LCA methodology

A Life Cycle Assessment study has been carried out at the Department of Mechanical and Aeronautical Engineering of the University of Rome "La Sapienza”, using SimaPro 5.1 software. Since each modification of the Pv system (glazed covering, heat recovery) on one side leads to a higher energy output, but, on the other side, it requires new components and materials with their energy content, the main aim of the LCA study is to investigate the effectiveness of these modifications. The energy and environmental impacts and savings of all the systems have been assessed by means of two aggregate indicators: Global Warming Potential at 100 years (GWP100) and consumption of Primary Energy Resources (PER). The characterization factors for both the indicators are taken from “Eco-indicator 95” method, implemented in the database of SimaPro 5.1 software. We focused our attention on these values because of their relevance and importance in environmental and energy saving strategies.

The comparison of the results and the effectiveness of the modification have been evaluated using two pay back time parameters: the Energy Pay Back Time (EPBT) and the CO2 Pay Back Time (CO2 PBT). As a matter of fact, by producing clean energy during their operation, PV and PVT systems avoid the Primary Energy Resources consumption and the CO2 emissions related to conventional energy sources. The PBT parameters are the outputs of an environmental cost — benefit analysis and they estimate the time period needed for the benefits obtained in the use phase to equal the impacts related to the whole life cycle of the analyzed systems. Only after those periods the real environmental benefit starts.

Table 3. Amounts of materials used in PV and PVT systems (3 kWp, 30 m2)

PV AND PV/T SYSTEM COMPONENT

Sub-component and material

Amount

(kg)

Multi-crystalline silicon photovoltaic module

PV cells (including cell contacts)

21

glazed covering (low iron glass)

225

lamination material (ethylen vinyl acetate)

39

aluminium frame

45

Electrical

Balance Of System

steel

10

copper

6

plastic (Poly Vinyl Chloride, PVC)

4

Reflectors

aluminium (diffuse reflector material)

90

galvanized iron (for reflector installation)

90

thermal insulation (polyurethane)

30

collector frame (aluminum profiles)

120

collector back cover (aluminium sheet)

30

Heat Recovery Unit

ONLY FOR PVT/TFMS SYSTEMS (aluminium sheet)

9

ONLY FOR GLAZED HRU: glazed covering (low iron glass)

375

ONLY FOR GLAZED HRU: additional collector frame for glazed covering (aluminium)

45

galvanized iron rods (support structure for horizontal roof)

120

Mechanical Balance Of System

galvanized iron rods (support structure for tilted roof)

90

aluminium (support structure for tilted roof)

30

pipes for air circulation (galvanized iron)

60

(support structure and air circuit)

copper

9

Fan for air circulation steel

12

Plastic (PVC)

3

heat exchanger (copper)

60

In the paper, the EPBT and CO2 PBT values for the analysed systems are given, considering the final use energy output as electricity for standard PV modules and as electricity and gas as heat for the suggested hybrid PVT systems. Life Cycle Assessment (LCA) methodology aims at assessing the potential environmental impacts of a product or a service during its whole life cycle, according to ISO 14040 international standards (1997). The performed study focuses on the life cycle of a 3 kWp PV (or PV/T) system, with an overall active surface of 30 m2. All the analyzed systems were modeled taking into account the following sub-parts: multi-crystalline silicon (mc-Si) PV modules; mechanical Balance Of System (BOS); electrical BOS (inverter and cables); PV module support structures for both horizontal and tilted roof installation; Heat Recovery Unit (HRU), with or without additional glazed covering, and, finally, the air circulation circuit. Consistently with the LCA approach, for all the listed components, the environmental indicators were calculated, from raw material extraction to end of life disposal. Table 3 summarizes, for each component, the type and the amount of material for the 3 kWp reference system.

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