smartgreenenergy.com – Source for quality information on efficiency, conservation, and clean energy


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 19, 2007

Ethanol? Good? Bad? Ugly?

Category: Ethanol – Dan 9:29 pm

While hanging out at the Sierra Club’s booth at last weekend’s Step It Up event in San Francisco, someone asked me “Can you explain the deal with Ethanol? Is it a good idea or not.”

As with many things, the answer is “it depends”.

Drawing from “ethanol.org” (the industry group promoting corn-based ethanol):

Ethanol is a clean-burning, high-octane fuel that is produced from renewable sources. At its most basic, ethanol is grain alcohol, produced from crops such as corn. Because it is domestically produced, ethanol helps reduce America’s dependence upon foreign sources of energy.

Ethanol is grain alcohol, the same alcohol, in pure form, that you get from fermented grapes, wheat, potatoes, or rye. Instead of mixing it with water, it’s mixed with gasoline.

There’s two issues to discuss here. First, why do we care about ethanol. And the second, how do you make it.

Why do we care about ethanol?

Ethanol, like gasoline and diesel, is a high energy density liquid fuel. It’s a potential substitute for gasoline to power our vehicles. And unlike diesel or gas, it’s made from biomass. The theory here is that growing plants uses the energy of the sun to take CO2 out of the air and convert it into biomass, you then convert the biomass into ethanol, and you essentially have a carbon neutral energy source.

This is the big appeal of ethanol. That said, it’s not a perfect fuel by any means:

  • It has a lower energy density than gasoline or diesel (roughly a third less). If you got 300 miles on a tankful with gas, you’d only get 200 miles on a tank of ethanol.
  • Ethanol is not compatible with some fuel system components. This is one reason that cars need specific adaptations to use E85 fuel
  • Ethanol absorbs water, whereas gas and diesel do not. Most existing petroleum pipeline are (surprisingly) not water free (water is heavier, and can collect in low spots). Putting ethanol or gas/ethanol mixtures in these pipes causes the water and other contaminants to be taken up by the fuel. Consequently, ethanol today is transported by truck, not pipeline.[3]

OK, not perfect. But a reasonable choice for a liquid fuel based on renewable biomass.

How do you make ethanol?

In the US today, ethanol is almost synonymous with corn. But corn has two issues: first it’s a relatively water and energy intensive crop to grow, and second we currently only produce ethanol from the grain. The result is that it takes nearly as much energy (mostly fossil fuel energy) to create the ethanol as you get from it[4]. I guess you could call this dumb green energy.

Brazil is also making large investments in ethanol, but it’s based on using Sugar Cane. The overall energy yield is roughly 8 times what you put into it, making this a much greener source of liquid fuel.

But to really make ethanol successful, one needs to look at what crops yield the most potential fuel per acre for the least input of energy and water. Here are some choices:

Crop US Gallons/acre
Miscanthus 1500
Switchgrass 1150
Sugar Cane 662
Corn 370

This is why switchgrass is often mentioned as the long term ethanol feedstock. The challenge is in making production from non-starch based sources. The term for this is cellulosic ethanol. Much work is now being done to generate ethanol from these alternate sources, and if this can ramp up to an industrial scale, then ethanol has great promise as a future liquid fuel.

April 18, 2007

LEED – A big deal for building efficiency

Category: LEED – Dan 8:34 pm

Lately I’ve been reading a lot about LEED™ — which stands for “Leadership in Energy and Environmental Design”. Buildings (residential, commercial, and industrial) are responsible for an estimated 43% of U.S. CO2 emissions[1], and LEED™ is the nationally accepted benchmark for design, construction, and operation of green buildings.First LEED Platinum Home in US

Next time you’re at a developer’s presentation (as I was a couple weeks ago for a proposed mountain community development), raise your hand and ask “Will you be LEED certified?”. If more and more developers hear this question, it will absolutely have an impact. These guys want to be perceived as green (or more to the point, the don’t want to be perceived as not being green…there is a subtle difference here). Make this an issue for every developer out there.

What is LEED™?

Let’s start with the words directly from the LEED™ section of the U.S. Green Building Council website.

LEED provides a roadmap for measuring and documenting success for every building type and phase of a building lifecycle. Specific LEED programs include:

  • New Commercial Construction and Major Renovation projects
  • Existing Building Operations and Maintenance
  • Commercial Interiors projects
  • Core and Shell Development projects
  • Homes
  • Neighborhood Development
  • Guidelines for Multiple Buildings and On-Campus Building Projects
  • LEED for Schools
  • LEED for Retail

LEED has many complex components, but what provides a common language and is something everyone can use is LEED Certification. You want to ask “Will this project be LEED certified?”. If the answer is yes, you can follow it with “At what level?”

There are four levels of LEED™ certification: Certified, Silver, Gold, and Platinum. Certification is determined based upon a points system, with investments in different green elements contributing to the overall score. LEED is unique in that it quantifies most of the “green credits”, for example 5% of the building materials must be from salvaged materials to earn a point for the “salvaged materials credit”. Points can be earned in six different topic areas[2]:

  • Site development (did you minimize stormwater runoff, increase urban density, include green space, …)
  • Water efficiency (what’s been done to reduce water consumption)
  • Energy efficiency (what’s been done to reduce the building’s energy needs)
  • Material selection (did you minimize construction waste, re-use an existing facade, use recycled or salvaged materials)
  • Indoor environmental quality (did you incorporate daylighting, use low off-emitting materials, provide operable windows)
  • Innovation in Design (did you incorporate innovative environmental features not covered in other areas)

LEED™ has a 69 point scoring system. Get 26 or more points to be Certified, 33 or more to get a Silver rating, 39 or more for Gold, and 52 or more for Platinum. What’s also interesting is this table available on Entermodal Engineering’s website that shows estimated costs and payback for different levels of LEED certification:

LEED™ Rating Certified Silver Gold Platinum
Energy Savings> 25 to 35%> 35% to 50% 50 to 60% >60%
Annual Utility Savings 40¢/ft2 60¢/ft2 80¢/ft2 $1/ft2
Typical Payback Under 3 yrs 3-5 yrs 5-10 yrs 10+ yrs
Incremental construction cost
Small Buildings 3% 7% 10% 15%
Small Buildings 1% 3% 5% 8%

What’s the bottom line on LEED™?

  • Ask for it! If you’re buying a home, if you’ve involved with a development, if you’re going to a citizen’s meeting on a new project, ask if they intend to get LEED certification!
  • Talk about it! If you see the certification plaque on a building, tell your friends. If a developer is seeking LEED certification, complement him on his choice to go green. Encourage your city government to demand that all new city buildings be LEED certified.
  • Get LEED certified. If you’re a building professional, look into getting LEED certification. Believe me — this is going to be a good career move!

Want to read more? Check out these sites:

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 11, 2007

Efficiency vs. Conservation? Is there a difference?

Category: Efficiency – Dan 8:24 am

Too often, I hear “efficiency” and “conservation” in the same breath. What’s worse, I often hear that to solve the climate crisis, we need to get people to conserve energy: drive less, turn their thermostats down to 65 (or lower!), turn all the lights off, and more.

I want to put a stake in the ground with my opinion on this subject.

Note I’m not going to argue that we, as a nation, have a tendency to waste energy. I’ll often see houses where every light is turned on (even near my home here in the SF Bay Area). People still drive 1/4 mile to pick up one food item. And don’t get me started on the commute, where 1,000s of people all sit, by themselves, in bumper-to-bumper traffic.

But getting people to conserve, to cut back on energy use by changing their behavior, requires a change in personal habits. Yes, many concerned and committed citizens will take these measures, but the majority of Americans will not. Conservation — belt tightening — is not going to cut carbon emissions or change how we as a nation use energy.

Efficiency is not the same thing. My home office, formerly a dark cold room in the downstairs of our home, is now brightly lit and a pleasure to work in. Usually I have four lights turned on – a desk light and 3 recessed ceiling lights. All compact florescents, they use a total of 52 watts. As a committed environmentalist, I still turn out the lights when I’m leaving, but I don’t have to work in the dark because I invested in efficient lighting.

Efficiency continues to be the best energy investment of all, because it doesn’t require that anyone develop any new habits to be effective. My food stays just as cold, my rooms are just as well lit, and I save energy because I have efficient appliances and lighting.

My opinion: If you’re an environmentalist, and you want to really address the challenge of global warming, you need to get the nation moving. If you begin by telling people they have to conserve, cut back, and do without — you’re off to a bad start because inherently that doesn’t seem like the American way. But efficiency is good business, and good business is an American trait that we can and should exploit to solve this problem.