ENVS 350 MidTerm Exam

Note: All Underlined words were important terms to use in your answer to a specific question. Most answers did not include these terms. Since you had a study question list in advance, you did have adequate preperation to proudce more exact answers than most of you did.

There were lost of "mercy" pionts given on answers which were more generic than specific. Don't come looking for more.

1. Explain why Peak Power is difficult for your local utility to deal with and what steps can be taken to help alleviate the problem:

   Answered well

   Need to discuss and define
   • Power plants runs best at constant/average output
   • Most Utility companies don't own "peaker" plants or have energy storag
   • have to buy power on the spot market which is very expensive
   • Have ON peak/OFF peak pricing; encourage electricity conservation

   
   
   

2. Emma Pool question:

   This question was answered well for those who did well on the exam and not correctly at all by others. This was explicitly discussed in class on Monday before the exam and is in the course notes.

   Counting errors go as the square root of the count. 100 people were asked. Random error is +/- 10 points. 55 is not scientifically significantly more than 45 due to the large random error. Would need to ask at least 1000 people for 55 vs 45 difference.

3. Peak vs Plateau Oil

   Answered fairly well but many of you confused production with processing. We can produce more oil than 85 MBD but there is no way to process that into refined crude oil because the refiniery infrastructure is saturated. That produces the plateau.

4. Singapore Toaster:

   Power = V x I; I = Power/Voltage = 1000/250 = 4 amps (tho most people didn't include the amps) <

5. Solar Thermal Electric
   • focus heliostats to a container of molten salts located on a central tower
   • molten salts heat up to 500-1000 K and retain that heat for 24 hours
   • Heat exchange with water makes steam
   • Higher capacity towers require more heliostats and eventually the heliostats get too far from the tower to focus the sunlight.

6. Sketch:
   

7. Sketch
   

   Most people left out the important neighbhood transformation between you local substation and you house.

8. Evolution of generation infrastructure:

   This question is entirely related to this chart shown and discussed in Week 1. The absolute key point is the tremendous rise of Natural Gas during this time period as a source of electricity. Very few people said this. This is discouraging. If you only learn/retain one thing about this class, it should be that the US plan is an increasing dependence on Natural Gas (NG) as an electricity source.

   

9. Exponential exhaustion timescale.

   This question is traditionally not answered well

   Answered: mostly generically and not specifically.

   Need to know three parameters:
   1. The exponential rate of resource consumption (k)
   2. The total Resource available (R)
   3. The current rate of resource usage (r_o)
   Those integrate together into an equation for an exponential exhaustion time:
   T_e = 1/k * ln (Rk/r_o +1)

   which many of you memorized but didn't understand its meaning.

   Mathematically, because 1/k is outside the Ln term, it dominates as the exhaustion timescale depends directly on 1/k but only depends on R logarthmically.

   Hence k, the consumption rate, dominates the calculation of T_e as changes in R only show through as LN (R).

   Hardly anyone said all of the above.

   The best qualitative version of the above is something like this

   Resource production is described by a Bell curve - this means you can calculate the depletion using the initial consumption and the growth rate.

   The doubling time of consumption occurs independently of R so k must dominate the exhaustion timescale so even if R is really 2R the resource is just exhausted in the next doubling time.

10. Wind exponential build out question:
    Yes there is an exact answer to this question using math I don't expect you to know. I do expect you to simply apply the doubling time and make an estimate:
    Wind build out doubling time = 70/15 = 4.5 years
    US electrical growth at 2% has 70/2 = 35 years doubling
    
    US: 1.5 TW in 2012 --> 3 TW in 2012+35 = 2047

    Wind: 50 GW in 2012
    100 GW in 2016.5
    200 GW in 2021
    400 GW in 2025.5
    800 GW in 2030
    1.6 TW in 2034.5
    Okay your there and its not even 2047 so sometime between 2030 and 2035 wind would be at about 50% of US. A more exact answer is sometime around 2025 but who cares --> the point is that wind is on a trajectory to reach this goal relatively fast.

11. Operation of PV, band gap; efficiency

    Answered Variably.

    • incoming solar photons have sufficient energy to move electrons from the valence band to the conductor band in some material
    • the amoung of energy required for this is the band gap energy
    • once in the conductor band the material the electrons flow through the material (i.e. a current is generated)
    • silicon is the material of choice due to its abundance
    • as the material heats up collisions between the free charge and the silicon nuclei in the lattice increase and so the internal resistance of the material increases and its ability to carry a current decreases

12. Data reliability question:
    
    While most of you said that the first 5 years worth of data should not be used - and they certainly shouldn't be - hardly anyone looked at the data closely to notice that the last 3 years flatten completely. That's a big problem in determining a "growth" rate if your own data has shown that you have, in fact, stopped growing.

13. Canadian Oil Question

    Certainly more cons than pros:

    Pros:

    • Economic Boom that creates Jobs
    • Strengthens relation to US
    • Can be very economically profitable for maybe a decade.
    • Extends oil availability timescale

    Cons:

    • Difficult Extraction Process
    • What's the point - global market penetration likely less than 5% (which you should have learning in HW 2)
    • Gigantic environmental footprint
    • Continues BAU
    • Its only a short term solution anyway.
    • Its stoopid.

    
    

14. Explain the qualitative parallel between the "energy dilemma" in the 1930s and our current situation as well as quantitative differences in the scale of the problem. What factors may limit our dream of having a rapidly developing green economy.

    Most people got lots of points for whatever they wrote but you got more points if you included some of the following points:

    • Both crises are strongly energy related - running out of fossil energy now; back then wanted a substitute for dirty coal
    • Similar idealogical goals between "sustainabily and green" and Mumford's Neotechnic Era Purification
    • we need large scale renewable energy projects; back then it was hydro
    • we need improved infrastructure
    • we need government initiated large scale wind and solar now that will create jobs/opportunity in a similar way that the hydro and other public works projects (e.g. roads, bridges, etc) did in the 1930s.
    • But the scale is much different now: back then, when completed, hydro projects produced 45% of the nation's electricity and this was done in 10 years!
    • Infrastructure takes a long time to build these days for lots of reason and wages are much higher now than then. Therefore, the equivalent of putting 150,000 people to work on various infrastructure projects in today's terms is more than we can afford with some initial stimulus package.
    • Congress has no committment to long term projects
    • An Obama Unit has already been spent and little of it went is this direction