Greening Marginal Lands

'Limbo Lands' can be reclaimed

Lauren Riga | Aug 23, 2011


Exelon and SunPower Corporation with the City of Chicago completed the nation's largest urban solar power plant on a 41-acre industrial brownfield in Chicago's South Side and in doing so, set off a potential trend.

Exelon City Solar is a 10-megawatt facility made from 32,292 solar photovoltaic (PV), powering up to 1,500 homes.  According to Exelon, this plant displaces more than 30 million pounds of carbon emissions per year, equivalent to taking more than 2,500 cars off the road.

The partnership is potentially huge. Renewable energy markets are rising as the U.S. aims for energy independence through the use of clean domestic sources.  Scaling up renewable energy systems on `limbo lands' can be a pragmatic approach to achieving such goals by generating clean, localized energy and thus, creating a more resilient energy infrastructure.  Marginal lands in urban areas that have no value to society or industry can advance innovative, more cost effective technologies and reduce the environmental impacts of energy systems.

"We took a property that was vacant for over 30 years, remediated it, and now has a productive use- 32,000 solar panels turning the sun's rays into clean energy," said Timothy Wirth from Exelon Power Corporation. 

As for Chicago, its communities benefit from this 2010 project, as Exelon City Solar created more than 200 project based and permanent jobs.  Exelon also reached out to local companies for labor and building materials, and the previously vacant brownfield now generates local revenue from property rent and real estate taxes.   

In 2008, the US Environmental Protection Agency (EPA) partnered with the Department of Energy's National Renewable Energy Laboratory (NREL) and launched a program called Re-Powering America's Land: Siting Renewable Energy on Potentially Contaminated Land and Mine Sites. This program encourages the siting and development of renewable energy projects on contaminated, underused land across the country, `limbo lands.'  Limbo lands can include: superfund sites; landfills; brownfields; abandoned mine sites; former industrial sites; and government developments.  Many of these sites are undesirable or unfit for residential or commercial use and have little monetary value.

Re-Powering America's Land aims to reuse sites, improve communities, create jobs, develop partnerships, decrease the use of green-space for siting renewable energy and increase the amount of renewable energy generated. 

"Contaminated properties such as Brownfields and landfills present positive opportunities for communities as locations for siting renewable energy facilities.Chicago's Exelon City Solar project is an excellent example of how an unproductive brownfield property can be turned into a valuable community asset," said Cathy Milbourn from the EPA.

In 2008, NREL conducted a feasibility study and identified nearly 500,000 sites and 15 million acres from land and mine sites across the United States.  Hundreds of thousands of inexpensive, underutilized 'brownfield' sites exist around the world that can provide space for renewable energy projects such as solar, wind, advanced biomass/biofuels and geothermal; or a combination of technologies.

Related uses can include manufacturing wind or solar panel parts, waste reuse or recycling and urban farming.  The EPA estimates that the total potential of energy from brownfields, without taking into account financial or logistical limitations is nearly 1 million megawatts, almost the amount of current U.S. electricity generating capacity. 

Brownfields offer available land with little or no competing uses and often have less red tape than new developments.  Many `Limbo' sites have critical infrastructure in place, such as access to transmission lines and transportation, and already zoned for development.  Projects tend to be smaller scale and more `shovel ready' for implementation. These are near-term high impact distributed energy systems that can be fed into the grid, leveraging underutilized sites, as opposed to clearing previously undisturbed lands.

Another advantage is their adaptability to higher uses in the future.  Landfill sites are commonly used for gas recovery projects, and New York City is going a step further by incorporating solar power installations on nearby landfills.  Clean energy projects on limbo lands have existed for years and many incentives exist to promote brownfield redevelopment. 

States are taking action to capitalize on unproductive urban lands to create clean, localized energy and stimulate the green economy through job creation.  The Land Use Institute
in Michigan conducted a state-wide survey on renewable energy potential on brownfield sites and found that converting brownfields to renewable energy facilities would generate 5,855 megawatts of electricity, around 17,500 jobs and more than $15 billion in investments.

Limitations can hinder the advancement of renewable energy on brownfields. Some potential barriers include lack of funding for siting and assessments, as well as limited technical and local government capacity.  High costs and low return on investments generate little business interest for smaller scale renewable projects. 

Re-Powering America's Land provides incentives and technical assistance to enhance community capacity.  They assist with determining the best technology and location for placement; as well as the potential energy generating capacity, returns on investment and the economic feasibility of renewable energy projects.

Clean energy means minimizing intensive demands on land, water and other resources we rely on for a sustainable economy, in addition to reducing fossil fuels. With necessary siting, partnerships and government incentives, these projects can be lower-cost with significant impacts.

Clean energy programs on brownfield sites is an innovative approach for environmental improvements and initiatives in power generation. It's the type of win-win scenario that U.S. decision-makers should pursue.

Lauren Riga is a freelance writer and energy analyst.

The editorial staff at is passionate about exchanging ideas and dedicated to promoting ongoing conversation about renewables and sustainable energy issues. We invite you to join and contribute to our online community. If you have an idea for an article or editorial contribution, please contact me via email,, or phone, 860.633.0090.

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CSP Heat Rate

Having looked at multi-MW CSP plants in the past, yes, the fuel is free, but there's a 20-25 year mortgage on the mirrors, so you'd better believe heat rate is important. Simple cycle CT heat rate is on the order of 10,000 BTU/kWh, CSP parabolic trough with multiple feedwater heaters and wet cooling can get down to ~8,500 BTU/kWh, and a modern combined cycle CT plant is on the order of 6,400 BTU/kWh if you believe GE's marketing material. CSP power tower should have a lower, and therefore better, heat rate than CSP parabolic trough given the higher TH afforded by molten salt as a working fluid compared to Dowtherm A / Therminol VP-1.

Comments are welcome, and can be sent to my email, aetaber at

Best regards,

Alan Taber

Large-scale solar generation of electricity in New Mexico

Heat Rate [efficiency] does not apply to solar and wind generation of electricity PNM foil informred us. 

We continue to investigate.


To: "clifford ho"
Cc:, "j rudisill", "greg nelson", "susan sponar">,, "dave",,,
Sent: Wednesday, August 24, 2011 11:24:56 AM
Subject: Heat Rate [efficiency] for solar and wind generation of electricity

Hello Dr Ho,

Ms Christodoulou and your photovolatic presentations were very informative, IMO.

You said that you were involved in Sandia Labs CSP program. Listen to what was said.

We are having a problem with determination of whether heat rate [efficiency] applies to CSP, photovoltaic, and wind generation of electricity.



From: "Greg Nelson" To:
Sent: Monday, April 11, 2011 5:34:21 PM
Subject: RE: heat rate for csp? geothermal heat rate

Don’t know.

From: []
Sent: Monday, April 11, 2011 5:33 PM
To: Nelson, Greg
Cc:;;; CAI Info; Shirley A. Lancaster;;;;;; ron chesser;; steve casey; dru jones;

Subject: Re: heat rate for csp? geothermal heat rate

Hello Greg,

Thanks for response.

You wrote, 'Heat rate is the amount of Btu's of fossil fuel burned to generate kWh's of electricity. Since CSPs don't typically burn any fossil fuel (unless they have supplemental firing), the term heat rate does not apply to CSPs.'

Then why does Geothermal have a Heat Rate of 29,050 BTU/kWh?



On the other hand I received,

From: "Jake Rudisill"
Sent: Tuesday, May 10, 2011 4:37:20 PM
Subject: Heat Rate misconception

Mr. Payne,

The definition of heat rate is not the heat content of just the fossil fuel inputting the conversion system—it is the conversion efficiency of the system with whatever is the heat input.

Every plant’s heat rate can thus be calculated.

Geothermal energy has a very high heat rate because it utilizes a relatively low grade of heat source—at its best, 350F, 100 psi steam, and thus 1200 btu/lbm. In a modern gas-fired boiler, steam is at 1000F and 2500 psi, with a much higher heat content of around 1770 btu/lbm.

heat rate

A measurement used in the energy industry to calculate how efficiently a generator uses heat energy. It is expressed as the number of BTUs of heat required to produce a kilowatt-hour of energy. Operators of generating facilities can make reasonably accurate estimates of the amount of heat energy a given quantity of any type of fuel, so when this is compared to the actual energy produced by the generator, the resulting figure tells how efficiently the generator converts that fuel into electrical energy.

Heat Rate (Energy Efficiency)

Overall thermal performance or energy efficiency for a power plant for a period can be defined as

fhr = H / E (1)


fhr = heat rate (Btu/kW, kJ/kW)

H = heat supplied to the power plant for a period (Btu, kJ)

E = energy output from the power plant in the period (kWh)

Perhaps you could tell us who is right?




Brown, by any other name is still Brown...


HELLO!!!   KNOCK, KNOCK...  Solar on BROWN sounds Green but..... Contamination doesn't dissappear just because it has a 20 or 25 year roof over it. At-least make a portion of the profits to be derived get used to Clean it up first!!! giving a future tax incentive. Don't just give it away to allow a FOR-PROFIT company the ability to milk rate payer's pockets for years to come.

I speak first as an Physicist specializing in Energy Systems, Secondly as someone who has and will continue to use BROWN Sites and Green them first before developing on them, and Thirdly, a parent of some of our future inhabitants....    

 Whoa is me... for all common sense is lost...... because of $$$