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Turn the freeways into urban powerplants! With solar-technology and a narrative design, the freeways re-emerge as contemporary structures.


Guidance on collaborative pilot

This is a pilot test of a new, collaborative approach for getting work done in the Climate CoLab. It will run during March and April of 2012.

Just like in the 2011 activities, anyone can create a proposal. But there is also a community proposal, where members are encouraged to work together in a collaborative way. Any member can contribute to the community proposal as long as they are logged in.

The community proposal is like a wiki, so the history of edits is tracked, and you can revert to prior versions of the proposal if desired.

Please also use the Comments to express your opinion on whether or not you would like to see this collaborative approach used in the Climate CoLab in 2012.

Feel free to organize the proposal as you see fit. One thought—it's good to have a brief summary of the overall proposal at the top, as an aid to readers.

Proposal Text


The project explores how architectural design could change both the function and the narrative of the  most symbolic structure of modern society: the freeway.

Even though Los Angeles provided a special inspiration to the project, the idea is applicable in most cities and regions with expensive land and lots of sun. Alternative locations along certain smaller roads, main drags or elevated bike paths or other infrastructure corridors are possible.

The project idea came to me as I was both fascinated and intimidated by the freeway system in LA. It is a mono culural place that has a huge impact on the daily life of all angelinos. I asked myself, how can this marvelous structure and symbol of the 50's be developed to meet the demands of today?

With Los Angeles County having 800 km of freeways – public land with existing points of access for maintenance – why not use some of it for the location of a large scale solar installation? Right in the middle of the city! A Solar Serpent built along the Santa Monica Freeway could generate 150 GWh per year, electricity that would be  instantly sucked up in the local grid with no transmission costs or losses.

As more cars will be electrical, the cars can be charged at re-charging stations powered by the freeway itself. The next phase of this would be special induction lanes that charges your car while driving.

In the transition period when there will be both gasoline, diesel and electric cars I propose to fan the CO2 rich air from the car exhaust fumes into linear algae ponds along the freeway for local production of bio-fuels.

The BIG idea is to create energy, a necessity of moden life, at an industrial scale locally in a city. By designing it holistically the basic needs of a city becomes part of the visual cityscape.

Half of the worlds population live in cities. Water and energy often come in a pipe from somewhere far away. This projects invites the public to understand how their city work and what it takes to sustain our way of life.

Category of the action

Reducing emissions from transportation

What actions do you propose?

Solar panels need unshaded sun which makes freeways with their big clearing an ideal site. Mounted above a road they also provide shade that would decrease the use of air conditioning on sunny days. But also: The high cost of UV degradation of paved freeway surfaces would decrease drastically. And noise will go down for the people living next to the freeway.

I chose to make a case study of the 24 kilometer long stretch of the Santa Monica freeway between Downtown and the beach. On average it is 40 m wide. This gives us a paved surface of one million m2 or 250 acres. This constitutes only 5 % of the LA County's freeway system.The Santa Monica freeway could house the equivalent of more than 500.000 polycristalline typical utility panels of 2 m2 each. The Santa Monica freeway would be become a local power plant.

In this example I will use a typical utility scale panel of 2 m2 with a peak capacity of 250W. 250W * 500,000 panels equals a max peak effect of 125MW for the entire system.

To make an estimate of annual production I have used the Australian governments estimates for solar panels (1). This gives an annual 1540 kWh/year/Wp for grid connected system in a location with 5.5 peak sunhours/day. (LA has 5.62 peak sunhours/day). This gives 1.9 GWh per year. According to the same source (1) the reduction in efficiency for horizontal mounting at 35 degrees latitude (LA is at 34 N) is 80 to 90 %. 190 GWh * 0.8 = 154 GWh ~ 150 GWh per year.

A frame to frame horizontal mounting minimizes flickering light (a road hazard) as well as maximizes the number of panels per acre since no distance to avoid shade caused by tilted panels is needed.

The efficiency of a photovoltaic panel decreases rapidly in high temperature, the ventilation of the panels backside is important to avoid efficiency losses. By mounting them on a canopy (compared to on a roof) ventilation on the backside is guaranteed.

150 GWh is enough to cover the electricity needs of for example Venice, CA with 40,000 inhabitants. Local production for local consumption in the grid with minimal transmission losses.

Important to note is that the efficiency and peak effect/m2 of solar panels is constantly increasing thus giving the proposed system a possible much greater output.


Possibility of algae-farming

Another resource for local energy production is the extraordinary high levels of CO2 locally on the freeway. The levels are - according to a 2005 USC survey (2) between 830-950 ppm which is sufficient for large scale industrial algae production. This study shows very high concentrations above the road surface and much lower concentrations in adjacent neighbourhoods.

According to Prof. Catherine Legrand of Linnaeus University, Kalmar, Sweden algae can grow with the input of polluted flue gas containing CO2 but also a mix of nitrogen oxides, sulphur and various toxic particles. She has made test with algae farms using the flue gas from a Cement plant i southern Sweden.

Adding flue gas made the algae grow at the same or a higher rate and with a 20-30% higher productivity compared to when a pure feed of CO2 is added (3).

This indicates that exhaust fumes from cars with concentrations of CO2 and other gases shown in the USC study has a potential of being used for algae production. This algae would be algae for bio-diesel or biomass production. Algae for health or food products need a cleaner feed of CO2.

However, in a conversation with Prof. Legrand she notes that she knows of no research being done on algae production fed by exhaust fumes from cars, only factories, powerplants and sewage water. This is confirmed by Dr. Greg Mitchell of San Diego Center for Algae Biotechnology at UC San Diego, he writes in an email (excerpt):

"Dear Dr. Tham, Thank you for your email appended below. Very interesting!! I do not know of any studies of algae grown on automobile exhaust (gasoline or diesel) but I expect that algae can utilize. No need for 100% CO2.  Particles and/or some of the organic / inorganic chemicals in exhaust might be toxic for some algae….maybe not for others. Would have to be tested. I am not aware of any data for such tests."

I also found an interesting proposal by inventor Param Jaggi (4) that use algaes placed in a box by the tail pipe to clean exhaust fumes from cars. 

Research on car exhaust would have to be done to evaluate the potential of algae farming by the road as well as research to determine the most energy efficiant way to fan the air into the algae ponds. These would be important factors in determining the feasibility of the idea.

An MIT study also shows that algae can adjust to the character of an exhaust source (5). This is relevant since the coctail of gases differ at different segments of a freeway.

In my sketched proposal the CO2 rich air is brought through pipes into linear covered algae ponds along the freeway. This would bring green tech jobs for farming, harvesting and processing to the very neighborhoods that today are the most disadvantaged by their proximity to the freeway.

The algae farm along the Solar Serpent is a possibility that does not make or break the Solar Serpent project. It is based on a technology that is less developed and commercially viable than solar power is today. Algae ponds would also only work in areas where the embankments of the freeway allow for it. These are the reasons why I have not  included the linear algae farms in the cost/benefit analysis.

Who will take these actions?

The Solar Serpent is a big project, possibly a public works project that could work in several scales and would have to be implementd in stages.

A Solar serpent highway would need to be a joint venture between local transport authorities, the city as well as a major energy producer and possibly a producer of solar panels.

The benefit is that the panels can be produced, used and recycled in the same city thus benefiting the local economy at all stages of the life-cycle of the urban solar power plant. In this way the proposal adresses the common ambition by mayors all over the world to become a "green-tech" city.

The strategy would be to use the fact that freeways are publicly owned land with existing points of access for maintenence.

Other possbilities:

The other way forward would be to identify a series of puclic infrastructure that is less contestable than the crowded freeways. Elevated bikepaths, bikehighways or transit corridors.

Or work with corporate landowners along the freeway in an adopt-a- (solar) highway type set-up.

Where will these actions be taken?

Even though the project have been first designed for Los Angeles, the possibilities are almost endless. The freeway is a part of life all over the world and discussions on what to do with these structures are vivid. Dig them down? Transform them to boulevards? Build sound barriers? Whatever one thinks of freeways they occupy established urban corridors and this is a huge advantage and potential for the distribution of the electricty that can be produced on this already urbanized land.

A city has by tradition a multilayered structure; subways, piping, highrises, shops, underground garages etc. This thinking should be applied on the freeways that now are relics from a modernist and today un-modern way of planning city spaces.

The Solar Serpent is a big project and would need public officials with a strong will-power and determination. The structure of the planning process is crucial and this would most likely affect the scale and shape of the project were it to be built in Phoenix, Beijing , Abu Dhabi or Italy.

How much will emissions be reduced or sequestered vs. business as usual levels?

Every watt hour produced would replace a watt hour produced elesewhere. The emissions reduction would therefor depend on how electricty is generally produced on the site. If produced by fossil fuels there is a big gain to be made.

According to the Us Energy Information Administration electricity produced by coal emitts 0.95 kg/kWh and natural gas 0.55 kg/kWh (6).

The 150 GWh projected annually in the Solar Serpent case study of Santa Monica Freeway would, if replacing coal powered electricty, reduce emissions by 142,000 tonnes of CO2 annually. If replacing natural gas powered electricty  it would reduce emissions by 82,000 tonnes of CO2 annually.

On a smaller scale cars driving under the solar serpent would use less gasoline because of smaller AC needs.

If combined with the linear algae-farms the CO2 levels would decrease even more. Every litre of bio-diesel replaces a litre of fossil-based fuel.

What are other key benefits?


Architectural benefits and the understanding of the city:

Someone called Los Angeles the Eden that lost its garden. Paradise city or not, the decayed and clogged freeways of today are no longer monuments that symbolize freedom and a promising future. The freeway system is in desperate need of a new narrative.

The Solar Serpent would give the freeway a radically different and bold presence in the city. Recharging stations along it clearly explains the connection between production and usage. I believe it is easier to accept living next to an architectural wonder than a concrete sound wall.  

I propose an architectural design that does not shy away from the monumental impact these roads have on the cityscape but instead add new functions and visible layers that are coherent with today's needs. By letting infrastructure be a visually powerful part of the city, inside and out, its citizens are allowed to understand and cherish the complexity of their daily urban life.

What are the proposal’s costs?

Below is a simplified attempt to estimate  the up-front installation costs of the proposed 125 MW Solar Serpent; this comparison does not take into account interest rate, state or federal subsidies, power purchase deals, tariff-systems and other financial factors that vary widely between regions, cities and companies. These and many other factors require a more in-depth analysis by experts in the field.

Rough cost estimate

The 2011 avarage price for >10 MW utility was $3.4 /W total installation cost (7). The price is similar for thin film and polycritalline´panels. Thinfilm has a lower weight which would minimize the structural costs.

The cost of constructing new transmission infrastructure or adding capacity to existing transmission lines can be 25 to 100% (1 - 4$ /W) of the installation cost for a >20MW system. (8)  This is a significant cost not included in the installation number. The extra cost of transmission could be drastically decreased with the Solar Serpent since the power would be sucked up locally in the existing urban grid.

Modules contribute the most to the price of installation (51%) whereas the two factors that would vary between the Solar Serpent and a conventional utility is labor costs (electrical and hardware labor plus installer O&P) contribute 14%, and installation materials (including supply chain costs) contribute 17%. (8)

The other major comparison to a traditional ground mount system is the cost of the canopy. I have compared it with parking canopy structures. The only comparative number I have found show they cost ~40% more than ground mounted systems (9). But since they tend to be small I adjust for the benefit of scale.  This gives a comparative cost of  $3.4/W +20% = $4.08 /W and a total of $510 million for the Solar Serpent of the Santa Monica Freeway in LA.

The average price of electricity in LA 2013 is 21.6 cent / kWh (10) thus the electricity produced per year, 150 GWh, is worth 150,000,000 kWh * 0.216 USD = $31.5 million per year.

Time line

The timeline would roughly consist the following steps:

1:Site specific preliminary study where local factors and possibilities are taken into account and different support structures and systems of panels are compared in a multi-diciplinary group of consultants. This stage would also include a gathering of all key players at the site for a collaboration agreement.

2: Mock-up with quick permitting process. Maybe as little as a 100 m stretch that would be a public sign of progress and way to attract further investment and public support as well as reference knowledge for modifications before the final design of a large scale utility.

3. Permitting and planning process for large scale utility. Collaboration between municipality, road authorities, the public, producers of solar modules, contractors and utility companies.

4. Possible PPA Power Purchase Agreement

5. Bidding

6. Construction in several phases. Each part would with its own electrical substations and other equipment be able to deliver electricity into the grid upon completion. Each phase would be reviewed for further improvements of the design.

Related proposals

After this idea was initially shown two interesting rail-projects have been built in Europe:

Blackfriars Solar Bridge, London

Belgian Solar Tunnel for trains

Solar Roadways is a a federally funded project that propose solar panels in the roadsurface instead of asphalt. That project is very inspiring since it also uses the infrastructure as producer and distributor at the same time. Solar roadways has its largest gains in less dense areas where the roadsurface is exposed to the sun most of the time and snowmelting and protection of wildlife makes a lot of sense. The Solar Serpent is different with its urban focus of highly used roads often with shading sound barriers or embankments. Solar serpent shades the cars (decreases the use of AC) and brings down the noice-levels for people living close by the freeway.


(1) "Australia's guide to environmentally sustainable homes: 6.7 PHOTOVOLTAIC SYSTEMS " (2010)

(2)  "Mobile platform measurements of ultrafine particles and associated pollutant concentrations on freeways and residential streets in Los Angeles, Atmospheric Environment 39 (2005) 3597–3610"

(3) "Using algal technology to capture CO2 from industrial flue gas" ÅF Green Advisor Report 2012, ÅFORSK (2012)

(4) "EPA Recognizes Environmental Innovation at Science Competition for High School Students / Param Jaggi Wins Patrick H. Hurd Sustainability Award" EPA Pressreleases (May 2011)!OpenDocument

(5) "Algae system transforms greenhouse emissions into green fuel" MIT Energy Research Council (July 2006)

(6) "How much carbon dioxide (CO2) is produced per kilowatt-hour when generating electricity with fossil fuels?" FAQ US Energy Information Administration (2013)

(7) "Photovoltaic (PV) Pricing Trends:
Historical, Recent, and Near-Term Projections"
(November 2012) Sun Shot, US Department of Energy

(8) "Residential, Commercial, and Utility-Scale Photovoltaic (PV) System Prices in the United States: Current Drivers and Cost-Reduction Opportunities" (February 2012) National Renewable Energy Laboratory

(9) "Capturing the Value in Solar Renewable Energy Projects", Center for A Better Life (#8 2011)

(10) "Average Energy Prices, Los Angeles-Riverside-Orange County" Bureau of Labor Statistics (May 2013)