The "burning" question for electric cars is how to compare them with gasoline. Last month I wrote about how wrong the EPA's 99mpg number for the Nissan Leaf was, and I gave the 37mpg number you get from the Dept. of Energy's methodology. More research shows the question is complex and messy.

So messy that the best solution is for electric cars to publish their efficiency in electric terms, which means a number like "watt-hours/mile." The EPA measured the Leaf as about 330 watt-hours/mile (or .33 kwh/mile if you prefer.) For those who really prefer an mpg type number, so that higher is better, you would do miles/kwh.

Then you would get local power companies to publish local "kwh to gallon of gasoline" figures for the particular mix of power plants in that area. This also is not very easy, but it removes the local variation. The DoE or EPA could also come up with a national average kwh/gallon number, and car vendors could use that if they wanted, but frankly that national number is poor enough that most would not want to use it in the above-average states like California. In addition, the number in other countries is much better than in the USA.

The local mix varies a lot. Nationally it's about 50% coal, 20% gas, 20% nuclear and 10% hydro with a smattering of other renewables. In some places, like Utah, New Mexico and many midwestern areas, it is 90% or more coal (which is bad.) In California, there is almost no coal -- it's mostly natural gas, with some nuclear, particularly in the south, and some hydro. In the Pacific Northwest, there is a dominance by hydro and electricity has far fewer emissions. (In TX, IL and NY, you can choose greener electricity providers which seems an obvious choice for the electric-car buyer.)

Understanding the local mix is a start, but there is more complexity. Let's look at some of the different methods, staring with an executive summary for the 330 wh/mile Nissan Leaf and the national average grid:

• Theoretical perfect conversion (EPA method): 99 mpg-e(perfect)
• Heat energy formula (DoE national average): 37 mpg-e(heat)
• Cost of electricity vs. gasoline (untaxed): 75 mpg-e($)
• Pollution, notably PM2.5 particulates: Hard to calculate, could be very poor. Hydrocarbons and CO: very good.
• Greenhouse Gas emissions, g CO2 equivalent: 60 mpg-e(CO2)

Nissan is touting that the EPA gave the new Leaf a mileage rating of 99mpg "gasoline equivalent". What is not said in some stories (though Nissan admits it in the press release) is that this is based on the EPA rating a gallon of gasoline as equivalent to 33.7 kwh, and the EPA judging that the car only goes 73 miles on its 24kwh battery.

I've written before about solutions to "range anxiety" -- the barrier to adoption of electric cars which derives from fear that the car will not have enough range and, once out of power, might take a very long time to recharge. It's hard to compete with gasoline's 3 minute fill-up and 300 mile ranges. Earlier I proposed an ability to quickly switch to a rental gasoline car if running out of range.

Looking at new electric cars like the Nissan Leaf, we see that to keep costs down, cars with a range of 100 miles are on offer. For certain city cars, particularly in 2-car families, this should be just fine. In my particular situation, being just under 50 miles from San Francisco, this won't work. It's much too close to the edge, and trips there would require a full charge, and visits to other stops during the trip or finding parking with charging. Other people are resisting the electrics for lesser reasons, since if you ever do exceed the range it's probably an 8 hour wait.

An alternative is a serial hybrid like the Chevy Volt. This has 40 miles range but a gasoline generator to provide the rest of the range and no "range anxiety." Good, but more expensive and harder to maintain because electric cars are much simpler than gasoline cars.

Here's an alternative: The electric car vendor should cut a deal with car rental services like ZipCar and Hertz. If you're ever on a round trip where there is range anxiety, tell the car. It will use its computer and internal data connection to locate a suitable rental location that is along your route and has a car for you. It will make all appropriate reservations. Upon arrival, your electric car would transmit a signal to the rental car so that it flashes its lights to guide you and unlocks its doors for you. (The hourly car rental companies all have systems already where a transmitter unlocks the car for you.)

In many cases you would then pause, pull the rental out of its spot and put your electric in that spot. With more advanced robocar technologies, the rental would actually pull out of its spot for you. Zipcar has reserved spots for its vehicles and normally it makes no sense for the renter to have just pulled up in a car and need the spot, but it should work just fine. At Hertz or similar companies another open spot may be available.

Then off you go in your gasoline car. To make things as easy as possible, the negotiated contract should include refill of gasoline at a fair market price rather than the insane inflated price that car rental houses charge. Later come back and swap again.

Back in 2008 I wrote a controversial article about whether green transit was a myth in the USA. Today I updated the main chart in that article based on new releases of the Department of Energy Transportation Energy Fact Book 2009 edition. The car and SUV numbers have stayed roughly the same (at about 3500 BTUs/passenger-mile for the average car under average passenger load.)

What's new?

I have some admiration for the PETA prize for vat-grown chicken. A winner of this prize would strongly promote PETA's ethical goals, as well as many environmental goals, for the livestock industry is hugely consumptive of land, as it takes far more grain to feed animals than it takes to feed us, per calorie.

I'm impressed with a great interactive map of the U.S. power grid produced by NPR. It lets you see the location of existing and proposed grid lines, and all power plants, plus the distribution of power generation in each state.

One of the questions raised by the numbers which show that U.S. transit does not compete well on energy-efficiency was how transit can fare so poorly. Our intuition, as well as what we are taught, makes us feel that a shared vehicle must be more efficient than a private vehicle. And indeed a well-shared vehicle certainly is better than a solo driver in one of todays oversized cars and light trucks.

But this is a consequence of many factors, and surprisingly, shared transportation is not an inherent winner. Let's consider why.

We have tended to build our transit on large, heavy vehicles. This is necessary to have large capacities at rush hour, and to use fewer drivers. But a transit system must serve the public at all times if it is to be effectively. If you ride the transit, you need to know you can get back, and at other than rush hour, without a hugely long wait. The right answer would be to use big vehicles at rush hour and small ones in the off-peak hours, but no transit agency is willing to pay for multiple sets of vehicles. The right answer is to use half-size vehicles twice as often, but again, no agency wants to pay for this or to double the number of drivers. It's not a cost-effective use of capital or the operating budget, they judge.

Weight

The urban vehicle of the future, as I predict it, is a small, one-person vehicle which resembles a modern electric tricycle with fiberglass shell. It will be fancier than that, with nicer seat, better suspension and other amenities, but chances are it only has to weigh very little. Quite possibly it will weigh less than the passenger -- 100 to 200lbs.

Transit vehicles weigh a lot. A city bus comes in around 30,000 lbs. At its average load of 9 passengers, that's over 3,000lbs of bus per passenger. Even full-up with 60 people (standing room) it's 500lbs per passenger -- better than a modern car with its average of 1.5 people, but still much worse than the ultralight.

I was reminded yesterday, after posting more on the cost-effectiveness of energy sources, to point out an interesting new book on the economics of energy. The book is Sustainable Energy With the Hot Air by David MacKay, a physics professor from Cambridge University. What's important about the book is that he pays hard attention to the numbers, and demonstrates that certain types of alternative energy are likely to never make sense, while others are more promising.

I only have a few faults to pick with the book, and he's not unaware of them. He decides to express energy in the odd unit of "kilowatt-hours per day" as he feels this will make numbers more manageable to the reader. Of course with time in the numerator and denominator, it's a bit strange to the scientist in me. (It's the same as about 42 watts.) In a world where we often see people say "kilowatt" when they mean "kilowatt-hour" I suppose one deserves credit for using a correct, if strange unit.

My real quibble is over his decision to measure energy usage at the tank, so that an electric car's energy usage is measured in the battery, while a gasoline car is measured in the fuel tank. Today we burn fuel to make electricity, and so electric cars actually consume 3 times the energy they put in the batteries. That's a big factor. MacKay argues that since future energy sources (such as solar) might generate electricity without burning fuel, that this is a fair way to look at it. This is indeed possible but I think it is necessary to look at it both ways -- how efficient the vehicles are today (and will be if we still generate electricity from heat) and how they might be in the future. Generating electricity from heat does complicate the math of energy in ways that people can't agree on, so I understand his temptation.

Yesterday I was also pointed out to a solar power site called SolarBuzz. This is a pro-solar-panel site, and is rare in that it seems to do its math right. I haven't looked at all the numbers, and I am surprised wthat with the numbers they show that they are such boosters. Their charts of payback times all focus on power costs from 20 to 50 cents/kwh. Those costs are found in Europe, and in the tiers of California, but the U.S. national average is closer to 10 cents, where there is no payback. They also use 5% for their interest rate, a low rate that is only found in strange economic times such as these -- but justifiable in a chart today.

Pure heating is highly wasteful

The earlier post on whether solar gives the best bang per buck in greening our electricity ran into some opposition, as I expected. Let me consider some of the objections and issues.

As a recap, I put forward that if we are going to use our money and time to attain greener electricity, what matters is how many MWH we take off the "dirty" grid (particularly coal plant output.) I measured various ways to do that, both green generation and conservation (which do the exact same thing in terms of grid offset) and worked out their cost, the MWH they take off the grid and thus the cost per MWH. Solar PV fares poorly. Converting incandescent bulbs to fluorescent in your own home or even other people's homes fares best.

A big part of the blame lies on the fact that crystalline silicon is an expensive way to make solar cells. It is, however, quite common since many PV plants started with technology from semiconductor fabrication.

Evangelical green

One frequent objection is that purchasing expensive solar panels today encourages the market for solar panels, and in particular better solar panels. Indeed, panel makers are generally selling all they can make. Many hope that this demand will encourage financing for the companies who will deliver panels at prices that make sense and compete with other green energy.

I call this being "evangelical green." Leading by example, and through encouraging markets. While I understand the logic, I am not sure I accept the argument.

Last week I wrote about what I consider the main goal of green electricity efforts, namely to stop burning coal. You can do that, to some extent, by removing demand from the grid in places where the grid is coal-heavy. Even in other places, removing demand from the grid will be fairly effective at reducing the production of greenhouse gases.

Update: Since this article a flood of cheap solar panels from China has been changing some of the economics discussed here. I have not altered the article but some of its conclusions deserve adjustment.

No matter what you do -- conserve, or put up solar or wind -- your goal is to take power off the grid. Many people however, consciously or unconsciously take a different goal -- they want to feel that they are doing the green thing. They want their electricity to be clean. This is actually a dangerous idea, I believe. Electrons are electrons. In terms of reducing emissions, you get the exact same result if you put a solar panel on your house than if you put it on your neighbour's house. You even get a better result if you put it on a house that's powered by a coal plant, so long as you also reap the benefit (in dollars) of the electricity it makes.

People don't like to accept this, but it's much better to put a wind turbine somewhere windy than on your own house. Much better to put a solar panel somewhere sunny than on your own house. And much better in all cases if the power you offset is generated by more by coal than at your house.

However, the real consequences are much deeper. The following numbers reveal it is generally a bad idea to put up solar panels at all, at least right now. That's because, as you will see below, solar panels are a terrible way to spend money and time to make greener electricity. Absolutely dreadful. Their only attribute is making you feel good because they are on your roof. But you should not feel good, because you could (in theory, and I believe with not much work in practice) have made the planet much greener by using the money you spent on the panels in other ways.

The true goal is to find the method that provides the most bang per buck in removing load from the dirty grid.

Keep reading to see the math and a spreadsheet with some very surprising numbers about what techniques do that the best.

There are many ways to go green, though as I have identified, the vast bulk of the problem is in just a few areas -- personal transportation, electrical generation, building design/heating/cooling and agriculture.

While those who focus on CO2 work from the fact that both Natural Gas and Coal, which produce 70% of the USA's electricity, emit CO2, coal is a much bigger villain.

We need renewable energy, such as solar power. Because of that, companies are working hard on making it cheaper. They can do this either by developing new, cheaper to manufacture technologies, cheaper ways of installing or by simply getting economies of scale as demand and production increase. They haven't managed to follow Moore's law, though some new-technology developers predict they someday will.

Last weekend I attended a small gathering in the Grand Tetons where Boone Pickens came to promote his new energy plan. The billionaire oilman is spending $56M of his own money per year on ads for this plan, and you will see them if you watch ads. Otherwise they are at his Pickens Plan web site.

In light of my recent studies into transportation energy efficiency I've learned a lot more about the energy budget of the USA and the world.

As part of my research into robotic cars, I've been studying the energy efficiency of transit. What I found shocked me, because it turns out that in the USA, our transit systems aren't green at all. Several of the modes, such as buses, as well as the light rail and subway systems of most towns, consume more energy per passenger-mile than cars do, when averaged out. The better cities and the better modes do beat the cars, but only by a little bit. And new generation efficient cars beat the transit almost every time, and electric scooters beat everything hands down.

A subject of debate in environmental circles revolves around whether the successful 70s opposition to nuclear power was a wise idea. At the time, it was never thought of as a choice between nuclear and coal, it was thought of simply as fear of the dangers of nuclear. Unexpectedly, it ended up being a push for coal, which of course kills far more people and emits more radiation than U.S. nuclear plants ever have.

It was good to see a major newsmagazine like Time do its cover story on the corn ethanol scam this week. I've been worried about corn as a source of biofuel for some time. So far, it makes no sense, and is only used because of the power of the corn lobby and senators from agricultural states. I've read various arguments (all with political agendas) about just how much petrofuel is burned in order to make corn based ethanol.

Note to new readers: This article explores the consequences of using so much fuel to produce our food. If you come out of it thinking it's telling you to drive rather than get some exercise, you didn't read it! But if you like surprising numbers like this, check out the rest of my Going Green section and other sections.

Burning gasoline is ruining the world. It accounts for 40% of greenhouse emissions, and a large percentage of other nasty emissions including the particulate matter that kills millions each year. Getting it has driven the world to wars. When you burn it, you pollute my air, hurting me, and you owe me something for it, which is a reason that gasoline taxes make sense even in a libertarian context.