Renewables Flashcards
What are the properties of renewable energies?
Intermittency, predictability, energy density, ease of storage, application, environmental issues, geographical constraints, size of resource, level of technology and economic issues
How do environmental impacts impact solar energy use?
Manufacturing, mining and processing, making PV cells produces toxic wastes such as silicon tetrachloride and small amount of cadmium, cleaning requires water and land occupation
What are some of the problematic properties of solar power?
Intermittency, reliability, energy density and locational constraints
What are photothermal power systems typically used for?
Heat water for low temp domestic uses such as space heatings or hot water
How can heat from solar power be stored?
Retained in a thermal store for later, usually an insulating tank containing water, sand or concrete
When may molten salt be used in thermal energy storage?
When the energy has been concentrated to produce much higher temp
How does solar energy heat water?
Sunlight passes through the glass panel and heats up water passing around the system, hot water is stored in the boiler, cold water sinks to the base of the boiler and is pumped back round again
What is passive solar architecture?
Designing buildings to maximise the absorption of sunlight for heating without the use of active working equipment, overheating can be reduced with a fixed solar screen that deflects sunlight or by adjustable screens or by ventilation
What do heat pumps do?
Use the change in state of a liquid to a gas to absorb heat from the atmosphere and release it within a building when the gas condenses to a liquid
How do photovoltaic cells work?
When pv cells absorb light, electrons are dislodged from atoms in the upper layer, they then flow along an electrical conductor from the electrically negative layer to the relatively positive lower layer
What are photovoltaic cells used for?
Power electrical appliances, solar farms are now used to deliver electricity for grid-connected use
What’s the average efficiency of residential panel?
20%
What are the solar power technology developments?
Multi-junction PV cells: three sub cells that each have different band gaps to absorb different parts of the solar spectrum
Anti-reflective surfaces
PVT hybrid systems: thermal cools PV cell and increases efficiency
Heliostats: changes angle for optimum
Self-cleaning panels
What is hydroelectric power?
Harnessing of the kinetic energy of flowing water (streams or rainwater flowing downhill)
How can the flow of water be controlled for use in HEP?
Increased and made consistent by the use of dams and raising the water level to therefore increase hydraulic head
What is the hydraulic head?
A measure of the energy within a fluid due to its pressure and elevation
What’s the conventional design of HEP station?
Comprises of a dam with a reservoir around it
What is the ideal site for a HEP station?
Large water catchment area, high total rainfall, low water turbidity, impermeable bedrock underneath reservoirs, low seismic activity, suitable topography, no serious land-use conflicts and close to consumers or electric grid
What are the environmental impacts of HEP station?
Reservoir creation, construction material, flooding land can destroy and create habitats and static water (leading to sedimentation and dom decomposition)
What are the impacts of HEP on the river?
Sedimentation will lower turbidity, flow is controlled by power station not natural, storing of surplus water upstream, some HEP are sued to meet peak demands so vary greatly in flow
What are some of the general impacts of HEP?
Obstructed fish migration, high acidity, increased erosion of channels and banks, loss of aquatic flora and fauna, low water table, downstream wetlands destroyed, sediments accumulates and colder water released
What are Kaplan turbines?
Axial flow turbines with blades that can be rotated to allow for variations in water flow, they can harness up to 90% of the kinetic energy of flowing water
What are helical turbines?
Similar to Archimedes screws, turned by water flowing down the screw to generate electricity, they have high efficiency, fish can be carried down the turbine without any harm
What are micro-hydro schemes?
Small scale projects, environmental impacts of damming rivers had restricted the use of HEP on many rivers, these divert part of the flow of a river without creating a barrier across the whole river
What are HAWTs?
Horizontal Axis Wind Turbines
What are VAWTs?
Vertical Axis Wind Turbines
How do HAWTs work?
Blades rotate around a horizontal shaft, they are the most common type used
Wha are the disadvantages of HAWT?
Must face the wind and a tall tower is needed and the tower must be strong enough to support the blade weight
How do VAWTs work?
Less advanced technology, it’s a vertical shaft with the blades rotating, larger blades are more efficient, but they have greater visual impacts
What’s the efficiency of VAWTs?
40-60%
What are the advantages of VAWTs?
No need for a tall tower and it doesn’t need to be turned to face the wind, they are also quieter and operate at lower velocities
How is power generated calculated in VAWTs?
Power is proportionate to the blade radius squared
What are the local constraints of wind power?
Polar regions better, topography can cause friction and coastal, flat and upland areas as well as the ocean have higher wind velocities
How does velocity increase kinetic energy?
Doubling in velocity is an eight-fold increase in kinetic energy
What are some of the environmental concerns with wind power?
Ecological impacts, land requirements, telecommunication interference and public opposition
What are some of the ecological impacts of wind power?
Located away from the bird migration routes, high bat populations, or sensitive habitats e.g. bogs where turbine foundations or access tracks may affect the hydrology of the area
What are some of the land requirements needed for wind power?
Need a large area to minimise ‘wind shadow’ effect, normally spaced 3-4 times the diameter of the blades, the land between however can still be used for other purposes e.g. agriculture
How does wind power impact telecommunication interference?
Radio and radar systems can be impacted
How can public opposition impact wind power?
Some object so they are often located away from scenic and urban areas
How is wind power affected by intermittency?
Only operate 1/3 of the time as slow speed doesn’t have enough power and high speed can damage the blades so turned off
What are the environmental impacts of wind power?
Manufacture and installation, noise, habitat damage, bird bashing and bat whacking, no harmful emissions, visual pollution and road safety hazards
What is the global production of wind power?
743GW
How are waves created?
Solar drive winds
What are some locational constraints of wave power?
Needs an exposed coastline with onshore winds and a long fetch, kinetic energy is the greatest with high, strong uni-directional winds and a long fetch allows waves to build up
How does wave power work?
A ‘box’ rests on the surface of the water, potential energy of the water as well as vertical kinetic movement of water can be harnessed. Incoming waves puts pressure on the air column trapped in the inverted vessel, the pressurised air turns a turbine
How can energy be lost in wave power?
Heat, noise and friction
What do point absorbers do?
They are floating structures which rise and fall as waves pass, this is attached to a non-moving base located on the seabed or in static deep water, the movement of the floating part turns a generator
What are terminator devices?
Breaking waves force water into a storage reservoir, which is above sea level, the water flows back to the sea passing through a turbine, which generates electricity. Sea walls may be used to increase their height of the waves and therefore the volume of water that enters the reservoir
What does the oscillating wave surge converter do?
As waves pass, water moves both horizontally and vertically, producing a cycle, this movement pushes a flat plate which moves pistons to pump fluid over a turbine to generate electricity
What does the surface attenuator wave power do?
A hinged floating device, as waves push pass, the sections move, pushing and pulling pistons which force fluid over a turbine, generating electricity
How does the oscillating water column work?
The rise and fall of water as waves pass forces water up and down in a submerged chamber, air that is forced out and in flows over turbines, which turn to generate electricity
What are some of the design problems with wave power?
Must be able to withstand storms and corrosion, difficult to anchor equipment off stormy coasts or in deep water, it’s also expensive to transport electricity
What are the environmental impacts of wave power?
Eyesore, may stop shipping activity, reduced fishing areas, manufacture and installation, anchoring can affect seabed but also create new habitats
What controls tides?
They are controlled by gravitational forces from the sun and the moon
What are tidal barrage?
Dams across and estuary or bay in which turbines are located so that all the water flowing in and out of the lake flows over the turbines
What are the disadvantages to tidal barrages?
High financial costs and environmental impacts great
How do tidal lagoons help tidal power generation?
If electricity demand is low, water can be pumped into a lagoon producing a water level higher than sea level, so electricity can be generated later when demand is high, but there is no tidal water flow
What are instream turbines?
They are fixed to the seabed and absorb the kinetic energy of the natural tidal flow, these harness much less energy but the environmental impacts are very low
What are the advantages of tidal power?
Position of sun and moon is very predictable and tidal barrage on a large estuary would have a large electricity output
What are the disadvantages of tidal power?
Intermittency makes demand difficult to meet, few suitable sites and environmental impacts much larger than other renewable schemes
What are the locational constraints with tidal power?
Gravitational forces affect all water bodies but suitable sites for economic exploitation are rare, seawater normally moves quite slowly but estuaries and headline may concentrate flow, large tidal range required and ideally a high tidal range
What are the environmental impacts of tidal power?
Materials, tidal levels, sedimentation, pollutants concentrations, tidal lagoons, wave velocity reduction, water quality and effect on wildlife
How does tidal power impact tide levels?
No longer extremes, meaning that mudflats are permanently flooded (wading birds habitats lost), there will no longer be the annual flooding of the upper marsh, hence the salinity will be reduced and a change to ecological succession will occur
How does tidal power impact tidal lagoons?
Similar impacts to barrages but on a smaller scale as they do not involve the whole estuary, there are more opportunities to involve impacts on the most sensitive features, such as not creating a barrier across the main channel so that migratory species can still pass through
How does tidal power impact in stream turbines?
Noise may affect marine animals such as whales and dolphins, the effects is localised but the installation of a large number dispersed over a large area could have a bigger impact than the lagoons or barrages
How does tidal power impact wave velocity?
Reduced velocity will reduce erosion but lower tidal amplitude means that wave action is concentrated on a smaller area of cliff, which may increase erosion, lower velocities will also mean that the estuary behind the barrage becomes silted up and needs dredging
How does tidal power impact water quality?
Higher water levels behind dams increases opportunity for recreation, pollutants may build up, increasing need for water treatment
How does tidal power impact wildlife?
Restricts movement of species e.g. fish and dolphins, some impacts as a dam
What are biofuels?
Any energy resources that have been produced by biological processes
How can energy be extracted from wood?
Burnt or roasted into charcoal
What can rapeseed oil be used for?
Transport
Why does charcoal have a higher calorific value than wood?
Volatiles are driven off during formation so the relative carbon content increases
How much CO2 is produced per kWh of energy in biofuels?
1.18kg
What are some fuels that can be harnessed?
Alcohol from carbohydrate crops and biodiesel from vegetable oils
How is alcohol extracted from sugar?
Fermentation by yeast, distillation the dehydration to form 100% alcohol
What are some waste products from biofuels?
Methane from anaerobic digestion of wastes, combustible crop wastes e.g. straw, incineration of combustible domestic refuse and landfill biogas
When does biogas form?
When organic material within landfill sites decomposes, gases such as methane and carbon dioxide are produced
What can biogas be used for?
Collected and burned to produce electricity in a combined heat and power plant to maximise its benefits
What’s a disadvantage of biogas?
Produces minor amounts of pollutants such as SO2 and NOx
What are the advantages of biofuels?
Supply rate can be controlled, easily stores until use, fuels can replace petrol use, carbon neutral and energy density of alcohol and biodiesel is nearly as high as fossil fuels
What are the disadvantages of biofuels?
Waste produced, land take, habitat destruction, energy density of straw, wood and miscanthus is lower than that of fossil fuels and intensive farming techniques release CO2
What are the locational constraints with biofuels?
Require fertile soils, suitable topography, suitable climate and biofuels from waste are produced wherever the source activity is located e.g. landfill, sewage wastes, forestry waste in rural areas
What are the environmental impacts of biofuels?
Habitat loss, fertiliser use, pesticide use and fossil fuels driving machinery
How can algae be used in new technologies for biofuels?
Some types of algae release hydrogen gas during photosynthesis, if they are deprived of sulphur, this hydrogen can be harnessed
How can anaerobic digestion be used as new technologies for biofuels?
Methane is the predominant gas in a biogas mixture, some bacteria (methanogens) grow under anaerobic conditions and produce large quantities of CH4, CO2 and H2
What is geothermal energy?
Heat energy from the radioactive decay of isotopes (uranium, thorium and potassium) is moved towards the surface by molten magma or hot water
What can geothermal energy be used for?
Exploited for space heating, hot water or electricity
What is advection?
Transfer of heat or matter by the flow of a fluid, especially horizontally in the atmosphere or sea
What are some geothermal low temperature schemes?
Springs or aquifers
What are some geothermal high temperature schemes?
Steam systems and hot dry rock systems
What are geothermal springs?
Groundwater is heated by hot rocks underground and may come to the surface in hot springs, this can then be used for district heating
What are geothermal aquifers?
Hot groundwater may be pumped to the surface from underground aquifers to be used in district heating, magma must be near the surface constructive and destructive margins and hot spots
What are geothermal steam systems?
Groundwater at very high temperatures may be brought to the surface using an extension borehole, producing steam at the surface that can be used to produce electricity
What are hot dry rock systems?
When there are hot rocks near the surface and no groundwater, two boreholes may be used, water is pumped down one and steam is extracted from the other, fracturing the rocks underground may increase the permeability and surface area exposed for heat absorption
What are the locational constraints with geothermal power?
Steam turbines require temperatures above 150C and requires relatively recent volcanic activity so that hot rocks are near the surface o the crust
What are the environmental impacts of infrastructure?
Steam and hot water pipes can provide obstacles to large mammals
What are the gaseous emissions involved in geothermal?
Small amounts carbon dioxide and hydrogen sulphide
What are the impacts of waste water in geothermal?
Can contain salts and heavy metals
How do new technologies impact geothermal energy?
New turbine tech boil and turn turbines at lower temps, water as cool as 60C can boil butane or pentane
What are the advantages of geothermal?
Sulphur emissions are only tiny amounts, low CO2 output, reliable and little land take
What are the disadvantages of geothermal?
Few sites suitable, large supply of groundwater that might be needed for water supply, hot rocks may cool with excessive extraction, thermal emissions from plants, liquid waste obtains dissolved salts and minor subsidence of overlying rocks
