RE2

We can measure the fluctuations of the solar constant with satelites => therfore we know, that it is more or less a regular pattern => overall it is not increasing or decreasing => doesn´t fit the climate change behavior

This is not caused by astronomy! But in the tropics we have a lot of rain and much more coulds => therefore the absolut radiation, that hits the ground is reduced (absorption, refelction)

In the Sub-Tropics we have much less rain and almost no clouds => higher solar radiation, especially direct irradience!

P: Power

A: Area

w: Frequency

h: Plank´s constant

c: Speed of light

T: Temperature

kB: Boltzmann constant

h*w= Energy of the photon

=> The Energy of a photon is not constant, but every photon has energy! Dependant on the wave lenght and therefore on the frequency.

When the energy of a photon is below the band energy gap, it can´t lift the electrons fom the valance band into the conduction band => no voltage and no current can be produced.

The Band Gap of silicon, a material that is often used for PV Cells, is 1.11 eV. = 1110 nanometer

visible light 400 - 780 nm => Infrared, visible light, (uv) is used by a PV cell

Longer wavelenght such as micro waves, radio waves,… are not used

Very short wavelenght like gamma rays have to much energy => they kick the electron out of the semi conductor

Uv van only be used by some cells

Measurements by Pyranometer (direct&diffuse) and Pyrheliometer (direct)

1) Sensible Heat Storrage (well known, low cost, lowest capacity, days to months)

Heat is stored by raising the temperature of a liquid or solid storrage medium like water, sand, molten salt, rocks,…

2) Latent Heat Storrage (newer, intermediate capacity and cost, hours to months)

Heat is stored by taking advantage of energy absorbed at constant temperature during phase change of a material (liquid/solid); It releases heat again, when it becomes soild again

3) Thermochemical Heat Storage (new, highest capacity and cost, hours to days)

Heat is stored by dissociating compounds AB into reaction products A and B

Upon recombination of the reactants, an exothermic reaction takes place and stored heat is recovered

The biggest benefit is, thta heat can be stored much esier than electricity. To store electricity a extra battery is needed => extra system costs.

Also CSP´s can reach much higher efficiency levels, because of an individual design instead of mass production.

Also CSP`s are in general much bigger plants, and due to the economics of scale, the production of electricity and heat is in comparison much cheaper.

Finaly, CSP´s have a wider varaity of thermal utilization.

• Wind (e.g. fouling and defocusing)

• Aerosols (e.g. chemical reactions and fouling)

• (UV-) radiation (e.g. chemical reactions)

• Humidity (e.g. corrosion and fouling)

• Sandstorms (e.g. abrasion of protective layers)

• Climate (e.g. temperature changes, frost, mechanical stress)

• Solar Tower (Heliostat)

  300 - 2000°C, efficiency 23 - 35%,

• Solar Dish Collector

  tempertaure 150 - 1500 °C, one big advantage => needs no water (Stirling engine), mediumn to good efficiency, but large moments and leverage forces and massive design of tracking system.

• Parabloic Through Collector

  tempertaure 50- 400 °C, efficiency 14 - 20%

• Linear Fresnel Collector

  temperature 50 - 450 °C, efficiency 18%

• Solar Chimney

  air is heated up (greenhouse), only exit is the tower with a turbine

• Solar Pond

  Temperature gradient in Pond (up to 90°C), no circulation (natural convection) due to different salinities. Needs an ORC and is expansive due to excavation

• Cosine Losses

• Wind => Mirror and Tower Movement

• Shading

• Reflection losses on mirror surface

• Optical Pathway Losses (clouds, fog, ….)

They are both, waves and particles

Photons are massless 0kg

Photons move at the speed of light, in vacuum 300 000 km/s

The shorter the wavelength, the higher the Energy of the photon

c = lamda (wavelength) * frequency

E = Plank´s constant * frequency

An ideal black body absorbs all incomming radiation completely and emits with a specific maximum intensity. The spectrum of radiation emitted by a black body depends only on its temperature!

absorptance = 1

emissivity = 1

reflectance = 0

transmissivity = 0

The sun is very close to being a black body!

The shown object is a reciever of a CSP Plant. Its purpose is to absorb the reflected solar radiation and turn it into heat.

1 = Evacuation Nozzle

2 = Absorber Pipe

3 = Vacuum

4 = Glas Envelope

5 = Getter

6 = Glas Metal Connection

7 = Bellows

A Getter is a chemically reactive material that is used to complete and maintain the vacuum in the glas envelope.

By minimizing surface heat losses of the absorber, pressure losses in pumps and pipes, piping costs and shading in the morning and evening hours!

The efficiency of the aborber depends on its temperature. The higher the temperature, the higher the radiation losses, the lower the efficiency!

• Steam Rankine Cycle:

  High tempertaures (540 °C), working fluid is water

  Pump => Evaporator => Trubine => Condensor => ….

• Organic Rankine Cycle:

  Lower temperatures (300 °C) working fluid is organic

  Pump => Regenerator => Evaporator => Trubine => Regenerator => Condensor => ….

• Stirling Process:

  working fluid is a gas (e.g air, helium, hydrogen), needs high temperatures

  Cumbustion engine, works with two pistons (working and displacer), can be linked by a regenerator. It is a reversible process, so if we put power in, we get a refrigerator

To produce 1 kg SG-Si by the Simens Process 176 kWh of energy are required. 19 kg of CO2 are emitted during that process.

To built a 100 Watt PV-Module, 0.7 kg of SG-SI are needed => 123 kWh => 13,3 kg of CO2

No, because the PV-Emissions are ca. 0,005 - 0,1 kg CO2 / kWh. The Production of H2 by electrolyse has a effficiency of around 50%. Therfore the production of H2 by PV would have emissions of 0,1 - 0,2 kg CO2 / kWh.

This is almost the same as natural gas! => not more sustainable!

• theoretical limits of converting solar power into energy

  ideal absorber with carnot machine max = 80 %

• inherent limitis of a PV Cell (Schockley Queiser Limit) High band gap energy => high voltage, low current => low efficiency, because many photons have not enough energy to lift the electrons in the conduction band

  Low band gap energy => low voltage, high current => high efficiency, because many electrons are lifted into the conduction band

  ==> max. 33 % (theoretical limit)

• technical limits of a PV Cell

  optical => reflection, transmission, shading

  electrical => ohmic, recombination

==> polycrystalline cells (15 - 20%), monocrystalline cells (15 - 25%), organic cells (10%), multi junction (tandem) cells (above 40%)

Because the electrons already have a higher energy level (vibrating) due to the higher temperatures. Therfore the electrons can gain less energy from the sun => open circuit voltage is reduced (current remains unchanged).

Additionally, the radiation losses of the PV Cell increase with increasing temperatures. According to Stefan Boltzmanns law, the radiation losses increase by the power of 4 when the temperature rises => big influence

Furthermore, heat also increases the electrical resistance => additional loss

• Organic:

  + No sophisticated materials

  + Can be printed

  + Many possible installation areas

  - much lower efficiency

• Crystalline:

  + Good efficiencys

  + State of the art

  + Cheap Production

  + Raw Material availability

  - bulky

No, for example wind and solar energy can not have the same importance in all countries!

Different countries should aim for different energy mixes, depending on their specific natural recources!

An integrated efficient grid enables the management of the energy mix within each country (daytime/season) and across the borders

Currently Wind is the second biggest power producer after Gas! Also, 95% of all new constructed power plants make use of renewable energies!

The capacity factor is important, because power plants do not operate at full power all the time! The theoretical limit can only be reached when we have wind and the turbine is not down for maintainance!

• Huge available resources (Wind)

• Improved social acceptability (not in my backyard)

• Lower environmental impacts

• Scale and Logistics (Ships)

• Potential for reduced LCOE

A wake is the name of an imaginary volume, that contains the air particles after they have passed the rotor. According to the law of action and reaction, it rotates in the other direction of the rotor.

The air velocity in the closer wake is reduced compared to the wind speed. At the rotor a pressure jump occurs!

Levelized cost of energy: Levelized cost of energy (LCOE) is defined as the average cost of the unit (kWh) generated by a system and is calculated by the ratio of the total annualized cost of the system to the total electrical load served.

1. (Water <Direct Evaporation>:

   1. the upper mean temperature level of the working fluid higherHigher thermodynamic efficiency

   2. The mean temperature of the heat transfer fluid is lower for direct evaporationreduced losses in the solar field

   3. No limitation up to 400 °C (as it is the case for thermal-oil)

   4. No additional components necessary for the heat transfer fluid cycleHeat exchangers,

      pumps

   5. Simple systemLow maintenance and operation costs

   6. Disadvantage: Higher pressures in the solar field

   7. Disadvantage: Heat transfer coefficient in saturated steam very low

      
      

   Oil <Indirect Evaporation>:

   1. In the solar field (lower pressure)

   2. Compact evaporator

   3. Disadvantage: Small live steam parameters due to pinch point limitation)

      
      

Once Through, Forced circulation, Injection cooling

Because they maybe need very fast control power! When the demanded power exeeds the supplied power, there is a slight drop of frequency and visa verse.

The PV modules can be used to control the grid.

The energy consumption becomes much smoother, the bigger and better connected a grid is!

east-west => more thermal energy / year

north-south => moore thermal energy in summer

Generally a east-west tracking is favoured!

Solar Wall, Eco-Nok, Solar Fence, Solar Air Collector,…..

In 2022 the annual energy bills could be reduced by 60 to 80% in households in Germany, Spain and Italy

Absorption => Lithium Bromite

Adsorption => Zeolite

2050 => 1/4 to 1/3 of all energy produced globally

In Europe it will be 230 to 450 GW (currently its 205 GW in Europe)

Most Common: horizontal axis, 3 bladed, upwind

Other concepts: 2 bladed, downwind, vertical axis

Denkmark 45% of its electricity demand, followed by Ireland, Portugal, Germany

The Betzlimit is the maximum Power that can be extracted from wind, independant from the turbine design. Cpmax = 0,6 with an axial induction factor of a= 1/3. The Aerodynamic efficiency is about 80%

The reason for the Betz limit is, that the power generated by the turbine is caused by the velocity difference before and after the turbine. => Wind can´t be stopped

P= 1/2*(roh)*A*V^3*Cp

When the speed doubles we get 8 times the power (cubed relation)

The rotational speed increases with thedistance to the root => This changes the AoA, but we want to have the same AoA over the whole blade lenght => twist the blade to compensate

Below rated wind speed you should keep the TSR constant (lamda=lamda*) to create the maximum possible power => AoA stays constant and pitch is 0°

This is done by a proper blade design => no control necessary

When the windspeed reaches the rated wind speed you want to reduce the AoA, so that the rotor doesn't spin faster (to avoid damages)

You can reduce the AoA by turning the rotor blades towards the wind (pitch increase)

Then the rotor speed stays constant and so does the power

When you can not pitch any further you need to stop the rotor (cut out)

The problem is, that with different speeds the generator produces different frequencies => the grid connection is only possible with additional power electronics

45 - 50%

When the nameplate power is produced, the rated windspeed is reached. At this point the operation mode is changed from constant TSR to constant power. This means we reduce the power coefficient by pitching the blades.

=> rotational speed = const, lamda = decrease, Cp = decrease

It is the windspeed, where the wind produces enough torque to overcome the friction in the gearbox and bearings => rotor starts to turn

The capacity factor is necessary, because a wind turbine can not opperate at full power all the time due to natural variability and its availability (e.g. maintainance). The capacity factor relates the actual produced power to what in theory would have been possible.

Cf= Produced Power in a given period / nameplate power * period length

• Bigger area

• Larger rotor (can not easily be upscaled)

• higher tower (less vertical shear)

• Atmospheric stability => turbulence and shear

• Wake behavior

• Terrain & Vegetation

• Interaction with the blades

pressure differenced caused by solar radiation

air flow from high to low pressure

corriolis force

centrifugal force

=> wee get a rotational behavoir => counter clockwise in the northern hemisphere

• Meterological Masts with cup anemometer, vanes for wind direction, pressure, temp. humidity

• Lidar Sensor

• Sodar Sensor

Special coating on absorbers to increase the absorption capacity, lowering the emissivity, reflectivity can also be decreased by porosity. Coating will be affected if there is oxidation or boundary layer diffusions

1st Generation

Monocrystalline Silicon, Multi Crystalline Silicon cells

2nd Generation

Amorphous – Si, Thin film Crystalline –Si, Cadmium Telluride Cd-Te, Multi Junction Gallium Arsenide GaAs

3rd Generation Dye sensitized, Organic, Quantum dot

Amorphous Silicon Thin Film Technology

65 % Silicon wafer development (36 % starting material, 35 % crystalline growth, 29 % sawing) 10% Cell manufacturing

25% Module fabrication

Cadmium Telluride Cd-Te

Larger throughput/day and Reduced material consumption

but

Lower efficiency

to avoid the wind shade behind the tower and the power loss when the rotor passes the tower

wind rose is a graphic tool used by meteorologists to give a view of how wind speed and direction are typically distributed at a particular location. The frequency of winds over a time period is plotted by wind direction, with color bands showing wind speed ranges. The direction of the longest spoke shows the wind direction with the greatest frequency

T rise, Density Low, power output goes down

because Cp Schmitz does not include frictional losses in bearings and gears and electrical resistance losses in generator or alternator