Mock 2025 / 2024 Flashcards
(30 cards)
Describe how the council can maximise solar energy in space heating, based of a passive model.
- direct gain
- conservatory
- trombe wall
what is direct gain?
- sun rays penetrate windows, absorbed into interior.
- double / triple glazed reduces heat loss further.
- longest part of building to face south.
- well insulated
- avoiding shadowing
- thermally massive (absorb sun during day, expel at night)
what is a conservatory?
-acts as a solar collector
- carries energy into building via air flow
- thick walls, habitable space
what is a trombe wall?
-greenhouse replaced by thin glazed air space in front of storage wall.
- radiation warms storage wall
- radiates through wall into house
- air circulates through ventilation
- thin walls, inhabitable space
describe two methods of water heating
Any two:
1. pumped solar water heating
2. thermosyphon solar water heating
3. geothermal
what is a pumped solar water heater
collector panel - collects heat and transfers to water tubes.
storage tank - stores heated water.
circulation system - transfers heated water from panel collector to storage tank
- sensors to measure temperature throughout system - turns on / off to rotate water.
what is a thermosyphon solar water heater?
collector panel - absorbs heat and sunlight
storage tank - installed above panel, water rises naturally when it heats up via convection
insulated metal box - sturdy structure provides insulation.
glass cover - acts as glazing, allows sun to enter, traps heat.
what is geothermal water heating
uses earths heat to heat water
can be open or closed loop systems
what is a closed loop water heater
uses clean water source in earths crust to heat water
two separate streams
abstracting on left - sucks up hot water
injecting on right - spits out cold water
what is a open loop water heating system
uses ground source heat pumps
transfers heat from ground to building
single stream of water, within a closed hole
If the River Arun in Bognor Regis is diverted to drive a hydropower turbine to produce electricity in a pumped storage energy system,
c) how much volume of water at 161.68m height is required to power the new building in the event of backup problems if 480 MW electricity is required per day and the turbine is 95% efficient.
- P = Eg / t
- Eg = pgHV(water)n
ans = 27x10^6 m^3
if the volume of water required is 27x10^6 per day, what hydro turbine should be used?
- calculate t in seconds
- calculate flow rate (Q=V(water) / t)
ans: Q= 312.5 m^3 s^-1 / francis turbine
An investor seeks to develop a novel solar panel that would trump other solar panel models in the market. GaAs semiconductors with a 1.42 eV band gap will be an ideal candidate for the Photovoltaic (PV) energy generation business If the GaAs semiconductor material was used to design a square-sized solar cell measuring 10 cm in Birmingham, UK, whose average sunlight is 4 hrs, find the
a) maximum energy (in W) harvested per unit area by the solar cell if the number of photons received is 3.21 × 1015 photons/s.
- calculate energy harvested for band gap (Energy in joules) Ej
- calculate energy harvested for protons (Energy in watts) Ew
- calculate time in seconds
- calculate area in meters
- calculate power / energy per unit area (P=E/A) W/m^2
ans: 1050 W/m^2
GaAs semiconductor with a 1.42 eV band gap.
Calculate the optimum wavelength of light for PV generation.
- calculate energy harvested for band gap (Ej)
- calculate wavelength (E = hv = hc / wavelength)
ans: 0.88x10^-6 m
A renewable energy and sustainability consultant had advised the investor to use a narrow band
gap semiconductor material to maximise energy harvesting within the visible spectrum. the consultant recommends using semiconductors such as silicon with a 1.12 eV energy vs GaAs with a 1.42 eV energy
band gap. Explain:
c) whether the consultant’s advice to the investor is misleading or not
- calculate energy for band gap (Ej = eV * eV constant) in joules
- calculate energy per photons ( Ew = Ej * photon constant) in watts
compare the two
1. smaller band gap = limited harvest space
ans= EGaAs = 7293x10^-7W/s, Esil = 5.75x10^-4 W
average annual wind speed = 4.15 m/s.
the minimum wind speed, 3.63 m/s,
maximum speed, 4.75 m/s.
If the wind speed data follows a
Rayleigh wind speed distribution, calculate the number of hours that such range of wind speed
a) occurred in a year.
P(Ua < U < Ub) = C(Ub) - C(Ua)
C(U) = 1 - exp ((-pi / 4) (U/u)^2)
multiply by year (seconds)
ans: 0.19 // 1664 hr
average annual wind speed = 4.15 m/s.
the minimum wind speed, 3.63 m/s,
maximum speed, 4.75 m/s.
If the wind speed data follows a
Rayleigh wind speed distribution, calculate the number of hours that such range of wind speed
b) was exceeded per year.
P(Ua < U < Ub) = C(Ub) - C(Ua)
C(U) = 1 - exp ((-pi / 4) (U/u)^2)
first half of equation removed due to Ub = infinity
ans = 0.36 // 3129 hr
average annual wind speed = 4.15 m/s.
the minimum wind speed, 3.63 m/s,
maximum speed, 4.75 m/s.
If the wind speed data follows a
Rayleigh wind speed distribution, calculate the number of hours that such range of wind speed
c) if the average wind speed is 4.77 m/s, what is the monthly instantaneous wind speed if the turbulent functions follow a Gaussian distribution f(u) = 0.038 u = wind speed.
standard deviation = 0
mean = 1
U(t) = U + u (t)
f(u) equation (formula sheet) rearranged for u
ans = 5.08ms
explain how material density affects the energy density of a flywheel
- flywheel is discs attached to sheet
- rotates to store mechanical energy as kinetic energy
- faster they rotate = more energy they store
maximum energy W = Ko / 4 * density
- if material density increases, maximum energy decreases
- ideal to use lighter materials with higher tensile strength
Identify and describe any fuel cell
Proton exchange membrane
Anode : hydrogen
electrolyte: polymer membrane
cathode: oxygen
- fuel enters through anode
- atom split into electrons and protons
- electrons flow to external circuit - generate electricity
- protons move through cathode
- combine with oxidiser to product by products
Describe bidirectional charging
bidirectional charging can be used for both V2G & V2B.
utilities EV batteries as a energy storage asset to improve grid demand.
bidirectional chargers can both give and receive a charge,.
1. 2 H bridge used to convert DC to AC
2. ac transfers to transformer
3. ac converted back to DC on other side
4. phase shifts control power flow (digital controllers)
What solar panels should be used to achieve best energy harvest
- mono crystalline
- pure silicon
- 20% efficiency
- most expensive
polycrystalline 15-17% efficient, Thin film 11% efficient.
if community generates too much energy, what two methods of energy storage could they use?
any two:
1. pumped energy storage
2. battery storage
3. flywheels
what is pumped energy storage
excess energy is stored as potential energy by pumping water to an elevation
when demand requires, water is released, driving a turbine to generate electricity
