Presentation1.pptx
- 1. Floating photovoltaics could mitigate climate change impacts on water body temperature and stratification. By Soumyajeet Guha 1MV17EE076 Under guidance By Dr subha R associate professor Technical Seminar
- 2. Abstract Floating solar photovoltaics, or floatovoltaics (FPV), are a relatively new form of renewable energy, currently experiencing rapid growth in deployment. FPV decarbonizes the energy supply while reducing land-use pressures, offers higher electricity generating efficiencies compared to ground-based systems and reduces water body evaporation. However, the effects on lake temperature and stratification of FPV both sheltering the water’s surface from the wind and limiting the solar radiation reaching the water column are unresolved, despite temperature and stratification being key drivers of the ecosystem response to FPV deployment. These unresolved impacts present a barrier to further deployment, with water body managers concerned of any deleterious effects. To overcome this knowledge gap, here the effects of FPV-induced changes in wind speed and solar radiation on lake thermal structure were modelled utilizing the one-dimensional process- based MyLake model. To resolve the effect of FPV arrays of different sizes and designs, observed wind speed and solar radiation were scaled using a factorial approach from 0% to 100% in 1% intervals. The simulations returned a highly non-linear response, dependent on system design and coverage. The responses could be either positive or negative, and were often highly variable, although, most commonly, water temperatures reduce, stratification shortens and mixed depths shallow. Modifications to the thermal dynamics of the water body may subsequently drastically alter biogeochemical processes, with fundamental implications for ecosystem service provision and water treatment costs. The extreme nature of response for particular wind speed and solar radiation combinations results in impacts that could be comparable to, or more significant than, climate change. As such, depending on how they are used, FPV have the potential to mitigate some of the impacts of climate change on water bodies and could be a useful tool for water body managers in dealing with changes to water quality, or, conversely, they could induce deleterious impacts on standing water ecosystems. These simulations provide a starting point to inform the design of future systems that maximize ecosystem service and environmental co-benefits from this growing water body change of use.
- 3. Introduction Increased energy demands and the urgent need to decarbonise are prompting the rapid deployment of renewable energy technologies. One such technology, solar photovoltaics (PV), has experienced exponential growth over the past 25 years and accounted for 57% of newly installed renewable energy capacity in 2019 . While solar PV has traditionally been ground- or rooftop-mounted, water-deployed, floating solar photovoltaics (FPV), known colloquially as floatovoltaics, have emerged in recent years. Global cumulative FPV capacity more than trebled among the top 70 FPV systems from 2018 to 2019 with a forecasted annual average growth rate of 22%. FPV systems are typically comprised of five main components: a pontoon of floaters, a mooring system, PV modules, cabling, and connectors. The specific design of a system can be adapted to suit water body function and application through variations to floater material, PV module type, orientation, and surface coverage . However, each combination of components will have a unique impact on the atmospheric drivers of lake dynamics, potentially resulting in a large variation in lake function impacts between systems. Secondly, FPV has been shown to deliver enhanced performance over ground-based PV due to the cooling effect of the hosting water body. The cooling yield has been found to vary across climates, with heat loss dependent on wind speed and the openness of the floating structure Thirdly, and also dependent on system design, FPV has also been shown to reduce evaporative losses substantially, potentially providing vital water savings for drought-stricken areas. Furthermore, studies have shown that hydroelectric dams operating in conjunction with FPV can optimise energy efficiency and improve system reliability. Here we address this knowledge gap by applying simulations from a one-dimensional, process-based model and data from a test lake in North West England. We simulate water temperature, mixed depth and stratification timing to (1) determine the sensitivity of a lake’s thermal structure to FPV deployed at varying scale. We then (2) consider the potential ecosystem consequences and implications for lake management in a changing climate.
- 5. Literature survey 1. Prospects of floating photovoltaic technology and its implementation in Central and South Asian Countries Many regions around the globe, especially South Asia including Afghanistan and Pakistan and Central Asia, have extreme difficulties in accessing portable water and a stable energy supply. Some areas are covered with arid soil and salty water, while others have power transmission problems. Water evaporation from reservoirs is also another problem during high temperatures, thereby posing additional energy and water demands. This paper discusses the multiple prospects of floating photovoltaic technology in different regions of the world and highlights the importance of such technologies in already water-scarce regions like South Asia and Central Asia. This technology will prove to be highly feasible as it is an environment friendly and cost efficient and will help in reducing evaporation, achieving sustainable water supply and clean energy production and reducing greenhouse gas emissions. There is very minimal work done on floating solar technology; thus, there is immense need to explore and research on this technology on every level through information sharing. 2. Integrating environmental understanding into freshwater floatovoltaic deployment using an effects hierarchy and decision trees In an era of looming land scarcity and environmental degradation, the development of low carbon energy systems without adverse impacts on land and land- based resources is a global challenge. 'Floatovoltaic' energy systems—comprising floating photovoltaic (PV) panels over water—are an appealing source of low carbon energy as they spare land for other uses and attain greater electricity outputs compared to land-based systems. However, to date little is understood of the impacts of floatovoltaics on the hosting water body. Anticipating changes to water body processes, properties and services owing to floatovoltaic deployment represents a critical knowledge gap that may result in poor societal choices and water body governance. Here, we developed a theoretically-derived hierarchical effects framework for the assessment of floatovoltaic impacts on freshwater water bodies, emphasising ecological interactions. We describe how the presence of floatovoltaic systems may dramatically alter the air-water interface, with subsequent implications for surface meteorology, air-water fluxes and physical, chemical and biological properties of the recipient water body. We apply knowledge from this framework to delineate three response typologies—'magnitude', those for which the direction and magnitude of effect can be predicted; 'direction', those for which only the direction of effect can be predicted; and 'uncertain', those for which the response cannot be predicted—characterised by the relative importance of levels in the effects hierarchy. Illustrative decision trees are developed for an example water body response within each typology, specifically, evaporative water loss, cyanobacterial biomass, and phosphorus release from bed sediments, and implications for ecosystem services, including climate regulation, are discussed. Finally, the potential to use the new understanding of likely ecosystem perturbations to direct floatovoltaic design innovations and identify future research priorities is outlined, showcasing how inter-sectoral collaboration and environmental science can inform and optimise this low carbon, land-sparing renewable energy for ecosystem gains.
- 6. 3. Optimization and assessment of floating and floating-tracking PV systems integrated in on- and off-grid hybrid energy systems Considering the targets of Thailand in terms of renewable energy exploitation and decarbonization of the shrimp farming sector, this work evaluates several scenarios for optimal integration of hybrid renewable energy systems into a representative shrimp farm. In particular, floating and floating-tracking PV systems are considered as alternatives for the exploitation of solar energy to meet the shrimp farm electricity demand. By developing a dynamic techno-economic simulation and optimization model, the following renewable energy systems have been evaluated: PV and wind based hybrid energy systems, off-grid and on-grid PV based hybrid energy systems, ground mounted and floating PV based hybrid energy systems, and floating and floating-tracking PV based hybrid energy systems. From a water-energy nexus viewpoint, floating PV systems have shown significant impacts on the reduction of evaporation losses, even if the energy savings for water pumping are moderate due to the low hydraulic head. Nevertheless, the study on the synergies between water for food and power production has highlighted that the integration of floating PV represents a key solution for reducing the environmental impacts of shrimp farming. For the selected location, the results have shown that PV systems represent the best renewable solution to be integrated into a hybrid energy system due to the abundance of solar energy resources as compared to the moderate wind resources. The integration of PV systems in off-grid configurations allows to reach high renewable reliabilities up to 40% by reducing the levelized cost of electricity. Higher renewable reliabilities can only be achieved by integrating energy storage solutions but leading to higher levelized cost of electricity. Although the floating-tracking PV systems show higher investment costs as compared to the reference floating PV systems, both solutions show similar competiveness for reliabilities up to 45% due to the higher electricity production of the floating-tracking PV systems. The higher electricity production from the floating- tracking PV systems leads to a better competitiveness for reliabilities higher than 90% due to lower capacity requirements for the storage systems. 4. The cooling effect of floating PV in two different climate zones: A comparison of field test data from the Netherlands and Singapore An enormous area could potentially be unlocked, when more photovoltaic (PV) systems would be deployed on water bodies. Especially in densely populated areas this opens a pathway for PV to contribute to the energy transition in a large scale. Another potential benefit of floating PV (FPV) systems is that they can outperform conventional PV systems in terms of energy yield due to the cooling effect from the water. However, there is very little field data available to quantify the cooling effect and compare it across different climatic conditions. The research presented here has thoroughly studied this effect and translated it into an estimated specific yield comparison between conventional and floating PV systems. The study is based on field tests that are located in two different climate zones: a temperate maritime climate (the Netherlands) and a tropical climate (Singapore). Irradiance weighted average temperatures of FPV systems have been compared with a land-based system in Netherlands and a rooftop system in Singapore as references. The best performing FPV systems showed 3.2 °C (Netherlands) and 14.5 °C (Singapore) lower weighted temperatures compared to their benchmarks. Open system designs, where the PV panels of the floating system are widely exposed to the water surface, lead to an increase in the heat loss coefficient of floating PV panels (a measure for the cooling effect) of up to 22 W/m2K compared to reference PV systems. Annual specific yields of the PV systems were estimated by the measured irradiance-weighted temperature difference and by a PVsyst model with inputs of the heat loss coefficients. Based on these calculations, we observe that the gain in energy yield from the cooling effect of FPV systems compared to the reference PV systems is up to 3% in the Netherlands and up to 6% in Singapore.
- 7. 5. Floating photovoltaic plants: Ecological impacts versus hydropower operation flexibility Floating photovoltaic power plants are a quickly growing technology in which the solar modules float on water bodies instead of being mounted on the ground. This provides an advantage, especially in regions with limited space. Floating modules have other benefits when compared to conventional solar power plants, such as reducing the evaporation losses of the water body and operating at a higher efficiency because the water reduces the temperature (of the modules). So far, the literature has focused on these aspects as well as the optimal design of such solar power plants. This study contributes to the body of knowledge by i) assessing the impact of floating solar photovoltaic modules on the water quality of a hydropower reservoir, more specifically on the development of algal blooms, and by ii) studying the impact that these modules have on the hydropower production. For the first part, a three-dimensional numerical-hydrodynamic water-quality model is used. The current case (without solar modules) is compared to scenarios in which the solar modules increasingly cover the lake, thus reducing the incident sunlight from 0% to finally 100%. The focus is on microalgal growth by monitoring total chlorophyll-a as a proxy for biomass. For the second part, as the massive installation of solar modules on a reservoir may constrain the minimum water level (to avoid the stranding of the structures), the impact on hydropower revenues is examined. Here, a tool for optimal hydropower scheduling is employed, considering both different water and power price scenarios. The Rapel reservoir in central Chile serves as a case study. The response of the system strongly depends on the percentage that the modules cover the lake: for fractions below 40%, the modules have little or no effect on both microalgal growth and hydropower revenue. For moderate covers (40–60%), algal blooms are avoided because of the reduction of light in the reservoir (which controls algal growth), without major economic hydropower losses. Finally, a large solar module cover can eradicate algal blooms entirely (which might have other impacts on the ecosystem health) and results in severe economic hydropower losses. Altogether, an optimum range of solar module covers is identified, presenting a convenient trade-off between ecology health and costs. However, a massive deployment of these floating modules may affect the development of touristic activities in the reservoir, which should be examined more closely. In general, the findings herein are relevant for decision-makers from both the energy sector and water management.
- 8. Methods 1. Site description 2. Modelling methodology 3. Input data 4. Thermal structure simulations 5. Model calibration 6. Data analysis
- 9. Methods (explained) • Site description The impacts of FPV on lake thermal structure were modelled for the south basin of Windermere, a typical monomictic, mesotrophic, deep and temperate lake in the Lake District, Northwest England. The south basin of Windermere is long and narrow in shape – with a maximum depth of 42 m, a mean depth of 16.8 m and a surface area of approximately 6.7 km2. As one of the most comprehensively studied lake systems in the world (Rooney and Jones, 2010), the wealth of understanding and availability of high-resolution meteorological and in-lake water temperature data make Windermere an excellent test system for this study. • Modelling methodology To resolve the effects of FPV on lake physical properties, we simulated lake variables by adapting an existing MATLAB model. MyLake is a one-dimensional process-based model, used to simulate the daily vertical distributions of water body temperature, evaporation and instances of ice cover accurately. In brief, the model initially computes the temperature distribution of the lake for the 24-hour time-step, taking into account diffusive mixing processes and local heat fluxes. A sequential process then accounts for convective mixing, wind-induced mixing, the water–ice heat flux and the effect of river inflow. The model has been successfully applied to various projects as a standalone simulation tool assessing lake thermodynamics and ice regime. Predominantly, model parameters were kept as per the user manual, with minor adjustments was made during calibration. • Model calibration The model was calibrated for a one-year period against observed water body temperatures. Standard calibration procedures were undertaken following. Briefly, calibration of the scaling of forcing variables was guided by Monte Carlo sampling of uniform parameter distributions. The Nash-Sutcliffe model efficiency coefficient (NSE) and the Root Mean Square Error (RMSE) for metalimnion top, Schmidt stability and volume average temperature were used to identify the best simulation. Slight modifications to scale the original driving data were required to achieve the optimum parameter values for the calibration year; these were + 2% for wind speed and + 13% for solar radiation.
- 10. • Thermal structure simulations The effect on wind speed and solar radiation (forcing variables) for a given percentage coverage of FPV is unknown and likely to vary substantially depending on the design of the deployment. While reductions to both forcing variables are likely, the relative proportions of these reductions remain to be determined. Here, the forcing variables were altered using a factorial design, simulating reductions at 1% intervals from 0% to 100%. A factorial design allowed the identification of non-linear changes and thresholds in the output variables; this was of particular importance given the range of FPV designs and surface coverages that exist between different systems. Considering reductions to the forcing variables as a whole lake average, not just in the footprint of the array, maximises transferability between systems with different FPV designs. • Data analysis Mixed layer depth and Schmidt stability were subsequently estimated from modelled water temperatures using Lake Analyze, a freely available physical limnological tool. Mixed layer depth was estimated using the metalimnion extent function, an algorithm that defines the approximate depth of the base of the mixed layer using a density gradient threshold of 0.1. Mean mixed layer depth for the stratified period of each scenario, along with annual mean mixed layer depth were calculated. The onset of thermal stratification was defined from the depth-resolved temperature simulations as the time when the temperature differential between the surface (0 m) and the bottom (42 m) of the lake exceeded 1 ◦C . Alterations to stratification duration were assessed by calculating the longest stratified period, defined here as the greatest number of consecutive days of stratification across the simulated period. This was then compared to the stratified period of the water body without FPV , permitting the calculation of a gain or loss in stratified days. Stratification onset and overturn days were derived from these data, with onset being the first day and overturn being the final day of the longest stratified period. Three simulation scenarios were considered in further detail. The first being an equal (1:1) reduction to each forcing variable. Given the relative proportions of reductions to forcing variables remain unknown and are likely to vary substantially depending on FPV design, two scenarios with scaled forcing variables were simulated. A ‘wind dominant’ scenario where the wind speed reduction scales as 80% of the solar radiation reduction and a ‘solar dominant’ scenario where the reduction to solar radiation scales as 80% of the wind speed reduction.
- 11. Result Modelled reductions to the forcing variables generally reduced annual mean surface water temperatures (Fig. 1a). Surface water temperature reductions were non-linear, with small reductions to the forcing variables having a negligible effect and larger reductions having an increasingly greater effect (Table S2). Increases in surface water temperatures occurred only in scenarios when wind speed was reduced considerably more than solar radiation. Similarly, annual mean bottom temperatures generally decreased, albeit less than surface temperatures (Fig. 1b). As could be expected, given the reductions in surface and bottom water temperatures, mean annual volume average temperature was reduced for all scenarios (Figure S2). In 2009 there was no ice-cover on the lake and, indeed, ice cover on Windermere is very rare. Nevertheless, simulations with more than a 90% reduction to the forcing variables resulted in sufficiently cold surface water temperatures for ice to form (Figure S3). Ice cover duration increased as the forcing variables were further reduced above 90%. For example, a 90% 1:1 reduction resulted in 22 days of ice cover, while a 98% reduction resulted in 43 days of ice cover. Each reduction to the forcing variables decreased total annual evaporation in comparison to the baseline (Fig. 2). At a 74% 1:1 forcing variable reduction, a threshold was crossed where dew formed on the lake surface, providing an annual net gain in water. Wind dominant scenarios (solar reduced by more than wind) saw greater reductions in evaporation than in solar dominant scenarios (Table S2).
- 14. Conclusion By simulating the response of a lake to FPV deployed at varying extent, this study has demonstrated patterns of increased impact with increased perturbation, ranging from negligible to very large. Based on these findings, future FPV designs should consider the following to maximise ecosystem co-benefits and limit potential harm: • Reductions in wind speed and solar radiation as an average across the lake cause a non-linear, complex response with the direction of these effects dependent on FPV array design, including coverage density • Low FPV surface coverages had a negligible effect on the thermal structure of the test system, while high coverages were a major disruptor of the archetypal thermal structure • FPV deployments may have impacts that are as, or more, influential than catastrophic climate change, therefore providing an opportunity to manage the effects of climate change on lake systems actively • Appropriate design and deployment of FPV will be required to mitigate the likelihood of hypolimnetic anoxia and to optimise changes in the composition of phytoplankton communities as FPV modifies lake thermal structure and light climate
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- 16. Thank you