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occupied by some other type of passive or active use e.g. recreation, the appropriate stakeholders must evaluate the relative merits of preserving the current use or redeveloping the
site for solar electricity generation.
2.4.2 Location
Interconnection Access Proximity of the landfill site to electrical grid infrastructure three-phase distribution
circuits is paramount to ensuring that electricity produced by a landfill-based PV system can be supplied to the electrical distribution system. In Rhode Island, the electric distribution utility,
National Grid, manages interconnection between distributed generation projects and the grid. Communication should be established with National Grid during the early stages of project
planning to evaluate interconnection feasibility Kennedy 2012. Personal communication. The electric load carrying capacity of the lines must be adequate to carry peak electricity loads
generated by a PV array e.g., greater than 1MW in the case of this study. According to the EPA and National Renewable Energy Lab NREL, distances over ½ mile between a solar energy
generation site and the nearest interconnection point tend to make a project unviable EPA and NREL no date. However, the maximum feasible distance required for grid tie-in is highly
dependent on the budgetary considerations of each individual project. Vehicle Access
Vehicle access is another consideration affecting the suitability of a landfill for solar energy development. Roads providing access to the site must be able to withstand traffic from
vehicles and machinery required for the installation, operation, and maintenance of the PV system. EPA and NREL recommend using one mile as a screening measure of whether building
or grading of access roads may be cost prohibitive, however, this will vary by site and project economics EPA and NREL no date.
2.4.3 Landfill Cap and Lining
Landfills receive a variety of waste materials, some of which may present a threat to the environment or human health. Landfill caps, a type of containment treatmentwaste management
practice, help manage this risk by forming a barrier between waste and the surrounding environment. Although cap technology does not directly reduce the amount, mobility, or toxicity
of landfill waste, it mitigates and controls the migration of harmful materials at the site Van Deuren et al. 2002. Properly designed and maintained landfill caps will continue functioning for
tens or even hundreds of years. There are several key functions of a landfill cap Van Deuren et al. 2002:
Minimize exposure of the waste
Prevent infiltration of water into wastes, thereby reducing contaminated leachate
Contain waste
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Control gas emissions from underlying waste
Create a land surface that can support vegetation andor be used for other purposes Traditional Covers
Choice of landfill cap design is determined by the environmental characteristics of a site, specific waste management needs, and cap regulations at the time of landfill closure. Typical
modern engineered caps consist of several layers, including a gas collection, barrier, drainage, protection, and surface layer Ch. 2 Figure 9. The gas collection layer is a geotextile or gravel
layer which allows corrosive gases generated by waste decomposition to migrate out of the landfill. These landfill gases are generally about 45 methane, 55 carbon dioxide, and traces
of other gases Republic Services 2010. Methane is explosive and, in combination with hydrogen sulfide H
2
S gas, produces nuisance odors Stafford et al. 2011. As such, it is important to control release of these gases from a landfill. The grading layer is used to keep a
steady, low-angled slope on the surface of the landfill to encourage water to run off gently. This is done to control erosion and to make sure that water does not pond on the landfill top deck. The
barrier layer consists of a low-permeability compacted clay liner, geomembrane, or composites of both. This layer acts to prevent water from infiltrating into the waste below. The drainage
layer comprises high-permeability materials such as granular soil andor geotextiles. This layer acts to receive and carry away water percolating down from the surface. The protection layer and
surface layer form a protective soil cover over the lower layers, and are often seeded with vegetation Ch. 2 Table 1 and Ch. 2 Figure 9.
Ch. 2 Table 1. Configuration of Cover Systems EPA 1993.
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Ch. 2 Figure 9. A Landfill Caps with Flexible PV Panels; B Traditional Landfill Cap Modified from Sampson 2009.
Solar Energy Covers Composite technologies such as the Solar Energy Cover SEC integrate renewable
energy production into the landfill cap system. Ch. 2 Figure 9 displays the design differences between a traditional landfill cap and the SEC system. In a traditional landfill cover, the
drainage, protective, and surface layers provide ballasting and protection material over the geomembrane. In the SEC design, these layers are replaced by a solar laminate layer lying
directly over the geomembrane, obviating the need for the additional ballasting and protective layers employed in the traditional cap design Ch. 2 Figure 10.
The SEC provides a number of benefits over a traditional cap design. It mitigates problems such as erosion, slope failure, and saturated soil conditions by diverting water off the
cap. Efficient channeling of rainwater off the cover also prevents ponding, which can result in pressure on the surface of the geomembrane. By eliminating the geocomposite and
soilvegetation layers found in a traditional landfill cap, the SEC makes the geomembrane easily accessible for inspections and maintenance. Forgoing these additional layers also helps lower the
costs associated with the landfill cap. In fact, the economics of integrating solar power directly into the cap may help create an incentive for communities to pay for capping a landfill CES
2011c; RIRRC 2011. Some of the drawbacks of SEC capping systems include the lower solar power generation
capacity of the flexible modules, degradation of modules by oxygen and UV light, vulnerability to wind shear, higher stormwater peak flows as a result of increased impervious surface area,
dangers to operations and maintenance workers resulting from the slippery plastic surface, and the risk that snow may cover up the solar cells because of fairly shallow slopes. Many of these
issues can be mitigated. For instance, anti-oxidants and UV-stabilizers can be used to protect the
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plastic, anchor tie-downs can be used to keep the films in place, and walkways can be constructed to safeguard workers. On the positive side, the slippery surface of the films can
enhance snow slide-off and the incorporated PV panels can act as heat sinks that help to melt snow RIRRC, 2011. Because of the aforementioned considerations, SEC caps technologies are
best suited for and most commonly used on landfill side slopes rather than on the landfill top deck CES 2011c; RIRRC 2011.
Ch. 2 Figure 10. Geomembrane Cap with Incorporated Solar Panels on Landfill Side Slopes in New York State Barton and Loguidice, P.C. 2011.
2.4.4 Topography
