Asked by GHIU
what are alternative energies? describe how tidal powered work? what is the formula for finding energy effiency? describe how the hybrid car can charge some of its battery?
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Brief answers to each part:
1) What are “alternative energies”?
- Alternative (or renewable) energies are sources of energy that are alternatives to conventional fossil fuels (coal, oil, gas). They are usually renewable or low-carbon. Typical examples:
- Solar (photovoltaic panels, solar thermal)
- Wind (onshore, offshore)
- Hydropower (large dams, small run-of-river)
- Tidal and wave energy
- Geothermal
- Biomass and biofuels
- Key characteristics: lower greenhouse-gas emissions (often), replenished naturally, and often more distributed than fossil fuels. Each has tradeoffs in cost, reliability, environmental impact and location requirements.
2) How tidal power works
There are two main families of tidal technologies:
- Tidal range (barrages and lagoons)
- A barrage or tidal lagoon traps water in a basin at high tide and releases it through turbines at low tide (or vice versa). The rising and falling tide creates a head (height difference) that drives turbines to generate electricity.
- A simple expression for the theoretical potential energy stored in a basin per tide is:
E = 1/2 * ρ * g * A * h^2
where ρ = water density (~1025 kg/m^3 for seawater), g = 9.81 m/s^2, A = basin area, and h = tidal range (m). (This is an idealized estimate; real output is lower because of turbine and hydraulic losses and timing constraints.)
- Tidal stream (tidal turbines)
- Turbines are placed in fast-moving tidal currents (like underwater wind turbines). The flowing water turns rotor blades which drive generators.
- The power available in a current is given by:
P = 1/2 * ρ * A * v^3
where A is the swept area of the turbine, v is flow speed, and ρ is water density. The actual extractable power is P_actual = Cp * P where Cp is the turbine’s power coefficient (limited by fluid-dynamics limits similar to the Betz limit for wind turbines).
- Other approaches: dynamic tidal power (cofferdam-like structures), oscillating hydrofoils, and tidal kite systems.
- Advantages: tides are highly predictable (timing and amplitude known well in advance). Disadvantages: high upfront civil works cost, site-limited, local environmental impacts (ecosystems, sediment) and maintenance in a harsh marine environment.
3) Formula for finding energy efficiency
- Efficiency (η) is the ratio of useful output energy (or power) to input energy (or power), usually expressed as a percentage:
η = (useful energy output / energy input) × 100%
or for power,
η = (P_out / P_in) × 100%
- Example: if a generator uses 1000 kWh of fuel energy and delivers 300 kWh of electrical energy, η = 300/1000 = 0.30 = 30%.
- Note: Real systems have multiple stages of conversion; overall system efficiency is the product of stage efficiencies. Losses include thermal, mechanical, electrical, and storage losses.
4) How a hybrid car can charge some of its battery
Hybrid vehicles charge their battery in several ways, depending on the type (mild hybrid, full hybrid, plug-in hybrid):
- Regenerative braking
- The electric motor acts as a generator when the car slows down. Kinetic energy (1/2 m v^2) that would otherwise be lost as heat in the brakes is converted into electrical energy and stored in the battery.
- Recovered energy ≈ η_rec * (1/2 m v^2), where η_rec includes losses in motor/generator, power electronics, and battery charge acceptance. Typical real-world recovery might be 50–70% of the recoverable kinetic energy, depending on speed, battery state-of-charge and system design.
- Engine-driven charging (series or power-split designs)
- In some hybrids (series hybrids) the internal combustion engine (ICE) drives a generator that charges the battery or directly supplies the electric motor.
- In power-split hybrids (e.g., Toyota Prius), a planetary gearset and electric machines allow the ICE to both drive the wheels and to drive a generator motor that charges the battery when needed.
- Charging from the engine is controlled to optimize fuel efficiency, emissions and battery state of charge.
- Plug-in charging (for plug-in hybrids)
- Plug-in hybrids (PHEVs) can be charged from the electrical grid using an external charger, giving a larger battery and longer pure-electric range.
Practical limits and notes
- Battery charge acceptance: batteries can only accept charge at certain rates (and acceptance falls at high state-of-charge). That limits regenerative capture on short, heavy braking events.
- Control strategy: hybrid control systems decide when to use the ICE, motor, or both to maximize fuel economy or performance, and to keep the battery within a target state-of-charge window.
- Efficiency chain: when recovering braking energy, consider motor/generator efficiency, inverter losses, wiring losses, and battery charging efficiency — multiply those to get overall regenerative efficiency.
If you want, I can:
- Show a worked numeric example of tidal power from a specific site or of energy recovered during braking for a car of given mass and speed.
- Explain differences between mild, full and plug-in hybrids in more detail.
1) What are “alternative energies”?
- Alternative (or renewable) energies are sources of energy that are alternatives to conventional fossil fuels (coal, oil, gas). They are usually renewable or low-carbon. Typical examples:
- Solar (photovoltaic panels, solar thermal)
- Wind (onshore, offshore)
- Hydropower (large dams, small run-of-river)
- Tidal and wave energy
- Geothermal
- Biomass and biofuels
- Key characteristics: lower greenhouse-gas emissions (often), replenished naturally, and often more distributed than fossil fuels. Each has tradeoffs in cost, reliability, environmental impact and location requirements.
2) How tidal power works
There are two main families of tidal technologies:
- Tidal range (barrages and lagoons)
- A barrage or tidal lagoon traps water in a basin at high tide and releases it through turbines at low tide (or vice versa). The rising and falling tide creates a head (height difference) that drives turbines to generate electricity.
- A simple expression for the theoretical potential energy stored in a basin per tide is:
E = 1/2 * ρ * g * A * h^2
where ρ = water density (~1025 kg/m^3 for seawater), g = 9.81 m/s^2, A = basin area, and h = tidal range (m). (This is an idealized estimate; real output is lower because of turbine and hydraulic losses and timing constraints.)
- Tidal stream (tidal turbines)
- Turbines are placed in fast-moving tidal currents (like underwater wind turbines). The flowing water turns rotor blades which drive generators.
- The power available in a current is given by:
P = 1/2 * ρ * A * v^3
where A is the swept area of the turbine, v is flow speed, and ρ is water density. The actual extractable power is P_actual = Cp * P where Cp is the turbine’s power coefficient (limited by fluid-dynamics limits similar to the Betz limit for wind turbines).
- Other approaches: dynamic tidal power (cofferdam-like structures), oscillating hydrofoils, and tidal kite systems.
- Advantages: tides are highly predictable (timing and amplitude known well in advance). Disadvantages: high upfront civil works cost, site-limited, local environmental impacts (ecosystems, sediment) and maintenance in a harsh marine environment.
3) Formula for finding energy efficiency
- Efficiency (η) is the ratio of useful output energy (or power) to input energy (or power), usually expressed as a percentage:
η = (useful energy output / energy input) × 100%
or for power,
η = (P_out / P_in) × 100%
- Example: if a generator uses 1000 kWh of fuel energy and delivers 300 kWh of electrical energy, η = 300/1000 = 0.30 = 30%.
- Note: Real systems have multiple stages of conversion; overall system efficiency is the product of stage efficiencies. Losses include thermal, mechanical, electrical, and storage losses.
4) How a hybrid car can charge some of its battery
Hybrid vehicles charge their battery in several ways, depending on the type (mild hybrid, full hybrid, plug-in hybrid):
- Regenerative braking
- The electric motor acts as a generator when the car slows down. Kinetic energy (1/2 m v^2) that would otherwise be lost as heat in the brakes is converted into electrical energy and stored in the battery.
- Recovered energy ≈ η_rec * (1/2 m v^2), where η_rec includes losses in motor/generator, power electronics, and battery charge acceptance. Typical real-world recovery might be 50–70% of the recoverable kinetic energy, depending on speed, battery state-of-charge and system design.
- Engine-driven charging (series or power-split designs)
- In some hybrids (series hybrids) the internal combustion engine (ICE) drives a generator that charges the battery or directly supplies the electric motor.
- In power-split hybrids (e.g., Toyota Prius), a planetary gearset and electric machines allow the ICE to both drive the wheels and to drive a generator motor that charges the battery when needed.
- Charging from the engine is controlled to optimize fuel efficiency, emissions and battery state of charge.
- Plug-in charging (for plug-in hybrids)
- Plug-in hybrids (PHEVs) can be charged from the electrical grid using an external charger, giving a larger battery and longer pure-electric range.
Practical limits and notes
- Battery charge acceptance: batteries can only accept charge at certain rates (and acceptance falls at high state-of-charge). That limits regenerative capture on short, heavy braking events.
- Control strategy: hybrid control systems decide when to use the ICE, motor, or both to maximize fuel economy or performance, and to keep the battery within a target state-of-charge window.
- Efficiency chain: when recovering braking energy, consider motor/generator efficiency, inverter losses, wiring losses, and battery charging efficiency — multiply those to get overall regenerative efficiency.
If you want, I can:
- Show a worked numeric example of tidal power from a specific site or of energy recovered during braking for a car of given mass and speed.
- Explain differences between mild, full and plug-in hybrids in more detail.
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