Volume I
Chapter 2. Landfill Solar Rhode Island Renewable Energy Siting Partnership
A major advantage of thin films over their rigid crystalline counterparts is that they can conform to changing ground conditions, which may develop in landfill applications as a result of
differential settlement of the waste beneath the PV array see arrow in Ch. 2 Figure 7. Additionally, the lower profile of flexible solar modules allows more space for waste in the
landfill. Thin film laminates may also reduce the cost and maintenance requirements associated with landfill caps by substituting for traditional capping material i.e. geomembranes, soil, and
vegetation and obviating the need for grass seeding, mowing, and irrigation. Water runs off the surface of PV laminates, which reduces concerns of rainwater infiltration into the landfill. This
safeguards the cap and reduces the frequency with which sediment must be removed from nearby retention ponds
CES 2011b. Due to their light weight, thin film laminates are recommended
for use on landfill side slopes where they pose less risk of slope destabilization than heavier, rigid panels Stafford et al. 2011 see Section 2.4.3 for more information. Thin film, however,
can also be deployed on rigid panels and is a good solution where acreage is not a limiting factor. Installed in the same manner as other rigid panels, this application is more advantageous than a
flexible application in cases where a landfill has vegetative cover and is subject to soiling from snow. A thin film array will capture more diffuse light at the beginning and end of the day and
outperform a rigid panel array of equivalent nameplate capacity, all else being equal.
Ch. 2 Figure 7. Flexible Solar PV panels with Arrow Indicating Slope Change Adapted from CES 2011a.
2.3.2 Orientation and Tilt
The orientation and tilt of PV panels must be configured to maximize the capture of solar energy. Optimal orientation for harvesting incident sunlight in the northern hemisphere is due
south i.e., “true”, not “magnetic,” south. The ideal tilt angle of PV modules varies according to
Page 202
Volume I
Chapter 2. Landfill Solar Rhode Island Renewable Energy Siting Partnership
time of year; in summer, when the sun appears higher in the sky, the ideal panel tilt angle is lower than in winter. At all times of year, PV panel efficiency can be maximized by placing
modules as close as possible to a 90° angle relative to incoming solar rays. Generally, tilt angle is calculated as the site’s latitude ±15°, although specific adjustments need to be made for each site
Stafford et al. 2011; Tansel et al. 2010.
2.3.3 Balance of System Equipment
PV panels require a variety of ancillary equipment, sometimes referred to as balance of system BOS equipment. This equipment includes mountsracks, ballastfootingsfoundations,
wiring, inverters, and transformers. Racks hold the module in place and maintain the proper angle between the panel and the
sun Ch. 2 Figure 8. The footing or ballast helps resist wind loading and holds the rack or mount in place MassDOER 2012. Solar arrays placed on landfills should not use foundations that
penetrate the ground as this compromises the landfill cap, exposing the PV system to underlying waste and corrosive landfill gases, while introducing rainwater into the landfill which can cause
contaminated leachate Stafford et al. 2011. Panel support systems that do not penetrate the ground include shallow poured concrete pillars, pre-fabricated concrete, slab, and ballast frames
Sampson 2009. Slab foundations are not recommended for landfills as they are heavier and can cause settling of the landfill waste. Settling can cause cracking and destabilization of the PV
panel arrays Sampson 2009. Site-specific cost, weight, and strength considerations determine which of the foundation choices are most suitable. Frost heave i.e. upward movement of soil
resulting from water volume expansion during freezing can occur in the upper few feet of the ground. This site-specific factor affects panels with foundations placed at or near ground level,
causing permanent alteration of panel tilt, structural problems, and other negative impacts. Electrical balance of system equipment includes the wiring, inverters, and transformers
required for operation of the PV system and transmission of electricity produced to the grid. Solar arrays produce direct current DC power, which an inverter changes to alternating current
AC, the form of current used by the grid. Transformers increase or decrease the voltage of the AC power between the solar array and the grid.
Page 203
Volume I
Chapter 2. Landfill Solar Rhode Island Renewable Energy Siting Partnership
Ch. 2 Figure 8. Rigid Panel PV Mounts with Row Spacing Indicated Adapted from Prweb.com 2012.
2.3.4 Pressure on Landfill Cap
