Chapter 5 Solar Thermal: Basics COPY

Question 1

Primary energy demand is increasing continuously during last 50 years, how does it look like in the next years?

Answer 1

• In OECD countries stagnation is observed
• China and India are the emerging markets with the largest increase
• In the near future steady increase is projected

Worldwide the energy content is going to reach 18 bio toe

1 toe = 41.87 GJ

Energy content of a coal wagon: 2790 GJ

Question 2

There are two types of solar thermal power plants?

Answer 2

• Using concentrated incident solar radiation on an absorber (CSP – Concentrated Solar Power)
• Without using concentrated solar radiation

Question 3

Explain what a photon is and give some of its properties

Answer 3

Photon (derived from Greek: phōs - “Light”) is an elementary excitation of the quantized electromagnetic field

It exhibits properties of both waves and particles —> Wave-particle duality

Photons are massless –> m = 0 kg

Photons move at the speed of light –> In vacuum this is 𝑐0 ≈ 300 000 Km/s

Question 4

How does frequency and wavelength relate to each other?

Give also the relationship between energy and the freq of a photon!

Answer 4

All wavelengths have the same propagation speed, 𝑐₀ in vacuum so

𝑐_{0 = lambda} * f

Planck’s constant describes the relationship between energy and frequency of a photon

Energy of an photon: 𝐸 = ℎ ⋅ 𝑓

Planck’s constant ℎ = 6.636 × 10−34 𝐽𝑠

–> The shorter the wavelength (or higher the frequency), the greater is the Energy of the photon

Question 5

Give the spectral range and name few of its ray types!

Answer 5

Question 6

What are the four interactions between electromagnetic wave and a material?

Answer 6

• Absorption
• Reflection
• Transmission
• Emission

Question 7

The darker the body:

• The higher is the degree of absorption alpha ?
• The lower the degree of absorption alpha ?

Answer 7

• The higher is the degree of absorption alpha

Question 8

The emissivity for perfect mirrors is equal to ?

Answer 8

0

Question 9

Complete the following table

Answer 9

Question 10

State Planck’s Law and explain what does it state!

Answer 10

Planck’s law describes the spectral density of electromagnetic radiation emitted by a black body in thermal equilibrium at a given temperature T.

• The wavelength of maximum intensity decreases with increasing temperature
• The higher the temperature, the higher is this maximum intensity

Question 11

What did Stefan-Boltzmann law add to the Plancks Law?

Answer 11

The law specifies the thermal power emitted by an ideal black body as a function of its temperature

So for a non black body: we add to the equation the emissivity variable _€(T)