Is a Tesla cleaner than a dirty diesel?

If you are a Minnesota driver, the answer is yes, but not by much it would not meet federal emissions standards for light duty vehicles. Including energy generation, a Tesla will produce slightly far fewer NOx emissions per mile than a “defeated” VW. But a Tesla in Minnesota is far three times dirtier, in terms of NOx emissions, than the average car on the road, or than federal emissions standards allow for light duty vehicles.

(I was kind of surprised by these results. If you think f I’m missing something here, let me know and I’ll make corrections to calculations and notes, as appropriate.)


Tesla is running this ad, apparently (UPDATE: this may not be an ad, but may have been produced by that twitter user. If you know the source, let me know), and Elon Musk says cars should be tested at random to see if they meet emissions requirements. This is in response to the Volkswagen Scandal.

It’s fairly clear at this point, that in many locations with cleaner electricity sources, EVs have a carbon benefit over ICE vehicles (this EPA calculator gives you results for your area). Minnesota is one of those places, even though our electricity still comes mostly from fossil fuels.

chart (3)

But what about nitrogen oxide (NOx), the pollutant at the heart of the VW Scandal? (Here’s a rundown of the bad stuff NOx does to things that breath air) A VW with a “defeat device” could emit up to 35 times the federal emissions limits for NOx. That could be as high as 2.45 grams or 0.0054 pounds per mile. So how does an EV, like the Tesla, compare?

A Tesla uses 33 kWh for every 100 miles traveled (or 0.33 kWh per mile). According to federal statistics, Minnesota power plants emit 1.4 pounds of NOx pollution for each MWh of electricity generated (Xcel Energy shows a similar 1.5 lbs/MWh in its reporting). That means a Tesla is responsible for 0.210 grams of NOx per mile. So, to fact check the ad: yes, driving a Tesla (in Minnesota) is slightly quite a bit cleaner than a diesel VW with a defeat device.

However, that Minnesota Tesla is responsible for emitting 1.5 times more NOx per mile than the dirtiest cars allowed on the road by federal emissions standards, and 3 times more NOx per mile than the allowable fleet average NOx emissions. So it’s too early for Tesla owners to get smug about their impact on the environment. In fact, they are squarely in dirty-diesel territory. (UPDATE: my math was off in the preceding calculation, it has been corrected). You might interpret that ad another way: Tesla has actually defeated emissions testing – by moving the tailpipe from the car to a distant power plant (UPDATE: again, not sure this is a real ad).

Electric vehicles can be better for NOx – if we kick coal

If you were driving a Tesla in Washington State, which has a NOx emissions rate of 0.3 lbs/MWh, you’d actually be emitting 35 percent less NOx per mile than the average light duty vehicle. Why? Because Washington residents get most of their electricity from emissions-free hydropower.

The break-even point seems to be 0.46 pounds of NOx/MWh, which is about equal to the emissions rate for the state of Oregon. This is what their electricity sources look like:

chart (4)

Oregon only gets 6 percent of its electricity from coal. Minnesota is currently at 50 percent. It’s clear what we need to do to make EVs cleaner: reduce Minnesota’s use of coal for making electricity.

We probably need to electrify transportation to meet the State’s aggressive climate action goals. However, we don’t want to just trade carbon benefits for dirtier air and all the associated impacts (asthma, deaths). We need to simultaneously begin the transition to electric vehicles, AND rapidly decarbonize and de-coal our electricity grid.


  1. Brendan Jordan asserts via twitter that 50 percent of Minnesota EV owners use wind power for their EV charging. This means they either buy, or their utility supplies, wind “credits” to supply the amount of electricity they use for EV charging. If the credit tracking system works, this wind is “additional”, and does in fact reduce emissions. If it’s true (I haven’t seen the data) that’s great, and just another argument for decarbonizing the whole grid. However, this is not the “default” when you plug your vehicle into a charging station at home or at work. Also free wind for EV charging is not offered by Xcel Energy, Minnesota’s largest utility.

Minnesota residential solar installation prices in line with national trends

Depending on how you count, this is my sixth post in a row here about solar. I’ll do my best to discuss something non-solar next time.

CY 2014 was the first year the Minnesota Department of Commerce required electric utilities to report on the total installed cost of distributed generation sources (like solar!) in their annual reporting on DG. Prior to that, they’d just been reporting the amount of resources that were interconnected. LBNL recently put out Tracking the Sun VIII, a report on national cost trends, so I thought I would compare.


I was kind of surprised to find out that in Minnesota, we’re basically right on track with national price trends. It would be nice to look at older data, but it doesn’t exist in the reports.

Nationally, installation prices have fallen an average of over 12 percent each year since 2009. If those kinds of cost declines continue, residential solar could be sub-$2/watt by the early 2020’s. Even in wintry Minnesota, sub-$2/watt rooftop solar (the most expensive kind of solar) begins to look competitive with natural gas and coal on a levelized cost basis.

The next Minnesota DG reports come out on March 1, 2016.

Only Wikipedia is accurately tracking solar PV capacity in Minnesota

GreenTech Media recently showed that the main energy statistics agency for the United States, the Energy Information Agency (EIA) was missing information on a whopping 45 percent of installed solar PV. The problem is with their methodology – they don’t count customer-sited solar, like systems on rooftops. GreenTech found that actual solar production was 50 percent higher than official estimates. Three states (CA, AZ, HI) now get more than 5 percent of their electricity from solar, something you wouldn’t know if you only consulted EIA.

Data for Minnesota is even worse. Users of wikipedia will get a far more accurate assessment (which is based on the Interstate Renewable Energy Council’s annual solar market trends report).

EIA data says that Minnesota produced no electricity from solar in 2012, and 2.7 gigawatt hours in 2013. Here is the chart from their Electricity Browser:


In reality, Minnesota produced something like 18.7 gigawatt hours from solar PV in 2013, or 592 percent more than EIA estimates.

I didn’t just use wikipedia data to make this estimate, I used data from the Minnesota Department of Commerce’s Annual Distributed Generation Interconnection Report, which utilities are required to submit each year showing existing and new DG facilities. The number above comes from only six utilities in Minnesota, which I think are some of the largest in terms of number of customers.


Here is the breakdown of installed capacity at the six utilities:


I couldn’t find a report on total installed PV capacity or production on Commerce’s website, but it could be hidden in dockets somewhere.

If you’re looking for accurate data on the growth of distributed generation, like solar, you can’t (yet) count on EIA. GreenTech outlines a bunch of reasons why this is important, including making the EPA’s Clean Power Plan to regulate existing power plants look harder to accomplish than it might be.

In Minnesota, solar is a small (0.04% of total generation in 2014), but growing part of the energy mix. Accurately tracking this growth is important for making good policy, especially in regards to distributed (customer-owned) generation, which is usually outside the control of utility planning processes.

Thoughts on Xcel’s 2030 Resource Plan

Xcel Energy, the state’s largest electric utility, has filed their 2016-2030 Resource Plan with the Public Utilities Commission. This begins a long process of commenting and modification until their plan is approved by that body (which can take years). The Resource Plan details what trends in usage Xcel expects, and what resources (like new power plants, etc) are needed to meet that demand. The plan is important because it identifies the infrastructure investments the utility will need to make, and also the resulting environmental performance, among many other details.

I’m slowly making my way through it, both for professional and personal interest, and hope to highlight some thoughts for you, my dozens of readers.

There are a lot of things to like in the plan, the first being that Xcel is planning to meet State greenhouse gas emissions reduction goals within their own system. This is unlike the previous plan, which showed emissions increasing between 2015 and 2030. The chart below, from Appendix D, compares the two plans. (State goals include a reduction of 15 percent by 2015, 30 percent by 2025 and 80 percent by 2050)

2030 CO2 Emissions Xcel

Most of the planned reductions in carbon pollution come from the addition of renewable energy resources to their system, as the chart below shows. By 2030, Xcel plans for 35 percent of their energy portfolio to be renewables.

Sources of CO2 reductions

However, I think the plan’s assumptions about the future cost of the solar portion of those renewables is probably too high.

Xcel plans to add over 1,800 MW of utility-scale solar to their system by 2030 (up from basically zero in 2015). This is a significant increase from the “reference case”, a ten-fold increase in fact. However, this slide was presented at a public meeting at the Public Utilities Commission:

Renewable Price ForecastXcel says this in Appendix J about their assumption:

As solar technology is still not fully mature, and costs are expected to decline and conversion efficiency to improve, it was assumed that the $95/MWh price holds throughout the study period. In effect, the assumption is that fundamental cost driver improvements will offset inflation.

So the rate of decrease in solar prices will match the inflation rate? Many sources have documented the dramatic decline in solar PV prices over recent years. Lazard seems to be an oft-cited source, and their 2014 Levelized Cost of Energy Analysis shows the price of energy from solar has dropped 78% since 2009. According to, the cumulative rate of inflation between 2009 and 2014 was about 10%. So, at least looking historically, this seems way off.

Of course, current precipitous declines probably won’t continue forever (most of the cost is now not modules). NREL says costs have been dropping on average 6 to 8 percent per year since 1998. If we assume just half of that decline per year (4 percent), solar energy would be around $51 per MWh in 2030. Using some very back-of-envelope calculations, a price difference of $46 per MWh in 2030 means costs for new solar energy shown in the Plan’s “Preferred Plan” scenario could be over-estimated by $97 million.

This is significant not just because the price estimates of the Preferred Plan may be too high. In preparing the plan, Xcel also ran seemingly dozens of other scenarios, some including CO2 reductions of over 50% in 2030 (compared with 2005). The price difference, according to Xcel, between the Preferred Plan scenario and the scenario with the largest CO2 benefit is $172 million (from Appendix J). These other scenarios which seem too costly may actually be more in line with what Xcel is currently asking to spend once dropping technology costs are factored in.

In praise of the prairie


As part of the “Our Fair State” series going on at this week, I’ve posted a short photo post praising the western Minnesota prairie.

When most people think summer in Minnesota, they think north: lakes, coniferous forests, large noisy black birds.  But Minnesota actually has four biomes, and I would consider the prairie grassland the most neglected when we engage in communal nostalgia for Minnesota summer.  Luckily, we have some great parks on the prairie where you can see a little of what Minnesota might have been like before settlement.  And it’s beautiful.

All the ways we subsidize growth

Over at, I reflect on a recent event I attended, ““Kicking the Habit: Unsustainable Economic Growth” that featured contributor Chuck Marohn delivering his Strong Towns message.  I focus on one issue that is featured prominently in the Strong Towns narrative: intergovernmental transfer payments which subsidize growth and potentially hide the true cost of development.

In Minnesota, we build roads really well. If you look at the metro area, we’ve created a system where despite wide differences in job and housing density, commute times are virtually the same whether you live in Dahlgren Township or Loring Park in downtown Minneapolis. We also have a semi-famous regional government that makes connection to the same wastewater system easy, no matter where you are in a 7-county region that includes both farms and skyscrapers. All these things (and more) are made possible by shared resources, often collected from one area or community type, and sent to another with a different character. Somehow we’ve determined that this is a good thing (for ease of access, equity, environmental protection, political will, etc) As I listened to Chuck I thought, “you’d really have to remake how local governments interact if you wanted to promote (or even test) the idea that our “most productive places” should be differentiated from our least productive.

I won’t attempt to figure out how this can be done. But I think it’s valuable to think about all these “transfer payments”. There are more than most people ever think about. So, here goes:

Read the rest.

National Climate Assessment: trouble ahead

duluth flood - mpr

A draft of the US National Climate Assessment was released about a week ago, and the outlook for changes headed to the Midwest and country as a whole is not good.  Minnpost has a good look at the Midwest section (emphasis mine):

Climate change will tend to amplify existing risks from climate to people, ecosystems, and infrastructure in the Midwest. Direct effects of increased heat stress, flooding,

drought, and late spring freezes on natural and managed ecosystems may be altered by changes in pests and disease prevalence, increased competition from non-native or opportunistic native species, ecosystem disturbances, land-use change, landscape fragmentation, atmospheric pollutants, and  economic shocks such as crop failures or reduced yields due to extreme weather events.

These added stresses, when taken collectively, are 

projected to alter the ecosystem and socioeconomic patterns and processes in ways that most people in the region would consider detrimental.

Much of the region’s fisheries, recreation, tourism, and commerce depend on the Great Lakes and expansive northern forests, which already face pollution and invasive species pressure – pressures exacerbated by climate change. Most of the region’s population lives in urban environments, with aging infrastructure, that are particularly vulnerable to climate-related flooding and life-threatening heat waves.

CC Midwest temp rise

Over at MPR, Paul Huttner also has a good overview, highlighting the coming “climate shock” of project 5-degree warming headed to Minnesota.


Bottom line?

This magnitude of warming will likely cause some dramatic… and potentiallyalarming changes in our Minnesota Landscape.

Our forests will shift north. Pine forests may dissapear, and transition to hardwood forests in significant sections of northern Minnesota.

Prairies will also overtake areas that are now forested…possibly even the parts of Twin Cities metro.

Increases in the frequncy of extreme rainfall events will create more events like the multiple “500 to 1,000 year” flood events seen in Duluth and southern Minnesota in the past 9 years.

The changes we’re already observing in Minnesota will continue…and the pace of change is likely to quicken in the next 30 years. Our children will live in a very different Minnesota than our parents did.

How are we doing to address this challenge?  Haven’t US greenhouse gas emissions gone down recently?  Yes, but unfortunately not enough, and we can’t just worry about US emissions.  From the report’s mitigation section (emphasis mine):

Even absent a comprehensive national greenhouse gas policy, both voluntary activities and a variety of policies and means at federal, state, and local levels are currently in place that lower emissions. While these efforts represent significant steps towards reducing greenhouse gases, and often result in additional co-benefits, they are not close to sufficient to reduce total U.S. emissions to a level consistent with the B1 scenario analyzed in this assessment. 

And remember, hitting that B1 scenario is critical if we want to avoid the most dangerous impacts and potentially runaway climate change.  For more on what the world might look like if we stay on the emissions path we’re on, take a look at the World Bank’s most recent report on 4-degree warming.

What is a carbon tax worth?

California has begun a historic cap and trade market in carbon, completing the first auction, with permits going for $10.09 per metric ton.  I’m not sure cap and trade and the offsets it allows are the right way to go. But when I read this, I wanted to understand what such a program might mean for an average Minnesota energy consumer (after all, California is a distant and foreign land).

Xcel Energy, the electricity provider for most of the Twin Cities metro, produced 0.5266 metric tons of CO2e per MWh in 2011.  At $10 per mt, that’s about $5.31 per MWh, or roughly half a cent per kWh.  The EIA says the average Minnesota residential consumption is 813 kWh per month.  This seems awfully high, but we’ll go with it.  At that rate, the average residential customer would pay an extra $4 per month on their electricity bill.

Natural gas is trickier to estimate an average for, although some 2005 data says perhaps 650 therms per year, per household, using metro assumptions about people per household.  That seems low.  We used over 1,000 therms the last two years, but our house is old.  At 0.005 mt of CO2e per therm, the tax would increase the price of natural gas 5 cents per therm.  If you use 1,000 therms per year, that’s about $4.50 more per month.

So if something like $10 per metric ton was imposed in Minnesota, residential customers might see a utility bill increase of $8 per month, or $96 per year.  The California Public Utilities Commission has proposed a means to eliminate that cost.  Residential customers would actually be paid a dividend from the revenue generated by the auctions, which they say would more than offset the cost of the carbon tax.  Commercial and industrial users are a whole other ball of wax I haven’t touched here, and higher energy prices probably means higher product prices.

All this is not to say that a carbon tax or cap and trade system is appropriate for Minnesota (or the US).  $10 per ton is likely too low, their could be serious equity issues with offsets and increasing energy prices, and other tricky stuff.  But at $10/ton, direct energy costs to residents probably wouldn’t break the bank.