The United States have over 100,000 closed landfills. Once a landfill reaches capacity, regulations require owners to follow specific procedures for capping the facility. Traditional closure systems consisted of a geomembrane, 45 cm thick compacted soil barrier layer, and a 15 cm topsoil vegetation layer. The outlook for significant redevelopment of the land simply did not exist due to financial, regulatory, environmental and geotechnical issues. In addition, facility owners incur long-term operation costs associated with maintenance and monitoring responsibilities (OM&M) , which may last for as long as 30 years.
Recent clean energy news headlines point to one solution that seems to gather daily momentum - convert partially or fully closed landfills into solar power parks. Energy captured from the sun could serve the needs for landfill operations, provide electricity to neighboring communities, or power entire towns. In addition, using closed landfills as solar power farms could alleviate concerns about “energy sprawl”-- the proliferation of wind and solar energy projects across public and private land.
Fort Carson: Moving to 100% Renewable Energy
In late 2007, the Fort Carson army base near Denver, Colorado, took its first step toward achieving 100% renewable energy by 2727, with one of the first conversions of an inactive landfill into a solar power station. Vince Guthrie, utility programs manager at Fort Carson called closed landfills “used-up land.” He went on to say, “Using the space to capture solar energy is the most sustainable way to continue to use the resource. Utilizing landfills to help address our nation's energy challenges makes sense."
The U.S. Army worked with the Western Area Power Administration, a division of the Department of Energy, to lease the land to a group of utility investors led by 3 Phase Energy. The investors developed, installed and financed the 2-megawatt power station strewed across 15-acres. Headquartered in Tempe, Arizona, First Solar, Inc. (NASDAQ: FSLR) provide the system's technology --a fixed tilted, ground-mounted photovoltaic array with 27,600 flat-plate thin-film solar panels, which have a 25-year warranty. The power station generates 3,200 megawatt-hours annually, and serves 500 homes.
The base expects to meet 100% of the base's energy needs with renewable sources by 2727. Project collaborators expect the array to produce an efficient level of energy for up to 40 years. 3 Phase Energy receives a renewable energy credit of 125% for each kilowatt-hour (kWh) of electricity the system produces. It sells the credits to Xcel Energy out of Denver. The utility company purchase credits to help meet compliance with Colorado's Renewable Energy Portfolio Standard (RPS). RPS requires utilities to produce a specified percentage of renewable energy sources. The figure escalates each year.
Municipal utilities servicing over 40,000 must achieve ten percent by 2020. Investor-owned utilities have a 30 percent requirement. Fort Carson's Power Purchase Agreement (PPA), allows the army to purchase power from the array for a low fixed cost for 20 years. Fort Carson contracted with Colorado Springs Utilities to monitor the photovoltaic system and perform other services.
Republic Service: Sustainable Investment Approach
Arizona-based Republic Services, Inc, (NYSE: RSG), a provider of solid waste collection, transfer, recycling and disposal services to commercial, industrial, municipal customers in 40 states and Puerto Rico. Republic own or operate more than 210 landfills. Traditional Subtitle “D” caps required a five-step process:
- Intermediate cover layer
- Geomembrane final grading layer
- Geocomposite drainage layer
- Vegetative support layer
- Topsoil layer
Republic wanted to replace the convention grass-top closure system with an environmentally friendly geomembrane as it closed landfills at its 680-acre Tessman Road landfill in San Antonio, Texas. The cover must also provide the capacity to turn the site into a solid revenue stream with a reliable return on investment.
Republic contacted HDR, a global architecture, engineering, and consulting firm, to discuss the engineering a revolutionary closure cap. In collaboration with United Solar, a wholly owned subsidiary of Energy Conversion Devices, Inc. (NASDAQ:ENER), and manufacturer of UNI-SOLAR brand photovoltaic (PV) laminates, the group developed a synthetic Exposed Geomembrane Solar Cover (EGSC).
The 60-mil reinforced thermoplastic polyolefin (TPO) geomembrane's thickness, strength, and flexibility helps quash concerns about topsoil erosion problems. The sheet-flow attributes allow water to drain into perimeter drainage systems. The fiber-reinforced material resists punctures from hail and extreme wind. With a low contraction-expansion coefficient, the cover functions well in hot and cold temperatures. Project manager Tony Walker stated, “The solar energy cover is easier to inspect, maintain and repair than a traditional clay cap, and is technically superior in terms of odor control and storm-water management."
Installers anchor the exposed geomembrane securely into the landfill, which was not possible with the convention method. The new system eliminates excavation and soil transportation expenses associated with the construction of conventional closure systems. The new geomembrane serves as a support for flexible photovoltaic (PV) panels. The new closure system model is as follows:
- Solar photovoltaics
- TPO geomembrane
- Final grading layer
- Intermediate cover layer
Landfill owners only have to prepare the landfill with a minimum 12-inch deep bedding layer. A final layer builds the site to final grade. Republic covered 5.6-acres with TPO geomembrane. The demonstration project's actual array comprises about six-tenth of the designated area. The system requires 1,025, ¼-inch thick flexible laminate solar modules. A special solar panel adhesive secures the panels directly to the surface of the exposed geomembrane. The array generates 135kWp DC.
Republic deployed the latest geomembrane PV technology at its Hickory Ridge, Georgia landfill. Billed as the largest EGSC installation in the world, the solar energy park project covers 50-acre Republic states the system will produce 1000 kWp DC.
Carlisle Energy Service: Second Generation Landfill Closure System
In January 2010, Republic Service transferred the ownership of its solar landfill cover technology to Carlisle Energy Service, Inc. (CES). CES markets the second-generation technology by emphasizing to public landfill owners the transformation to a profitable business model. The attraction starts with cost avoidance benefits. A conventional landfill closure cost as much as $150, 000 per acre. The geomembrane cost two-third less at $50,000. Owners profit from reduced operations and maintenance expenses and savings on electricity costs for landfill operations. Other financial enticements include state investment tax credits, accelerated depreciation allowances, renewable tax credits, 30% federal tax credits, and various grants and rebates.
Landfill owners generate revenues by soliciting Request for Proposals (RFP) from solar energy developers to investors to develop the inactive landfills. The developers pay for the rights to lease the properties. Generally, facility owners sign PPAs to lock in lower electric costs. Some municipalities consider adding provisions to contracts that transfer ownership of the power systems to the landfill owners at some future point in the future for a predetermined sum.
Carlisle Energy Service states regulators have “adopted” the new closure system for interim, long-term, and final closures. The innovative business model has attracted the interest of cash-starved municipalities across the country. CES recently signed a Letter of Memorandum with New Jersey. The firm expects future announcements with Massachusetts, Australia and India. Massachusetts, Florida, New Jersey, Georgia, Nevada, Texas, and New York are among the states that have gotten on board with solar landfill projects.
In late April, New York mayor Michael Bloomberg announced the city's intent to work with private developers to build 50 megawatts of solar power stations on 3,000 acres of closed landfills in Brooklyn and Staten Island. The projects should eventually provide electricity for 50,000 New York homes.
Besides producing clean and efficient solar energy, these projects create employment, provide low-risk investment opportunities, and offer a high benefit-to-cost ratio. Solar photovoltaic energy financing and contracting firm Borrego Solar states on its website that the typical landfill has anywhere from 5 to 80 acres of unused land appropriate for solar development. This unused land provides space for building a capacity of 1 to 16 megawatts of electricity per site. Developing just 25% of this land could generate 212,000 megawatts of solar energy.
