V1003 Science & Society Homework #5
Show all calculations and do this on your own.
Population and emissions
a) What percentage of the world are Americans?
b) What percentage of global emissions are from the US?
c) What is the global average per capita carbon emission (please note the units)?
d) what would global emissions be if everyone on the world lived like Americans (that is, if they had the same per capita emissions as an American)? How much larger is this than current emissions?
e) based on what we learned from the population lecture, and putting aside any technological advances for now, how should we expect emissions to change in the coming decades (less than today, same, or greater – and why?).
Global Population: 6.7 x 109 people
Global CO2 emissions: 28.4 x 109 tons/year
US Population: 3.04 x 108 people
US CO2 emissions: 5.7 x 109 tons/year
Can you and your family power your own home?
A kilowatt is a unit of power, equal to the energy you’d expend to climb about five flights of stairs. A kilowatt-hour (kWh) is one kilowatt of power used over one hour, and it is the common unit of measurement on your electricity bill.
a. The average American household uses 11,000 kWh of energy per year. If you exercise on a stair-machine (or any other climbing exercise equipment) for an hour on the high setting you burn about 300 watts of energy, or 0.3 kWh. A stair-machine is basically a leg-powered electrical generator. Let’s assume that these generators operate at about 50% efficiency (the rest is lost as heat and friction) so 300W of your effort for an hour generates 150Wh (0.15 kWh). Could a family of four adults power their home energy needs if each person had their own Stairmaster electric generator?
3. The US electricity consumption each year is4.0 x 1012 kWh.This year, a company called Desertec has a business plan to put solar panels in the Sahara to provide solar-powered electricity to Europe. Here’s the link if you are interested – very large scale projects are happening:
Let’s do a few simple calculations to see if it’s reasonable to replace the US electricity demand with solar power.
- First, we need to calculate the US electrical energy in W (1 kW = 1000 W), as if all US electricity production was lighting one big light bulb. To do this divide by the number of hours in a year:
______Wper year
- At midday, a sunny desert location gets about 1000W/m2 of sunlight. Solar panels are about 10% efficient at capturing this energy so you can assume that 1 square meter of PV panels produces 100 W of power per m2. How many square meters of PV panels would you need to replace the global fossil fuel electricity demand?
______m2
- Now, convert this to square kilometers:
______km2
- and now calculate the dimensions (in km) of the real-estate square represented by this area.
______kmon a side
- The US territorial area is 1.0 x 107 km2, what percent of the US is this square that would provide all electrical power for the country?
______percent
4. Let’s consider the cost of this system as well. One of the largest solar power plants planned in the US will be in Florida. The estimated cost is about $150 million for a 25 MW (25 x 106 W per year) plant. Use this to estimate the cost of the system you estimated in question 3.
a. ____
b. if the build out were to be spread out evenly over 20 years, what’s the annual cost to build out this system? ______