiation. Erb’s model and Chandrasekaran and Kumar’s model are not parametric models. T-model is used to model a transistor and is not related to radiation.

11. How do decomposition models compute diffuse solar radiation?
a) From specific information of environmental conditions
b) From measuring instruments
c) From global solar radiation data
d) From ASHRAE model

Explanation: Decomposition models use global solar radiation data to estimate and compute diffuse solar radiation. Parametric models require specific information of environmental conditions to compute diffuse solar radiation.

12. Decomposition models are based on correlation between ____________
a) global solar radiation and active radiation
b) diffuse and UV radiation on vertical surface
c) diffuse and total radiation on inclined surface
d) diffuse and total radiation on horizontal surface

Explanation: Decomposition models are based on correlation between diffuse and total radiation on horizontal surface. UV radiation is a part of the total received solar radiation.

13. Which of the following does the correlation of decomposition models (between diffuse and total radiation on horizontal surface) depend on?
a) Hourly clearness index ratio
b) Daily clearness index ratio
c) Hourly global horizontal radiation
d) Yearly extraterrestrial radiation

Explanation: The correlation of decomposition models (between diffuse and total radiation on horizontal surface) depend on hourly clearness index ratio. It is the ratio of hourly global horizontal radiation to hourly extraterrestrial radiation.

14. The clearness index is a measure of atmospheric effects in an isolated place.
a) True
b) False

Explanation: The clearness index is a measure of atmospheric effects in an isolated place. It is used by decomposition models to estimate diffuse solar radiation data from global solar radiation.

15. Nijegorodov’s model revised the constants of ASHRAE’s model.
a) True
b) False

Explanation: Nijegorodov’s model revised the constants of ASHRAE’s model using a computer program. It was used to predict hourly and daily global solar radiation in Botswana.

Sanfoundry Global Education & Learning Series – Solar Energy.

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