Energy payback and life-cycle CO2 emissions of the BOS in an optimized 3·5 MW PV installation



This study is a life-cycle analysis of the balance of system (BOS) components of the 3·5 MWp multi-crystalline PV installation at Tucson Electric Power's (TEP) Springerville, AZ field PV plant. TEP instituted an innovative PV installation program guided by design optimization and cost minimization. The advanced design of the PV structure incorporated the weight of the PV modules as an element of support design, thereby eliminating the need for concrete foundations. The estimate of the life-cycle energy requirements embodied in the BOS is 542 MJ/m2, a 71% reduction from those of an older central plant; the corresponding life-cycle greenhouse gas emissions are 29 kg CO2 eq./m2. From field measurements, the energy payback time (EPT) of the BOS is 0·21 years for the actual location of this plant, and 0·37 years for average US insolation/temperature conditions. This is a great improvement from the EPT of about 1·3 years, estimated for an older central plant. The total cost of the balance of system components was $940 US per kWp of installed PV, another milestone in improvement. These results were verified with data from different databases and further tested with sensitivity- and data-uncertainty analyses. Copyright © 2005 John Wiley & Sons, Ltd.