In a solar photovoltaic (PV) cell, what physical process converts sunlight into electrical current?

Sunlight heats the silicon, which expands and mechanically drives a generator Photons excite electrons in the semiconductor, freeing them to flow as electric current Infrared radiation is converted to heat, which drives a small Stirling engine Ultraviolet light splits water molecules, releasing hydrogen that powers a fuel cell

Commercial silicon solar panels have an efficiency of approximately 20-24%. Where does the other ~76-80% of the solar energy go?

It is stored as chemical energy inside the silicon crystal lattice It is mostly reflected or converted to heat, because many photons have too little or too much energy to free electrons efficiently It escapes as ultraviolet radiation re-emitted by the panel It drives the inverter, which converts DC to AC power

How does a concentrated solar power (CSP) plant differ fundamentally from a solar PV farm?

CSP uses multi-junction solar cells that capture a broader spectrum than standard silicon panels CSP uses mirrors to focus sunlight onto a heat exchanger to produce steam that drives a turbine; PV converts sunlight directly to electricity CSP converts infrared radiation only, while PV uses visible light only CSP is only suitable for rooftop installation; PV requires large desert sites

The Betz limit states that a wind turbine can extract at most 59.3% of the kinetic energy in wind. Why can't a turbine extract 100%?

Wind turbine blades are always tilted slightly off the wind direction, wasting some energy If the turbine extracted all kinetic energy, the air downstream would be stationary and would block more air from reaching the blades The generator inside the turbine is limited to 59.3% electrical conversion efficiency Turbulence created by the blades reflects 40.7% of wind energy back upwind

The power available in wind varies with the cube of wind speed. If wind speed doubles from 5 m/s to 10 m/s, by how much does the available wind power increase?

2 times 4 times 8 times 16 times

Why is hydroelectric power described as 'highly dispatchable' compared to wind and solar?

Hydroelectric turbines convert 100% of water energy to electricity, unlike wind turbines Hydroelectric reservoirs store enough energy to power a country for centuries Hydroelectric output can be increased or decreased almost instantly by opening or closing sluice gates, matching demand precisely Hydroelectric plants use the same water repeatedly, so they never run out of fuel

Pumped-hydro storage is currently the world's largest energy storage technology. How does it store electrical energy?

Large superconducting magnets store electrical energy in a magnetic field During low demand, electricity pumps water uphill to an upper reservoir; during high demand, water flows back downhill through turbines generating electricity Water is electrolysed to hydrogen during low demand and burned in a gas turbine during high demand Water pressure is increased in sealed tanks and released through micro-turbines when needed

A solar farm has a capacity factor of 20%. A 100 MW solar farm therefore generates how much energy in a full year (8,760 hours)?

876,000 MWh 438,000 MWh 175,200 MWh 87,600 MWh

What is the key engineering advantage of geothermal energy for electricity generation compared to wind and solar?

Geothermal is cheaper per kWh than any other energy source Geothermal produces more electricity per square metre of land than solar PV Geothermal provides baseload power 24/7 with a high capacity factor, independent of weather conditions Geothermal turbines require no cooling water, eliminating one major engineering challenge

Integrating large amounts of wind and solar into a national electricity grid creates which primary engineering challenge?

Voltage harmonics — renewable generators produce AC at a different frequency than 50/60 Hz Transmission loss — renewable energy degrades over long-distance power lines Grid balancing — generation and demand must match at all times, but wind and solar output varies independently of demand Material shortage — solar panels and wind turbines consume rare minerals that will run out

Green hydrogen is produced by using renewable electricity to electrolyse water. What is the energy carrier in this process, and what is the by-product when it is used in a fuel cell?

Oxygen is the energy carrier; CO₂ is the by-product in the fuel cell Hydrogen is the energy carrier; water is the only by-product when used in a fuel cell Water is the energy carrier; hydrogen is extracted during electricity generation Methane is the energy carrier; it is produced from hydrogen and CO₂ in a Sabatier reactor

Tidal power is sometimes described as more predictable than wind or solar. Why?

Tidal turbines are installed on the seabed where wave action does not affect them Tidal power is generated continuously, day and night, unlike solar Tidal patterns are determined by the gravitational effects of the Moon and Sun, which can be predicted centuries in advance The deep ocean maintains a constant temperature that drives a reliable heat engine