The Role of National Energy Policies and Life Cycle Emissions of PV Systems in Reducing Global Net Emissions of Greenhouse Gases
1.1. Energy Matrix and Greenhouse Gas Emission Factors
1.2. Public Policy to Incentivise Distributed Renewable Generation
2. Life Cycle Assessment of Solar Photovoltaic Systems
2.1. LCA Methodology
- Greenhouse gas emission rate (GHGe-rate), given by the following equation :
- Payback time emission, given by the following equation:
|CED = Einput + EBOS||CED (cumulative energy demand) is the sum of Einput: primary energy entering the life cycle (MJp) and the EBOS: energy required by the balance of system (BOS) (MJp).|
|Eagen||annual electricity generation by the PVSS (MJ).|
|ng||average conversion rate of primary energy into grid electricity in the country where the panel is installed.|
|Einput||includes the energy required for module manufacturing, transportation, installation, operation, and maintenance, and its final decommissioning or recycling.|
|EBOS||is the energy required for BOS components, including support structure, cabling, electronic and electrical components, inverters, and batteries for standard isolated systems.|
|GHGe-rate||is the GHG emission rate per unit of electricity generated by the PVSS (g CO2-eq/kWh)..|
|GHGe-total||comprises the total GHG emissions during the life cycle (g CO2-eq).|
|EELCA-output||is the total electricity generated by the PVSS during the life cycle (kWh).|
|Payback Time Emission||indicates how many PVSS years of operation will be required to offset the emissions generated during the manufacturing and installation process (Equation (3)).|
2.2. System Boundaries
- For the studied PVSS, energy consumption was considered in the phases of: manufacture of the modules, assembly and installation of the system and operation (25 years assumed).
- Direct emissions from the photovoltaic module manufacturing process and emissions associated with the energy use for the manufacture of PVSS were accounted for.
- Data of emissions from transportation and the recycling process were also considered.
- The average data available in the literature for the energy values incorporated in the production of PVSS and the balance of system were used.
- All stages of the PVSS production process were carried out in China.
- The PVSS real electricity generation data for 1 year was used. The data from 2018 were the only publicly available during the time this study took place. Future work will look into the integration of longer historical datasets. For the projection of electricity generated by PVSS, an increase of losses by 0.7% per year was considered  to represent normal wear.
2.3. PVSS Materials, Energy, and Carbon Inventory
2.4. System Balance (GHG Emission Rate and EPBT from PVSS)
- Literature was the source of the energy values required in photovoltaic systems and their installation structures, given in MJp/m2;
- The area of each PVSS and the electricity values generated by each evaluated photovoltaic plant were collected from the Sunny portal , who is a supplier of photovoltaic systems.
- Equation (1) was used to calculate the EPBT.
- The values were converted from primary energy to electrical energy by using the total primary energy required for each PVSS (MJp), expressed in MJ and then converted to kWh.
- To calculate the GHG value from the electricity needed to manufacture and install the photovoltaic system, the emission factor of the electrical matrix of the country in which the photovoltaic system was manufactured, expressed in g CO2-eq/kWh, was used.
- Literature was the source of the estimated values of GHG emitted directly in the acquisition and manufacture of PVSS components, expressed in g CO2-eq/m2.
- Direct and indirect GHG emissions from the systems were combined.
- The electricity generation data for each analyzed photovoltaic system was used.
- Equation (2) was used to calculate the GHG emission rate in g CO2-eq/kWh.
- For the projection of electricity generated by PVSS in the year following the actual data collected (2018), an increase of losses by 0.7% per year was considered  to represent normal wear.
- To calculate emissions avoided during each plant’s useful life, the total electricity generated per year (in MWh) was multiplied by the annual projected NIS emission factor (in tCO2/MWh).
- The return time of the emissions generated in the manufacture of the systems was calculated using Equation (3).
3. Case Study: PV Electricity Generation in Brazil
4. Results and Discussion
4.1. PV System EPBT and GHG Emission Rate
4.2. Additional Analysis
- There is only data available for one year of electricity generation of the systems studied and the outputs were projected for the remaining 24 years of useful life despite any possible upgrades or downgrades during this period;
- For the calculation of the emissions avoided by the installation of the systems, it was considered that the emission factor of the matrix remains constant and equal to 2020 levels;
- Future work, if hourly PV generation data are available, could perform a comparative analysis with hourly data from NIS emission or marginal factors.
Institutional Review Board Statement
Informed Consent Statement
Data Availability Statement
Conflicts of Interest
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|Maximum||Area (Thousand. km2)|
|City and state||Assú/RN||Ubajara/CE||Jaraguá do Sul/SC||Rio Verde/GO||Campo Novo do Parecis/MT||São José do Mipibu/RN||Jaraguá do Sul/SC||Cacique Doble/RS||Itajaí/SC||Campo Mourão/PR|
|Annual irradiation (kWh/m2.year)||2154||2026||1469||1998||1952||2141||1469||1766||1586||1871|
|Annual electricity generation|
|Annual Total (MWh)||173.8||67.5||75.3||82.4||161.7||106.4||71.3||55.2||98.8||59.0|
|Annual Yield (kWh/kWp)||1609||1312||977||1268||1156||1487||1015||1061||1280||1135|
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Lima, G.C.d.; Toledo, A.L.L.; Bourikas, L. The Role of National Energy Policies and Life Cycle Emissions of PV Systems in Reducing Global Net Emissions of Greenhouse Gases. Energies 2021, 14, 961. https://doi.org/10.3390/en14040961
Lima GCd, Toledo ALL, Bourikas L. The Role of National Energy Policies and Life Cycle Emissions of PV Systems in Reducing Global Net Emissions of Greenhouse Gases. Energies. 2021; 14(4):961. https://doi.org/10.3390/en14040961Chicago/Turabian Style
Lima, Gabriel Constantino de, Andre Luiz Lopes Toledo, and Leonidas Bourikas. 2021. "The Role of National Energy Policies and Life Cycle Emissions of PV Systems in Reducing Global Net Emissions of Greenhouse Gases" Energies 14, no. 4: 961. https://doi.org/10.3390/en14040961