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