Abstract: . . .  insulation reduces heat gains during months in which cooling is required and heat loses during months in which heating is required. The difference in heat transfer through the roof area occupied by the photovoltaic modules for each month was computed using the following equation, ( ) t - - = ? t d t t R 1 R 1 A Q o a o PV o ( 2 ) where t o is the outdoor ambient temperature measured using the manufacturer’s supplied sensor, ºC (ºF) t a is the 21.7 ºC (77 ºF) assumed indoor ambient temperature A is the area of the roof occupied by the photovoltaic modules, m 2 (ft 2 ) R o is the thermal resistance of the original roof, 4.05 m 2 ·K/W (R-23.0 ºF· ft 2 ·hr/Btu) R PV is combined thermal resistance of the original roof and the PV system’s insulation, . . .
. . .  calculator are considerably greater that those projected using the information provided by the utility. Reasons for the large discrepancies may include the fact that the EPA’s solar calculator uses emissions data from all the electric utilities within the state of Maryland and assumes that the photovoltaic panels are tilted towards the sun at an angle that optimizes annual performance. Additionally, the EPA algorithm may also assume a conversion efficiency greater that the actual efficiency of the equipment used in this installation. Finally, it should be noted that neither methodology takes into account the reduced space conditioning loads resulting from the additional thermal insulation associated with the photovoltaic system. SUMMARY A 35-kilowatt . . .
. . .  performance. Additionally, the EPA algorithm may also assume a conversion efficiency greater that the actual efficiency of the equipment used in this installation. Finally, it should be noted that neither methodology takes into account the reduced space conditioning loads resulting from the additional thermal insulation associated with the photovoltaic system. SUMMARY A 35-kilowatt roof top photovoltaic system has been installed at the National Institute of Standards and Technology in Gaithersburg, MD. The system became operational on September 14, 2001 and represents NIST’s first on-site source of renewable energy. The total installed cost of the system was $239,945. During the past year the system has provided 35,676 kWh of electrical energy. . . .
. . .  performance. Additionally, the EPA algorithm may also assume a conversion efficiency greater that the actual efficiency of the equipment used in this installation. Finally, it should be noted that neither methodology takes into account the reduced space conditioning loads resulting from the additional thermal insulation associated with the photovoltaic system. SUMMARY A 35-kilowatt roof top photovoltaic system has been installed at the National Institute of Standards and Technology in Gaithersburg, MD. The system became operational on September 14, 2001 and represents NIST’s first on-site source of renewable energy. The total installed cost of the system was $239,945. During the past year the system has provided 35,676 kWh of electrical energy. In addition . . .
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