Solar Energy

DLR testing the use of molten salt in a solar power plant in Portugal

Published

3 years ago

October 26, 2021

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DLR testing the use of molten salt in a solar power plant in Portugal

Engineers from the German Aerospace Center
have taken an important step towards using molten salt as a heat transfer medium in parabolic trough solar power plants. Together with the University of Evora and industrial partners, a team from the DLR Institute of Solar Research has for the first time begun operating the solar field of the Evora parabolic trough test plant in Portugal with molten salt.

This innovative technology is helping to further reduce the costs of operating solar thermal power plants. With their integrated storage systems, solar thermal power plants are the only technology able to generate large amounts of power from solar energy around the clock.

Current state-of-the-art commercial parabolic trough power plants use a special thermal oil as the heat transfer medium. The oil absorbs concentrated solar radiation collected using mirrors, converts it into heat and transfers it via pipelines to a heat storage unit or a steam turbine to generate electricity. The heat storage tank, filled with molten salt, can hold the thermal energy at temperatures of up to 560 degrees Celsius for a period of 12 hours and release it again when the demand for electricity increases.

The power plant needs heat exchangers to transfer the heat from the oil to the salt in the storage tank, but some energy is always lost during this transfer before it can later be converted into electricity. The maximum possible operating temperature of the oil used is approximately 400 degrees Celsius, which limits the efficiency of the energy conversion. Researchers and industry are therefore looking for ways to further increase the temperatures in solar power plants in order to lower the costs of electricity generation.

One promising way to raise temperatures in parabolic trough power plants is to use molten salt not only as a heat storage medium, but also as the heat transfer medium in the collector field. Depending on the composition of the molten salt, it can withstand significantly higher temperatures than thermal oil – up to 565 degrees Celsius. Another advantage is that the storage tanks can be filled directly with molten salt from the solar field – eliminating the need for a heat exchanger.

In order to demonstrate this approach, the DLR Institute of Solar Research, together with the University of Evora and companies from Germany and Spain, has been building a solar parabolic trough test facility using molten salt as its heat transfer medium. The work started in 2016 and has taken place as part of the High Performance Solar 2 (HPS2) research project, which is funded by the German Federal Ministry for Economic Affairs and Energy (BMWi). The aim of the project is to demonstrate that parabolic trough power plants can be operated safely and economically with molten.

A technical challenge when using molten salt as a heat transfer fluid is that heating of all the pipelines is necessary. To prevent the molten salt from solidifying as the plant is filled, electrical trace heating must be used to preheat all salt-carrying components.

Successful initial filling and test operation of the system at 300 degrees Celsius

The collector modules of the HelioTrough 2.0 generator from project partner TSK Flagsol, which are now filled with molten salt and connected to each other, provide a total thermal output of up to 3.5 megawatts across a total length of 684 metres.

Currently, the plant operates with a ternary salt mixture from the project partner Yara, which has the advantage of a lower melting temperature compared to a binary salt solar salt mixture and can absorb heat up to a temperature of approximately 500 degrees Celsius. In addition to its use in solar thermal power plants for electricity generation, this salt mixture is also of interest for solar process heat supply systems.

Starting from an initial temperature of 300 degrees Celsius, the engineers want to gradually increase the operating temperature up to 500 degrees Celsius. In the coming weeks, the other components of the salt circuit will be brought into operation in Evora. In addition to the two-tank storage system, this includes the steam generator and the measurement equipment.

“We are very satisfied with the way the first filling went. Our next goals are to gain operating experience, fill all further components with molten salt step by step and test regular operations and also critical operating scenarios,” says Jana Stengler, head of the Fluid Systems Group at the DLR Institute of Solar Research, on the results of the initial testing.

The HPS2 plant is designed to also be operated with solar salt, a mixture of potassium nitrate and sodium nitrate, to achieve even higher temperatures of up to 565 degrees Celsius. Higher temperatures in the solar field allow for higher efficiencies in the conversion of solar energy into heat and heat into electricity, which lowers the cost of generating electricity.

“Power plants using the technology from HPS2 can be built more easily and operate more efficiently. This reduces electricity production costs by up to 10 percent,” says Mark Schmitz from the project partner TSK Flagsol, underlining the importance of the project for future solar thermal power generation. “That is an enormous step for a single technical change. At the same time, it makes longer storage durations of 12 full-load hours and more economically achievable.”

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Solar Energy

Shedding light on solar farm impacts in deserts through energy meteorology

Published

17 hours ago

January 4, 2025

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Shedding light on solar farm impacts in deserts through energy meteorology

by Simon Mansfield

Sydney, Australia (SPX) Jan 06, 2025

Utility-scale solar farms, often deployed in desert habitats, are a cost-effective way to generate power compared to rooftop solar panels. However, these large installations interact with sensitive desert ecosystems, prompting researchers to explore their environmental effects through the growing field of “energy meteorology.”

A study published in Advances in Atmospheric Sciences by Professor Carlos Coimbra of the University of California San Diego investigates the thermal interactions between solar farms and their surrounding environments. This work examines how solar farm operations influence local temperature and humidity and how these environmental factors affect the farms themselves.

Energy meteorology traditionally focuses on the impact of weather on power systems. Professor Coimbra’s research broadens this scope by assessing the reciprocal effects of solar plants on local climates. By calculating thermal balances specific to solar panels’ material properties, the study derives relationships between complex variables, such as convective heat transfer coefficients and radiative fluxes. These calculations enhance understanding of how solar farms modify their environments and how these modifications can be accurately measured or modeled.

Additionally, the study introduces a novel method for classifying regional microclimates based on the optical depth of cloudy atmospheres. This classification can inform solar farm design and operation, complementing conventional cloudiness and radiation indices used for resource planning.

Professor Coimbra highlights the importance of rigorous scientific inquiry into solar energy’s environmental effects. “It behooves us in the solar energy research community to answer concerns and criticisms that the solar power industry encounters with the best possible science,” he states. While the overall thermal impact of solar farms may be negligible or even positive, the research community must address discrepancies in current findings and focus on fundamental thermal processes.

This research aims to inspire both solar engineers and energy meteorologists to delve deeper into the environmental dynamics of utility-scale solar installations. As Professor Coimbra emphasizes, the study serves as a foundational guide for exploring energy meteorology’s potential to improve solar farm sustainability and environmental compatibility.

Research Report:Energy Meteorology for the Evaluation of Solar Farm Thermal Impacts on Desert Habitats

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Solar Energy

University of Maryland to develop renewable energy systems for ocean monitoring systems

Published

2 days ago

January 3, 2025

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University of Maryland to develop renewable energy systems for ocean monitoring systems

by Clarence Oxford

Los Angeles CA (SPX) Jan 03, 2025

University of Maryland researcher Stephanie Lansing has been awarded $7.8 million from the Defense Advanced Research Projects Agency (DARPA) to spearhead the development of a biologically powered energy system aimed at transforming power generation for ocean monitoring devices worldwide.

Current ocean monitoring devices, essential for understanding marine ecosystems, tracking climate change, and maintaining national security, rely heavily on lithium-ion batteries or extensive underwater cables for power. Lansing’s groundbreaking project aims to replace these conventional systems by harnessing microorganisms and specialized bacteria to fuel a marine microbial energy source capable of delivering a steady 10-watt output for over a year.

“This unique collaboration of interdisciplinary experts will produce a bioinspired system that has game-changing potential to provide direct electric power to improve sensing capabilities while protecting and limiting the impact to the environment through use of this unique bioenergy system,” explained Lansing, a professor in UMD’s Department of Environmental Science and Technology.

The system, known as the Persistent Oceanographic Device Power (PODPower), employs a sophisticated mechanism that gathers ocean microbes and organic material into a specialized fermentation chamber. Bacteria in this chamber pre-process the material into an efficient “fuel” for other bacteria colonizing the electrodes of the microbial fuel cell, generating usable electricity.

Key design features include a fish-gill-inspired collection net, a corkscrew-shaped auger for organic matter transport, and a dual cathode system to enhance energy output. These innovations are expected to overcome limitations of earlier microbial fuel cell technologies.

Funded under DARPA’s BioLogical Undersea Energy (BLUE) program, PODPower aligns with initiatives to exploit ocean biomass for sustainable power solutions. Beyond the $7.8 million allocated for Phase 1 development through 2026, an additional $3.4 million may be granted for Phase 2, aimed at generating 100 watts of power and deploying systems across multiple environments.

The project involves collaboration with experts from Battelle, George Washington University, Harvard University, UMD Baltimore County’s Institute of Marine and Environmental Technology (IMET), James Madison University, Johns Hopkins University, University of Delaware, and Yokogawa Corporation of America.

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Solar Energy

Unveiling the impact of climate-driven low solar and wind energy events in China

Published

2 days ago

January 3, 2025

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Unveiling the impact of climate-driven low solar and wind energy events in China

by Clarence Oxford

Los Angeles CA (SPX) Jan 03, 2025

A groundbreaking study spearheaded by Dr. Yue Qin and Dr. Tong Zhu from Peking University has offered critical insights into the spatiotemporal dynamics and underlying causes of compound low-solar-low-wind (LSLW) extremes in China. Through advanced climate modeling and diagnostic techniques, this research sheds light on a growing challenge for renewable energy systems.

“Our results suggest that under compound LSLW extremes, renewable energy generation could be significantly compromised,” explained Dr. Yue Qin. “Even more concerning, climate change could intensify the frequency of such events, escalating threats to China’s renewable energy supply and potentially hindering progress toward carbon neutrality.”

China’s ambitious target of carbon neutrality by 2060 hinges on expanding solar and wind energy, yet these renewable sources are inherently variable and sensitive to weather patterns. While extensive studies exist on individual renewable energy challenges, this study uniquely addresses the compounded effects of simultaneous low solar and wind energy availability, a critical but understudied issue.

The findings underscore a significant topographic influence on the occurrence of LSLW extremes, with a national average of 16.4 days annually. Particularly in eastern China, these events reduce renewable energy output by approximately 80% compared to typical conditions. Projections under various climate scenarios indicate a nationwide rise in the frequency of such events, with areas like the Tibetan Plateau and northwestern China predicted to experience substantial increases.

“In particular, a striking increase of compound LSLW extremes’ frequency occurs under SSP370 scenario with aerosol emissions increase due to the assumption of a lenient air quality policy,” said Licheng Wang, the study’s lead author. The study found that elevated aerosol levels play a major role by weakening wind speeds and reducing solar radiation.

The researchers also evaluated inter-grid electricity transmission as an adaptation strategy. Results show this approach could mitigate over 91% of the frequency and 59%-85% of the intensity of LSLW-induced energy failures. Xizang (Tibet) emerged as a key region for reducing LSLW-related renewable energy shortages across China. However, infrastructure constraints, including geographical and economic challenges, limit the development of high-voltage electricity transmission in this region. Enhancing renewable energy projects in Xizang could be vital for achieving China’s carbon neutrality goals.

Dr. Yue Qin emphasized the importance of informed planning: “By revealing the geospatial and temporal evolution of compound LSLW extremes and their underlying physical mechanisms under climate change, our study emphasizes that these events are not random but predictable. This underscores the importance of proactive preparation and mitigation to address this pressing challenge.”

Research Report:Unraveling climate change-induced compound low-solar-low-wind extremes in China