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June 2, 2007

Local vs. Regional vs. National Sources

Category: Alternative Power,General – Dan 9:24 am

I just spent 2 days in New York City. It’s quite a stark contrast in some respects (at least from an outsider’s viewpoint), because the SF Bay Area is so conscious about energy efficiency and alternative sources, whereas you find plenty of incandescent lights powered by coal fired plans in New York.

Yet in some ways, New York City is inherently efficient. The population density is high, and the city so crowded that car travel is impractical so vast numbers of people ride the subway or walk to work. Indeed according to the “Inventory of New York City Greenhouse Gas Emissions” report, carbon emissions measured per capita are only 7.1 metric tons per person in New York, less than San Francisco at 11.2 metric tons and far below the national average, at 24.5.

From an energy source standpoint, however, New York is not a place where power will come from rooftop solar cells and backyard windmills. I’ve been to meetings where concepts like Community Choice Aggregation are discussed, and often (maybe a bit too often), the idea that every community should strive to be energy independent is raised. While nice in concept, there’s a reason why people, communities, and nations trade, and energy is another commodity that is often best produced in one location and moved to where it is needed. Indeed in a recent Stanford Magazine an article titled “A Crude Awakening” looked at the issue of national energy independence, and concluded that while oil addiction is a threat to national security, a “go it alone” attitude is even worse.

I agree that calling the problem “energy dependence” and therefore seeking energy independence is the wrong way to think about this problem. Talking about energy independence feeds the xenophobic impulse that occurs all too easily in American politics. And it suggests to other countries that they should seek independence rather than a more cooperative approach.

In practical terms, smart green energy solutions need a mix of local, regional, and national energy sources. When it is possible and practical to use local solar and wind resources, it makes tons of sense; local sources don’t require long distance (and inefficient) energy transmission, and they create some redundancy in the system that reduces the effect of outages and supply disruptions.

But at the same time, the vast wind resources in the midwest, the untapped solar potential of the southwest, numerous geothermal sites, and other sustainable sources can and should contribute to the overall national energy picture. Cities like New York will never be “energy independent”, nor should they. National energy policy should take into account these regional and local differences, and create a framework for smart and often very different solutions can thrive.

May 12, 2007

Personal choices

Category: Efficiency,General – Dan 6:42 am

What can you do to save energy, and to move the world toward a more sustainable future? When I tell people about this site, many assume that the primary focus is on personal choices.

My initial thought here is that although there are myriad things that individuals can do to contribute to the solution, all these things are in the current context of where and how we live. And that inherently limits what we can do as individuals. For example, if you currently live in the suburbs, and your job is 30 miles away, and there is no public transit, your choices are limited. Unless you move or change jobs (both hard choices), you must drive to work, and your car choices are limited to what’s on the market.

So here are two lists, one of things that are relatively easy to do, and the other a list of things that will have a greater impact but will require a change in habits:

Easy to do
Big impact
  • Install energy efficient light bulbs – Just do it. These CF lights are now inexpensive and save money and carbon.
  • Drive less – Think about the trips you make, and combine them. Cut out unnecessary trips. For most people, cutting driving by 20% is relatively easy.
  • Unplug your extra freezer or refrigerator – If your extra fridge is only used occasionally, unplug it the rest of the time. You might save 10% on your overall electric bill.
  • Choose clean power – If you can specify power source when you buy electricity, spend the (usually small) extra money and specify you only want green power.
  • Choose Energy Star appliances – There is usually an incremental cost, but again it is relatively small and the cost savings and impact (especially with refrigerators) can be quite large.
  • Get a home energy audit – Of course you should then implement the suggestions. Some will be small and make a big difference, others will be an investment that will pay off over time.
  • Buy locally produced food and products – One of the big hidden energy costs is transportation for the things we eat and consume.
  • Use less water – What’s water got to do with energy you ask? For starters, water is heavy to move. If you live high on a hill, you may already be paying a surcharge, because pumping water up the hill costs more than delivering to people on the flatlands. It takes lots of energy to deliver water, and it also takes energy to treat the water.
  • Buy carbon offsets – Again, these are not too expensive. Effectively you are investing in projects to reduce carbon use, and carbon offsets allow that investment to be tied to your personal carbon use.
  • Install solar hot water heating – Solar hot water makes sense in so many places. The incremental cost is small, and the benefit is that your hot water heater hardly ever comes on, and you don’t have to feel guilty about long showers!
  • Get an efficient car – The car you drive is your most important personal climate decision.
  • Fly less – From a personal perspective, air travel is the #1 carbon producer. If you fly for business, look to how you can reduce trips and do more on the phone. When you do fly, make the trip count — stay longer and make one trip count for two.
  • Move downtown – Cities are energy efficient. You have transit options, you can walk to shops and businesses. A bicycle becomes a practical means of travel.
  • Downsize – Smaller homes consume less energy. And (as one article puts it), you’ll have less space so you’ll buy less junk.
  • Become a vegetarian – This is hard, but meat production is energy intensive, so eating less meat has a big impact on carbon use. One list also recommends loosing weight (every 50 pounds you loose will give you a 1% improvement in gas mileage).

In general, I’m not in favor of preaching sacrifice — it doesn’t work for the population at large and won’t solve the problem. But from a personal perspective, you can make a difference. And there is an aspect of changing the culture of energy consumption. In the Nov/Dec issues of Stanford Magazine, there was an article “A Crude Awakening”, documenting a debate of energy experts. One quote stands out here:

This has to become a public policy issue. It’s not right now. Think about the way the market for cigarettes worked in this country 50 years ago, and think of how it is structured now. We have not just taxes but regulation – they can’t be advertised on television – and a national campaign trying to educate people about the health concerns. We need a similar effort on this issue.

Cigarettes have almost become socially unacceptable in many parts of the country. At least it’s a start if you develop energy saving habits and lifestyles, and show others the way forward.

April 28, 2007

What about nuclear power?

Category: General – Dan 7:45 pm

Nuclear power is undergoing something of a renaissance these days. And in many ways, it’s preferable to fossil fuel powered electricity. So is nuclear good? Bad? Dangerous? The lessor of 2 evils?

How does nuclear power work?

Most power today is based on burning fossil fuels. When you burn coal, oil, or natural gas, the energy results from a chemical reaction. For example, natural gas is primarily methane (CH4), which consists of 4 hydrogen atoms and 1 carbon atom. When it’s burned, the methane combines with oxygen in the atmosphere (O2), and you get 1 molecule of carbon dioxide (CO2) and 2 molecules of water (H2O).

Nuclear power is based on a completely different reaction, a fission reaction. Certain heavy atoms (all of those with atomic numbers higher than Lead, including Uranium, Plutonium, Thorium, Radium, etc.), while stable in the short turn, will decay. This decay process gives off both particles (neutrons, alpha particles which are essentially helium nuclei and beta particles which are essentially electrons), and as well as gamma rays. When this decay occurs, a small amount of the matter is converted to energy. Einstein’s famous E=MC2 equation determines how much energy. M is the mass lost — and in any given decay this is quite small. But C (a constant) is the speed of light, which is huge, and squared is — well — huge squared. So each of these tiny decays releases considerable energy. What’s more, some decays release neutrons, which can serve to encourage additional atoms to split, causing a chain reaction. If you can control this, you have a fuel that creates enormous amounts of energy of heat, and will continue to do so for a long time.

Beyond the above chemistry and physics, the actual operation of a power plant is the same. The heat from these sources is used to boil water, which drives a steam turbine, generating electricity.

Nuclear power compared with coal

In some ways, nuclear power compares favorably with coal:

  • Very little fuel is required. Because the nuclear reaction generates so much energy, the quantity of fuel needed is quite small. The average thermal energy in a ton of coal is roughly 6150 kilowatt-hours(kWh), compared with 2 billion kWh/ton for nuclear fuel[1].
  • The energy generation process itself produces no greenhouse gas.
  • Nuclear power has no smokestack wastes; the waste product is contained in the same small quantity of fuel that you started with. A coal plant on the other hand produces an incredible waste stream in the form of slag and fly ash, which includes oxides of silicon, aluminum, iron, calcium, magnesium, titanium, sodium, potassium, arsenic, mercury, sulfur, uranium and thorium, plus oxides of carbon, nitrogen, and sulfur.

The problems with nuclear

Nuclear plants are expensive in part because they are designed to avoid radiation releases at all cost. This is ironic, because coal powered facilities release an incredible amount of radiation. Quoting from a recent report from Oak Ridge Laboratory:

“[The] population exposure from operation of 1000-MWe nuclear and coal-fired power plants amounts to 490 person-rem/year for coal plants and 4.8 person-rem/year for nuclear plants. Thus, the population effective dose equivalent from coal plants is 100 times that from nuclear plants.”[1]

Really, if release of radiation and other hazardous materials is the criteria, we need to shut down coal plants now, never mind the danger of greenhouse gasses.

But the issues with nuclear power fall in three other categories:

Security – That same concentrated power that makes nuclear desirable as a fuel unfortunately makes it desirable for creating bombs. And to realize the full potential of nuclear power, you need breeder reactor technology that allows you to extend the fuel supply, and this is particularly dangerous from a security perspective.

Waste disposal – I’d argue this problem isn’t as big as we make it out to be, but still this problem has not been solved, and doesn’t show any signs of being solved.

Risk – It’s a little known fact that in the U.S. in 1957 the Price-Anderson Nuclear Industries Indemnity Act limits the liability of the nuclear power industry to $10 billion, after which the US government picks up the tab. In January 2006, Standard & Poor’s declared that “an electric utility with nuclear exposure has weaker credit than without”. And utilities are reluctant to invest in a technology where one mistake (witness Three mile island) effectively kills a multi-billion dollar investment.

The bottom line

So what about nuclear power? In my view, the theory is good, but the practical implementation is full of issues that make it a non-starter for a post-fossil fuel future. Ongoing research is fine, if for no other reason than we have an enormous quantity of nuclear waste to address.

Beyond this however, is the issue of radioactive releases from coal facilities. If you’re worried about radiation, and if nuclear power scares you because of the risk of radiation exposure, you’re picking on the wrong technology. First go after the coal plants — it’s a much greater risk and we need to eliminate coal burning for many reasons, and radiation is yet another!

April 18, 2007

Quick Summaries

Category: General – Dan 7:31 pm

I frequently get questions like “just give me a quick 2 minute summary about ethanol — is it good or bad?”. In response to this type of question, I’m creating this new information category, which will contain short pieces on specific topics of interest, for example “About Plug-in Hybrid Cars”. Each of these articles is designed to provide a short layman level summary of the technology to help with understanding. Here’s what’s available to date:

  • Understanding Hybrid Cars – Covers what hybrid cars are, why they exist, and the different approaches to hybrid car design.

April 15, 2007

Understanding Hybrid Cars

Category: General – Dan 2:57 pm

The Hybrid Car

A hybrid car is an automobile that includes both a gasoline/diesel/ethanol powered motor and an electric motor and a battery. The combination of these systems work together to improve overall gas mileage.

Hybrid technology is not new. Train locomotives combining diesel and electric motors have existed since the 1920s, and were widely adopted after WWII.

Hybrid cars are designed to leverage the best features of all components.

  • Electric motors can provide torque at zero RPM, providing an efficient means to get a car moving from a standstill.
  • Electric motors can generate power when a car is slowing down. This can be used to recharge the battery — effectively recycling power used earlier to get the car moving.
  • Gas and other liquid fuels have a high energy density, so using gas as the primary fuel allows a car to travel several hundred miles before refueling.
  • A gas tank can be refilled in a matter of minutes.
  • The infrastructure to provide gas and diesel already exists.

A hybrid car is designed to take advantage of these factors.

Types of hybrid cars

There are three main hybrid variations:

  • Parallel hybrid systems – In a parallel hybrid car, both the gas and electric engines work in parallel to drive the vehicle. Honda’s Civic and Insight both use parallel technology, with the electric motor tightly integrated with the gas engine. Effectively, a parallel system acts like a standard car, with the electric motor serving three roles:
    • The gas engine can be shut off when the car is stopped with no starting worries, because the electric motor is powerful enough to start both the engine and the car at the same time.
    • When quick acceleration is needed, the electric motor serves as a booster. This allows the gas engine to be much smaller and thus more efficient.
    • When the car is braking, the electric motor serves as a generator to help recharge the battery.
  • Serial hybrid systems – A serial hybrid car is an electric car that uses a gas or diesel engine to charge the battery. The car is powered entirely by the electric motor(s). The proposed Chevy Volt would use this type of system. Because the gas engine is only used to charge the battery, it can be optimized for this task and thus be far more efficient than a traditional gas engine that has to work at a variety of speeds and loads. If a serial hybrid is equiped with a relatively large battery, it can serve as a plug-in hybrid, which allows charging the battery at night by pluging it in, which reduces or eliminates the need for the gas charging engine to come on.
  • Hybrid hybrid systems – That’s not a typo! Toyota’s Prius, at low speeds or when the emissions control system is cold, will run on the electric motor alone (like a series hybrid), but at higher speeds the gasoline engine also runs to provide the additional required horsepower (like a parallel hybrid). This is finessed by their “hybrid synergy drive”.

Hybrid pros and cons

Most hybrids today are pure parallel hybrids (like the Hondas) or hybrid hybrids like the Prius, Camary, and Ford Escape. In large part, these cars share much in common with traditional gasoline powered cars.

The biggest advantage of these cars is improved fuel economy. Adding the electric motors allow use of much smaller, more fuel-efficient gasoline engines, and by enabling recapture of energy during braking they further extend fuel range. The disadvantage of today’s hybrids is additional cost (more compoents plus expensive batteries) and complexity.

True serial hybrid cars can potentially change the landscape. Electric cars allow you to eliminate the clutch, transmission, and differential, greatly reducing complexity. They eliminate oil changes (for the electric motors at least), lowering maintenance costs, indeed by all measures, electric powered cars require far less maintenance. And serial hybrid cars can likely be provided in “big battery” versions that can work as plug-in hybrids for the majority of local trips, while relying on the gas powered on-board generator for extended journeys.

Schematics

Here are some schematics to help clarify how each system works.

Traditional automobile


For comparison purposes, here is a sketch of a traditional gasoline powered automobile.
Schematic - Gasoline powered car
Gas from the tank powers a gasoline engine. This is connected through a transmission to power the tires. Looks simple, but both the engine and the transmission are complex components with hundreds of moving parts.

Parallel hybrid

The next schematic shows the configuration for a parallel hybrid car, for example a Honda Insight.
Schematic of a parallel hybrid system
In this configuration, the gas engine and electric engine turn as one. The electric motor acts essentially as a booster for the gas engine, and when breaking the electric motor acts as a generator to recharge the batteries.

Serial hybrid

This schematic shows the configuration for a true serial hybrid, where the gasoline engine only serves to charge the battery, and all motive power is provided by the electric motor.
Schematic of a serial hybrid system
This particular variation still includes the transmission, but because electric motors can deliver high torque at both high speeds and at a standstill, it is possible to eliminate the transmission and instead power each wheel directly with a motor as shown here:
Schematic of a serial hybrid system with direct motor drive
Note that the serial hybrids, if equiped with larger batteries, can serve as plug-in hybrids, because all the motive power is provided by the motor and the gas engine is only used to recharge the batteries.

Prius “hybrid hybrid”

The Toyota Prius is neither truly serial or truly parallel. Using a special power spliter (the “hybrid synergy drive”), power from either the gasoline engine or the electric motor can power the car. When braking, the motor again acts as a generator to recharge the batteries.Schematic for a Toyota Prius

Electric only

The simplest schematic of all shows a pure electric car. Here, batteries power the motors, which directly drive the wheels. No transmission, no clutch!
Schematic for an Electric Car

April 14, 2007

Efficiency FAQ

Category: General – Dan 7:27 am

Q:How do I respond to friends who say that energy conservation is just another term for freezing in the dark?

A: First, emphasize efficiency – the idea that by building efficiency in, the savings is automatic and painless. Have them read my post on Efficiency vs Conservation. Tell them that much has changed since the energy crisis of the 70’s! Today’s compact florescent lights are as bright as traditional bulbs, work in almost every situation, and cut energy use by 80%. If you replace your old refrigerator (the #1 consumer of electricity in your house) with an energy star model, it can cut energy use 20% to 50%. Modern natural gas furnaces can achieve 93% efficiency. Setback thermometers mean you don’t have to remember to turn the heat down at night. Ask your local utility to perform an energy audit of your house or apartment, and implement their suggestions. Efficiency isn’t about “doing with less”, it’s about making smart energy and economic choices.

Q: It seems impossible that America could cut energy use in half – what makes you think this can be done?

A: Japan uses half as much energy per capita. The same holds true for Germany, and other countries in Europe. Even China has higher gas mileage requirements than the US. The bad news is that America wastes huge amounts of energy. The good news is that this provides the opportunity for tremendous efficiency gains.

But the key to this is to stop doing stupid things! It only costs 5% to 10% more to build an efficient “green” building that dramatically reduces energy requirements. It costs a bit more to get an energy star appliance. If we cut sprawl and build higher density homes closer to workplaces and transit centers, we further reduce energy requirements. But buildings last a long time, and every time we build an inefficient building or manufacture a gas guzzling car, we’re creating a long term problem.

Q: How can we get people to think about conservation all the time, instead of just when there is a crisis?

A: The key is to take efficiency and conservation measures that don’t require you to constantly think about them. For example, you have to make it a new habit to turn lights off when leaving the room, whereas compact florescent lights save money and energy without need to remember anything. Buying a hybrid car allows you to automatically use less gas whenever you drive. Of course there are many ways to save energy with conscious day to day choices, but by laying the groundwork, you can save energy every day without any special efforts.

Q: In what ways does what I eat affect energy use?

A: There are three big factors. First, the energy required to create the food; grains and vegetables generally require much less energy than meat. Second, the processing required; in general the more processed the food, the more energy was required. And finally, the distance the food had to travel to arrive at your table.

Q: Isn’t there a limit to how much we can reduce gasoline consumption?

There are certainly cases where an energy-dense liquid fuel like gasoline is required. But the majority of gasoline use is for individuals making relatively short local or commute trips. Technologies like plug-in hybrid cars mean we can substitute electric power generated by renewable sources for petroleum based gasoline, without sacrificing the flexibility of driving long distances when necessary. Combined with ethanol, we can indeed drastically reduce gasoline consumption.

Big picture FAQ

Category: General – Dan 7:12 am

Q: The things I can do to help seem tiny compared to this huge problem. What can I do to have a bigger impact?
A: You can make a big impact in at least three ways.

  • First – walk the talk. Implement energy conservation in your own world, and become a real-life example of how conservation is practical.
  • Second – share your knowledge and passion about this issue. The more people who understand this problem is real and urgent, and the more they understand that there are practical and viable solutions, the faster we can all contribute to the solution.
  • Third – take steps to change government policy. Write those letters. Make those calls. Add your voice to a growing consensus that government needs to help lead and drive positive change.

Q: Doesn’t the government have to play a major role here?

A: Absolutely. While actions you can take as an individual will help, governments can mandate fuel economy standards, tax policy, and regulations that can greatly accelerate (or unfortunately hinder) adoption of a rational long-term energy policy.

Q: What can we do to get more people on board?

A: To get people on board, they have to first understand there really is a problem. Second, people need to recognize that it’s not too late, and there are things they can do today to improve the situation.

To help people understand that there is a problem, point out that even George Bush now admits that global warming is real and that we have to change our energy strategy. In fact, there are many former skeptics who are now fully on board.

As far what people can do, first and foremost they can take a stand, and when asked say “Yes, I believe it’s a huge issue”. Beyond that, there are simple measures everyone can take to reduce their own personal energy use, and they can start writing and phoning their representatives to make America Leads into our nation’s energy policy.

Q: Why the urgency? Mankind has survived big problems in the past – won’t we get through this as well?

A: Mankind will certainly make it through this crisis. The question is: “What will the world our children inhabit look like?” If the oceans rise only 3 feet, numerous coastal cities like Miami, New York and many others will experience regular and costly major floods. Katrina-like hurricanes with the associated devastation and costs will become a regular occurrence. With a higher sea-level rise, we’ll have to abandon much of Florida and the gulf coast. There will be severe impacts on agriculture and fresh water supplies. Impacts in some countries will be even more disruptive. Will mankind survive? Yes. But because global warming is an environmental crisis of enormous scale, we cannot simply afford to wait any longer to drastically reduce carbon emissions. Should we do everything in our power to avoid it? Absolutely.

Q: Isn’t an 80% reduction just an absurd goal? How is it possible to reach it?

A: Certainly it’s not an easy goal, because as a nation we have to be proactive. This needs to become an effort on the scale of the Apollo moon program, with the political change like with saw with the civil rights movement.

But there’s plenty of good science and technology research that shows it’s absolutely practical. For example, the American Solar Engineering Society (ASES) study shows that a pragmatic breakdown in energy sources by 2030 would be:

  • 20% from wind energy
  • 7% from concentrating solar power sources
  • 7% from photovoltaic cells
  • 8% from biomass
  • 6% from ethanol or alternative liquid fuels
  • 9% from geothermal sources
  • 3% from hydropower
  • 11% from existing nuclear facilities
  • 29% from natural gas

Combine this with a dramatic increase in efficiency (40% to 50% reduction in energy use) and you’ve achieve the goal.

Q: It seems impossible that America could cut energy use in half – what makes you think this can be done?

A: Japan uses half as much energy per capita. The same holds true for Germany, and other countries in Europe. Even China has higher gas mileage requirements than the US. The bad news is that America wastes huge amounts of energy. The good news is that this provides the opportunity for tremendous efficiency gains.

Q: I’ve heard China is building dozens of new coal power plants. Doesn’t this undo anything we might achieve?

It is true that China is continuing to invest in coal to meet their growing energy needs, but that doesn’t relieve America of its responsibility to invest in efficiency and renewable power and reduce carbon output. We’re in a position to lead. And if America leads and shows the world a better, more efficient and more cost effective approach to meet power needs, China will follow.

If you have additional questions you’d like to see answered, please submit a comment!

Step-it up day – What are we pushing for?

Category: General – Dan 6:56 am

Step it up – the national day of climate action, is today.

What are we pushing for when we say “climate action”? Step it up has it right: CUT CARBON 80% BY 2050!

Impossible? Crazy? Not at all. We have the technology, and numerous studies have been done showing that, with a combination of Wind, Concentrating Solar Power (CSP), Photovoltaic, geothermal, biomass, and biofuels, – in combination with efficiency – we can achieve such reductions. The goal of this blog is, in large part, to help people understand that these goals are achievable! I’ve added some new high-level questions to the FAQ today to address some of these issues.

What we lack is political will! I’ll be out there with my signs, because this is the day to be visible. And then come back here, and work behind the scenes to lobby that this is possible, it is practical, and it’s necessary.

How do we achieve such a dramatic reduction? Here are some of the roadmaps that have been published:

Everyone is asking “what can I do”. Most important today – get out there and join a rally. Then get back and contact your legislators!

April 13, 2007

Cars, electric motors, and batteries – an in-depth look

Category: General,Plug-in Hybrids – Dan 8:58 am

Ever since I wrote the Mythbuster’s post “Hurdles remain for Plug-in Hybrids?“, I’ve been thinking more about the engineering logic of electric and plug-in hybrid vehicles. Here’s a quick rundown.

Batteries – Bad news *but*…

First, in doing the research for the earlier article on Hydrogen for Cars, I looked up information on energy density and found a complete table[1] showing both “volumetric density” (energy content for a given volume) and “gravimetric density” (energy content for a given mass) for a long list of common and not so common energy storage choices. Here’s a few lines of data based on this table:

Material Volumetric (kwH / liter) Gravimetric (kWh/kg)
Diesel 10.9 13.8
Gasoline 9.7 12.2
Ethanol 6.1 7.9
Liquid H2 2.6 39
Lithium-Ion Batteries 0.3 0.1

In terms of conventional fuels, Diesel and Gasoline deserve their popularity rating — they have high energy density, both in terms of volume (taking up a smaller part of your car) and weight (less mass to accelerate). And frankly, battery energy density stinks. How is it possible to even conceive of an electric car? Fortunately, battery energy density is the only bad news in this article.

Electric motors – A big win

When you do the comparison of electric motors to gasoline or diesel engines, you get an entirely different picture, in numerous dimensions.

  • Power efficiency – Gas and diesel engines get hot. They require complex cooling systems to eliminate waste heat. The result is that a gas engine typically only uses about 15% of the potential energy in the gasoline to drive the car, whereas electric motors are 75% efficient or higher. Tesla claims their engine is 85% to 95% efficient.
  • Full torque at zero speed – Gas and diesel engines don’t produce power unless they are spinning, and thus require a clutch to get things moving. Electric motors can generate full torque at a stand still. Indeed this is the reason that modern powerful railroad trains are pulled by “Diesel-electric” engines — in effect a hybrid engine with electric motors powering the wheels and no clutch.
  • Regenerative braking – Once you’ve burned the gas, the only thing you can do with excess energy is to use conventional brakes to convert the car’s kinetic energy to heat. With an electric motor, you can slow down and recover the kinetic energy, and put it back into the battery. Typically you can recover over 40% of a car’s kinetic energy in this fashion. This is why a Toyota Prius gets such superior city gas mileage — nearly half of the energy “lost” when the car stops at the light can be reused to start it again.
  • Fewer moving parts – The typical DC electric motor, as would be used in these cars has only a dozen or so mechanical parts, and only the main wheel bearing has friction and wear from mechanical contact. Contrast this with typical gas or diesel engines, that have literally thousands of mechanical parts and hundreds of bearings. Can you say “reliability”?
  • No extra rotating stuff – Typical gas powered cars have hundreds of pounds of rotating steel. When you step on the gas to accelerate, you not only have to get the car up to speed, you have to get all this rotating steel in motion. This huge rotating inertia means you need a bigger engine. A car powered by an electric motor can four small electric motors, one for each wheel, eliminating all this rotating metal.
  • No clutch, no transmission, no differential – We already pointed out that you can get rid of the clutch because electric motors produce torque at zero speed. They also produce relatively flat torque throughout up to several thousand RPM. Unless you want an ultra high performance electric car (like the Tesla for example), you don’t need a transmission. And if you put one motor on each wheel, you don’t need a differential or a transfer case. Four wheel drive comes along for free!
  • Less weight – A Tesla has one electric motor, which weighs about 70 pounds and is designed for a high performance sports car. Compare this with a typical gasoline engine, which can easily weigh 300 to over 500 pounds[3]. Not to mention the weight of the clutch, transmision, and differential, which can easily add up to another 300 pounds or more.
  • No oil changes – Without the many moving parts, and without the high heat, explosions, and pressures of a gas engine, and you eliminate oil and oil changes. Yes, there is lubrication in the bearings of an electric motor — it’s generally good for the life of the motor.

Bottom line here is that electric motors offer huge advantages over gas and diesel engines.

So there’s good news and bad news

So batteries have terrible energy density, while electric engines are great. So what?

Let’s do some math.

Working from the gas tank forward with the gasoline powered car…

  • A typical car has a 15 gallon gas tank.
  • Gas weighs between 5.8 and 6.5 lbs/gallon, so our tank will hold about 90 pounds of gasoline.
  • Gas has the energy equivalent of 12.2 kWh/kg, which means our tank of gas has about 450 kWh of energy.
  • The gas engine is only about 15% efficient, so the useful energy we have on board is about 67 kWh.

Now let’s work backwards to see how much battery we really need on board for the electric.

  • First, the electric motor is about 90% efficient, so whereas the gas car stored about 450 kWh of energy in gasoline, we’d only need to store about 75 kWh (67 / 90%).
  • Then we can factor in regenerative breaking, which in city driving provides us with another 40+ percent. So we can reduce the needed 75 kWh by 40% to 45 kWh.
  • We’ve run out of efficiency magic, and it’s time to buy batteries. 45kWh of batteries, at 0.1 kWh/kg, yields a battery pack weight of 450 kg, or about 990 lbs.
  • While 990 lbs sounds like a huge weight, remember to subtract the weight of the gas (90 lbs) and the weight of the gas engine, transmission, differential, and clutch. So we’re really only off by about 300 pounds.

The point here; yes, batteries don’t have anywhere near the energy density of gasoline, and that is and issue. But electric engines are so efficient, and they allow you to eliminate so much weight, that they compensate for a good portion the battery’s weakness.

How do you go the last mile (pun intended) to make batteries adequate? Plug in hybrids! Reduce battery size by half or more (say 300 pounds max), put in an ultra efficient gas engine to recharge the batteries (it can run at a constant speed, it needs no clutch, it needs no transmission), and most of the time your car can run happily on battery power, and when you need the extended range, you have your on board charging unit. Smart, green energy.

Note there were a couple articles that were especially useful to write this post:

Tesla Motors white paper “The 21st Century Electric Car”
Aurica Labs paper “Building the World’s Fastest Electric Car”

April 7, 2007

Energy uses – What’s the point anyhow?

Category: General – Dan 7:32 pm

In the world of alternative energy, there’s constantly a focus on energy sources. But as I’ve discussed in the Energy Big Picture entry, it’s a matter of source, transmission, storage, and use. In this posting, I’d like to start the conversation on energy usage.

Nobody needs energy. We need the things that energy does for us. I’m going to boil this down to five, and only five things:

  • Lighting – In ancient times, when the sun went down, human activity diminished as well. Today, we take lighting for granted. We use energy today to create light.
  • Heat – Heat is essential for living and cooking, not to mention many industrial activities which are heat dependent. Arguably the first use of energy by humans was to create heat for cooking and comfort.
  • Motion – We use energy to move ourselves and our goods from one point to another. Motion is also a key requirement for a variety of industrial activities.
  • Cooling – A relatively modern use of energy is to cool things down. Cooling allows us to preserve food, to make hot climates comfortable, and cooling is also important in various industrial processes.
  • Electronics – You might argue that this is a catch-all category, but there is today a vast number of relatively new uses for energy that are inherently electrical in nature. Note I was tempted to call this category “communications”, but I think it goes beyond that.

Consider a car as an example. Really, you don’t need a car. You need transportation — the ability to get from point A to point B with whatever goods you need to carry. You’re using energy to move you and your goods. The car could be efficient or not. It could run on gasoline, or dried buffalo dung, you don’t really care. The point is that it moves you from point A to point B.

What’s the point of looking at uses in this rather abstract way? Because when we want to talk about smart green energy, how we define smart has to do largely with what we are trying to accomplish — in other words, the use that we are using energy to achieve.

More detail in the next post!