Wednesday, November 11, 2019
Pratik Raj Khadka

In 2017, cumulative solar PV capacity reached almost 398 GW and generated over 460 Terra Watt hour, representing around 2% of global power output. Utility-scale projects account for over 60% of total PV installed capacity, with the rest in distributed applications (residential, commercial and off-grid). Over the next five years, solar PV is expected to lead renewable electricity capacity growth, expanding by almost 580 GW. In Nepal as well, solar PV technology is set to rise to the top renewable energy source, after hydropower, and contribute to the nation’s energy mix scenario. In 2019, Nepal’s Department of Electricity Development approved survey licenses for 21 locations to prepare for the possible installation of 56 solar plants, which could have a combined solar capacity of 317.14 MW, with the largest planned solar energy project of 120MW in Dhalkebar, Mahottari. With increase in solar PV installations worldwide, the energy payback of these systems as a whole is an important element that we might have been missing out. With the global trend, increase in development of solar PV systems in our country and alarming issues of environmental impacts worldwide, it is a necessity that we become cautious of the systems we build and try to minimize its impact on the environment.

LCA (Life Cycle Assessment) is an important tool that can be used in PV systems’ design to optimize its cleanliness. It is an approach to environmental management system involving the quantitative evaluation of a product’s overall environmental impact. Only after observation of LCA results of different components, we can quantitatively determine the overall system’s CO2 emission and energy payback, and hence the cleanliness factor. The ability of LCA to quantitatively characterize the system’s cleanliness can be utilized to measure the relation of system we build with the environment. It offers an important advantage in system analysis by quantitative measurement of otherwise qualitative factor: relation with the environment. It can be incorporated into system design procedure so as to ensure carbon emission during the elements’ manufacturing is overcome as soon as possible. This will allow the system to be more carbon negative in its overall life cycle, in comparison to the system built without considering the emissions during its manufacture.

For building a carbon-aware system, the total system should be divided into the possible elements that can build its overall size. All the variations that can suffice the technical and financial requirements should be listed. Then, the CO2 emissions and energy requirements during all of its elements manufacture shall be taken out. This can be done by using software like SimaPro, Gabi, OpenLCA, etc. The energy payback shall also be calculated considering the overall system output simulations. Finally, after careful analysis, the system components are to be selected so that the emission and energy requirement of the overall system is minimum.

For an example, LCA result shows that for PV modules of 235-460 Wp capacity, the least energy required is for 235-260 Wp followed by 320-350 Wp and 435-460 Wp. Similar is the CO2 emission characteristics.

However, though the individual module result suggests the use of 245-260Wp modules, the result for different system sizes can be obtained differently. Therefore, it is important to calculate the LCA considering all the components of the overall system.

For instance, considering 1MW system and calculating the number of PV modules of different capacity required in the system, following results can be obtained.

Though minimum CO2 emission and Energy requirements were obtained for PV module of range 245-260 Wp , considering 1MW system, the least CO2 emission and Energy requirement is now obtained for modules of range 320-350 Wp. Therefore, the emission and energy requirement characteristics can be different depending on the number and size of components used in the system. Thus, it is important to quantitatively view all the elements in the overall system and design in its basis.

Conclusively, for large size utility scale projects, when design decisions are taken considering only technical and financial factors, the overall objective of using solar resource: clean energy, is pushed further. However, when the LCA results are considered, the overall system can be designed at the meeting point of financial, technical and environmental constraints. It helps reach the energy payback period faster, thus adding to the cleanliness factor of overall PV system use. Therefore, in the recent years where questions about the environmental impacts of technology have grown stronger, LCA can be a useful tool to minimize the environmental effects of PV power systems without compromising on the output.

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