Green-Roof Integrated Photovoltaic Canopy (GRIPV-c)

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Green-Roof Integrated Photovoltaic Canopy (GRIPV-c) is a study being conducted by Marc Perez, Christina Ho, and Nathaniel Wight with the support of Columbia University and Alfred E. Smith CTE High School students (Ashley Grant, Brandon Harvey, Michael Smith, William Alicea, Jared Hatcher, Marco Dwyer, Warrick Balfour). GRIP-c aims to evaluate data collected from four model houses, one housing a control roof, another with a green roof, a standard fixed photovoltaic system, and a GRIPV-c system. The study is ongoing and is looking at temperature, relative humidity, and solar insolation data to qualitatively and quantitatively assess the positive impact of a combined green roof and photovoltaic canopy system on the health of the green roof vegetation, the PV canopy system efficiencies, and the efficiency of roof mounted HVAC air handling units.


<ul><li> 1. THE GREEN-ROOF INTEGRATED PHOTOVOLTAIC CANOPY (GRIPV-C) Exploring Aesthetic and Environmental Synergies EAEE E4006 Field Methods for Environmental Engineering Columbia University, Spring 2011 Marc Perez Christina Ho Nathaniel WightABSTRACTIn the urban environment, space is a premium. From micro-studios to multi-functional furniture,optimizing usage of available space is a critical part of the city lifestyle. Finding purpose forunderutilized space is becoming increasingly important; further, as square foot of usable spaceincreases, so does value. In terms of real estate, no space can go unused and rooftops are fair gameparticularly in the realm of energy efficiency. A variety of methods exist for use of roof top area forenergy offset purposes, but most have been studied independently of each other. Few examples ofresearch exist that study the synergistic effects of combining these elements.Green-Roof Integrated Photovoltaic Canopy (GRIPV-c): Exploring Aesthetic and Environmental Synergiesaims to evaluate data collected from four model houses, one housing a control roof, another with agreen roof, a standard fixed photovoltaic system, and a GRIPV-c system. The study aims to usetemperature, relative humidity, and solar insolation data to qualitatively and quantitatively assessthe positive impact of a combined green roof and photovoltaic canopy system on the health of thegreen roof vegetation, the PV canopy system efficiencies, and the efficiency of roof mounted HVACair handling units.It is anticipated that for the GRIPV-c there is equivalent vegetation growth, and approximately 0.5%improvement in PV performance due to improved cooling of 10 F. Improvements in roof mountedHVAC is roof area to building volume ratio dependant, but is anticipated to result in 35%improvement on thermal performance for a building with a ratio similar to the enclosure.BACKGROUNDFew studies have examined the synergies between green roofs and Photovoltaic (PV) arrays andthere remains a great need for further testing. Several notable examples provide a foundation andjustify the need for continued research.For example, Brownson, Iulo andWitmer of Penn State presented resultsat ASES 2010 outlining the gains inperformance (both of the green roofsubstrate and of a PV system atop it)based on analysis of Penn States 2009Natural Fusion home they designedfor the 2009 Solar Decathlon. TheNatural Fusion home employed deepsedum trays on the roof with low-lying Solyndra/ Green-roof canopy atop the Natural Fusion homemixed vegetation and a canopy severalinches above holding Solyndra^Tm CIGS (Cadmium-Indium-Gallium di-Selenide) PV cylinders.The solyndra system is unique because each cylinder is coated completely on every surface with the </li> <li> 2. CIGS semiconductor material. The idea behind the cylinders that performance can be improved vis-a-vis a traditional fixed-tilt PV array by always having some portion of the cylinder normal to thesuns position--and to use reflected radiation from the underlying roof surface that passes through thespaces between the cylinders. Although the Natural Fusion GRIPV system described in the papersby Brownson et. al provides a summary description of this interesting application of a novel PVtechnology, a 2002 paper by Kohler et. al, presented at Rio 02, examines and identifies the keysynergies unique to GRIPV systems in much more thorough detail.Furthermore, Kohler et. al examine somewhat un-conventional GRIPV designs in that their green roofincorporates plants growing up to a height of 40 cmand required periodic (annual trimming) to maintainheight. The picture at left displays one of theseGRIPV-tested systems which features 1-axis trackingand multi-crystalline PV modules.The positive interactions measured and identified inthe study were:1) Green roofs reduce operation temperature of the PVsystem, thus increasing efficiency and energy yield2) The PV array offers shading for the green roof, thusimproving growth of plants and increasing speciesvariety.We also seek to measure this reduction in back-of-module temperature, given the temperature drop in the local micro-climate from the green roofsevapotranspiration in our study and thereby simulate performance gains vis-a-vis a more traditionalPV system.Both the GRIPV systems referenced above share the common shortcoming of not allowing for synergistic use of space on the roof. On buildings were point-loading considerations are not an issue and green roofs provide the potential for a recreational park-setting for the occupants, the PV array would be better situated at an elevation above head-height. Our experimental study hopes to explore and quantify the benefits outlined by Kohler et. al under a new design paradigm: the GRIPV-canopy. In addition to these benefits, we will be simulating the reduced burden on HVAC loads given reduction in surface temperatures and addition ofThe GRIPV system with intensive green roof and moncrystalline PVin Kohler et al, 2002 photovoltaic generating capacity. 2 </li> <li> 3. STUDY SITEBronx Design &amp; Construction Academy1 is located in The South Bronx, one of the poorestcongressional districts in the United States. BDCAs certified Career and Technical Educational (CTE) programs allows economically disadvantaged students to get unparalleled hand-on instruction in the trades, thereby provide a way out of the poverty cycle. A majority of BDCA graduates will find jobs upon graduation. BDCA high school offers endorsed diplomas in the Building Trades including plumbing, carpentry, electrical practice and installation, architectural drafting, and Heating, Ventilating, and Air Conditioning. These diplomas enable graduates to obtain Master Licenses from the NYC Department of Buildings. Once licensed, graduates can open their own contracting firms. Additionally, BDCA (formally Alfred E. Smith CTE HS) partners withEdward J. Molloy for Initiative for Construction Skills that provides students the unique opportunityto enter NYC Unions upon graduation. Since 2001 Alfred E. Smith has repeatedly helped placeover 20 percent of each graduating class in high-level union jobs,including MTA, Metro North, Long Island Railroad, SmallsElectrical Construction Inc., and New York City SchoolConstruction Authority to name a few. Many others findprofessional jobs in Plumbing, Electrical, Carpentry, AutoMechanics, HVAC as well as Pre Engineering. AES is associatedwith New York Electrical Contracting Association, New YorkBuilding Congress, New York Building and Construction TradesCouncil of Greater New York, Building Trades EmployersAssociation, Architectural Construction and Engineering (ACE)Mentoring programAlfred E. Smith CTE HS also offers the training to put technical education to the test in regional and National competitions. Year after year Smith students practice what theyve learned, compete, and consistently take home trophies from Skills USA and the National Automotive Technology Competition. BDCA provides CTE opportunities for special needs students. Specifically, 20 percent of the AES student body has an Individualized Education Program (IEP). Smith is one of the last standing schools in this city that provides self-contained classes and integrated Career &amp;Technical Education shop classes for a large IEP population. Many of these IEP students haveexcelled in their respective trades and have gone on to secure employment. In addition, Alfred E.Smith CTE HS provides free adult classes at night for the community; Smith is not only aneducational facility for adolescents, but also for the community.1 3 </li> <li> 4. For partial fulfillment of our grade in the course E4006 Field Methods for Environmental Engineers,we collaborated with students on the Smithcampus to construct model homes. We arecurrently monitoring the different rooftopsystems in an effort to demonstrate that solarphotovoltaic and green roof technology are notmutually exclusive. With the help of BDCAstudents we designed and built four modelhomes, each with a different rooftop coveragetypes: Control with gravel bed, Greenroof only,Mock solar PV coverage only, Green roof withmock solar PV coverage.METHODOLOGY1. Experimental Set UpTo assure that the data collected is consistent and comparable, specially designed monitoringenclosures were constructed and co-located adjacent to each other. Four enclosures were designed tocollect the data used to calculate the performance and efficiency improvements of the GRIPV-csystem. Additionally, a stand to hold a pyranometer and ambient temperature and relative humiditymonitor was constructed and located with the monitoring enclosures.The enclosures are designed to withstand the loading of the maximum roofing weights and to behighly sealed to prevent air/energy leakage. They are approximately 2 x 2 x 4 long and areconstructed from 2 x2 cedar dowels, 1 rigid insulation, and sealed with silicon sealant. They arepainted with a flat black paint so that the enclosures act as a black body to absorb maximumradiation energy. 4 </li> <li> 5. Enclosure 1 is the control with a standard gravel bed roof. Monitoring parameters for this enclosureinclude internal temperature, and near surface roof temperature.Enclosure 2 is the standard green roof installation. Monitoring parameters for this enclosure includeinternal temperature, and near surface green roof temperature. Varietal sedum trays were used forthe green roof materials. The tray depths are approximately 4.Enclosure 3 is the standard solar roof installation. Monitoring parameters for this enclosure includeinternal temperature, near surface roof temperature and rear solar panel temperature.Enclosure 4 is the GRIPV-c system. Monitoring parameters for this enclosure include internaltemperature, near surface roof temperature and rear solar canopy temperature.The below pictures show Smith students framing the model homes and calibrating and labeling thesensors. 5 </li> <li> 6. 2. Modeling Photovoltaic System Performance from Empirical DataSilicon-based Photovoltaics are adversely affected (in terms of solar/electric conversion efficiency)by elevated temperatures and to a lesser extent by decreased solar radiation. In this section, wedevelop a modeling tool to interpret Irradiance and back-of-module temperature data from ourexperimental setup and calculate expected energy generation and therefore, expected cost savings.We have chosen to model the JAMS(L) 72-180 solar module as the physical basis for our modelingbecause the manufacturer, JA Solar was as of Q1 2011 the dominant player in solar module salesworldwide. It was thought that by using specifications from the best selling solar module as such,our results would best allow themselves to be generalized.2.1 Deriving Current/Voltage Characteristics from the Shockley Diode Equation:To model the dependencies, we needed to estimate the current/voltage (I/V) characteristic curve forthis module using the Shockley diode equation. We model these I/V curves as a function of manyparameters (which will be detailed below) as such: qV IL I0 e nkT 1 Imod = qV R I 1+ I0 e nkT 1 s L nKTIn the equation above, Imod is the module current given the module voltage (V) and temperature (T).(It is a modified version of the Shockley-Diode equation, solved for the module current instead of for voltage as it is typically given.)The light-induced current, IL , is calculated as such:...</li></ul>


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