The Nissan Leaf Energy Efficiency Meter Would Be More Useful If It Was Accurate

The Nissan Leaf is a great car, and a great early entry in defining what an electric car can be. The acceleration is quick, smooth, and effortless. The drive is pleasantly comfortable and astonishingly quiet. The short range is more than adequate for my daily driving needs, and I can charge it up every night in my garage. I never have to think about going to a gas station for a fill up.

It's nice. In fact, it's so nice that I couldn't imagine going back to an ICE car for my commuter car. The replacement for the Leaf, when I need to get one, will definitely be another EV. If we can get a bigger, affordable EV with a 200+ mile range to replace our Prius when the time comes, we'll probably do that, too.

Not everything is perfect, of course. Having a realistic range of 70-80 miles can be limiting on busy days, and I haven't gone far outside the city since I got it home. It takes some adjustment to live with a car with that kind of range. If you're like me, and you don't charge everyday and only charge to 80%, you can't jump in and drive all over town without a little planning first. It takes some getting used to, but for the most part it's not a hindrance at all.

However, there is one issue with the Leaf that I have not gotten used to because I cannot understand why Nissan got it wrong or why they haven't fixed it. That nuisance is the grossly inaccurate energy efficiency meter. It really bugs me that Nissan reports inflated numbers for this measurement. It would be so much more useful to know the actual miles/kWh the car was getting so that I could know how much it cost to drive without an external power meter, and the GOM (Guess-O-Meter) would also be more accurate.

How Do I Know The Energy Efficiency Meter Is Wrong?

Before I get too far into discussing the consequences of the efficiency meter, I should show exactly why I think it's off. I talked about this briefly in my in-depth report on a year and a half of mileage data, but I've learned a few things since then so this should make more sense.

Let's look at a typical couple days of commute in the summer. Even though the numbers tend to vary because of changing temperature and traffic patterns from day to day, the trends that these numbers show are very representative of what I see on my daily commute. I'll start the morning with an 80% charge and the GOM reads 84 miles-to-empty in ECO mode. The temperature outside is about 70℉. This GOM reading agrees with the efficiency meter, which reads 5.0 miles/kWh from the previous day's drive. If you assume that you have 21 kWh of useable battery energy, multiply by 5.0 miles/kWh, and take 80% of that result, you get ... 84 miles.

Why 21 kWh and not the 24 kWh that the battery is rated as? Well, there's a certain amount of reserve charge that the car will never allow you to use to protect the battery from damage, and the charger will never completely charge the battery for the same reason. The amount of useable energy ends up being about 21 kWh in practice.

Now clearly, the GOM is assuming that I'll get 5.0 miles/kWh of driving efficiency on this charge, and if I achieve that, I should be able to go 84. In reality? Not. A. Chance. After going to and from work, I've traveled 22.5 miles and the GOM reads 54 miles. It appears that the GOM lost about 8 extra miles. The next day I go another 22.5 miles and the GOM reads 21 miles. I've lost another 10 miles on the GOM. If I extrapolate from the original 84 estimated miles at the rate that the GOM is losing miles, I'll probably be able to go another 15 miles on the leftover charge. Here's the extrapolation as a chart:

In total, I could go 60 miles on an 80% charge. That equates to 3.57 miles/kWh, but what does my efficiency meter read? 4.9 miles/kWh, and the next day I get another 82 miles on the GOM. This is clearly wrong, unless I really only used 9.2 kWh out of an available 16.8 kWh  on the 80% charge. That does not sound reasonable, so the only explanation is that the efficiency meter is lying to me.

Why Is My Leaf Trying To Give Me a Snow Job?

I'm really confused here. With a little simple arithmetic, it's blatantly obvious that the efficiency meter is reporting bogus numbers, and those numbers are affecting the GOM's accuracy as well. It doesn't even matter that I'm driving in ECO mode at 55 mph and not really getting the efficiency benefits of ECO mode. The car should still be able to measure the battery power being used and miles being driven and do a simple division. Heck, I can do it myself after the fact without knowing for sure what the kWh levels are and come up with a much more reasonable efficiency number anyway.

The point is, the car should be able to calculate this number very accurately. All it needs is a circuit that measures the voltage and current coming out of the battery, accumulate the product of those values over time to get energy consumed, and then divide the miles traveled in that time by the accumulated energy value. Why isn't Nissan doing this? Is it to make me feel better about how great my EV's efficiency is? Because it's not working, and I'm not fooled.

Look, I understand the desire to report the best numbers possible to put the car in the best possible light. As an engineer, I get that it's very tempting to measure performance with rose-colored glasses, and there's a lot of pressure from marketing and management to inflate metrics. But this efficiency number doesn't lend itself well to optimistic reporting. It's too obvious when it's wrong, and it's not at all useful to the driver of the car if it's not accurate.

In fact, reporting an inflated efficiency number is worse than useless because I'm constantly reminded that this great car, with all of its high-tech monitoring and control systems, is incapable of giving me a transparent and honest account of its energy usage. I know that the real measurements are being done and are available within the ECU. Somehow the battery management system and motor control system need to know the amount of power coming from or going to the battery to properly control acceleration and regenerative braking, and the odometer must be within a certain tolerance as well. Why can't the car report energy efficiency accurately on the dashboard?

Nissan Could Do Much Better

Correcting the energy efficiency meter would be a great start. With an accurate efficiency number, the GOM would improve dramatically, and I could more easily calculate the cost per mile for my driving. I know the cost is low, but I'd like to know what it actually is instead of some optimistic, sugar-coated nonsense.

I think Nissan could do even better, though. There are also power losses in the on-board charger and the battery when charging, and I'm sure the Leaf knows the power going into the charger already because it has to control the process. The Leaf could report a charging efficiency number as well. It could also combine the charging and driving efficiency measurements by taking the number of miles driven since the last charge and dividing it by the amount of energy used to recharge the battery, similar to the way you calculate mpg with an ICE car.

With that overall efficiency number I could easily calculate the real cost of driving the Leaf. Actually, the Leaf could do it for me if I could enter what I pay for electricity, the same way I can enter the price of gas in my Prius so it can calculate cost for me. Wouldn't that be nice. I'm sure plenty of Leaf owners would love a feature like this, if it was accurate. In the meantime, I can do this measurement manually if I buy a $30 electricity usage monitor and measure the electricity used to charge my Leaf at the outlet. I'm planning on doing just that because, well, inquiring minds want to know.


The Rest of the Leaf Series:
Part 1: The Acquisition 
Part 2: The Summer Drive 
Part 3: The Winter Drive
Part 4: Frills and Maintenance
Part 5: The Data
Part 6: The Future
Part 7: The Energy Efficiency Meter

If It Could be Anything With Four Wheels, What's Your Dream Car?

The automotive market is changing faster than it ever has in history. With all of the new hybrids, EVs, and PHEVs becoming available, it would be fun to stop and think for a minute about what would make a great future car. If the sky's the limit, if all of the current technical limitations were lifted, what would be the best new features to have in a car to make it the most comfortable, convenient mode of transportation? I'll impose two limitations: no flying and no teleporting. Allowing those two things seems like cheating. It's too easy to say, well, I want a flying car, of course, that folds up into a briefcase, and be done with it. I want to really think about what features would change the driving experience for the better. At the same time, I'll let my imagination run a little wild, so some of these things may never be possible. But we can dream, can't we?

Make it a family-sized car. I have a young and growing family, and we like to take road trips. That means a bigger car would be much more convenient for driving across the country and going on camping trips with all of our gear. I'd like a station wagon or minivan sized car that could both seat seven when we have extra passengers and have plenty of cargo space when just the four of us are traveling.

It'll be a pure EV. The performance, efficiency, and comfort of an electric motor driven car can't be beat. I'm thinking Tesla Model S performance and comfort here, but with even better efficiency. EVs are currently getting 2.6-3.5 miles/kWh, on average. I'd want it to do 5.0 miles/kWh easily in normal driving conditions at 65 mph, and it should have close to zero energy loss when charging or discharging the battery.

How about a 700+ mile range. With a metal-air battery, super capacitor, or some other technology that makes much higher kWh/lb capacities possible, a 700+ mile range would allow me to drive all day without having to stop to charge. I'd also only have to charge once a month for my normal daily commute. Of course, if charging stations were widely available and cheap, I could live with a 400-mile range and charging when we stopped to eat on road trips. Charging stations would definitely need to be available at hotels to recharge while we're sleeping.

I want solar charging. And not just any solar charging, I want a solar paint job that converts sunlight to electricity with at least 50% efficiency with some advanced nanotechnology paint material. Coupled with the huge battery capacity and great mileage efficiency, I would almost never have to actually charge this car. It would do all the charging for itself. Of course, with that kind of solar absorption efficiency, the color choices would likely be reminiscent of the Ford Model T days. I could have it in any color I wanted, as long as it was black. Maybe a nice deep iridescent blue would still be possible. I'd take that in a heartbeat.

Heck, how about the windows, too. The windows could also be auto-tinting in bright sunlight with the tint absorbing more solar energy. The roof could also be made of this solar glass to give a nice panoramic sky view. The glass would be shatter-proof to be safer in accidents, and the driver could have the ability to change the state of the glass for more viewing transparency or more solar absorption for charging. This solar glass would provide the added benefit that the car would not get so hot in the midday sun because the solar energy would be partially absorbed as electricity.

The car should drive itself. I could switch to manual override if I wanted, of course, but the car should otherwise be fully-automated. I could simply tell it where I wanted to go, and the car would take me there unassisted, giving me plenty of time to spend on things I'd much rather be doing than driving, like reading a book, watching a movie, or catching up on my news feed during the daily commute or playing travel games with my family on vacation. If we're on a road trip and the car is getting low on charge, it should automatically re-route to an inductive charging station, park over an open charger, and recharge enough to get to the destination. Then it would continue on its merry way. Along with the advanced sensors and controls for automated driving, the car would have all of the standard safety features: airbags, ABS, traction control, stability control, etc.

It's connected. The car is connected to the internet so that it can coordinate with charging stations, Google maps, traffic reports, roadside assistance, and much more. It can also be a wireless access point for all of our devices. I'll have access to all of my online movies, music, books and apps while being driven around by my personal chauffeur.

And that is all I would want in my dream car. That's not too much to ask is it?

The Digital Revolution Will Change Our Relationship with Energy

The Industrial Revolution lasted for about 80 years, from 1760 to 1840, and brought us disruptive innovations in energy with steam power and communication with the telegraph. The Technical Revolution, from 1860 to 1920, did the same with the diesel engine and electricity generation for energy and the telephone and radio for communication. These technologies were a major driving force for productivity and the economy, and they changed the very nature of how we live our lives.
Now we are in the midst of The Digital Revolution where the widespread use of computers and the internet are continuously changing how we interact with other people. Yet, we haven't seen a major disruption in how we produce and use energy in a way similar to that characterized by the last two technological revolutions. That change is surely set to come, and the way that the internet has changed our relationship with each other could show the way that our relationship with energy will change.

First, a Disclaimer

It seems that some people thought from my last article that I was portraying myself as an expert in the future of EVs. Let me be completely clear that I am not an expert in that, nor in this article on the future of energy. My expertise comes solely from what I read about the subject, and my desire to wrestle with complex ideas and combine trends together to speculate about the future. If at any point it seems like I don't know what I'm talking about, that's because I don't, but quite possibly, neither do you. The future of technology is notoriously hard to predict, yet it is still great fun to do, so I like to keep an open mind.

In speculating about future technology, I try to look at general trends without looking specifically at what is possible today. Doing that may carry me past the edge of possibility, but that is where real disruptive advances in technology happen. The naysayers are always right at first, but they are only right until someone who's likely not paying attention comes along and proves them wrong. That's when the impossible becomes possible. So, here's fair warning that there is hand-waving optimism ahead. If that offends you, stop reading now, but if you enjoy dreaming about eternal possibilities, then let's have some fun.

Oil and Coal vs. Solar

The amount of solar energy that hits the Earth's surface is simply astounding. Let's do some quick and dirty calculations to get an idea of how much energy we're talking about here. Since these will be incredibly large numbers, we'll use petawatt-hours (PWh) as the energy unit of measure. That's a watt-hour with 15 zeros behind it.

We can approximate the surface of the Earth as a disc that the sun's rays hit. The area of that disc multiplied by the solar constant of 1,366 watts per square meter gives the amount of solar radiation that hits the Earth's surface in an instant. The radius of the Earth is about 6,371 km, giving a disc area of 127.5 * 10^12 square meters and an energy flux of 174 PW. Multiply this by 24 hours to get the amount of solar energy reaching Earth's surface in a day - about 4,180 PWh.

As a point of comparison, the total energy used by commercial energy sources from 1880 to 2000 is about 4,806 PWh. Let that sink in for a moment. The Earth is bathed in nearly as much energy from the sun in one day as the world used in 120 years. We might want to think about capturing some of that energy. Of course, we can't capture anywhere near all of that solar energy. Much of it is absorbed by the oceans, plants need it for photosynthesis, and the Earth needs a fair amount for warmth to support life. But the World's energy usage in 2010 was about 150 PWh, or about 0.41 PWh per day. That's rounding error compared to the amount of solar energy we're getting in a day.

If we were to capture some of this energy using solar PV panels, it's difficult to think about how much we could reasonably capture starting from all that is available, so let's come at it from the other direction of how much we need to satisfy our energy needs. Limiting things a bit further, let's look at the energy needs of the U.S. Here is a great chart of the U.S. energy usage in 2012, from Lawrence Livermore National Labs (click to enlarge):

For our purposes, we'll convert Quads to PWh, with 1 Quad equaling 0.293 PWh. That means the U.S. used 27.9 PWh of energy in 2012, mostly coming from natural gas, coal, and petroleum. But look at how much was wasted in electricity generation and transportation. Electricity generation was only 32.5% efficient and transportation was abysmal at 21% efficient. Most of that energy was expelled as heat, as well as a significant amount of wasted electricity because utilities need to generate extra supply for demand spikes.

Solar (and wind) is inherently different than fossil fuels because the energy is there regardless of whether we use it or not. Any amount of energy we can capture for useful purposes can be thought of as energy that was reclaimed from the vast amount of unused renewable energy that's available. And once solar power plants are installed, the maintenance and operating costs can be much lower than coal power plants or oil refineries because the energy source does not need to be constantly dug out of the ground and consumed by the plant; it's already freely available without any extra effort to keep generating electricity.

Because of the way that residential, commercial, and industrial sectors use electricity that already uses raw resources, as well as their relatively high efficiency compared to generation and transportation, let's ignore them and focus on the amount of energy consumed from electricity generation and transportation that does useful work. If we were to replace all of that coal and oil (and natural gas, nuclear, etc) with solar energy, we would need to generate 5.27 PWh of energy per year.

How much solar panel area would that require? From the National Renewable Energy Lab, we can estimate that on average the U.S. receives about 5.5 kWh per square meter per day, or 2.0 MWh per square meter per year, of solar energy. Solar panels are far from perfect, though. If we assume they are 20% efficient at converting solar radiation into electricity, we would need 13,200 square km of solar panels to supply the U.S. electricity and transportation needs. That's about 110 square meters, or 1,180 square feet, of solar panels for every U.S. household. It's a lot, but still doable.

On a side note, that 20% efficiency estimate is likely on the low side for the future, considering the continuous advances made in solar cell efficiency as shown in this chart from the NREL:

On the other hand, assuming that all of our transportation needs will be supplied with electricity is highly unlikely. I do believe that the energy market for transportation will become much more segmented with biofuels, hydrogen fuel cells, and electricity all competing with gas and diesel in the transportation sector for quite a long time. The point of combining our electricity and transportation needs together is to get a rough idea of what it would take to transition most of our fossil fuel use to a more sustainable form of energy.

Where to Put All of Those Panels?

If we have learned anything from the internet, it is that distributed, networked solutions can be extremely powerful. What happens if we bring some of that knowledge to our energy problem? For the first time in modern history the prospect of the average person having their own personal power plant is within reach. The cost per watt for solar cells is dropping like a rock and quickly reaching or even surpassing the cost for coal or natural gas generated electricity, as shown in the following chart from the DoE:

However, this chart is already outdated. According to recent market research, we are now at $0.50 per watt for solar cells instead of $1.00 per watt, and we're heading for $0.36 per watt by 2017. After that solar will be cheaper than coal or natural gas are today. In the mean time, those fossil fuels are getting more expensive as they get harder to recover in more remote reserves and as the quality of those resources diminishes because we're using up the highest quality reserves first.

If all of these solar panels were installed as massive projects sponsored by the government and power utility companies, it would truly be a huge undertaking, similar to the U.S. interstate highway system. But if the installation was widely distributed, it would be much more like the formation and growth of the internet, and the main issue would be the manufacturing of huge quantities of solar panels. So how could we make significant progress in covering 13,200 square km of space with solar panels?

Rooftop installations on residential, commercial, and industrial buildings: Once solar panels are cheap enough that their break-even point with traditional electricity is 3-5 years or less, every individual consumer and business is going to have a huge incentive to convert to solar. If the panels are financed, consumers and businesses will be able to reduce their monthly energy costs immediately, and then they'll have substantially reduced energy costs once the panels are paid off.

Solar canopies in parking lots: There are huge areas of parking lots across America that could be partially covered with solar panels. Businesses could have that electricity available for their employees and customers to charge electric cars, or sell the surplus electricity to utility companies.

Solar panels on cars: I brought up the idea of adding solar panels to electric cars as a way to extend the range of the car's battery, but for everyday driving they would serve equally well for charging the battery without ever having to plug it in. On a typical day I drive less than 25 miles to and from work, and my car sits in the sun for the entire day. If I could have 5 square meters of 20% efficient solar panels on my car, they would nearly replenish the battery everyday. More efficiency directly translates into more miles per day. Considering that the average American drives less than 40 miles a day, this is a significant amount of driving sourced directly from the sun, and if the battery didn't need the extra charge, the car could be plugged in so that the elecricity went back to the grid.

Solar panels on semi-trailers, buses and trains: There are 5.6 million semi-trailers registered in the U.S. with a typical roof surface area of 100 square meters. That's 560 square km of area being hauled around the country by trucks. If they were fitted with solar panels on top and a decent sized battery underneath, the extra energy could supplement hybrid semi-truck engines to increase their efficiency. Similar logic could be extended to buses and trains.

Wind turbines: As long as wind turbines stay competitive with solar panels, wind farms and consumer wind turbines can carry a lot of the necessary energy load. They're also a good compliment to solar because in a lot of places and at many times when the sun isn't shining, the wind is blowing.

Traditional power plant sized installations: There will still be a significant need for large-scale installations of solar power plants and wind farms because not everyone has the space or the desire to have their own solar panels or wind turbines.

Distributed Energy Generation Will Change Everything

Once a significant portion of the population is generating their own power, and they're connected through the grid, things will start to get very interesting. When enough people were connected through computers and the internet and barriers to self-publishing content came crashing down, things changed in completely unpredictable ways. People did not foresee the development of Wikipedia, Facebook, and Twitter and what they would do to serve as platforms for individual, freely-shared content creation.

Prior to the internet, content creation was primarily controlled and distributed by publishing and broadcasting companies. Individuals only had access to public exposure through these companies. Media was centralized in a way very similar to how electricity and oil companies are now. Individuals depend on getting their energy from these sources, but what will happen when that changes? The role of utility companies will surely change.

Those companies that cannot adapt will get left behind, like encyclopedia producers and some newspapers did when the internet changed the rules for communication. If utility companies are to survive, they'll have to figure out how to make more of a business of metering and managing power from its widely distributed sources and less from generating it themselves. Once people are both producers and consumers of energy, there will be much more of a need to keep tabs on their net energy usage. Some people will be net producers and others will be net consumers, and energy will be shared within a much more interconnected network. I'm not sure what the oil companies will do.

It is really difficult to predict what will happen when people producing their own energy is the norm. All I can think of is that energy will be cheaper and the friction inherent in the current centralized system will be eliminated. When that happened to the telecommunications industry, we saw drastic changes in our society. And every time we capture a cheaper and more abundant source of energy, like coal in the Industrial Revolution or petroleum in the Technical Revolution, we also see drastic changes in our society. We are still in the midst of the Digital Revolution, and we are likely about to see both a reduction in the cost of energy and a change from centralized to distributed energy. I honestly can't imagine what is going to happen because of that, but I can say one thing. It's going to be big.

An EV Future is Inevitable

In the near future EVs (electric vehicles) will increasingly replace ICE (internal combustion engine) vehicles as our primary form of transportation, and that pace is going to accelerate. I am convinced that this is inevitable for three main reasons: the economics of EVs, the pace of innovation in EVs, and the ERoEI (Energy Returned on Energy Invested) of solar and wind vs. oil.

At this point it is very unlikely that any other technology under development has the potential to replace EVs as the way we're going to get around in the future. Any other technology would not only have to beat ICE cars on price, performance, and efficiency, but it would have to overcome the large and growing gains that EVs are already making in these areas.

Soon EVs Will Cost Less Than ICE Vehicles - Outright

This year GM dropped the price of the Chevy Volt by $5,000. Nissan dropped the price of their Leaf models by $2,500-$3,500 and introduced a new economy model starting at only $28,800. That's before the $7,500 federal rebate. Some states offer substantial tax credits on top of that, and now that the Leaf is more widely available, you can easily walk out of a dealership with a Leaf S for $20,000 or less. Compare that to a similarly equipped Toyota Prius II with an invoice price of $23,700, and you can see the edge that the Leaf is quickly developing against other cars even before fuel costs are tallied.

You can still get a Corolla, Civic, or similar car for less than a Leaf S, but for how long? In only two years the Leaf's price has dropped substantially, and other EVs are following suit. The Chevy Spark EV is starting at $27,500 and the BMW i3 is starting at $28,500 - both before incentives and credits and way sportier to drive than a Corolla or a Civic. The reason for these low and falling prices is likely the comparatively simple design. EVs are pretty much a battery driving a motor with a charger tacked on. Certainly, there are sophisticated electronics in the mix, but every modern car has a healthy dose of electronics. The electronics in EVs just serve a different function. Instead of controlling fuel injection and valve timing, it's managing a battery and a motor. The battery is where most of the cost is currently, but we are already seeing that drop as economies of scale start having an effect. There is a lot of room in EV production to wring out cost inefficiencies, whereas with ICE cars, most of those price reductions are long gone.

When more than half the price of an EV is in the battery, and the battery price has plenty of room to fall, ICE cars are going to find it tough enough to compete. But then you have to pay at the pump, too. According to the EPA at fueleconomy.gov, the average annual fuel cost of a typical 2013 vehicle with 23 MPG driven 15,000 miles per year is $2,350. For a car that averages 30 MPG, such as a Toyota Corolla, that comes down to $1,850 per year. For a Prius with 50 MPG, you can get down to $1,100 per year. The Leaf blows them all away with an average charging cost, according to the EPA, of $500 per year!

That means the Leaf can cost over $100 less per month to drive than a typical economy car, and remember that there's essentially zero maintenance on it as well. With gasoline prices more than likely to continue going up in the future, and battery costs going down, ICE cars will only get more expensive as EVs get cheaper. The idea should not be that EV prices will eventually converge with ICE prices. Instead, we are quickly reaching a crossover point where prices between the two diverge with EVs handily beating ICE cars on price as well as comfort and performance. The Leaf S can arguably already claim that position, and a real tipping point is not far off.

EVs Are at the Point Computers Were in the Early 1980s

EVs have a couple of major drawbacks that currently stop most people from considering them as their primary car: charging time and range. To that I say, EVs are in the early stages of a new technology wave similar to where computers and the internet were in the early 1980s. Think about how fast computer technology advanced in the 80s and 90s. They were slow and clunky and couldn't do much by today's standards, but their performance and capabilities were doubling every 18-24 months, courtesy of Moore's Law.

Batteries don't have a similar doubling law, but the amount of effort going into increasing their capacity will likely yield major improvements in the next decade. Technologies like lithium-air and sodium-air batteries and super capacitors show good promise, and the range really only has to double twice from the Leaf's 75 miles before it's comparable to a typical ICE car. That could easily happen in the next 6-10 years while battery prices hold at their current price or continue to drop. One more doubling past that, and EVs really start to make ICE cars look irrelevant.

Charging will become a non-issue even more quickly. Nissan already cut their charge times in half at Level 2 charging stations - from 8 hours for the 2011-2012 Leafs to 4 hours for the 2013 Leaf - with a 6.6 kW on-board charger. Other manufacturers have similar charge times, and there's also the Level 3 quick chargers that can charge a battery to 80% in 25 minutes. One thing is clear; EVs are advancing at a rate that is repeatedly making last year's models obsolete, similar to what was happening to computers over the last few decades.

If the EV of the near future has a 300-mile range and can be charged in 4 hours or less (the Tesla Model S is already there, but at 2-4 times the price of other EVs), the only real place that ICE cars still hold an advantage is with long road trips. If you want to drive 600 miles in a day, even an EV with a 300-mile range could be inconvenient. I think it would still be quite doable if the charging infrastructure was in place so that when you stop every hour or so to stretch your legs you can charge for 25 minutes. That would extend the range enough to go the whole day, and then you would charge overnight to start again the next day with a full battery.

I think there's a better solution, though. Most of that driving time will be spent under the sun, and solar panels are improving rapidly. What better way to extend the range than to slap some high efficiency panels on the car's roof and drive all day long? I'm sure that solar panels will reach the point where it would be possible to have an EV with infinite range as long as the sun is out, and on cloudy days you could fall back to plug-in charging or maybe inductive charging. If and when solar panels get good enough, they could provide the electric power for the motor directly to save some charging and discharging of the battery. Any extra power generated when the motor doesn't need it - either when coasting, stopped, or parked - could be stored in the battery for later. If you think about how often cars are just sitting outside parked in the sun, solar panels would be a huge win.

Clearly EVs are still in their infancy, and they are developing quickly. In 2011 the Leaf was the first EV intended for mass market sale to private consumers. The Chevy Volt was the first PHEV (plug-in hybrid electric vehicle) that same year. Now there are over a dozen EVs and PHEVs to choose from, and more are being announced every month. Nissan alone plans to produce 5 EV models. It won't be long before consumers will have EV options in every size class of car. The current state of EVs and the rate of innovation is truly reminiscent of the early days of personal computing, and in 30 years we will be as amazed at how much the automotive industry has changed as we are now with the telecommunications industry.

There is More Sunshine Than Oil

We have developed a massive infrastructure built on oil over the last 100 years that has enabled tremendous economic growth, but also a short-sighted dependence on a limited natural resource. Our transportation infrastructure is especially dependent on oil, and it is becoming clearer by the day that the amount of oil left in the ground is likely less than what we've already pulled out and is increasingly hard to get at. That means that every barrel of oil we suck out of field reserves costs more than the last one. That is why shale oil and tar sands are now economically viable oil fields to develop. If crude oil was still $40/barrel, those unconventional oil sources would be economically off-limits, but at $110/barrel they're profitable.

But stop and think about what crude oil really is. It is a concentrated and stored form of sunlight. Over millions of years, plants converted the sun's rays into organic material and animals fed on those plants, creating more organic material. All of that organic material died, decomposed and made its way into the oil reserves that we are now drilling and pumping out of the ground. The process takes so long and is so indirect that these reserves are a one-time deal. We are expending an enormous amount of effort digging sunlight out of the ground, and all the while it is shining us right in the face. There are much more immediate forms of energy that we can harvest more directly from the sun, and we already are doing so in limited quantities.

Growing crops that can be used to produce ethanol is one more direct method. It cuts out the time needed to decompose, concentrate, and store the sun's energy in the form of oil. However, the process of making ethanol takes more energy, produces a fuel with less energy content, and uses land that could be used to grow food instead. Hydroelectric dams and wind turbines are even more direct ways to generate usable energy from the sun through the water cycle and air currents, respectively. Both of these mechanisms are byproducts of the sun's rays shining through our atmosphere.

The most direct way we can convert sunlight into energy is by using solar PV (photovoltaic) panels to generate electricity. New concentrated PV panel arrays can be over 80 times more efficient than ethanol produced from sugar cane when comparing energy generation per acre of land. Even a new advance process of ethanol production that cultivates a form of algae that actually sweats the stuff is less than 1/5th as efficient as these CPV panels, and more electronics advances are coming down the pipeline to make CPV even more efficient.

If you look at the amount of energy returned on energy invested for each of these energy sources, and even more important, the trajectory of each of them, it becomes painfully obvious that oil is on its way out and solar and wind are on their way in.

While various forms of oil are becoming less ERoEI efficient, solar and wind power are becoming more efficient, and the amount of potential in these new renewable energy technologies is incredible. That means gasoline can only get more expensive in the future. It may stay even with its current prices as more people make the switch to renewable power, reducing the pressure on oil demand, but it can't get cheaper because there is a large and growing cost to extraction. Oil companies are not going to sell for less than it costs them to deliver the oil to market. Electricity generation is already one third to one quarter of the cost per mile as a vehicles power source, and solar and wind power will only make those costs drop further as more efficient renewable power plants come online. They are going to not only be able to replace oil as a source of energy, but also drive economic growth for the foreseeable future.

Solar and wind power are also a great match for EVs for three main reasons. First, they can generate the car's fuel directly with much greater efficiency. Oil production has efficiency losses every step of the way from drilling and extraction of harder to reach reserves, transportation of crude oil, the refining process, transportation of gasoline, and finally burning the fuel in an engine that's 25-30% efficient. In contrast, an EV hooked up to solar panels is directly converting solar energy to electric energy and dumping it in a battery that powers an electric motor that can be over 95% efficient. There are some losses going into and out of the battery, but they are nothing compared to the losses involved in the ICE car supply line.

Second, the extra storage capacity in EV batteries can smooth out the sporadic nature of renewable energy sources. Imagine if we had millions of EVs in the US with batteries that could collectively store hundreds of Gigawatt-hours of energy. This amount of extra storage in the grid would smooth out most of the intermittent supply problems of solar and wind power, and with most cars being charged at night, they would also help regulate total energy consumption during off-peak hours for hydroelectric and wind power so that it doesn't go to waste.

Finally, once EVs have enough range, consumers could reserve a portion of their battery power to source back to the grid during peak energy usage hours, but that may not even be necessary. As batteries get retired from service in vehicles, power companies are already planning to use them for extra storage, neatly solving the battery recycling issue. This could also be done on a smaller scale by individuals. My Leaf's 24 kWh battery is almost enough to cover my home's electricity needs for an entire day. If I could convert it to be used for storage for solar panels or a wind turbine, I could go completely off the grid and still be able to weather temporary power generation shortages from cloudy or calm days. My home would become a self-sufficient power plant. The combination of renewable energy and EVs gives people the possibility of true personal energy independence for the first time since the industrial revolution started.

The Future is Now

EVs are the future of transportation, and as their prices drop, battery technology improves, and renewable energy advances, it will become undeniable. Right now there are a lot of people who refuse to believe that EVs will actually succeed or actively want to see them fail. I can only say that these people are on the wrong side of history. Don't underestimate the power of technological progress. In thirty years those naysayers are going to look like the people that thought the internet was a fad. EVs are a big part of the next technology wave that's currently building strength. Are you ready to ride that wave, or are you going to let it wash right over you?


The Rest of the Leaf Series:
Part 1: The Acquisition 
Part 2: The Summer Drive 
Part 3: The Winter Drive
Part 4: Frills and Maintenance
Part 5: The Data
Part 6: The Future
Part 7: The Energy Efficiency Meter

A Year and a Half of Nissan Leaf Mileage Data

I've spent the last few weeks talking about how I got a Leaf, how it drives in the summer and the winter, and how little maintenance is needed. Now it's time to go into a detailed analysis of the mileage data I've been logging ever since I brought the car home. There are some issues with the data that I will get into, but hopefully, we can glean some valuable insights from it.

Methodology, or How do I Log All of This Data and Stay Sane?

After my nearly-out-of-charge experience driving home from the Rochester dealership to Madison, I figured I wanted to know how the battery would behave in this new electric car over a long period of time and a wide range of driving conditions. I immediately started a mileage log where I recorded the number of miles on the GOM post-charge, the high and low temperature as measured by the car's thermometer during the trips between charges, and the number of miles on the GOM and the odometer right before plugging in. Since my commute to work is slightly more than 11 miles, and I use the Leaf primarily for that commute, most of the trips between charges are either 22 miles in the winter or 45 miles in the summer. In the summer I can safely do two commutes on an 80% charge, but in the winter I don't chance it.

One of the issues with taking the data this way is that the temperatures associated with the driven miles are not very accurate. For each set of trips between charges, I end up with a single high and low temperature. In the summer when I do two commutes on a charge, there can be a lot of variation in temperature between the two commutes, and that is not captured well in the data. If I had it to do over again, I would have recorded a temperature for each trip and calculated a weighted average temperature for each charge cycle. In fact, I've started doing that now, so in a few months I should have some more accurate temperature data to compare to what I already have. As it is, I calculate an average temperature from the high and low temperatures.

The other major issue is that I am fully depending on the car's measurements and representation of the battery charge level. The Leaf's miles-to-empty readout is called a Guess-O-Meter for a reason. It moves around a lot, and in my experience, it is always optimistic - more so in ECO mode. I could have invested in a GID meter that reads the battery's charge level directly off of the Leaf's CANbus, but I didn't do this for two reasons. First, I didn't know about this meter early on, and I didn't want to invalidate the data I had already taken by changing my methodology. Second, I wanted this to be a real-world test of what an average Leaf owner will experience over the long term. The average person is not going to buy a meter and measure their battery everyday. They're going to depend on the Leaf's telematics, so I thought it best to do the same.

Data in the Raw

After entering all of the data into a Google spreadsheet, I did some quick data corrections. On a handful of charges, I charged to 100% instead of 80%, so I scaled the GOM readings for those charges to 80% to make later comparisons easier. Then I took the midpoint of each high and low temperature set to have an average temperature value for each charge cycle. Here's what the post-charge GOM and temperature data looks like as a time series (click to enlarge).

Conveniently, the GOM miles and temperature are on the same scale. Immediately, you can see that there is a correlation between these two series, although it's far from perfect. In a number of places, big changes in temperature do not correspond to big changes in the GOM readout. A couple other observations come out here. One is that the GOM readout changes markedly near the end. That is because of the software upgrade I had done on June 28th, and you can see that it reduced the GOM's optimism somewhat. The second is that 2012 was warmer overall than 2013 so far. The early winter months were milder and warmed up much faster than 2013, and the summer spent much more time over an average temperature of 75℉. That will be significant later on.

One other thing I changed during the data collection was when I drove in ECO mode or D(rive) mode. At first I always drove in ECO mode, but in the end of May this year I switched to D mode on the beltline because I wondered if the regenerative braking was being too aggressive when I was going 55mph. I thought I might get better mileage in D mode, but it turned out to make absolutely no difference and no change is noticeable in the data. I did learn that ECO mode adds a flat 10% to the GOM. That may be a good estimate for city driving, but at constant freeway speeds ECO mode and D mode are basically equivalent unless you're running the climate control. There is no mileage benefit to one or the other so I'm switching back to ECO mode because I like the accelerator behavior more in that mode. For the purposes of this data analysis, everything is converted to ECO mode values to keep calculations consistent.

Estimating the Battery's Capacity from the GOM

There's not much more we can deduce from the raw time series, so let's try putting it into a more useful form. The obvious thing to do is plot the post-charge GOM reading against temperature, so here's a scatter plot of that.

I plotted the data for 2012 and 2013 in different colors so that you can see how they differ. The 2012 data has a lot more samples in the 50-60 degree range and above 80 degrees. The 2013 data has more samples clustered below 30 degrees with a near void in the 50-60 degree range. The data is certainly noisy, but there is a definite correlation between GOM miles and temperature. That trend seems to peak right around 75 degrees and then starts to tail off at hotter temperatures, but at a much slower rate than it does at freezing temperatures. It's a bit hard to draw more conclusions from the higher temperatures because of a lack of samples up there.

What we can do is calculate a regression line to get a linear estimation of the GOM-Temperature relationship. I ran regressions for all of the data and 2012 and 2013 separately, and here is what came out:

	All	2012	2013
slope	0.219	0.189	0.237
slope-sigma	0.0119	0.0154	0.0164
intercept	68.8	71.6	66.4
intercept-sigma	0.62	0.82	0.84
r^2	0.541	0.484	0.622

The regression coefficient, which is a measure of how closely the data fits the regression line with 1.0 being a perfect fit, is pretty good considering the GOM data is so noisy. It's a bit worse for the 2012 data and a bit better for the 2013 data. To get a better idea of what this data is telling us, we can plot the estimated miles-to-empty value for a given temperature using the slope and intercept values. Let's do that for the 2012 and 2013 regressions between 0 degrees and 75 degrees, and I'll include 3-sigma error lines above and below the main regression lines. I'll also scale the lines so that the 2012 75 degree point represents 100% of full capacity. I stop at 75 degrees because it's unclear from the data what the trend is above that temperature.

Now this is interesting. It looks like the Leaf's battery loses about 15-25% of its capacity in temperatures below 15℉. The 2013 line is probably pulled lower because there is a lot more data at low temperatures for that year, but overall, that agrees with what I was experiencing on the road. It also looks like my battery lost a bit less than 2% of its capacity over 18 months. That seems pretty good to me. If loss continues at that rate, my battery wouldn't go below 70% capacity for more than 20 years, and it would still be useable to me at that point!

I bet charging to 80% and not ever using quick charge stations has helped keep the battery healthy. It's nice to see that taking good care of the battery is having a positive effect. I just hope that the charge loss in years to come stays linear. Of course, with taking into account the error bands, the real capacity loss could be higher or lower than 2%. It would be nice if Nissan would give you a capacity loss value in percent during the annual battery checks, but they only report the number of bars of capacity out of twelve that the Leaf's display already gives you.

How About Calculating Battery Capacity Another Way

Instead of using the Leaf's GOM to estimate battery capacity directly, we can calculate an estimated range for each charge cycle and look at the charge loss between 2012 and 2013 from that data. The range can be estimated by calculating the ratio between the number of miles traveled and the difference in the GOM readings for each charge cycle and multiplying that by the post-charge GOM reading scaled to 100% charge, i.e.

Range = Charged_GOM/0.8 * miles/(Charged_GOM - Post_Trip_GOM)

 Plotting these ranges against the average temperature for each trip gives us the following scatter plot:

Whoa, that is some noisy data! I plotted the first five months of data in yellow to show that there was even more variation in the beginning. It seems that the Leaf goes through a pretty long learning period of about 2500 miles. Even with those points removed, this data is quite diffuse, and the regression coefficient is only 0.28. Also, the regression lines for the 2012 and 2013 data cross, which doesn't seem right at all. However, if we take the average of all of these ranges, we get 75.5 miles. That is really close to the EPA's estimation of a 73 mile range for the 2012 Leaf, so we're probably on the right track.

One of the problems with using the Leaf's GOM reading to calculate range is that after a charge it is estimating the miles-to-empty using the data from the previous charge cycle to attempt to predict the future. Since we already know the future temperature for each trip that the GOM is trying to predict, we can plug that average temperature into the linear estimation formula to get a better estimate of the starting miles-to-empty for each charge. Then we can plug that number into the equation above for calculating the range. Here is the plot that we get from that exercise:

This scatter plot looks a bit better, although it is still pretty noisy. That 2013 point that shows nearly a 90 mile range at 15 degrees is clearly an outlier. The first five months still show that the Leaf is in a learning mode for its prediction algorithm. Remember, the GOM is still being used to estimate the miles-to-empty right before charging when doing these calculations. The average of this data is 75.0 miles, so that still agrees closely with the EPA estimate. The regression analysis shows some improvement as well.

	All	2012	2013
slope	0.237	0.215	0.222
slope-sigma	0.0215	0.034	0.028
intercept	61.1	64.3	60.5
intercept-sigma	1.18	2.06	1.43
r^2	0.371	0.34	0.334

The overall regression coefficient improved considerably, and the regression coefficients for the individual years aren't much worse. However, there is considerably more uncertainty in all of the coefficients than there were for the battery capacity estimates. It is still informative to plot the regression lines, but the 3-sigma error lines are much wider.

Note that for the estimated range, the slopes for the two years are almost identical, possibly because the data during the learning period was removed. The range varies from a minimum of about 55 miles in extreme cold to more than 85 miles in pleasantly warm temperatures, or more than 20% variation over this temperature range. The difference in the two lines equates to approximately a 4% loss of range, but with the large error bands, it's quite possible that the real loss would be higher or lower. A 4% loss would still be respectable, and it would take more than 11 years to hit 70% of full range.

I should stress that these linear estimates are just that - estimates. The range values were calculated from a linear estimation, and I have never driven my Leaf from a 100% charge to "turtle" mode, where the car limits the speed to a crawl to conserve charge and protect the battery from completely discharging. Thus, I don't actually know what the real range is at any temperature, let alone over a range of temperatures. What these plots do show quite well is that even if you did drive the Leaf until it's near empty, there's a lot of variation from one charge cycle to the next, and you won't have a good idea of its overall range unless you do a lot of those measurements. Treating the battery that harshly is not recommended, and would accelerate the capacity loss, so I prefer to play with estimation techniques.

We're Not Done Yet

So far we have seen that the GOM data I'm working with is highly variable. I'm going to speculate that the variation is actually due to the comparatively short range of the Leaf, and that if its range was about four times larger, it would be at least as accurate as the mileage estimators on normal ICE cars. To model this assumption, I took the data from the previous plots and summed every five samples of the post-charge GOM, post-trip GOM and trip miles, and I did a five-sample running average of the temperature data that was weighted by the trip miles. If I then run this data through the range estimation equation, I get a set of estimated ranges for a 300-mile range Leaf with the assumption that I'm charging it to 80% and driving it almost to empty.

Now that data looks much more correlated to temperature. I removed the first five months of data again for this plot, and I combined all of the rest into one color since comparing the two years isn't useful with the modifications that were done to the data. The regression coefficient on this set of samples is now 0.72, showing much more predictive accuracy versus temperature.

Some may quibble with the fact that it looks like I'm just running the data through a running average, and of course the data will look tighter after I do that. But that is entirely the point. If the Leaf had a 300 mile range instead of 75 miles, the telematics would have many more miles of range and the associated driving conditions to make a good estimate and adjust it. Like so many other issues with EVs, the issues with highly variable range and what appears to be an inaccurate GOM would evaporate with a much bigger range.

A 300-mile Leaf would likely have an even more accurate trip computer than this plot portrays because the data it would be processing would be much less disjointed. (Also, remember that my temperature data could have been taken in a more accurate way.) The current job of the GOM is practically impossible because it's working with only tens of miles between charges, and it's trying to predict the range on a charged battery for as yet unknown driving conditions based primarily on the previous cycle's driving conditions. No wonder it's a Guess-O-Meter. Increasing the range in future EVs will certainly improve the GOM's ability to estimate range.

And Finally We Come to the Issue of Miles/kWh

I'm quite pleased to see that my Leaf's battery has probably only lost 2% of its charge in 18 months. It is also nice to see that the huge variations in range estimation are likely due to the simple fact that the Leaf has a much shorter range than a normal ICE car. What about that other number that the Leaf's telematics display so prominently: the miles/kWh? My Leaf has varied from 4.0 miles/kWh to 5.1 miles/kWh between winter and summer. Does that agree with all of this data?

If I assume that the battery is at a full capacity of 24 kWh in the summer, my range estimate of 80.5 miles equates to 3.4 miles/kWh, which is a far cry from 5.1 miles/kWh. The battery appears to be at about 80% of full capacity, or 19.2 kWh in the winter, so my range estimate of 64.3 miles equates to the same 3.4 miles/kWh. The Leaf must be estimating based on a fixed kWh number, so if we assume it's 24 kWh, that results in 2.7 miles/kWh. The average of 2.7 and 3.4 is 3.05 miles/kWh, which is really close to the EPA's estimate of 2.94 miles/kWh.

Why is the Leaf over-reporting this number? It's possible that it's using a lower value for the usable capacity of the battery and that the battery is more efficient in the 80%-20% range that I have been using it. But if we assume that the Leaf's measurement is accurate, then there would only be 16 kWh of usable energy in the battery. That seems a bit too low. Without knowing more about the battery measurement system design, I'm suspecting that it's a combination of usable capacity, optimal efficiency range, and over-reporting.

I'm not too pleased about that last reason. The miles/kWh is a critical measure of the efficiency of the car, and Leaf owners would benefit much more from an accurate reporting of this measurement for fuel savings calculations than the happy-but-ignorant feeling that comes from an inflated value. I hope that Nissan corrects this measurement in the future, or that the EPA can force more accurate reporting.

Other than that one issue, I'm quite happy with how this analysis has turned out. It appears that I have a healthy battery that will serve me well for many years to come, and the range is more than enough for my daily driving needs, even if it's a little variable. I'm definitely sold on the idea of EVs and believe that they are a solid, reliable alternative to ICE cars in the right circumstances with even more potential in the future.

Next week I'd like to shift from thinking about the past year and a half of Leaf ownership to thinking about the future of EVs.


The Rest of the Leaf Series:
Part 1: The Acquisition 
Part 2: The Summer Drive 
Part 3: The Winter Drive
Part 4: Frills and Maintenance
Part 5: The Data
Part 6: The Future
Part 7: The Energy Efficiency Meter