Energy Resources - Renewables Flashcards
Which energy resources can be described as solar-driven?
- Solar
- Biofuels
- Wind
- Wave
- HEP
How do photothermal systems work?
Photothermal panels absorb sunlight to heat water (does not produce electricity)
What are photothermal systems used for?
- Space heating
- Domestic hot water
How are photothermal systems designed?
Long thin pipes to increase SA:V
How does passive solar architecture work?
Buildings can be designed in certain ways either to heat or cool them
What are examples of PSA in the Northern Hemisphere?
- Build windows on long, south-facing walls to absorb more heat
- Build windows on long, north-facing walls to absorb less heat
What is an example of PSA which is globally applicable?
Use light reflective surfaces or dark surfaces to alter heat absorption
How does a solar-assisted heat pump work?
- Liquid/refrigerant with a low BP changes state to a gas when passed through the panel
- Gas is compressed back into a liquid and releases heat energy
- Liquid passed through a heat exchanger to heat water
How is a photovoltaic cell configured?
- Silicon sandwich
- Top layer is negative as it is doped with phosphorus (adds e-)
- Bottom layer is positive as it is doped with boron (removes e-)
How can the layers of a PV cell be described?
- N layer is electron rich
- P layer is electron poor
How does a PV cell work?
- Excess electrons in N layer gain Ek in the Sun
- Electrons move through the conductor to the P layer
- Continuous movement of electrons creates a current
What is a heliostat?
A device which alters the angle of a solar panel so it is at the optimum angle for sunlight absorption
What is a parabolic reflector?
A concave structure which concentrates sunlight to a focus point (produces increased temperatures)
What is concentrating solar power?
Mirrors are used to reflect sunlight to a central point and heat salt to a molten salt
What is the main advantage of CSP?
- Salt heated to above 100C
- Molten salt retains heat for long periods and can be used to boil water at night
How do anti-reflective surfaces work?
Solar panels can be grooved or textured instead of having a shiny layer to increase sunlight absorption
How do multi-junction PV cells work?
Multiple layers of material absorb different wavelengths of light (greater amount can be absorbed)
How do PVT hybrid systems work?
Heat energy is absorbed for space heating when temperature is to high for PV cells to work efficiently
Where are transparent PV cells used?
Windows
How do self-cleaning solar panels work?
- Hydrophobic layer
- Rainfall runs off at an increased rate and carries off dust particles
What is GPE?
The energy of an object due to its position above Earth
What features are needed for a HEP scheme?
- Large catchment area
- Regular precipitation
- Valley with steep sides
- Low turbidity water
What is a high head HEP scheme?
- Head in excess of 50m
- Low rate of water flow with greater vertical drop
What is a low head HEP scheme?
- Head below 5m
- High rate of water flow with smaller vertical drop
What is a run of the river HEP scheme?
HEP scheme which doesn’t store water or divert its natural flow
What is a Kaplan turbine?
HEP turbine with blades which can be rotated to increase efficiency
What is a helical turbine?
HEP turbine where water flows down a screw to turn it and generate electricity
What are advantages of helical turbines?
- Fish can be carried through without harm
- Can use high turbidity water without being damaged
How is wind generated?
Blows to equalise differences in high and low pressure caused by heating from the Sun
What are some locational factors required for wind energy?
- Regular high wind velocity
- High altitudes or coastal
- UK has SW prevailing winds
What type of wind turbines are the most common
HAWTs
What are advantages of HAWTs?
- Advanced technology
- More efficient than VAWTs
What are advantages of VAWTs?
- Wind can be from any direction (can be used in cities)
- Less noise pollution
- Operate at lower wind velocities
What are disadvantages of HAWTs?
- Stress cracking on the blades
- Requires taller towers
- Heavier generator
What are disadvantages of VAWTs?
- No very large VAWTs have been built
- Lower efficiency than HAWTs
How do blade tip fins work?
Curved edges on blades reduce wind resistance and turbulence, therefore increasing efficiency
What are blade tip fins an example of?
Biomimetics - shark fins
What are nacelle brushes?
Brushes places between blades and the nacelles to reduce air escaping (more Ek can be absorbed by the blades)
What are direct drive turbines?
No gearbox is present so electricity can be generated at lower wind velocities
What is the main disadvantage of direct drive turbines?
Generates DC rather than AC and therefore requires an inverter
What are helical VAWT blades?
Concave blades which reduce wind resistance and therefore generates at lower velocities
What is a wind-assisted ship?
A ship which uses wind power to reduce the energy consumption of a ship
What is the main disadvantage of wind-assisted ships?
Wind is intermittent and therefore cannot be the only energy resource used
What type of energy is harnessed from waves?
Kinetic energy from the vertical movement of waves
What factor produces large waves?
Strong winds
Which sites are best for harnessing wave power?
- Far out at sea
- Large fetch (open water)
How does a point absorber work?
- Floating structure which is attached to the seabed
- Piston rises and falls as waves passes (drives a generator)
How does an overtopping device work?
- Breaking waves force water into a storage reservoir above sea level
- Water flows back to sea through a turbine at the base
How does an oscillating wave surge converter work?
- Passing waves produce a cycle of horizontal and vertical movement
- Large paddle oscillates and pumps fluid over a turbine to generate electricity
How does a surface attenuator work?
- Hinged floating device
- Passing waves push and pull pistons to force fluid over a turbine to generate electricity
How does an oscillating water column work?
- Rising and falling water forces air to move vertically in a submerged chamber
- Air is forced in and out and flows over a turbine to generate electricity
What crops can be grown for biofuel use?
- Wood (charcoal)
- Elephant grass (miscanthus)
- Corn/sugarcane (ethanol)
- Rapeseed/sunflowers (biodiesel)
Which waste materials can be used as biofuels?
- Incineration of domestic waste
- Landfill biogas (CH4)
- Combustion of crop waste (straw)
- Anaerobic digestion
What is the energy density of biofuels?
Most are low energy density but alcohol and biodiesel have a similar energy density to fossil fuels
What energy do biofuels utilise?
Stored energy from recent photosynthesis
What is the main advantage of biofuel use?
Carbon neutrality - releases the same amount of CO2 as it absorbed during photosynthesis
What are the main environmental impacts of biofuels?
- Habitat loss
- Pesticide use
- Fertiliser use
- CO2 from intensive farming
What is hydrogen from algae?
Some types of algae produce hydrogen during photosynthesis, which can be used as a fuel
What is anaerobic digestion?
The break down of waste to produce fuel in the absence of oxygen
What does anaerobic digestion produce?
- Biogas for fuel or gas supply
- Digestate for fertiliser or livestock bedding
Where does geothermal heat originate?
- Radioactive decay within Earth’s core of elements such as uranium and thorium
- Residual heat from the formation of the universe
How does geothermal heat reach the surface?
Molten magma rises within the mantle towards the crust
What are the two types of geothermal schemes?
- Low temperature
- High temperature
What are low temperature geothermal schemes?
- Geothermal springs bring heated groundwater to the surface for district heating
- Geothermal aquifers provide hot groundwater for district heating
What is the main disadvantage of low temperature geothermal schemes?
No electricity is produced as no steam is present
What are high temperature geothermal schemes?
- Geothermal steam systems bring hot water through a borehole to produce steam
- Hot dry rock systems inject water through a borehole to heat it and recover steam through a second borehole
At what temperature do high temperature geothermal schemes occur?
100C+
What factors are needed to harness geothermal energy?
- Large magma intrusion
- Heat source 150C+
- Recent volcanic activity
- Hot rocks close to the surface
- Tectonic activity
How do binary cycle geothermal power plants work?
- Water as cool as 60C can be used to boil butane or pentane in liquid form
- Produces electricity at lower temperatures
- Water pumped underground for heating (not to BP)
What technology does a binary cycle power plant use?
Heat exchanger
What are the main environmental impacts of geothermal energy?
- Waste water contains salts and heavy metals
- Releases some CO2 and hydrogen sulfide
What source of energy is used for tidal power?
Gravitational attraction between the Earth and the moon
What is a tidal barrage?
- A dam across an estuary or bay
- Gates are shut at high tide and water is released through turbines at low tide
What is a tidal lagoon?
- A barrier surrounding a selected part of an estuary
- Fills at high tide and water is released through turbines at low tide
What are in-stream turbines?
Turbines fixed to the seabed which harness the Ek of tidal flow
What is the main advantage and disadvantage of in-stream turbines?
- Low environmental impact
- Harnesses less energy than barrages and lagoons
How does a tidal reef differ from a tidal barrage?
The reef is not as tall as the barrage and therefore marine wildlife can move over it
What are the main disadvantages of tidal power?
- Few suitable locations
- Sedimentation
- Pollutant concentration
- Blocks shipping routes
What is the main advantage of tidal power?
Predictable (25 hour tidal cycle)
What is the 25 hour tidal cycle made up of?
- Two periods of high tide
- Two periods of low tide
