Renewable Energy Practice Questions

Correct answer: The generation of a voltage when a material is exposed to light

The photovoltaic effect occurs when photons of light strike a semiconductor material, such as silicon, knocking electrons loose and creating an electric current. This allows for the direct conversion of sunlight into electricity without any moving parts.

Correct answer: Tidal energy

Tidal energy captures the kinetic energy from the rise and fall of ocean tides, which are primarily driven by the gravitational interaction between the Earth, Moon, and Sun. It is a highly predictable form of renewable energy compared to wind or solar.

Correct answer: Methane

Biogas is primarily composed of methane (50–75%) and carbon dioxide. Methane is produced by methanogenic bacteria breaking down organic matter in an oxygen-free environment, and it can be burned for heating or electricity generation.

Correct answer: Run-of-the-river plant

Run-of-the-river hydroelectric systems divert a portion of a river's flow through a turbine before returning it downstream. These plants typically have a smaller environmental footprint than large-scale dam projects because they do not flood large areas of land.

Correct answer: The decay of radioactive elements within the Earth

Geothermal energy originates from the original formation of the planet and the continuous radioactive decay of isotopes like uranium, thorium, and potassium in the Earth's core and mantle. This heat is transferred to the surface via water or steam.

Correct answer: Rotor blades

The rotor blades are designed with an aerodynamic profile similar to airplane wings. As wind passes over them, it creates lift, causing the blades to rotate and turn a shaft connected to a generator.

Correct answer: Mirrors or lenses that focus sunlight onto a small receiver

CSP systems use heliostats (mirrors) to concentrate solar energy to heat a fluid, which then produces steam to drive a turbine. Unlike standard photovoltaics, CSP can often store thermal energy in molten salt to generate power even after sunset.

Correct answer: To act as a battery by storing potential energy in the form of water

During periods of low electricity demand, excess power is used to pump water to the upper reservoir. When demand is high, the water is released back down through turbines, converting gravitational potential energy into electricity.

Correct answer: Cellulosic ethanol from wood chips or switchgrass

Second-generation biofuels are produced from non-food crops or agricultural residues containing cellulose and lignin. This reduces the 'food vs. fuel' conflict associated with first-generation biofuels like corn ethanol.

Correct answer: Blocking of fish migration routes and flooding of land habitats

While dams provide carbon-free electricity, they significantly alter river ecosystems. They can block the path of migratory fish like salmon and lead to the displacement of human and animal populations through the creation of large reservoirs.

Correct answer: Betz's Law

Betz's Law establishes that the maximum theoretical efficiency of a wind turbine is approximately 59.3%. This is because if a turbine were 100% efficient, the wind would stop completely after hitting the blades, preventing further airflow.

Correct answer: Water vapor

A hydrogen fuel cell combines hydrogen and oxygen to produce electricity through an electrochemical reaction. Because there is no combustion of carbon-based fuels, the only emissions are pure water and heat.

Correct answer: Solar power

Intermittency means an energy source is not available on demand at all times. Solar power is intermittent because it is generated only during daylight hours and varies with cloud cover, so it needs storage or backup capacity for round-the-clock supply. Geothermal, biomass, and hydropower plants can run steadily whenever they are needed.

Correct answer: Iceland

Because it sits on a mid-ocean ridge with intense volcanic activity, Iceland draws almost all of its electricity and heating from renewable sources, with geothermal supplying roughly a quarter of its electricity and the bulk of its space heating. India, Brazil, and Germany have negligible geothermal generation.

Correct answer: To convert direct current into alternating current

Solar panels generate direct current (DC), but household appliances and the electrical grid run on alternating current (AC). The inverter performs this conversion, and it is a separate device from a charge controller, a tracker, or a battery bank.

Correct answer: Biomass

Biomass is theoretically carbon neutral because the carbon dioxide released during combustion equals the amount the plants absorbed while growing. In practice this depends on sustainable harvesting and on limiting emissions from processing and transport.

Correct answer: Driving a heat engine with the ocean's surface-to-deep temperature difference

OTEC exploits the temperature gradient in tropical oceans, using warm surface water to vaporise a working fluid such as ammonia that drives a turbine, and cold deep water to condense it again. It can supply steady baseload power unlike wind or solar, but remains expensive to build.

Correct answer: The ratio of actual energy produced to the maximum possible output

Capacity factor measures how much of the time a plant effectively runs at full rated power over a period. A solar farm typically reaches only about 20 to 25 percent, while a geothermal plant can exceed 90 percent, because sunlight is unavailable at night.

Correct answer: Crystalline silicon

Crystalline silicon dominates first-generation solar cells because it is abundant, chemically stable, and made with manufacturing processes inherited from the semiconductor chip industry. The other materials belong to thin-film and multi-junction cell families.

Correct answer: Using a building's windows, walls, and floors to collect and distribute heat naturally

Passive solar design manages heat through the structure itself, with no pumps or fans. Large south-facing windows admit winter sun, and thermal mass such as concrete floors absorbs that heat during the day and releases it at night, cutting the need for active heating.

Correct answer: Photovoltaic Effect

The photovoltaic effect is the process by which solar cells convert sunlight directly into electricity. When photons strike a semiconductor, they release electrons, generating current. This principle is fundamental to solar power generation.

Correct answer: Geothermal Energy

Geothermal energy comes from heat stored beneath the Earth's surface. It can be used for electricity generation and direct heating. This energy source is reliable and not dependent on weather conditions.

Correct answer: Capture wind energy

Wind turbine blades are designed to capture the kinetic energy of the wind. As wind flows over the blades, it creates lift and causes rotation. This mechanical energy is then converted into electricity.

Correct answer: Batteries

Batteries are commonly used to store excess electricity generated by solar panels. They allow energy to be used when sunlight is not available. This improves the reliability of solar systems.

Correct answer: Hydroelectric Energy

Hydroelectric energy uses the flow of water to spin turbines, generating electricity. It is one of the oldest and most widely used renewable energy sources. Dams and rivers are often used for this purpose.

Correct answer: Methane

Methane is the main component of biogas, produced during the breakdown of organic matter without oxygen. It is a combustible gas used for cooking and electricity generation. Carbon dioxide is also present in smaller amounts.

Correct answer: Solar Energy

Solar energy depends heavily on sunlight availability, making it weather-dependent. Cloud cover and nighttime reduce energy production. This intermittency is a key challenge for solar power.

Correct answer: Lower emissions

Renewable energy sources produce significantly lower greenhouse gas emissions compared to fossil fuels. This helps reduce climate change and environmental pollution. They are also sustainable over the long term.

Correct answer: Concentrated Solar Power

Concentrated Solar Power (CSP) systems use mirrors or lenses to focus sunlight onto a small area. This produces heat that generates steam to drive turbines. It is different from photovoltaic systems that directly produce electricity.

Correct answer: Regulate battery charging

A charge controller regulates the voltage and current going to batteries. It prevents overcharging and extends battery life. It is an essential component in solar energy systems.

Correct answer: Tidal Energy

Tidal energy uses the rise and fall of ocean tides to generate electricity. This movement is caused by gravitational forces of the moon and sun. It is predictable and sustainable.

Correct answer: Crop residues

Crop residues like corn stalks and sugarcane bagasse are commonly used for biomass energy. They can be converted into biofuels such as ethanol or biogas. This helps utilize agricultural waste effectively.

Correct answer: Naturally replenished

Renewable energy resources are naturally replenished over time. Examples include sunlight, wind, and water. They are sustainable and do not run out like fossil fuels.

Correct answer: Generator

The generator in a wind turbine converts mechanical rotation into electrical energy. It is driven by the spinning rotor. This is the final step in producing electricity from wind.

Correct answer: Geothermal Energy

Geothermal energy is ideal in volcanic regions due to high underground heat. Steam and hot water from beneath the Earth's surface are used to generate electricity. Countries like Iceland utilize this extensively.

Correct answer: Dependence on wind availability

Wind energy depends on the availability and speed of wind. If wind is not consistent, energy generation decreases. This intermittency is a major limitation.

Correct answer: Solar panels

Solar panels can be easily installed on rooftops to generate electricity for homes. They convert sunlight into electrical energy. This is one of the most accessible renewable energy solutions.

Correct answer: Water vapor

Hydrogen fuel cells produce electricity by combining hydrogen and oxygen. The only byproduct is water vapor. This makes it a clean energy source with no carbon emissions.

Correct answer: Solar Energy

Deserts receive abundant sunlight, making them ideal for solar energy generation. Large solar farms can be installed in these regions. This maximizes energy output.

Correct answer: Store excess energy

Pumped-storage systems store excess electricity by pumping water to a higher reservoir. When energy demand increases, the water is released to generate electricity. This helps balance supply and demand.