Topic 8

how storage hydroelectric system works

Water flows from the upper reservoir, because of gravity, through turbine(s) that rotate generator(s) to produce electricity. The water then flows into the lower reservoir where it remains until electricity demand lowers. When this occurs, the turbines spin backward to pump the water back into the upper reservoir so it can once again be used to generate electricity when needed.

profit of storage hydroelectric systems

during periods of high electricity demand, power is generated by releasing the stored water through turbines, but during periods when the demand for electricity is low/ electricity is cheap the water is bumped back to the upper reservoir

why number of wind turbines irl higher than on calculations

* the efficiency is less than 100%, as not all KE of air can be converted to KE of blades
* air needs to retain KE to escape, energy lost to friction in turbine

energy changes in pumped storage hydroelectric system

PE of water to KE of moving water to KE of turbines connected to the generator to electrical energy

energy losses in the PSH system

* friction losses in walls of pipe and generator bearings
* thermal energy losses in electrical resistance of components
* water requires KE to leave system so not all can be transferred

how thermal energy of burning gas becomes electrical energy

internal energy of steam particles transfers to KE of turbine to KE of generator producing electrical energy

degraded energy

no longer available for the performance of useful work

results from solar energy incident on Earth

wind energy

generator in nuclear power station converts

kinetic energy into electrical energy

control rods

control the amount of power being released, absorb neutrons, maintain a constant rate of fission

moderator

slows down velocity of neurons, makes fission more likely to occur

coolant

gets hit by neutrons and the KE of neutrons captured in the coolant used to make electricity

fuel rods

tubes of enriched uranium where fission takes place

critical mass

amount of fissile material that will allow fission to be sustained

greenhouse gasses

transmit ultraviolet radiation byt absorb infrared radiation

carbon fixation

process wherein photosynthetic organisms (such as plants) turn inorganic carbon into organic compounds 

conduction

heat energy is transmitted through collisions between neighboring atoms or molecules

convection

the rising motion of warmer areas of a liquid or gas, and the sinking motion of cooler areas of liquid or gas, sometimes forming a complete cycle.

insolation

Incoming Solar Radiation.

radiation

energy that comes from a source and travels through space at the speed of light

fuel

source of energy in useful form

fossil fuels non renewable

rate of production of fossil fuels much smaller than rate of usage, so will run out

reasons of widespread use of fossil fuels

readily available, cheaper production of electrical energy, for possible to generate sufficient energy without them

why worlds energy consumption is provided by fossil fuels

wide availability, ease of transportation, large energy density

specific energy

energy that can be liberated per unit mass

energy density

energy that can be liberated per unit volume

why enhanced greenhouse effect can result in increased temperature on Earth’s surface

atmosphere absorbs more infrared energy and heats up, atmosphere radiates in all directions, Earth’s surface absorbs some of this extra infrared radiation hence temperature increases

processes and energy changes that occur through when thermal energy is produced in a nuclear power station (U-235)

U-235 fissions - neutrons are produced, neutrons have high energy and transfer KE energy to moderator, moderator energy transferred to coolant

role of heat exchanger of the reactor in generation of electrical energy

allows transfer of thermal energy between reactor and coolant

role of turbine of the reactor in generation of electrical energy

coolant transfers thermal energy to steam, steam allows turbine to drive generator

processes in power station where energy is degraded

heating the working fluid in the exchanger, the working fluid passing through the turbine, cooling the working fluid having passed through the turbine

greenhouse gas

frequency of vibration is close to that of the frequency of infrared radiation, absorbs the infrared radiated by the surface of Earth,the part of the radiation that is re-radiated back to Earth will cause the temperature of the surface to rise

disadvantages of using solar power

takes a lot of space, low efficiency, power fluctuates according to weather, no power at night

how energy losses in the energy transmission are minimized

transmit at high voltage, use step up transformer to reduce current (lower current - resistance losses reduced), large cable cross section, good conductor used for cable

advantage of PS system

pumped storage on demand

disadvantage of PS system

needs to be restored before reuse

absorption

the Earth radiates radiation in the infrared region of the spectrum, the greenhouse gases have energy level differences corresponding to infrared energies, \n and so the infrared photons are absorbed

why solar radiation not affected by absorption

most incoming radiation consists of photons of much shorter wavelength than those radiated by the Earth, so these cannot be absorbed

emissivity

ratio of power emitted by body to the power emitted if it was a black body

albedo

fraction of power incident on a surface that is reflected

how is electrical power generated?

fuel is heated to boil water, which produces pressurized steam. the pressurized steam drives the turbine, which starts spinning and drives the generator, which produces electrical power by electromagnetic induction

solar panels vs photovoltaic cells

solar panels heat up water (solar → thermal), but photovoltaic cells solar → direct current

photovoltaic cells

the light incident on photovoltaic cells emits electrons, creating a potential difference across the panel