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above ground to avoid shading from vegetation, or panels with higher tilt angles tend to be more exposed to winds, requiring stronger, heavier mounts to hold the modules in place Stafford et al.
2011; MassDOER 2012. These heavier loads can place greater strain on landfill covers and side slopes. PV panels themselves are typically certified to withstand maximum mechanical loads of
50 lbsft2, which equates to wind speeds of approximately 105 mph, or speeds typical of a Category 2 hurricane Sampson 2009;
NHC 2012.
2.2.3 Snow Loading
Snow loading on the PV array depends on a multitude of factors. These include the water content of the snow, depth of snow, cloud cover which prevents snow from melting, panel tilt
which, at steep angles, causes snow to slide off, and freeze-thaw cycles which can cause ice to build up on the modules and prevent snow from sliding off Stafford et al. 2011; MassDOER
2012. Snow loading generally has a more significant effect on the mounting structure than on the panels themselves. Typically, permitting for a solar project will require that a structural
principal engineer provide evidence that the supporting structure can handle a certain level of snow loads. Panels themselves are engineered to support maximum loads of 50 lbsft
2
, which is approximately equivalent to a 10-inch thick ice layer. Ground-level snow loads in Rhode Island
average between 30 and 40 lbsft
2
, within the range withstood by most PV systems ASCE, 2005. However, not all solar panel manufacturers cover snow damage in their warranties.
2.2.4 Hail Impacts
Hail impacts on the PV array may cause both physical andor electrical damage. PV modules should be able to withstand such impacts in the event of falling hail ASTM
International 2012. ASTM International E1038-10 conducts hail impact tests on PV modules demonstrating the ability to withstand one inch hail balls at terminal velocity of 52 mph ASTM
International 2012.
2.2.4 Temperature Effects
Solar panels operate more efficiently at lower temperatures SolFocus 2012. Panel manufacturers use standard conditions of 25°C 77°F to establish published module efficiencies
Stafford et al. 2011. At higher temperatures, PV modules can have more than a 20 reduction in energy output relative to these published efficiencies SolFocus 2008. Records from TF
Green airport from 1949 to 2011 show maximum monthly temperatures above 77°F standard conditions for PV panel testing occurring during each month from March through November,
with extreme highs reaching 100-104°F in July, August, and September NCDC 2012. Average high temperatures during the summer are 78°F, 83°F, and 81°F for June, July, and August,
respectively. These temperatures are within the typical PV operating conditions, indicating that average Rhode Island temperatures do not present problems for PV operations Weather Channel
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2012. However, on extreme temperature days, losses in panel efficiency may occur SolFocus 2008.
2.2.5 Shading Obstructions
To optimize PV system output, shading of panels by trees, buildings, or other obstructions should be avoided. Baseline shading effects are typically determined based on
conditions 90 minutes after sunrise and 90 minutes before sunset, as well as at noon on the winter solstice December 21
st
, when the sun is at its lowest zenith of the year MassDOER 2012. In the New England region, the setback ratio for shade-producing obstructions should be a
minimum of 3:1. For example, a solar array should maintain a 150’ buffer from a 50’-tall tree line in the easterly, southerly and westerly directions. Setback ratio in the northerly direction
should be 1:1 to provide a fall zone for potentially unstable obstructions, such as trees, utility poles, etc. In addition to shade-producing obstructions, PV module efficiency is reduced if
grasses or other vegetation reach above the height of the panel mount. Regular cutting of vegetation can alleviate this potential problem.
2.3 PV System A variety of technologies exist to extract energy from the sun. The simplest application of
solar power, called “passive” solar, uses building design principles as a means to collect, store, and distribute solar energy in the form of heat. More complex “active” solar systems can
generate heat solar thermal, or produce electricity photovoltaics. The RESP solar landfill
analysis focused exclusively on photovoltaic systems, which rely on receptor panels to convert sunlight to electricity. Several technologies exist within the general category of photovoltaic
systems, each optimized for different objectives and varying conditions. The type of technology selected and the design specifications employed during installation are a third determinant, in
addition to sunlight and landfill characteristics, of the technical viability of developing solar electricity generation on landfills.
2.3.1 Photovoltaic Technologies
