Techno-economic and life cycle assessment of agrivoltaic system (AVS) designs.

Land use competition between agricultural activities and ground-mounted solar photovoltaic (PV) deployment has increased worldwide attention to hybrid agriculture, and PV systems known as agrivoltaic systems (AVS) in efforts to increase the efficiency of energy and food production and minimize the land use competition. However, little is known about AVS's economic feasibility and environmental tradeoffs. Here we aim to evaluate the techno-economic and environmental impacts of four AVS configurations (full density, half density, mono-axial tracking, and bi-axial tracking) and compare their performance against PV-only systems. We used the life cycle revenue generated from a hectare of land area ($/ha) as a functional unit of our analysis. We found that all AVS configurations outperformed PV-only systems in the economic feasibility assessment, where bi-axial tracking was the best-performing AVS. Further, we developed a case scenario for agricultural farmers to determine the minimum selling price of electricity required for AVS to compete with the economic performance of crop-only farms. We found that the AVS designs require additional incentives (2¢ - 6¢ per kWh of electricity generation) to be as competitive as the crop-only farms. The life cycle environmental assessment demonstrated that the AVS has better environmental performance than PV-only systems, with ∼15-55 % less environmental impacts per functional unit. On average, electricity generation accounts for ∼80 % of AVS environmental impacts, while food production and water demand account for ∼20 %. Additionally, a sensitivity analysis conducted on various uncertain parameters, such as crop yield, water demand, electricity selling price, crop selling prices, discount, and inflation rates, while varying these parameters across broader ranges, indicates that AVS designs become a more economically and environmentally sustainable alternative over PV-only systems in the majority (>66 %) of the data analyzed.

Social Acceptance of Greywater Reuse in Rural Areas.

Like many countries, Palestine suffers from water scarcity. Here, treated greywater is considered an essential nonconventional water resource. We aim to identify some wastewater reuse and disposal practices in rural areas and assess the acceptance level of different reuses of greywater. We conducted a survey analysis in four villages with a strong agricultural activity of the western Bethlehem Governorate. The level of acceptance of greywater reuse was generally independent of demographic variables like family size, income, or water bill, with a few exceptions regarding gender, age, and level of education. Centralized treatment was more valued than treatment at home, which presented similar acceptance levels than no treatment and might indicate a lack of trust in this alternative. The only reuse alternative trusted across treatments was bush irrigation (3.53-3.86 on a five-point Likert scale), but other options without clear, direct human contact like crop irrigation (3.14-3.62), stone cutting (3.19-3.36), and construction (3.12-3.42) also received considerable support. Reused perceived as having direct contact with humans was rejected, as it was the flushing of public toilets (2.59-2.7), aquaculture (1.98-2.37), olive pressing (1.85-1.94), and drinking (1.62-1.72). Relatively new reuse, car washing (2.95-3.17), was somewhere in between, partially because of its novelty. To increase this and other reuses, we strongly encourage local authorities to inform the population about the potentialities of greywater reuse.

Environmental impacts of recycling crystalline silicon (c-SI) and cadmium telluride (CDTE) solar panels.

There has been a substantial growth in the deployment of solar photovoltaic (PV) panels in the past couple decades. Solar PVs have a life span of about 25 years and much of the deployed PVs will soon reach their end of life (EoL). It is now timely to plan for the EoL of PVs to recover valuable materials and recycle PV modules sustainably. The goal of this study was to analyze the environmental impacts of different recycling methods for crystalline silicon (c-Si) and CdTe panels. A life cycle assessment (LCA) was performed for delamination and material separation phases of recycling solar panels. The LCA results showed that the recycling of c-Si and CdTe PVs contribute 13-25% and 3-4%, respectively to the entire PV lifecycle impacts. Also, for both c-Si and CdTe PVs, the thermal-based recycling methods resulted in lower environmental impacts than chemical and mechanical methods, except for pyrolysis. Nitric acid dissolution used for c-Si PV recycling had the highest impacts among all methods since the material consumption for this method has not been optimized for industrial use. Results from this study suggested that current techniques used in recycling of PVs, produce higher impacts than extraction of Al, Si and glass for c-Si and extraction of glass for CdTe. Lastly, this study identified which materials to prioritize for highest economic and environmentals benefits from recycling. These will be Ag, Al, Si, and glass in c-Si modules, and Te, Cu, and glass in CdTe modules.

Ecological network analysis of growing tomatoes in an urban rooftop greenhouse.

Urban agriculture has emerged as an alternative to conventional rural agriculture seeking to foster a sustainable circular economy in cities. When considering the feasibility of urban agriculture and planning for the future of food production and energy, it is important to understand the relationships between energy flows throughout the system, identify their strengths and weaknesses, and make suggestions to optimize the system. To address this need, we analyzed the energy flows for growing tomatoes at a rooftop greenhouse (RTG). We used life cycle assessment (LCA) to identify the flows within the supply chain. We further analyzed these flows using ecological network analysis (ENA), which allowed a comparison of the industrial system to natural systems. Going beyond LCA, ENA also allowed us to focus more on the relationships between components. Similar to existing ENA studies on urban metabolism, our results showed that the RTG does not mimic the perfect pyramidal structure found in natural ecosystems due to the system's dependency on fossil fuels throughout the supply chain and each industry's significant impact on wasted energy. However, it was discovered that the RTG has strong foundational relationships in its industries, demonstrating overall positive utility; this foundation can be improved by using more renewable energy and increasing the recycling rates throughout the supply chain, which will in turn improve the hierarchy of energy flows and overall energy consumption performance of the system.

Diversity analysis of water sources, uses, and flows from source to use in the USA.

Diversifying a system can reduce risk from- and increase resilience to perturbation. For this reason, the concept of diversity has been used in many different fields but its use in analyzing engineering infrastructure has been limited. In particular, the diversity of water sources and uses and the diversity of how sources are connected to uses (flow) have never been analyzed. In addition, the relationships between diversity and economic efficiency of water systems remain uncertain. In this study, we addressed these topics by conceptualizing and quantifying water source, use, and flow diversity in the USA. Water source and water use data were collected from the US Geological Survey for 2000, 2005, and 2010. Diversity was calculated with the Shannon Weaver Index. The overall mean water use diversity by state was 0.79 ±â€¯0.31 (N = 150) and increased from 0.63 ±â€¯0.31 in 2000 to 0.89 ±â€¯0.28 by 2010, reflecting overall decreases in high-use categories, like thermonuclear power, and relative increases in already low domestic use. In contrast, source diversity showed no change over time, with an overall state mean of 0.82 ±â€¯0.28 (N = 150) but varying between states largely due to differences in geographic and climatic factors influencing regional water sources. Water flow diversity also showed no change over time, averaging 1.00 ±â€¯0.43 (N = 150), higher than both source and use diversity. The mean water use efficiency for all states over the study period was 52 ±â€¯60 $/m3 of water and was positively and strongly related to both source and use diversity. Thus, the USA water system diversity is sensitive to factors logically expected to influence both source and use, and directly affects water use efficiency.

Management of rainwater harvesting and its impact on the health of people in the Middle East: case study from Yatta town, Palestine.

Water-related diseases are a primary problem in Palestine where many residents revert to harvested rainwater as their primary water source due to water shortages within the area. From an environmental engineering perspective, it is already well known that certain situations (e.g., cross contamination) reduce drinking water quality and ultimately cause diseases in a population. In this study, we investigated the social practices and situations that may lead to lower disease occurrence. Towards this goal, we surveyed 382 residents in Yatta to collect data on the water-related diseases that they experienced and the specific situations that might affect the disease occurrences such as the residents' practices (i) for maintaining a high quality of cistern water, (ii) for maintaining the environment around the cistern, and (iii) for managing the wastewater. In addition, we measured the physicochemical and microbiological parameters in cisterns to support the qualitative survey data. The measured parameters, including turbidity, salinity, free available chlorine, total Coliforms, and fecal Coliforms, were above Palestinian Standard Institution (PSI) and World Health Organization (WHO) guideline levels, suggesting a potential infectious hazard. The poor quality of the water was also observed by residents based on change in taste and by visually noting floating impurities, turbidity, and green coloration. Survey results showed that observations of the poor quality in cisterns and surrounding environment had statistically significant correlation with most of the water-related diseases. Additionally, frequently emptying the septic tank contributes to improving the observed water qualities. Therefore, residents should be encouraged to continue to observe the water quality in the cistern, improve the surrounding environment of cistern, and empty their septic tank frequently, to keep the water diseases away from their households.

Environmental Impacts from Photovoltaic Solar Cells Made with Single Walled Carbon Nanotubes.

An ex-ante life cycle inventory was developed for single walled carbon nanotube (SWCNT) PV cells, including a laboratory-made 1% efficient device and an aspirational 28% efficient four-cell tandem device. The environmental impact of unit energy generation from the mono-Si PV technology was used as a reference point. Compared to monocrystalline Si (mono-Si), the environmental impacts from 1% SWCNT was ∼18 times higher due mainly to the short lifetime of three years. However, even with the same short lifetime, the 28% cell had lower environmental impacts than mono-Si. The effects of lifetime and efficiency on the environmental impacts were further examined. This analysis showed that if the SWCNT device efficiency had the same value as the best efficiency of the material under comparison, to match the total normalized impacts of the mono- and poly-Si, CIGS, CdTe, and a-Si devices, the SWCNT devices would need a lifetime of 2.8, 3.5, 5.3, 5.1, and 10.8 years, respectively. It was also found that if the SWCNT PV has an efficiency of 4.5% or higher, its energy payback time would be lower than other existing and emerging PV technologies. The major impacts of SWCNT PV came from the cell's materials synthesis.