Heat engine captures energy as Earth cools at night – Physics World

Report on a Novel Heat Engine for Night-time Renewable Energy Generation

Introduction: Addressing Gaps in Clean Energy

Researchers at the University of California Davis have developed a novel heat engine capable of generating renewable energy during the night. This innovation, led by Tristan Deppe and Jeremy Munday, harnesses the temperature differential between the Earth’s surface and deep space. The technology presents a significant advancement toward achieving key Sustainable Development Goals (SDGs) by offering a solution to the intermittency of solar power, thereby reducing reliance on fossil fuels and expensive energy storage systems.

Alignment with Sustainable Development Goals (SDGs)

The development of this heat engine directly supports the global agenda for sustainable development by contributing to several critical SDGs.

• SDG 7: Affordable and Clean Energy: The primary contribution of this technology is providing a consistent and clean source of energy after sunset. By complementing solar power, it enhances the reliability of renewable energy grids and promotes energy access for all.
• SDG 13: Climate Action: By offering an alternative to fossil fuel-based power plants that often provide baseload power at night, the engine has the potential to significantly cut carbon emissions, directly contributing to climate change mitigation efforts.
• SDG 9: Industry, Innovation, and Infrastructure: This research exemplifies innovation in sustainable technology. Its successful implementation can lead to the development of new, resilient, and sustainable energy infrastructure.
• SDG 11: Sustainable Cities and Communities: The engine can be deployed as a decentralized power source, enhancing the energy security and sustainability of communities, potentially powering applications like air circulation in residential buildings.

Technological Framework and Operational Principles

Harnessing the Earth-Space Thermal Gradient

The engine operates on the fundamental principles of thermodynamics, utilizing two vast heat reservoirs to generate mechanical work.

1. Heat Source: The Earth’s surface, which absorbs solar energy during the day and maintains an average temperature of approximately 15° C.
2. Heat Sink: Deep space, which has a constant temperature of around -270° C.

The system functions by radiatively coupling one side of the engine to space. This is achieved by emitting thermal energy as infrared radiation within the “atmospheric transparency window,” a specific range of wavelengths that passes through the atmosphere with minimal absorption.

Prototype Design and Performance

The proof-of-concept was demonstrated using a modified Stirling engine. The key components and experimental results are outlined below.

• Hot End Assembly: An aluminum mount connected to the engine’s bottom plate was pressed into the soil to absorb ambient heat from the Earth.
• Cold End Assembly: A black-coated plate was attached to the top of the engine, designed to efficiently radiate infrared heat upwards towards space.
• Performance Metrics: In outdoor trials, the prototype successfully maintained a temperature difference greater than 10° C between its hot and cold ends.
• Power Output: The engine generated over 400 milliwatts (mW) of mechanical power per square metre throughout the night, sufficient to operate a small mechanical fan. The device was also configured to produce both mechanical and electrical power simultaneously.

Future Projections and Contribution to a Sustainable Future

Scaling for Global Impact

The initial demonstration is a promising step towards a commercially viable technology. The researchers project that with further improvements, the system could achieve a power output of up to 6 watts (W) per square metre under similar conditions. If deployed at scale, this heat engine could fundamentally alter the renewable energy landscape by mitigating one of the core challenges of solar power. Its widespread adoption would accelerate progress towards achieving SDG 7 and SDG 13 by providing a reliable, 24-hour, carbon-free energy solution, thus reducing the global carbon footprint and fostering a more sustainable and equitable energy future.

Analysis of Sustainable Development Goals in the Article

1. Which SDGs are addressed or connected to the issues highlighted in the article?

The article on the new heat engine addresses several interconnected Sustainable Development Goals (SDGs) by focusing on the development of a novel renewable energy technology.

• SDG 7: Affordable and Clean Energy

  This is the most prominent SDG addressed. The article introduces a new heat engine designed to be a “reliable source of renewable energy at night,” directly tackling the intermittency of solar power and reducing the need for “fossil fuel sources.” The entire focus is on generating clean energy from a naturally occurring temperature difference.

• SDG 9: Industry, Innovation, and Infrastructure

  The article highlights scientific research and technological innovation. The development of the prototype Stirling engine by researchers at the University of California Davis is a clear example of enhancing scientific research to create “clean and environmentally sound technologies.” The project represents an innovation aimed at upgrading energy infrastructure.

• SDG 13: Climate Action

  The technology described has direct implications for climate action. By providing a clean energy alternative to fossil fuels, especially during the night, the article explicitly states that the heat engine could help in “cutting carbon emissions.” This directly contributes to mitigating climate change.

2. What specific targets under those SDGs can be identified based on the article’s content?

Based on the article’s discussion of the new heat engine, several specific SDG targets can be identified:

1. Target 7.2: Increase the share of renewable energy

   By 2030, increase substantially the share of renewable energy in the global energy mix. The article directly supports this target by presenting a new technology that generates renewable energy. It addresses a key weakness of solar power—the “lack of power generation at night”—thereby helping to increase the overall reliability and potential share of renewables.

2. Target 7.a: Promote access to clean energy research and technology

   By 2030, enhance international cooperation to facilitate access to clean energy research and technology, including renewable energy, energy efficiency and advanced and cleaner fossil-fuel technology, and promote investment in energy infrastructure and clean energy technology. The research itself, conducted at a university and published in Science Advances, is an act of advancing and disseminating clean energy research. The development of the prototype is a step towards new clean energy technology.

3. Target 9.5: Enhance scientific research and upgrade technology

   Enhance scientific research, upgrade the technological capabilities of industrial sectors in all countries, in particular developing countries, including, by 2030, encouraging innovation. The work of Tristan Deppe and Jeremy Munday in creating and testing a new type of heat engine is a direct example of scientific research leading to technological innovation with practical applications.

4. Target 13.2: Integrate climate change measures into policies

   Integrate climate change measures into national policies, strategies and planning. While the article doesn’t discuss policy, it presents a technological solution that enables such integration. The engine’s potential for “cutting carbon emissions” makes it a tool that can be used to achieve climate goals outlined in national strategies.

3. Are there any indicators mentioned or implied in the article that can be used to measure progress towards the identified targets?

The article provides specific, quantifiable data and qualitative descriptions that can serve as indicators for measuring progress.

• Indicator for Target 7.2 (Renewable energy share)

  The article provides a direct measure of the technology’s energy generation capacity, which is a key component of this indicator. It states the prototype was able to extract “more than 400 mW per square metre of mechanical power throughout the night.” Furthermore, it provides a future projection, predicting that improvements could enable the system to “extract as much as 6 W per square metre.” These figures are concrete indicators of the technology’s potential contribution to the renewable energy mix.

• Indicator for Target 9.5 (Research and innovation)

  The existence of the research project and its publication in a scientific journal (Science Advances) serves as an indicator of research and development activity. The successful demonstration of the prototype, which was able to “run a mechanical fan” and “produce both mechanical and electrical power simultaneously,” is a qualitative indicator of successful innovation moving from concept to application.

• Indicator for Target 13.2 (Climate action)

  The primary implied indicator is the potential for greenhouse gas emission reductions. The article links the technology directly to this outcome by stating it could open “a new route to cutting carbon emissions.” While it does not quantify the potential reduction, it establishes a clear causal link: by reducing reliance on fossil fuels at night, the technology contributes to climate change mitigation.

4. Table of SDGs, Targets, and Indicators

Source: physicsworld.com