SEP Collaborative: Pathways to Scalable, Efficient and Sustainable Soil Borehole Thermal Energy Storage Systems

NSF可持续能源途径（SEP）项目隶属于NSF可持续发展科学、工程和教育（SEES）倡议，将支持科罗拉多大学博尔德分校的John McCartney教授及其同事和科罗拉多矿业学院的Ning Lu教授及其同事的研究项目。该项目的目标是了解土壤钻孔热能储存（SBTES）的基本多物理过程、工程挑战、环境影响和实施策略。非饱和土壤的热水力特性和相关的耦合热、水和蒸汽流动过程将被设计成一个热管，加强传热。这与传统的井眼或含水层热能储存系统完全不同，后者依赖于传导或水的提取/注入来将热量从地下传递到地下。本研究的目的是寻求能量注入SBTES系统的最佳可扩展效率，并随后提取直接用于建筑供暖或发电。为实现这一目标，具体任务包括：(1)建立现场规模的试验设施，以评估不同钻孔配置下的热注入和热回收效率；(2)评估密集仪器土壤槽内的水、蒸汽和热流耦合过程及其潜在的环境影响；(3)从不同的试验中表征非饱和土壤的非线性输运特性；(4)验证和建立可扩展的数值模型，以检验长期运行、效率和效率。(5)探索提高热交换效率的工程方法。另一项平行工作是通过评估政策和探索性SBTES站点的用户体验，评估住宅、社区和工业规模地下储能的实施策略。这些地点建立了能源回收的高效率，但尚未充分分析与不同政策战略有关的使用趋势、实施障碍或社会经济问题。初步估计表明，与其他储能解决方案相比，SBTES系统的资本成本较低，可以通过节约能源快速收回成本。由于SBTES是闭环系统，并且地下水流动不会显著影响渗透区的热迁移，因此预计其对环境的影响较小。该项目将有助于培养具有广泛技能的劳动力，这些技能可应用于新兴的可再生能源技术，包括水文学、土木工程、热力学、环境影响分析和能源政策。双方将在各自招收和留住来自不同背景学生的过往记录的基础上，结合学生交换和积极参与两所大学的任务，并将为有效培训确定轨道和既定课程。成功实施SBTES系统的社区将被用作案例历史，形成短期课程的基础，这些课程将由pi向社区和政策制定者提供，以确保更广泛地实施这项技术。SBTES系统预计将通过将可再生热源与可持续热能储存解决方案相结合，在减少住宅和商业建筑供暖所需的电力或天然气量方面发挥重要作用。通过考虑本研究中对传热的改进，可以提高能量回收的效率，为社区提供可扩展的、可持续的直接利用供暖。此外，在某些情况下，提取的热量也可以利用热电技术（双循环发电厂）转化为电能，从而减少温室气体排放。SBTES系统可以在平衡太阳能热板等可再生能源技术的成本和效率方面提供一个关键因素，影响这些技术的命运。虽然这些能源是可再生的，但能源往往是在不需要的时候或在远离需要的地方产生的。SBTES系统几乎可以在美国的任何地方实施，以提供可持续的存储解决方案。SBTES系统扩展到不同应用的潜力为克服这些系统的前期成本带来的社会经济问题提供了一个重要的策略。

The NSF Sustainable Energy pathways (SEP) Program, under the umbrella of the NSF Science, Engineering and Education for Sustainability (SEES) initiative, will support the research program of Prof. John McCartney and co-workers at the University of Colorado at Boulder, and Prof. Ning Lu and co-workers at the Colorado School of Mines. The goal of this project is to understand the fundamental multi-physics processes, engineering challenges, environmental impacts, and implementation strategies for soil borehole thermal energy storage (SBTES) of heat collected from solar-thermal panels. The thermo-hydraulic properties of unsaturated soils and associated coupled heat, water, and vapor flow processes will be engineered to form a heat pipe, enhancing heat transfer. This is a transformative departure from conventional borehole or aquifer thermal energy storage systems, which rely on conduction or water extraction/injection to transfer heat into or from the subsurface. The objective of this research is to seek the optimum scalable efficiency of energy injection into SBTES systems and subsequent extraction for direct use in building heating or electricity generation. To reach this objective, specific tasks include: (1) constructing a field-scale test facility to evaluate the efficiency of heat injection and withdrawal for different borehole configurations, (2) evaluating coupled water, vapor and heat flow processes and potential environmental impacts within densely-instrumented soil tanks, (3) characterizing the nonlinear transport properties of unsaturated soils from the different tests, (4) validation and establishment of a scalable numerical model to examine the long-term operation, efficiency, and environmental impact of SBTES systems, and (5) exploration of engineering approaches to enhance the heat exchange efficiency. A parallel effort will be to assess implementation strategies for residential-, community-, and industrial-scale subsurface energy storage through evaluation of policies and user experience from exploratory SBTES sites. These sites have established high efficiencies of energy recovery, but usage trends, barriers to implementation, or socio-economic issues related to different policy strategies have not been fully analyzed. Preliminary estimates indicate that SBTES systems have low capital cost compared to other energy storage solutions, permitting rapid cost recovery through energy savings. Low environmental impact is expected because SBTES are closed-loop systems and because groundwater flow will not significantly affect thermal migration in the vadose zone. This project will contribute to generation of a workforce with a broad set of skills that can be applied to emerging renewable energy technologies, including hydrology, civil engineering, thermodynamics, environmental impact analyses, and energy policy. The PIs will build upon their track records of recruiting and retaining students from diverse backgrounds, will incorporate student exchange and active participation in tasks at both universities, and will define tracks established courses for effective training. Communities which have successfully implemented SBTES systems will be used as case histories, forming the basis of short courses which will be given by the PIs to communities and policy makers to ensure wider spread implementation of this technology.SBTES systems are expected to be play an important role in reducing the amount of electricity or natural gas required to heat residential and commercial buildings by integrating renewable heat sources with a sustainable thermal energy storage solution. By considering the improvements in heat transfer investigated in this research, the efficiency of energy recovery can be improved to provide scalable, sustainable direct use heating for communities. In addition, in some cases extracted heat may also be converted into electricity using thermal-electricity technologies (binary cycle power plants), reducing greenhouse gas emissions. SBTES systems could provide a key element in balancing the cost and efficiency of renewable energy technologies such as solar-thermal panels, influencing the fate of these technologies. Although these energy sources are renewable, energy is often generated at times when it is not necessary or in locations far from where it is needed. SBTES systems can be implemented in nearly any location in the US to provide a sustainable storage solution. The potential for SBTES systems to be scaled to different applications provides an important strategy for overcoming socio-economic concerns with the up-front costs of these systems.