Our Energy Future: Resources, Alternatives and the Environment 1st. Edition by Christian Ngo, Joseph Natowitz | 9780470116609 | 0470116609 | Holooly

Principles of Environmental, Energy Management

Our Energy Future: Resources, Alternatives and the Environment

51 SOLVED PROBLEMS

Question: 6.4

One ton of municipal refuse has a calorifi c value between 6 and 12 MJ/ kg. Collecting and disposing of it require about 5000 MJ/ton. Calculate the number of toe corresponding to 1 ton of refuse. In France, a city of 100,000 inhabitants generates about 35,000 tons of refuse per year. Calculate the ...

Verified Answer:

1 toe = 42 GJ. Therefore 1 ton of refuse is equal ...

Question: 6.2

We have the following data: 1 toe = 42 GJ = 11.6 MWh. The combustion of 1 toe gives 3.7 tons of CO2 . One ton of dry wood equals 5.22 MWh. Since there is space between the pieces of wood, the volume corresponding to 1 ton is about 2 m³. Assume an oil-fired boiler has an efficiency of 80% and a ...

Verified Answer:

To heat the house 15,000 kWh/year is needed. This ...

Question: 7.1

Assuming the solar constant to be 1370 W/m² and the radius of the earth (supposed to be a sphere) R = 6370 km, calculate the power arriving at the top of the atmosphere and the energy received per day and per year. Electricity production was 1.8 × 10^4 TWh in 2005. Compare that number to the solar ...

Verified Answer:

The earth is seen from the sun as a disk of radius...

Question: 6.3

Calculate the area necessary to produce the fuels currently necessary for the French fleet of road vehicles (≈50 Mt/year) using sugar beets (3.3 – 3.5 tep/ha), corn (1.5 – 1.7 tep/ha), or rapeseeds (≈3 toe/ha). The total cultivated areas available in France are equal to 18.4 Mha. ...

Verified Answer:

The areas necessary are 15.2 – 14.3 Mha for sugar ...

Question: 6.1

The oversimplified photosynthesis reaction Light + 6H2O+ 6CO2→C6H12O6 + 6O2 requires 4.66 × 10^−18 J per elementary reaction. Calculate the energy per mole in kilowatt-hours and the energy per ton of carbon synthesized. At least 36 photons are needed to drive the photosynthesis reaction above (in ...

Verified Answer:

The energy per mole is 2.8 MJ or 0.78 kWh. This co...

Question: 4.1

The power P emitted by a black body at absolute temperature T is given by the Stefan – Boltzmann law: P=(T/64.5)^4 W/m² Calculate P for an average temperature of −18°C on the earth (which would be the case if no greenhouse effect exists) and for a temperature of 15°C (that with the natural . ...

Verified Answer:

Applying the Stefan–Boltzmann law to the two tempe...

Question: 7.2

A 1-m² photovoltaic module costs 600 € and produces 100 kWh/year. Assuming a price of electricity from the grid of 0.1 € /kWh (and no additional incentives), calculate the payback time for the module. How much should the price of the module be so that it can pay for itself in a decade? ...

Verified Answer:

Six hundred euros is the cost of 6000 kWh of elect...

Question: 8.1

A geothermal aquifer supplies hot water at a temperature of 70°C at a flow rate of 10 L/s. The hot water is used in a district heating system at a temperature of 40°C. It is assumed that all the thermal energy can be transferred through a heat exchanger. The geothermal aquifer is used for 150 days ...

Verified Answer:

The annual flow rate is

130\times10^{6}[/la...

Question: 16.4

In France the total distance driven by cars in 2006 was 555 × 10^−9 km. Assume that all French cars are to be powered by fuel cells. Further assume that conventional electrolysis will be used to produce the hydrogen needed (energy density 4 kWh/Nm³ ) for this purpose. If 1 kg of H2 is needed per ...

Verified Answer:

One normal cubic meter contains 90 g of

\ma...

Question: 9.1

Consider a 3-MW wind turbine operating at a wind speed of 15 m/s. Its global efficiency (turbine, gearbox, and generator) is supposed to be 30%. What should be the swept area and the size of the rotor? ...

Verified Answer:

The power of the wind needs to be

3\times10...

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