Wikiversity

Design for the Environment/Low Carbon Energy for California

< Design for the Environment

This page is part of the Design for the Environment course

The problem of carbon emissions and greenhouse gases has grown over the years to become one of the leading issues facing the world today. In the United States alone, the State of California has already taken measures to reduce their carbon emissions. In 2006, Governor Arnold Schwarzenegger signed legislation to lower carbon emissions to 1990 levels by 2020.[1]

Strategically located along the coastline, the city and county of San Francisco has access to a variety of natural resources not readily available to other landlocked cities. Furthermore, the city itself has already begun looking into various energy alternatives.[2] This allows for San Francisco to be a suitable city to base this report on.

In 2007, San Francisco consumed about 5,510,000 MWh of energy.[3] In line with this, the objective of this report is to analyze several possible low carbon emission energy alternatives to provide 50% of this total power consumption.

Three options will be considered for this report: gas turbine power (baseline), solar power and lastly, tidal power. The next section details the results from each aspect of the analysis as well as a final recommendation on which alternative would be the most feasible.


Project Information

edit

Chan, Marina (dfe09.lowcarbon)

Chua, Timothy (tim.chua)

Erkaya, Yalim (Yalim erkaya)

Lee, David (leedav11)


Highlights and Recommendations

edit

The Functional Analysis shows that the IGCC gas turbine would be the best alternative. The technology already has years of development behind it. The large number of solar panels required and the insufficient information available for tidal turbines make both alternatives unattractive.

Using the Economic Input-Output Life Cycle Assessment (EIOLCA), it can be seen that in all stages of the life cycle the gas turbine produces the most emissions. This is largely due to the gas turbine’s use phase where it requires coal to be burned. Although a solar farm and a tidal farm have similar overall GWP, a solar farm would be the better alternative for the purpose of this analysis due to its lower CO2 emissions.

According to the Streamlined Life Cycle Assessment (SLCA), solar power is the best alternative out of all three. The largest contributing factors being the use of recyclable materials, the least use of virgin materials and the least energy intensive processes.

From a Cost Analysis perspective, the IGCC gas turbine is significantly cheaper than the other alternatives. The IGCC gas turbine would cost approximately $50,000 per year if the total costs were divided over its lifetime. A solar farm will cost approximately $2.3 million per year while a tidal farm will cost around $4.9 million per year.

Based on the Societal Analysis, an IGCC gas turbine is the most feasible alternative. Although gas turbines have several societal downsides, they also have the biggest impact in terms of creating stable jobs and useful by-products.

Taking all aspects into consideration, a solar farm would seem the best alternative due to its lowest CO2 emissions. Its costs, however, are impractical when compared to the costs of an IGCC gas turbine power plant. The IGCC gas turbine is also advantageous over the solar farm in terms of functional and societal analyses. There is also a sequestration method for IGCC gas turbines that could lower CO2 emissions to zero which would satisfy the low carbon objective.

Therefore, with the CO2 sequestration an IGCC gas turbine would be the most feasible alternative for low carbon electricity for California.


Functional Analysis

edit

The following is the functional overview of each alternative: gas turbine, solar, and tidal power.

Gas Turbine Power

edit

Gas turbines create electricity through the internal combustion of fossil fuels or non-renewable fuel to drive turbines. Although there are several types of gas turbines, the Integrated Gasification Combined Cycle (IGCC) gas turbine will be used for this analysis. It has 45-50% efficiency and can produce power from syngas and natural gas. IGCC gas turbines have stable and cheap fuel costs [4] as well as potential zero carbon emissions.[5]

The gas turbine power plant will be able to generate 543 MW of power and can produce up to 5.5 TWh annually [6]; more than enough to complete the given power generation objective.

Solar Power

edit

Solar photovoltaic (PV) cells create electricity from the sun’s rays. Although no electricity can be generated at night, batteries can store energy created during the day which can be used as an electricity source instead. Mono-crystalline silicon PV cells, which will be used in this analysis, can convert 15% of the sun’s energy into electricity which is the highest efficiency from other types of PV cells.[7]

In order to achieve the given objective of power generation, the solar farm would need to generate 754.8 MW of power assuming 10 hours of operation per day. Since one solar panel can create 210 W of power [8], a total of 3,594,286 solar panels are needed.

Tidal Power

edit

Tidal turbines use the movement of water mass to create energy. Underwater currents turn turbine blades creating mechanical energy which is then converted into electricity by a generator in the shaft.[9] Tidal turbines are conceptually similar to wind turbines.[10]

A single tidal turbine produces 1.2 MW of electricity and can operate 20-22 hours per day.[11] To achieve the given objective, a tidal turbine farm with 315 turbines should be constructed 1-4 miles off the coast.[12]


Economic Input-Output Life Cycle Assessment

edit

The EIOLCA method utilizes an online economic database that models inter-industrial economic relationships as well as the associated environmental impacts of all industries in the United States. The method provides an quantitative way of comparing the three power generation methods.

Global warming potential (GWP) of greenhouse gases (GHG) and toxic releases are compared among the three alternatives with the assumption that each will generate 2.7 TWh/year. Each alternative is broken down into 5 life cycle stages: pre-manufacturing, manufacturing use, transportation and end of life, with the exception of Gas Turbine Power.

The cost of each alternative in different stages are researched or estimated. The dollar value input into the EIOLCA database gives the GWP emissions and the toxic releases for each alternative. The economic data for each alternative are based on:

  • Gas turbine:[6]

The following are the comparative results for each alternative. The tables below show the total GWP emissions and toxic releases of each alternative. Graphs for CO2 emissions and toxic releases are also provided for convenience.

 

 

 

 

Comparing EIOLCA values of each alternative, it can be seen that the gas turbine power plant has the most toxic releases as well as the most GWP emissions. This was already the expected outcome since a solar farm and a tidal farm have no emissions during their use life. Gas turbine power plants emit the most especially since it burns coal all throughout its use life. This is clearly not the most feasible alternative especially when considering the amount of emissions alone.

According to the tables, solar power and tidal power have very similar amounts of overall GWP emissions. However, tidal power has more CO2 emissions as solar power has more CH4.

Streamlined Life Cycle Assessment

edit

Since solar panels and tidal turbines can be considered more as products while gas turbine power plants more as processes, the SLCA has been modified in order to compare all three alternatives within the same level.

Pre-manufacturing includes all the raw materials involved in other stages of the life cycle. This also includes material inputs for power generation for the gas turbine. Manufacturing includes the production of the solar panels and the tidal turbines for the solar and tidal farms, respectively. Since the delivery stage is almost identical for all alternatives, this stage has been replaced by a construction stage. The construction stage accounts for the construction of the solar and tidal farms themselves. The manufacturing and construction stages are identical for the gas turbine power plant to keep consistent with the other alternatives. Values in the manufacturing stage will be used as well for the construction stage for the gas turbine power plant. The use stage includes the maintenance of each alternative and finally the disposal stage includes disposal and decommissioning of all alternatives.

The table below shows the scoring matrix for the SLCA.

 

Pre-manufacturing

edit

The gas turbine power plant requires coal to generate power. The extraction of coal is an energy intensive process and gives off a considerable amount of solid residues in mining as well as liquid residues through mine drainage. The coal used in the gas turbine also gives off a large amount of GHGs. These contribute to the low score of the gas turbine.

Solar panels use recyclable materials as well as no energy intensive extraction of virgin materials. There are also no solid, liquid or gaseous residues which give the solar farm a high score.

Tidal turbines have composite parts as well as anti-corrosive chemicals. They also require energy intensive extraction methods. These heavy extraction methods also contribute to large solid residues and liquid residues. Other materials in tidal turbines are also indirect producers of GHGs which account for the tidal farm’s low score.

Manufacturing

edit

Gas turbine construction will be discussed further in the construction stage.

Solar panels use recyclable materials. They also require energy intensive processes in component manufacturing. As well, there are minimal solid, liquid and gaseous residues which give the solar farm a high score.

Tidal turbines require a small level of toxic material. Production also requires energy intensive processes. Solid residues are recyclable and liquid residues are biodegradable. There are also minimum gaseous residues. The use of toxic materials gives the tidal farm a lower score than that of the solar farm.

Construction

edit

Construction materials are cheap and recyclable for gas turbine power plants. The processes are energy intensive although solid, liquid and gaseous residues are minimized which gives the gas turbine power plant an average score.

Solar farms and tidal farms have no material inputs as well as no solid, liquid and gaseous residues. However, construction of the tidal farm requires a higher amount of energy and equipment which give the solar farm a higher score than the tidal farm.

Use

edit

The gas turbine power plant uses chemical sorbents and coal which is neither renewable nor reusable and the energy used in this stage is minimal.[25] It has highly toxic solid residues but also has very useful by-products.[25] There are minimal liquid residues but a high amount of gaseous residues in the form of GHGs. These give the gas turbine power plant a low score.

Since solar panels are made of recyclable materials, replacement parts are made up of recyclable materials as well. There is little maintenance needed and produces no solid, liquid and gaseous residues which give the solar farm a high score.

Tidal turbines require new materials for replacement components. Sometimes energy intensive equipment may be required as well. However, there are no solid, liquid or gaseous residues which give the tidal farm an average score.

Disposal

edit

For the gas turbine power plant material diversity is not minimized although most are recyclable. Plant decommissioning also does not require energy intensive methods. Furthermore, solid residues are recyclable and there are no liquid and gaseous residues. These give the gas turbine power plant a high score.

Solar panels are no longer recyclable once produced. In addition, the batteries have toxic chemicals which require special disposal methods. Although there are no gaseous residues and minimal energy is required, the solar farm still gets a low score due to the toxic chemical content of the batteries.

Tidal turbines are mostly made of non-recyclable materials. They also require a high amount of energy to dispose. Tidal turbines also have non-recyclable oil as liquid residue. Due to these, the tidal farm gets a low score.


Cost Analysis

edit

Costs are calculated based on the required objective which is to generate 50% of San Francisco’s power consumption (2,755,000 MWh).

Gas Turbine Power

edit

The cost analysis of the IGCC power plant is divided into 2 possible configurations. First of which would be an IGCC power plant with a CO2 sequestration process and the other configuration would not have the CO2 filter. The analysis assumes that an IGCC power plant life span per construction capital cost is 30 years.[26]

The final cost of having a zero emission CO2 filter is $49.4 million, which costs 32.4% higher than not having a zero emission CO2 filter. The recently proposed carbon tax law in California would charge an average of $42,272 / MTCO2E to industries.[27] The equivalent CO2 released from 2700 GWh of power using a coal-based IGCC would be 1.9595 MT (1600 lb/MWh).[28] 1.95 MT of CO2 is equivalent to $82430.4 under the new carbon tax in California. In comparison to the zero CO2 emission sequestration process, the carbon tax is merely 0.366% the capital investment required in today’s dollar.[5]

The figure below is the combined IGCC capital cost breakdown of the two configurations.

 

The total cost break down in percentages is shown in the graphs below. It is interesting to note that majority of the costs incurred (other than capital investment) are related to service sectors that are indirectly related to the power plant. The figures below show the total cost break down for the two scenarios proposed.

   

The cost associated with the chemical reactants are totaled to be $4.0389 million (1997 USD), which is only 8.23% of the total annual cost of generating 2700 GWh. The projected cost of installing a by-product disposal and filtering system on a conventional coal-fired power plant would be 10.81$/kW/year.[29] So the cost for a conventional coal-fired power plant with a capacity of 550 MWh would be $6.021 million/year, which is approximately 50% more than an IGCC gas turbine.

Solar Power

edit

A table summarizing all the costs of a solar farm are included below:

 

It must be noted that some costs are taken as approximations and may not necessarily be the most accurate value.

As mentioned, 3,594,286 panels are required. Given that one 210W solar panel costs $874[8], the solar panels would cost $3,141,405,964 in total.

Land plays a major factor in the creation of a solar farm. The desert area in San Joaquin County will be a suitable location for a solar farm. According to treehugger.com, 120,000 solar panels would cover 100 hectares (247.1 acres) of land.[13] This means 7401.23 acres of land are required for the farm. A certain 28 acre patch of land in the San Joaquin area is being sold for $340,000.[14] Using this as a basis, 8,180.3 acres of land will cost $89,872,079.

An inverter is needed to convert the electricity to a usable form (DC to AC). Inside the inverter are six batteries which store generated energy which is not being used. 18,870 inverters are needed continuously running 40 kW of power. This would cost $994,395,866 in all.[15]

To maximize exposure to the sun, solar panels are attached to a tracker which follows the sun. 399,366 trackers are needed costing $1,857,051,900[17]. As well, these trackers are mounted on steel poles in which one end is planted onto the ground that costs $445.76 per item resulting $178,021,388 in total.[18][19]

The amount of wiring is unknown so an assumed 4,000,000 feet of wiring is allotted which costs $50,000.[20]

The transmission lines that connect the solar farm to the city of San Francisco will also be considered. The approximate distance between San Francisco and San Joaquin is 91.9 miles. This leads to a total cost of $21,137,000 for transmission lines.[21]

In total, all the capital costs of assembling a solar farm are approximately $4.42 billion. This number is an approximate number as several other costs have not yet been included.

It is assumed that labor costs would also play a role. Four plant managers will be checking the solar farm constantly for any need for maintenance and on average they are paid $549,928 per year.[30] Another assumption is that there needs to be personnel present in case any repair work is needed. An average worker gets paid $82,395 per year.[31] These basic operating costs amount to $632,323. This will be a yearly cost over the lifetime of the solar panels which is 20 years.

According to the U.S. Department of Energy, there are no readily available recycling processes for solar panels.[32] However, some of the PV components, such as the conductor metals within the panel can be recycled. In general though, the panels will be disposed into landfills without any other processes done on it. Assuming each panel weighs 40.8 lbs (0.0155 ton) then it will cost approximately $86,213,994 to dispose of the solar panels.[33]

Turbine Power

edit

A summary of the costs for a tidal farm is included below.

 

The capital cost of such a tidal farm would include the manufacturing and placing of the tidal turbines to the intended site as well as the transmission lines that are needed to transmit the electricity. The cost of the land of the site where the turbines will stand is assumed to be insignificant because it is underwater. Study shows that each turbine is estimated to cost around $15 million.[12] The same study also states that each year an amount of $750,000 is incurred as maintenance costs for a single turbine.[12] At the end of a turbine’s useful life, almost all the parts of the turbine would be disposed. Many of the parts lose their ability to be recycled because the chemicals used to coat these parts against corrosion in sea water make them either too energy intensive, if not impossible, to recycle. In addition, some of the components are made of composite materials which are non-recyclable.[22]

The total capital cost of a tidal turbine farm that can power half of San Francisco would be $5.01 billion. The operating and maintenance costs would be another $4.73 billion over the course of its lifetime of 20 years. Disposal of the farm would cost around $11 million. The total cost, estimated to $9.75 billion in 20 years is still lacking other costs including taxes, among others. This calculation assumes all the turbines survive to the end of their life, and none are lost prematurely due to damage, weather or other factors.

Societal Analysis

edit

All three alternatives share one common societal advantage: they create more jobs. The jobs the plants may create are for construction workers, operators and maintenance laborers.[28] As well, both solar and tidal farms generate no noise pollution to distract nearby communities while power is being generated.[34][35]

However, each alternative also has their downsides. Smog is a by-product of gas turbines.[36] This is not only harmful to the health of those who live around the plant but dirties properties as well.[37] A societal drawback for a solar farm is amount of land used. Since a large number of solar panels, inverters, and batteries are needed in order to sustain a large amount of power, a lot of land is used[13] which can be for other purposes such as agriculture or housing. A disadvantage of a tidal farm is that during construction of the tidal farm many of the marine habitats may be ruined thus potentially killing marine life living in the area.

References

edit
  1. ↑ Office of the Governor, “Gov. Schwarzenegger Signs Landmark Legislation to Reduce Greenhouse Gas Emissions,”[Online Document], 2006 Sept 27, [cited 2009 Mar 20], Available HTTP: http://gov.ca.gov/index.php?/press-release/4111/
  2. ↑ A. Frucci, “San Francisco Working on Ambitious Solar Plan, Rebates and Loans for Solar Installations,” [Online Document], 2007 Dec 12, [cited 2009 Mar18], Available HTTP: http://gizmodo.com/gadgets/renewable-energy/san-francisco-working-on-ambitious-solar-plan-rebates-and-loans-for-solar-installations-333045.php
  3. ↑ Energy Consumption Data Management System, “Electricity Consumption by County,” [Online Document], 2009, [cited 2009 Mar 5], Available HTTP: http://www.ecdms.energy.ca.gov/elecbycounty.asp#results
  4. ↑ G. Parkinson, OEMs Getting Ready for Coal Gasification, Turbomachinery International, May/June 2004.
  5. ↑ 5.0 5.1 Poly Power Station IGCC – 5th year of commercial operation, Teco Energy, Oct 2000
  6. ↑ 6.0 6.1 T.L. Buchanan, “Market-based advanced coal power systems,” [Online document], 1998, [cited 2009 Mar 19], Available HTTP: www.netl.doe.gov/coalpower/gasification/pubs/pdf/marketbased_systems_report.pdf_ _Apr. 1, 2003
  7. ↑ National Energy Foundation, “Active Roofs: Types of Photovoltaic (PV) Cell,” [Online Document], 2008 July 18, [cited 2009 Mar 2009], Available HTTP: http://www.nef.org.uk/greencompany/active-pv-cells.htm
  8. ↑ 8.0 8.1 8.2 Wholesale Solar, “Model: KD210GX-LP 210 Watt solar panel,” [Online Document], 2007, [cite 2009 Mar 20], Available HTTP: http://www.wholesalesolar.com/products.folder/module-folder/kyocera/KD210GX-LP.html
  9. ↑ Sea Generation, “The Seagan Turbine,” [Online Document], [cited 2009 Mar 13], Available HTTP: http://web.archive.org/web/20090529195858/http://seageneration.co.uk/downloads/recent/General%20Documents/Seagen%20Facts%20EXTERNAL%202.pdf
  10. ↑ McAdam, R, “Tidal Turbines,” [Online Document], 2009, [cited 2009 Apr 1], Available HTTP: http://www.soue.org.uk/souenews/issue7/tidalturbines.html
  11. ↑ Y. Li, Barbara, J. Lence, M.C. Sander, Modeling tidal turbine farm with vertical axis tidal current turbines, Student Member of IEEE
  12. ↑ 12.0 12.1 12.2 12.3 C.M. Vega, “San Francisco: PG&E backs new study of bay’s tidal power,” [Online Document], 2007 Jun 20, [cited 2009 Mar 7], Available HTTP: http://www.sfgate.com/cgi-bin/article.cgi?f=/c/a/2007/06/20/BAGDGQIBCS1.DTL
  13. ↑ 13.0 13.1 13.2 J. Thomas, “Powering 20,000 homes: The World’s Largest Pv Solar Farm Opens,” [Online Document], 2008 Feb 15, [cited 2009 Mar 20], Available HTTP: http://www.treehugger.com/files/2008/02/powering_20000.php
  14. ↑ 14.0 14.1 Land and Farm, Prices for land in California, [Online Document], [cited 2009, Mar 20], Available HTTP: http://www.landandfarm.com/lf/asp/search_results.asp?booltext=san+joaquin&source=front&submitted=yes
  15. ↑ 15.0 15.1 Selectronic, “Inverters”, [Online Document], 2009, [cited 2009 Mar 22], Available HTTP: http://www.selectronics.com.au/documents/Price_List_1st_January _2009_Inverters.pdf
  16. ↑ Eco Vantage Energy Inc, “Wattsun Tracker (ES190),” [Online Document], [cited 2009 Mar 20], Available HTTP: http://www.ecovantageenergy.com/catalog/items/item1877.htm
  17. ↑ 17.0 17.1 Wholesale Solar, “Zomeworks Trackers,” [Online Document], 2007, [cited 2009 Mar 20], Available HTTP: http://www.wholesalesolar.com/trackers.html
  18. ↑ 18.0 18.1 Wholesale Solar, “Solar Panels- All Brands – Lowest Prices:,” [Online Document], 2007, [cited 2009 Mar 13], Available HTTP: http://www.wholesalesolar.com/solar-panels.html
  19. ↑ 19.0 19.1 McMaster-Carr, “Tubing,” [Online Document], [cited 2009, Mar 13], Available HTTP: http://www.mcmaster.com/#steel-tubing/=15xoqq
  20. ↑ 20.0 20.1 Action- Electronics, “MAGNET WIRE, coil WIRE, INDUCTOR WIRE, TRANSFORMER WIRE, MOTOR COIL WIRE”, [Online Document], [cited 2009, Mar 13], Available HTTP: http://www.action-electronics.com/magnetwire.htm
  21. ↑ 21.0 21.1 L Duke, J.E. Lionberger, “3-D Modeling boosts transmission capacity,” [Online Document], 2001 Jul, [cited 2009 Mar 20], Available HTTP: http://uaelp.pennnet.com/Articles/Article_Display.cfm?Section=Articles&Subsection=Display&ARTICLE_ID=106814
  22. ↑ 22.0 22.1 Mike Page, “Who is going to manufacture tidal turbines?,” [Online Document], 2008 June 27, [cited 2009 Mar 5] Available HTTP: http://www.imeche.org/NR/rdonlyres/2D9BCD32-0171-43E9-A939-AB474EF9E0CF/0/TidalGenerators.pdf
  23. ↑ Hank Green, “World’s Largest Tidal Turbine First Pictures,” [Online Document], 2009, May 20 [2009 Mar 5] Available HTTP: http://www.ecogeek.org/content/view/1653/1/
  24. ↑ NSWMA WASTEC, “MSW (Subtitle D) Landfills,” [Online Document], 2009[cited 2009 Mar 24] Available HTTP: http://www.environmentalistseveryday.org/publications-solid-waste-industry-research/faq/municipal-solid-waste-landfill.php
  25. ↑ 25.0 25.1 Novel Gas Cleaning/Conditioning for Integrated Gasification Combined Cycle Volume I – Conceptual Commercial Evaluation optional Program Final Report, 2005 Dec 31, pg 100
  26. ↑ IGCC Feasibility Analysis - January, 2005, The Erora Group, 2005 Jan
  27. ↑ J. Moresco, “Carbon Tax purposed in California,” [Online Document], 2008 Feb 11, [cited 2009 Mar 16], Available HTTP: http://www.redherring.com/Home/23736
  28. ↑ 28.0 28.1 Edison Mission Group, “Carson Hydrogen Power Project,” [Online Document], 2007 May 29,[cited 2009 Mar 18], Available HTTP: http://web.archive.org/web/20091009231205/http://www.energy.ca.gov/2007_energypolicy/documents/2007-05-29_workshop/presentations/Kostrzewa_Carson_Hydrogen_Power_Project.pdf
  29. ↑ G. Offen, “Mercury Issues for Coal-fired Power Plants: Emissions, Fate and Health Effects, Controls,” [Online Document], 2004 Dec 7, [cited 2009 Mar 19], Available HTTP: http://www.in.gov/dnr/reclamation/files/Mercury_for_ISMR_(Offen_12-04_-_Rev_12-6).pps
  30. ↑ Salary.com, “Salary Wizard Basic Report” [Online Document], [cited Mar 24] Available HTTP: http://swz.salary.com/salarywizard/layouthtmls/swzl_compresult_national_SC16000160.html
  31. ↑ Salary.com, “Salary Wizard Basic Report” [Online Document], [cited Mar 24] Available HTTP: http://swz.salary.com/salarywizard/layouthtmls/swzl_compresult_national_SC16000077.html
  32. ↑ U.S. Department of Energy, “ PV Panel Disposal and Recycling”, [Online Document], 2009, [cited 2009 Mar 13], Available HTTP: http://www1.eere.energy.gov/solar/panel_disposal.html
  33. ↑ NSWMA WASTEC, “MSW (Subtitle D) Landfills,” [Online Document], 2009[cited 2009 Mar 24] Available HTTP: http://www.environmentalistseveryday.org/publications-solid-waste-industry-research/faq/municipal-solid-waste-landfill.php
  34. ↑ Ergon Energy, “Windorah solar farm – a beacon of sunlight,” [Online Document], [cited 2009 Apr 5], Available HTTP: http://www.ergon.com.au/Resources/Windorah_Solar_Project.pdf
  35. ↑ Alternative Energy, “Tidal Power,” [Online Document], [cited 2009 Apr 5], Available HTTP: http://www.alternative-energy-news.info/technology/hydro/tidal-power/
  36. ↑ Sierra Club, “Dirty Coal Power,” [ Online Document], 2009, [cited 2009 Mar 19], Available HTTP: http://www.sierraclub.org/cleanair/factsheets/power.asp, access March, 19, 2009
  37. ↑ Reuters, “Polish coal plant tops EU’s “dirty thirty” list,” [Online Document], 2009 Apr 3, [cited 2009 Apr 5], Available HTTP: http://www.reuters.com/article/environmentNews/idUSTRE5324DR20090403
Retrieved from "https://en.wikiversity.org/w/index.php?title=Design_for_the_Environment/Low_Carbon_Energy_for_California&oldid=1534974"