energy system

GEOL 241 Fall 2017 Lecture 23: The Transportation Problem

Homework Essay #4 due via Blackboard, Friday November 24th, 5pm

2 page limit (see formatting guidelines on syllabus) – works cited can be in addition

Assume you are called upon to provide advice to the US Department of Energy (DOE) about where it should focus its attention strategically for the next 10-20 years. Based on what you have learned in this class, write an essay that makes the case for the one most important area where you think the DOE should put its effort. What do you think the greatest challenge will be in developing the energy system for the future? What are some ways that we might overcome the challenge you have identified?

As in the case of the prior essay assignments for this class, we are not looking for a “right answer” but are interested in you thinking about this issue. Establish the basis for your argument in what we have learned in class, supplemented by your own reading.

Transportation à ~30% of U.S. energy consumption

Transportation is the major use of petroleum, and relies on oil as an energy source

Some questions we want to answer about energy in transportation

1. What is so great about petroleum-derived gasoline? Why do we rely on it today for transportation? What are some of the

problems with relying on petroleum?

2. What are the alternatives to oil, and what are their pros and cons? Natural gas? Biofuels? Hydrogen? Electric cars?

3. How can efficiency play into the transportation picture? Can we change our basic approach to transportation (including public transport) and save energy? How do other modes of transport, such as airplanes and trains, fit into the picture?

Transportation is mostly about petroleum!

Remember that gasoline, diesel, and jet fuel are all different products from petroleum refining…

so pretty much all of our transportation fuels ultimately come from oil today (and conversely, the predominant use for oil is for transportation…)

Transportation is predicted to remain about petroleum in the future…

But will it, should it, and what are the alternatives?

Why we rely on petroleum-derived gasoline for transport: Energy density!

Recall from last lecture:

Fossil fuels have very high energy density – think about why this is so important for transportation!

High energy density

by volume, but low

by mass

Highest energy density

by mass

Some of the problems with relying on petroleum for transportation

1. Economic security – reliance on imports affects the US national balance sheet

In 2012, deficit of oil import was 55% of total US deficit

1. Energy security – in terms of maintaining supply, and the sociopolitical costs that are involved

2. Potentially destructive CO2 emissions and other pollutants (e.g. photochemical smog)

Oil affects our national economic balance sheet!

So we should be thinking carefully about securing

petroleum for the future – and about alternatives.

Possible alternatives to dependence on petroleum for transport

1. Reduce consumption (e.g. through higher efficiency, or less use of transportation)

1. Replace with biofuels

2. Replace with natural gas

3. Use electric vehicles

4. Replace with hydrogen

BIOFUELS

Energy density is lower than for petroleum fuels, but not that much lower

BUT we have seen some of the problems with biofuels at the large scale – think about your calculations in lab about the land area required for these to replace oil…

NATURAL GAS • Plentiful & inexpensive today • “Clean” relative to diesel and petrol/gasoline • Used in some public bus systems, government car fleets, etc.

BUT energy density by volume is low – requires very large tanks & limited range Or can compress gas, but: • Little compression infrastructure in place • Will eventually run out • Produces CO2

HYDROGEN FUEL

Packs a big punch per mass, though also bulky like natural gas

BUT big problem is source – there are no “natural pockets” of H2 gas!

If H2 is not a naturally abundant fuel, what is this “hydrogen economy” revolution all about?

HYDROGEN FUEL

How hydrogen works as a fuel:

2 H2 + O2 à 2 H2O + energy (note that this is a chemical reaction – it is not the nuclear reaction we discussed related to H-fusion!!!)

If we put energy in, we can run this reaction backwards and “make” hydrogen from water.

In effect, H2 becomes a (convenient and efficient?) way to store energy. Of course – just like with electricity – we have to get this energy from somewhere else! It is a secondary source of energy.

So how could this actually work in practice?

Hydrogen fuel is basically an energy storage solution It is not a primary source of energy. But it’s potentially a

good way of storing energy – high energy density.

How does it work? How do we get the H2 fuel?

One way to get H-fuel: Hydrogen from natural gas

Overall process: CH4 + 2 H2O + heat à CO2 + 4 H2

This is the source of most H2 fuel produced today

It is: Relatively clean

BUT it also: Produces CO2 (though less than gasoline/diesel)

Requires (non-renewable) natural gas source Requires additional heat input

An alternative way to get Hydrogen fuel: H2 from electrolysis

• pass electrical current through water

• hydrogen dissociates from oxygen and collects on positive terminal

• bubbles of H collected for use as fuel

The problem: low efficiency (requires a lot of electrical energy to get a little H fuel)

Electrolysis requires input of electrical energy

Most electricity comes from coal – which we have seen has nasty side effects (CO2, SO2)

There is also an efficiency problem:

Efficiency of power plant ~33% Efficiency of electrolysis ~65% (optimistically) Total efficiency ~21% at absolute best

This compares to ~20% efficiency for car engine running petroleum, so maybe just as well to use a “normal” car?

Electrolysis requires input of electrical energy

Could use renewable energy source (wind, solar) but would need to greatly increase total electricity production to make this possible.

This is currently a long way away and in the meantime does it make much sense to try to shift to electrolysis-derived H2?

Current cost of H2 from methane ~ $0.80/kg Current cost of H2 from electrolysis ~ $3.80/kg

What the future might hold:

Photolytic (solar-driven) water splitting

A potential alternative to electrolysis

Looks simple and attractive, but we don’t currently have the technology to make this work!

Clearly an exciting area of ongoing research… and if it works, a total game changer?

The other problem is how we use the H2 fuel!

How hydrogen works as a fuel:

H2 + O2 à H2O + energy

We actually need to get this energy out in a useful form.

Not like this, hopefully….

The Hindenburg disaster in 1937 – a hydrogen airship explosion

Hydrogen Fuel Cells

Run electrolysis in reverse, to produce electricity and water from H2 and O2.

Theoretical efficiency ~85%

Practical efficiency ~65% or less

Compare to heat engine efficiency ~20%... not too bad

So what’s the catch?

Hydrogen Fuel Problem #1: Efficiency

Overall efficiency for H2 storage estimated at about 20-30%, lower than for battery technologies

(though most of the efficiency losses with H2 are in the production, e.g. via electrolysis)

Hydrogen Fuel Problem #2: Cost! • Toyota Mirai, one of first production-line hydrogen cars • Available for sale in California in 2015 (where there are 10

fuel stations) • Total 700 cars to be made this year • Costs $57,500, but Toyota loses money on each one sold

(as much as $100,000 including development costs?)

Possible solutions

1. Reduce consumption of petroleum based fuels

2. Replace with biofuels

3. Replace with natural gas

4. Use electric vehicles

5. Replace with hydrogen

The showdown for the future? Electric vs. Hydrogen

VW, Tesla, Nissan: electric all the way!

Toyota, Hyundai, GM: more into the hydrogen (but not ignoring electric vehicles)

Electric • Convenient to charge (needs only a plug)

• More efficient that fuels cells (by about ~3x in total) • But short range

• Can the electricity infrastructure cope with wide adoption?

Fuel cells • Long range (300 miles without refueling, vs. Tesla S requiring

minimum 20 minutes for 200 mile charge) • No need for heavy and expensive batteries

• Few fueling stations at the moment – and who will build them?

NOTE: The total “lifecycle” environmental costs of electric vs. fuel cells cars remains unclear.

Possible solutions

1. Reduce consumption of petroleum based fuels

2. Replace with biofuels

3. Replace with natural gas

4. Use electric vehicles

5. Replace with hydrogen

REMEMBER: Both of these require a primary source of energy… e.g. electricity from coal or other renewable source…

They are NOT “free energy”

Electric cars rely on the electricity grid

How does nighttime demand interface with production of renewable electricity?

Is there enough infrastructure for widespread adoption of electrical cars? Could residential grids cope?

Possible solutions

1. Reduce consumption of petroleum based fuels

2. Replace with biofuels

3. Replace with natural gas

4. Use electric vehicles

5. Replace with hydrogen

What about changing the way we use transportation, to increase efficiency of energy spent per mile travelled, etc.?

We’ve talked about looking at alternatives to using oil for transportation, and many of these have promise.

But are there also ways that we reduce energy consumption for transportation overall?

• Less driving? More public transport?

Trains are much more efficient than cars… in fact they are in principle amongst the most efficient means of transportation.

So we should just build more trains in the US and Australia, right?

Trains are only a solution if they get enough use! San Jose light rail has been cited as an example of a train system

that gets so little use it consumes more energy per passenger mile that solo drivers!

Low urban density in some countries (such as the US and Australia) makes public transport likely to be less efficient than in

places with high urban density (e.g., Europe or Asia)

We’ve talked about looking at alternatives to using oil for transportation, and many of these have promise.

But are there also ways that we reduce energy consumption for transportation overall?

• Less driving? More public transport?

• More efficient cars on the roads?

FEDERAL FUEL ECONOMY STANDARDS PROGRAM (CAFE):

Each model year, manufacturers are required to (1) achieve average of 27.5 mpg for fleet of new passenger cars (2) achieve average of 20.7 mpg for fleet of new light duty trucks

Gasoline consumption is down roughly 2.8 million barrels/day from what it would be without CAFE (translates to a 7% reduction in CO2)

Makes a small but substantive difference

Why don’t we increase efficiency standards yet further?

Fuel Efficiency

We’ve talked about looking at alternatives to using oil for transportation, and many of these have promise.

But are there also ways that we reduce energy consumption for transportation overall?

• Less driving? More public transport?

• More efficient cars on the roads?

• Less transport in the first place?

Telecommute: only 5% of employees do so today

Internet shopping: reduce travel to stores, delivery to shops (as long as using serial delivery, e.g. US Mail, etc)

Telephone or Video conferencing or selling, rather than air transport

Internet websites saving journal, book and document production from trees, and trips to the library

E-books and newspapers

More home entertainment

BUT AT WHAT SOCIAL COSTS???

Transportation Substitutions

Where does air travel fit in this picture?

Where does air travel fit in this picture?

Planes are actually quite efficient ways of going quickly…

but we also go a go quite fast in them, and total a lot of transportation miles that way, so use a lot of fuel!

Across the US, air travel is a small portion of total energy use

What would it actually take for everyone to be able to fly?

Fuel consumption for 787 Dreamliner is ~0.024 liters of jet fuel per km per seat

Distance from LA to San Francisco: 390 miles = 630 km People in the world: 7 billion

Fuel needed for everyone to fly from LA to SF: 0.024 x 630 x 7 x 109 = 105 x 109 liters fuel… just for everyone to

be able to fly LAX->SFO one way!

Global airline fuel production ~ 5000 barrels per day 5000 x 119 liters/barrel x 365 days/year =

217 x 106 liters fuel produced per year Almost 1000x less than needed for everyone to be able to fly

But if you fly a lot….

Assuming we drive about 10,000 miles/ year, we use about 40 kWh/day for cars

One intercontinental flight (8,800 miles) would equate to 12000 kWh per passenger – or about 30 kWh/day over a year

But remember… need to add another 30 kWh/day for each 9,000 miles flown. Think about what this means for someone flying 100,000 miles in a year...

From David Mackay’s Sustainability without the hot air