Spatially explicit life cycle assessment of 5 sun-to-wheels pathways finds photovoltaic electricity and BEVs offer land-efficient and low-carbon transportation
04 January 2013
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| Direct land use, life cycle GHG emissions (excluding indirect land use change), and life cycle fossil fuel requirements to generate the transportation services provided by 17.8 × 1012 MJ NCV of gasoline, the amount used in transportation in the US in 2009. Credit: ACS, Geyer et al. Click to enlarge. |
A new spatially-explicit life cycle assessment of five different “sun-to-wheels” conversion pathways—ethanol from corn or switchgrass for internal combustion vehicles (ICVs); electricity from corn or switchgrass for battery-electric vehicles (BEVs); and photovoltaic electricity for BEVs—found a strong case for PV BEVs.
According to the findings by the team from the University of California, Santa Barbara and the Norwegian University of Science and Technology, published in the ACS journal Environmental Science & Technology, even the most land-use efficient biomass-based pathway (i.e., switchgrass bioelectricity in US counties with hypothetical crop yields of more than 24 tonnes/ha) requires 29 times more land than the PV-based alternative in the same locations.
Furthermore, PV BEV systems also have the lowest life cycle GHG emissions throughout the US and the lowest fossil fuel inputs, except for locations with hypothetical switchgrass yields of 16 or more tonnes/ha. Including indirect land use effects further strengthens the case for PV BEVs, the researchers suggested.
Biofuels for ICVs and bioelectricity for BEVs use photosynthesis to convert solar radiation into transportation services, that is, they are sun-to-wheels transportation pathways. While photosynthesis has a theoretical maximum energy conversion efficiency of 33%, the overall conversion efficiency of sunlight into terrestrial biomass is typically below 1%, regardless of crop type and growing conditions. Therefore any biomass-based energy pathway is very land-use-intensive. As a result, biomass-based transportation pathways are increasingly seen as a threat to food supply and natural habitats.
A third type of sun-to-wheels pathway is the use of photovoltaics (PV) to convert sunlight directly into electricity for BEVs...Existing environmental assessments of biofuels and photovoltaic energy pathways use average biomass and PV yields, even though these yields vary widely between geographical locations. Spatially-explicit assessments are more informative, since pathway performance depends on location, and land use decisions are always local by nature. This article presents life cycle assessments of five different sun-to-wheels conversion pathways for every county in the contiguous U.S: Ethanol from corn or switchgrass for ICVs, bioelectricity from corn or switchgrass for BEVs, and PV electricity for BEVs using cadmium telluride (CdTe) solar cells. The assessments include the production and use of the transportation energy (the fuel cycle) and the life cycle of the vehicle.
—Geyer et al.
The functional unit of the assessment was 100 km driven in a compact passenger vehicle during one year. The team calculated three environmental indicators for each county of the contiguous US:
Land area required for the corn and switchgrass fields or the PV installation—i.e., direct land use measured in m2/100 km driven.
Total global warming potential from the vehicle and fuel life cycles, measured in kg CO2 equiv/100 km driven.
Total fossil fuel consumption from the vehicle and fuel life cycles, measured in MJ of net calorific value (NCV) per 100 km driven.
The system boundary includes vehicle production, use, and end-of-life management, as well as fuel production and use. In the case of PV electricity, the fuel cycle consists of production, use, and end-of-life management of the PV system.
GHG and fossil fuel data for the production of corn and switchgrass and their conversion to ethanol are based on the EBAMM Model, which was combined with crop yield maps and updated with data from version 1.8c.0 of the GREET model and other recent literature. Among the assumptions were:
NCV of corn and switchgrass is 18 MJ per kg, and that 2.53 kg of corn and 2.62 kg of switchgrass are required to produce 1 L of ethanol with 21.2 MJ NCV.
Energy consumption and GHG emission values of the biorefineries include coproduction credits and in- and out-bound logistics. The crop-to-electricity conversion model assumes that half of the biomass is converted in biomass boilers and the other half is co-combusted with coal to generate electricity.
Inventory models for both product systems are based on Ecoinvent data and reports. A biomass-to- electricity conversion efficiency of 32% was used, and an electricity transmission and distribution efficiency of 92%.
The PV system life cycle is based on 2005 technology and production data.
Economic input−output life cycle assessment (EIOLCA) was used to derive energy and GHG values for the production of a compact ICV; data on 2005 Li-ion battery technology was added to model PHEVs of equivalent size. The resulting energy and GHG values are 102,000 MJ and 8,500 kg CO2eq per compact ICV, and 1700 MJ and 120 kg CO2 equiv/kWh of Li-ion battery.
A 150 km (93-mile) -range BEV model was derived by increasing the battery size in the PHEV model. This may overestimate GHG emissions and fossil fuel consumption of BEV production, the researchers noted, since they merely added the battery to an ICV and did not deduct the internal combustion engine or related components.
Together with the maximum range of 150 km and a maximum depth of discharge (DOD) of 0.8, the BEV energy demand translates into a required battery size of 33.75 kWh. The life cycle mileage of both vehicles is assumed to be 240,000 km (149,000 miles).
Among their findings were that relative to the gasoline baseline, the PV and switchgrass scenarios would also reduce associated GHG emissions and fossil fuel consumption from production and use of vehicles and fuels by 75−80% relative to gasoline ICVs. The PV-based pathway would reduce life cycle GHG emissions, including vehicle production, by almost 80%, from 1.92 to 0.41 billion tons of CO2 equiv.
Vehicles powered with switchgrass electricity or ethanol come second and third with 0.46 and 0.48 billion tons of CO2 equiv, yet these numbers do not include any GHG emissions from indirect land use change, the researchers noted.
The three sun-to-wheels pathways with the lowest fossil fuel requirements are switchgrass ethanol for ICVs; switchgrass electricity for BEVs; and PV electricity for BEVs; with 4.7, 5.4, and 5.2 trillion MJ.
For both BEV-based pathways, more than 85% of fossil fuels are consumed during vehicle production. Of all the 5 sun-to-wheels systems, corn ethanol for ICVs had by far the highest land requirements, GHG emissions, and fossil fuel requirements.
Assuming that the economics of PV and BEV technology will further improve and issues of material availability, and electricity transmission and storage can be resolved, PV offers land-efficient and low-carbon sun-to-wheels transportation. Unlike fuel crops, PV electricity does not have to compete with food production and biodiversity for fertile land and could potentially replace all gasoline used in US transportation.
—Geyer et al.
Resources
Roland Geyer, David Stoms, and James Kallaos (2012) Spatially-Explicit Life Cycle Assessment of Sun-to-Wheels Transportation Pathways in the US. Environmental Science & Technology doi: 10.1021/es302959h
Assuming that they are talking about large solar arrays rather than rooftop ones, in fact they use several times the area that the panels cover.
Of course that is still way better than biofuels, but it is not only very expensive still, and provides power during the day when a lot of people are going to want to charge at night.
The same job can be done at far less cost and with a fraction of the land use with nuclear plants which run day and night.
Posted by: Davemart | 04 January 2013 at 02:57 AM
More evidence of the idiocy that exist in the California higher education system. What they missed during breaks for surfing at UC Santa Barbara is that the corn belt has long dark and cold winters. PV BEV will not work. It is not a matter of costs.
Second, until such a time as there is excess solar generated power, these LCA are an example counting the same benefit twice. If solar reduces the environmental impact of making power, it has nothing to do with BEV.
Third, like all BS from California; they do not have a clue about the rest of the world. Farmers grow corn for animal feed. Processing out some of the excess energy from growing corn to make electricity or ethanol, reduces the environmental impact of growing corn in the corn belt.
The best choice for UC Santa Barbara might be PV to charge cars during the day because they do not grow corn.
Posted by: Kit P | 04 January 2013 at 05:06 AM
"The PV system life cycle is based on 2005 technology and production data."
Come on. You can do better.
Posted by: Hey_ghis | 04 January 2013 at 05:32 AM
Oh my, but how will our masters be able to maintain us in perpetual debt. Jeez, someone could actually endow themselves with freedom from a tethered existence on the grid.
Kit P : It sucks living in Iowa, but the rest of the country shouldn't be required to accept your version of slavery.
Posted by: Brotherkenny4 | 04 January 2013 at 06:47 AM
You have to use the grid as a "battery" for PV EVs - otherwise you have to charge every day around noon, which makes no sense.
Thus, you separate the two (PV and EV) completely.
The thing is to have low carbon electricity - from any source (Nuke, wind, PV, biomass).
Then you can use it in BEVs or PHEVs.
Once you are charging from the grid, it becomes an accountancy problem: if I put 20 KwH of PV power into the grid during the afternoon, and then charge my car with 20 KwH at night, do I count the PV power I put in, or the "grid mix" power that I take out ?
In my opinion, you should use Grid Mix power as the charging source - if your PV lowers the CO2 level of the grid, good for you.
Anyway, PV takes less ground area than biofuels, but switchgrass looks good from a CO2 point of view.
+ you could substitute wind for PV, but at a larger scale (not house by house).
Posted by: mahonj | 04 January 2013 at 08:01 AM
".. even the most land-use efficient biomass-based pathway (i.e., switchgrass bioelectricity in US counties with hypothetical crop yields of more than 24 tonnes/ha) requires 29 times more land than the PV-based alternative in the same locations."
29X better isn't a tossup. The huge advances in PV and BEV the last 7 years would only amplify and reaffirm the results.
Kit P, since California has several times the agricultural output of Iowa http://stuffaboutstates.com/agriculture/index.html - your opinion is likely wrong again.
Posted by: kelly | 04 January 2013 at 08:24 AM
Their data and assumptions are crazy. An acre of switch grass or even corn is not the same as an acre of PV. Even looking at their data, switch grass ethanol + ICE seems to win but as Davemart points out the real win would be nuclear + BEV. Also, I live in "flyover country" and I do not want it covered either with wind turbines or PV.
Posted by: sd | 04 January 2013 at 09:12 AM
What Davemart said.
Posted by: Nick Lyons | 04 January 2013 at 10:02 AM
Having all those PV panels covering the Mojave dessert will to do in the Dessert Ground Squirrels. These folks just aren't green enough.
Posted by: Mannstein | 04 January 2013 at 11:28 AM
Actually, for a roof tilted at latitude in the temperate zone, the annual solar energy received does not differ as widely as one may think. Compare the solar radiation in San Diego with that in Regina, Saskatchewan, Canada, which is about 600 miles north of Des Moines, Iowa
A south facing roof in San Diego that is tilted at 33.73 degrees towards the south annually receives a daily average of 5.77 kWh/m^2/day in solar radiation. The daily averages for the two extreme months, August and December, are 6.62 and 4.67 kWh/m^2/day, respectively.
A south facing roof in Regina that is tilted at 50.43 degrees towards the south annually receives a daily average of 5.04 (kWh/m^2/day) in solar radiation. The daily averages for the two extreme months, August and December, are 6.25 and 3.06 kWh/m^2/day, respectively.
In summary, at worse, the Regina figures are at least 2/3 of San Diego's.
These numbers are from NREL's PVWATTs calculator which defaults to a directly south, latitude-tilted roof but you can change the city, tilt and azimuth to whatever.
http://rredc.nrel.gov/solar/calculators/PVWATTS/version1/
Posted by: NorthernPiker | 04 January 2013 at 12:58 PM
We don't a 100% all or nothing solution. Using a mix of power sources for transportation fuel and not relying only on PV or only on biofuels or only on nuclear is probably a good thing.
That said, PV and PEVs have significant synergies that can be leveraged to provide a substantial portion of transportation fueling requirements. This article states that 1.1E6 ha of PV could replace the US transportation gasoline. This is almost exactly the same area as the land used for non-residential parking in the US. Hence, every car that spends a substantial amount of time parked in one of these parking areas during the daylight hours could potentially be charged directly by PV installed above the parking area for at least part of its power. Because the PEV supplies the electric storage and if it is a PHEV or EREV its own alternate backup, the intermittentcy of the PV is not an issue.
For larger installations, the levelized cost of PV electricity would yield a lower fuel cost per mile than a gasoline powered car, even a Prius. So all that is needed is for the cost of the PEV to decline to a more competitive price.
This is not a 100% solution. Not all cars park in parking lots during the day, and not all parking lots have enough cars parked in the daytime to warrant being completely covered by PV for EV charging. However perhaps 1/3 to 1/2 of vehicle fuel could be replace in this way.
Posted by: nmcotwpv | 04 January 2013 at 04:42 PM
One thing the Governement could do, not that it would be a wise idea... but they could require all new construction to have PV panels, limit it to industry/retail space and provide government low interest loans to cover the cost (as an incentive) and fine those that chose to opt out. So in the long run we'd be out a few million in interest and depreciated dollars and unpaid loans, but the net could be considered very low cost as its not injecting "money" per se but rather an incentive that would be costly to ignore.--- it certainly will be less intrusive than the health care plan
There are millions of sq ft of rooftop on warehouses and the like that could be used for PVs.
In a neighboring state, a congress women and her nephew(iirc) have a similar plan with wind, the government will subsidize new wind production to help cover the cost... and wind is booming, especially for her nephew. Not that I think that collusion is bad or anything, but it sends the wrong message sometimes.
Posted by: CheeseEater88 | 04 January 2013 at 11:55 PM
Typical morons. The reason corn ethanol does far better then they expect in the us is because its source of corn is almost exclusively used as cattle feed AND its byproduct is cattle feed that is better for the cow to digest....
On top of that because the us needs more gasoline and has excess diesel and nat gas... ethanol production and corn production that uses nat gas and diesel... is very useful here.
Much less useful elsewhere where they need ther diesel and dont have such a large mass of cattle feed from corn.
Posted by: wintermane2000 | 05 January 2013 at 03:23 AM
I trust them to not make such a beginner's mistake. Of course they took the land area covered by the solar farms, not the net panel area. Or perhaps a mix of rooftop/parking lot canopy/free field installations. The first two categories having zero land use.
When solar is only a part of the generation mix, timeshifting daytime solar power to the night is not what takes a lot of storage. Especially since consumption already is low during the night. We need charging infrastructure that allows people to plug in during the day while at work, so solar power can be used when it is available.
Electricity from new built nuclear power plants is more expensive than even solar PV. And the price of the latter is still falling, so the difference will only get bigger in the future. Let go of your 'nuclear is cheap' dogma. It is simply not true. If it is so cheap why don't the investors line up? I guess the people who make the decisions do know and accept the whole truth because it's their money that is on the line. You are still wearing your rosy coloured glasses I guess.
Posted by: Arne | 05 January 2013 at 03:36 AM
Northernpiker,
You're numbers are rather surprising.
If you lookup Amsterdam (my approximate location), you'll see a summer/winter difference of about 6:1, which I can confirm with the real time data from my PV system. But Amsterdam and Regina are at roughly the same latitude. Are Canadian winters really that sunny? Because in The Netherlands, largest part of the difference between summer and winter is not the sun's angle and shorter days, it is the cloudiness of our winters.
Posted by: Arne | 05 January 2013 at 03:45 AM
Regina is a prairie city, downwind of the Rockies. "It experiences a dry humid continental climate with warm summers and cold, dry winters, prone to extremes at all times of the year. Average annual precipitation is 388 mm (15.28 in) and is heaviest from June through August, with June being the wettest month with an average of 75 mm (2.95 in) of precipitation."
Posted by: ai_vin | 05 January 2013 at 07:58 AM
Are Canadian winters really that sunny?
It's not that easy to stereotype anything about Canada, we're a very large country. In fact you could fit The Netherlands within our second smallest province.
Posted by: ai_vin | 05 January 2013 at 08:11 AM
Anne...there are many sunny cities in western Canada. Sunshine hours per year = 2405 in Calgary; 2372 in Winnipeg; 2338 in Regina; 2329 in Saskatoon; 2299 in Edmonton but only 2193 in warm Victoria.
Amsterdam has only 1500 hours, London, 1400 hours, Tokyo 1600 hours etc. You are not in the best place for Solar Power?
Phoenix is one of the most sunny city with 4000 hours.
Posted by: HarveyD | 05 January 2013 at 08:32 AM
As solar cells efficiency goes from 10% and 20% to 30%, 40% and 50+% and storage cost goes from $1000/kWh to less than $100/kWh, Solar power will quickly become the energy source of choice, specially in places like Phoenix (and many other places) with 4000+ hours of sunny weather per year.
Places between 3000 and 4000 hours of sunshine a year will also become good candidates.
Amsterdam and London with only 1500 and 1400 hours will have to spend more for Solar power.
Posted by: HarveyD | 05 January 2013 at 08:39 AM
Getting back to the original post, the purpose of LCA is too identify better ways of doing things.
Of course this a really bad LCA.
“land-use efficient ”
I just started a new project this week for a nuke plant. The photo of the nuke plant is really interesting if “land-use efficient ” is a criterion. With a foot print about the sise of a Wallmart, the building that houses three 1000+ MWe reactors and steam turbines. This 3000+ MWe of generation could supply power for 3 million BEV for 60 years.
If something has been proven and practical for 40 years, projecting 60 years is established and approved by the NRC. Projecting 80 years in not much of a stretch.
For about 40 years people who do not make electricity have been telling me that wind and solar can replace something. We keep experimenting with wind and solar and the answer is someday. All we learn is that wind and solar is not a very practical way to produce energy.
Posted by: Kit P | 05 January 2013 at 11:51 AM
Do not give up too soon on Solar energy because the price of Nuclear energy is going up while Solar + storage is going down. If the current trend is maintained, both sources may cost about the same by 2025/2030 or so.
After 2030, clean renewable solar energy may cost less than nuclear.
USA is fortunate with more than enough sunny (4000 hours/year) places to produce all the e-energy required for the next 6+ billion years.
Maybe, USA could have two e-networks; one solar in the south and one nuclear up north to satisfy the pros and cons?
Posted by: HarveyD | 05 January 2013 at 12:11 PM
Expected hours per year at rated power for a nuke = 8760 hours
Sometimes nuke plants power down but that is what the grid operator expects.
“Sunshine hours per year = 2405 in Calgary ”
Expected hours per year at rated power for a fixed PV = 60 hours
The power produced is a function of time or the area under the curve. We would only expect PV to produce rated power for an hour a day during the summer moths assuming no clouds.
Various factors effect equipment aging or how long things lasts. Lots of effort has gone into studying aging especially at nuke plants. Old nuke plants frequently run breaker-to-braker (the generator output breaker closes to the grid after a refueling outage runs until the next refueling outage).
The expectation for wind and solar is that it does not work because it does not work almost all the time. If it happens to be working that is okay. A nuke plant produces a millions dollars a day in power. A rooftop PV produces $2 worth of power on a good day. Nobody cares. Of course the home owner who is paying retail could save $4/day.
LCA might show a benefit but it is only a benefit if large numbers of people spend $40k on PV panels to charge $40k BEV.
benefit x 0 = 0 benefit
Posted by: Kit P | 05 January 2013 at 12:18 PM
KitP...you forgot to mentioned that Solar production hours are mostly during peak demand hours and that future low cost storage would supply energy 24/7 with (essential) excess sunlight hours production.
One can easily calculate the max size of panels required which could be between 2X and 3X the average consumption depending of the size of the storage unit, consumption criteria, sunshine hours per day etc.
NB: One of the first thing to do would be to change the 10 SEER to 13 SEER A/C units for 26 SEER Heat Pumps and better insulate the doors, windows, ceilings, walls and floors.
Of course the size of the installation required would be very different where sunshine hours are 4000/365 = 10.95 in Phoenix and 1500/365 = 4.1 hours/days in Amsterdam.
An emergency EPU could be required in some places.
Posted by: HarveyD | 06 January 2013 at 09:21 AM
Distiller's grains are not a complete diet for livestock, and are toxic to many at levels well under 50%. I recall reading a report that DDG kills feeder pigs at over 30%. This puts a hard cap on the amount of "excesss carbohydrate" which can be turned into fuel; cattle are ruminants, and their stomach flora crack cellulose into simple carbs which they can digest. Cattle will even grow on a diet of newsprint and urea. Grass has very little in the way of protein and fat, and it's no surprise that cattle don't tolerate DDG very well.
The problem with using BEVs to balance RE generation is that a very high fraction of the fleet needs to be BEVs for this to work, and that's not going to happen quickly or cheaply if it happens at all.
Posted by: Engineer-Poet | 06 January 2013 at 11:54 AM
All I know e p is that I was told distillers grains are easier on a cow then regular corn is something having to do with sugars or something. I have a feeling corn isnt actualy the best feed for cattle and is likely only a low bulk of thier diet and that distillers grains can up that percentage somewhat.
Posted by: wintermane2000 | 06 January 2013 at 12:49 PM