Fossil (conventional) fuels:
- exhaustible resources and emission of greenhouse gasses and pollutants
- Petrol, coal, fossil fuels limited amount of resources + emission of GHG
Solutions trias energetica: 3 step approach is followed to make a sustainable decision
1) Using renewable energy sources:
o permanently available and sustainably used:
solar energy, wind energy, hydropower, geothermal energy and biomass
For production of heat and / or electricity
2) Switch to renewable energy sources
o Replacing fossil fuels with sustainable alternatives
3) More efficient use of current energy sources
o If there is no possibility to use renewable energy then non renewable energy must be
used in the most efficient way
Efficient use of energy means that the energy is reduced to a minimal level without reducing the
standard of living
This lecture provides an overview of the most frequently used systems based on solar energy, wind
energy, hydropower, geothermal energy and biomass.
- Hydropower as most used renewable power generation in the world
Conventional power plant:
- Thermodynamic machine with working fluids
o Water in two fases
- Thermodynamic cycle
o Water is used in liquid fase
o Water is used in gaseous stage = steam
- In the boiler the water becomes steam
o Steam as important energy carrier
o Steam is transported to have the energy in another place
o Steam is used to drive a steam turbine (in this example) => rotational energy =
mechanical energy is transferred to electricity generated
- Steam needs to be reused
o Steam needs to be could down in condenser back to a fluid
o Cooling liquid (lake water…) is used to condensate the steam => this cooling liquid is
heated and can’t be disposed into the lake
Cooling tower to cool down the cooling liquid (large heat exchanger)
,
Large chimney that gives air from the bottom to the top of the tower, here
the cooling water is sprayed into to tower
- Condensed steam (=water) goes back to boiler
Cycling process
1.Solar energy
Advantages:
- Abundantly available!
- Great potential => can met all energy needs
Disadvantages:
- Economic? Practical? Because of concentration of energy + cost to make solar energy is more
expensive then coal, fossil fuel
- Large surfaces of land is needed
- Only available in specific periods and on specific locations => need to be sunny
3 processes to convert the solar energy to useful energy:
Heliochemical process =
Solar energy is converted into biomass by means of photosynthesis
- Process produces fossil fuels
Heliothermal process =
Solar energy is directly converted into useful heat
- Is used by solar collectors
Helioelectrical process =
Solar energy is converted directly into electricity with solar cells or by photovoltaic cells.
Use technology to make optimum use of sunlight (eg solar panels, solar boilers ...):
active applications = devices are used like photovoltaic cells to harvest the energy
Passive applications (eg architecture, trombe wall)
o = design of a house to collect energy example orientation of house and windows of
the house
o Trobe wall = wall that receives solar energy during the daytime and can radiate that
energy during the night into the house
Solar radiation
- Less than a billionth of the energy (1,7 x 1017 W) emitted by the sun strikes the earth (= solar
constant or total solar irradiance = 1373 W/m² that is received at the upper layer of the
atmosphere).
o Solar constant = 1373 W/m²
- Sun = blackbody with T = 5780 K
, Specific spectral distribution of the wavelengths
- Lights that we can see by eye
- UV, IR => shorter wave lengts that can’t be
seen with the eye
- Shape of the spectrum = shape of light
emitted by black body
- Black body = surface that emits its maximum
amount of energy at a specific temperature
- Sun is a black body with a temperature equal
to the surface temperature of the sun
Yellow = sunlight at the top of the atmosphere
Red = radiation at sealevel
Parts of the yellow curve are missing because of absorption of molecules
- Attenuation of solar radiation by molecules in the atmosphere
o Absorption by O2,O3, CO2 and H2O and scattering or reflection by particles
o About 950 W/m² on a clear summer day available
o Scattering is responsible for the bluish colour of the sky and for red sunrises and
sunsets. Violet and blue light is scattered and get’s visible for the eye
o Optical phenomenon
1.1. Flat-plate solar collectors
- To convert solar energy into thermal energy (mostly used to produce hot water)
o The heat is mostly used for hot sanitary water (kitchen use etc.)
o Can also be used for floor heating etc.
- Figure: Thermosyphon solar water heater system:
o Compact system located on rooftops of warm regions
o water heating system which operates on a natural
circulation
o Does not have a pump
o Solar plate receives solar energy and heats the water
o Water will rise because of the heat and transported to
tank
o Tank has warm water that can be used in house but will cool down again and move
down in the system to 5
- Active closed loop solar water heater system:
o uses a pump for the circulation of water containing antifreeze fluid
o hot water vessels are stored inside => more used in colder countries where the water
could freeze
o Anti-freeze fluid is used => water can’t be used for utilities
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