High Performance Reduction/Oxidation Metal Oxides for Thermochemical Energy Storage (PROMOTES)

Thermochemical energy storage (TCES) offers the potential for greatly increased storage density relative to sensible-only energy storage. Moreover, heat may be stored indefinitely in the form of chemical bonds via TCES, accessed upon demand, and converted to heat at temperatures significantly higher than current solar thermal electricity production technology and is therefore well-suited to more efficient high-temperature power cycles. The PROMOTES effort seeks to advance both materials and systems for TCES through the development and demonstration of an innovative storage approach for solarized Air-Brayton power cycles and that is based on newly-developed redox-active metal oxides that are mixed ionic-electronic conductors (MIEC). In this paper we summarize the system concept and review our work to date towards developing materials and individual components.

Hydrogen Production via Catalytic Autothermal Reforming of Desulfurized Jet-A Fuel

On-board hydrogen production via catalytic autothermal reforming is beneficial to vehicles using fuel cells because it eliminates the challenges of hydrogen storage. As the primary fuel for both civilian and military air flight application, Jet-A fuel (after desulfurization) was reformed for making hydrogen-rich fuels in this study using an in-house-made Rh/NiO/K-La-Ce-Al-OX ATR catalyst under various operating conditions. Based on the preliminary thermodynamic analysis of reaction equilibrium, important parameters such as ratios of H2O/C and O2/C were selected, in the range of 1.1–2.5 and 0.5–1.0, respectively. The optimal operating conditions were experimentally obtained at the reactor’s temperature of 696.2 °C, which gave H2O/C = 2.5 and O2/C = 0.5, and the obtained fuel conversion percentage, hydrogen yield (can be large than 1 from definition), and energy efficiency were 88.66%, 143.84%, and 64.74%, respectively. In addition, a discussion of the concentration variation of CO and CO2 at different H2O/C, as well as the analysis of fuel conversion profile, leads to the finding of effective approaches for suppression of coke formation.

Development of Rotary Engine Based Micro-DG/CHP System

Small scale Distributed Generation with waste heat recovery (<50 kW power output, micro-DG/CHP) is an expanding market supporting the widespread deployment of on-site generation to much larger numbers of facilities. The benefits of increased overall thermal efficiency, reduced pollutant emissions, and grid/microgrid support provided by DG/CHP can be maximized with greater quantities of smaller systems that better match the electric and thermal on-site loads. The 3-year CEC funded program to develop a natural gas fueled automotive based rotary engine for micro-DG/CHP, capitalizing upon the unique attributes engine configuration will be presented including initial performance results and plans for the balance of the program.

Calorimetric Evaluation of Novel Concentrating Solar Receiver Geometries With Enhanced Effective Solar Absorptance

Direct solar power receivers consist of tubular arrays, or panels, which are typically tubes arranged side by side and connected to an inlet and outlet manifold. The tubes absorb the heat incident on the surface and transfer it to the fluid contained inside them. To increase the solar absorptance, high temperature black paint or a solar selective coating is applied to the surface of the tubes. However, current solar selective coatings degrade over the lifetime of the receiver and must be reapplied, which reduces the receiver thermal efficiency and increases the maintenance costs. This work presents an evaluation of several novel receiver shapes which have been denominated as fractal like geometries (FLGs). The FLGs are geometries that create a light-trapping effect, thus, increasing the effective solar absorptance and potentially increasing the thermal efficiency of the receiver. Five FLG prototypes were fabricated out of Inconel 718 and tested in Sandia’s solar furnace at two irradiance levels of ∼15 and 30 W/cm2 and two fluid flow rates. Photographic methods were used to capture the irradiance distribution on the receiver surfaces and compared to results from ray-tracing models. This methods provided the irradiance distribution and the thermal input on the FLGs. Air at nearly atmospheric pressure was used as heat transfer fluid. The air inlet and outlet temperatures were recorded, using a data acquisition system, until steady state was achieved. Computational fluid dynamics (CFD) models, using the Discrete Ordinates (DO) radiation and the k-ω Shear Stress Transport (SST) equations, were developed and calibrated, using the test data, to predict the performance of the five FLGs at different air flow rates and irradiance levels. The results showed that relative to a flat plate (base case), the new FLGs exhibited an increase in the effective solar absorptance from 0.86 to 0.92 for an intrinsic material absorptance of 0.86. Peak surface temperatures of ∼1000°C and maximum air temperature increases of ∼200°C were observed. Compared to the base case, the new FLGs showed a clear air outlet temperature increase. Thermal efficiency increases of ∼15%, with respect to the base case, were observed. Several tests, in different days, were performed to assess the repeatability of the results. The results obtained, so far, are very encouraging and display a very strong potential for incorporation in future solar power receivers.

Rechargeable Personal Air Conditioning Device

A rechargeable personal air-conditioning (RPAC) device was developed to provide an improved thermal comfort level for individuals in inadequately cooled environments. This device is a battery powered air-conditioning system with the phase change material (PCM) for heat storage. The condenser heat is stored in the PCM during the cooling operation and is discharged while the battery is charged by using the vapor compression cycle as a thermosiphon loop. The conditioned air is discharged towards a single person through adjustable nozzle. The main focus of the current research was on the development of the cooling system. A 100 W cooling capacity prototype was designed, built, and tested. The cooling capacity of the vapor compression cycle measured was 165.6 W. The PCM was recharged in nearly 8 hours under thermosiphon mode. When this device is used in the controlled built environment, the thermostat setting can be increased so that building air conditioning energy can be saved by about 5–10%.

Comparison Analysis for TES System in Solar-Aided 600 MW Coal-Fired Power Generation System and Solar-Alone Power Generation System

With the shortage of fossil fuels and its negative effects on the environment, solar energy as one type of renewable energy has attracted increasing attention both socially and politically. There are two approached to use solar energy for generating electricity, i.e., using solar energy to directly to make work or integrating solar energy into fossil-fueled plant. The solar-aided coal-fired power generation (SACPG) mechanism is proven an effective way to use solar energy efficiently. In this paper, SACPG system and solar-alone parabolic trough CSP plant are modelled respectively. A comparison discussion related to TES system between SACPG system and solar-alone CSP plant is presented. The aim is to find what role of TES system will play in these two different systems. Through analysis, the role TES system plays varies in solar-alone power generation system and SACPG system. For solar-alone power generation system, the main function for TES system lies in storing surplus solar heat. Besides, there exists an optimum loop number with highest annual SEE with a specific TES hour. However, TES system for SACPG system not only stores the surplus solar heat, but also adjusts working condition. With the help of TES system, the working condition could be set as the high-pressure extraction steam could be totally replaced by solar heat. By doing so, annual solar power generation and annual SEE could be improved compared with that without TES system.

Numerical Analysis of a Large-Scale Hydraulic Wind Farm With Integrated Hydraulic Energy Storage

Offshore wind farms are presently facing numerous technical challenges that are affecting their viability. High failure rates of expensive nacelle-based electronics and gearboxes are particularly problematic. On-going research is investigating the possibility of shifting to a seawater-based hydraulic power transmission, whereby wind turbines pressurise seawater that is transmitted across a high-pressure pipeline network. A 9-turbine hydraulic wind farm with three different configurations is simulated in the present work and a previously developed method for open-loop pressure control of a single turbine has been adapted for this multiple-turbine scenario. A conceptual quasi-constant-pressure accumulator is also included in the model. This system is directly integrated within each hydraulic wind turbine and it allows the output power from the wind farm to be scheduled on an hourly basis. The shift in control methodology when integrating storage is illustrated in the present work. Simulation results indicate a strong relationship between hydraulic performance attributes and the specific wind turbine array layout. The beneficial effects of storage can also be observed, particularly in smoothing the output power and rendering it more useable. Finally, the energy yields from 24-hour simulations of the 9-turbine wind farms are calculated. Integrated storage leads to a slight increase in yield since it eliminates bursts of high flow, which induce higher frictional losses in the pipeline network.

Cost Optimal Strategies of High Temperature Thermal Energy Storage Systems in Combined Heat and Power Applications

As variable generation electricity sources, namely wind and solar, increase market penetration, the variability in the value of electricity by time of day has increased dramatically. In response to increase in electricity demand, natural gas “peaker plants” are being added to the grid, and the need for spinning and nonspinning reserves have increased. Many natural gas, and other heat source based, power plants exist as combined heat and power (CHP), or cogeneration, plants. When built for industrial use, these plants are sized and run based on heat needs of an industrial facility, and are not optimized for the value of electricity generated. With the inclusion of new, less expensive thermal energy storage (TES) systems, the heating and electricity usage can be separated and the system can be optimized separately. The use of thermal energy storage with CHP improves system economics by improving efficiency, reducing upfront capital expenditures, and reducing system wear. This paper examines the addition of thermal energy storage to industrial natural gas combined heat and power (CHP) plants. Here a case study is presented for a recycled paper mill near Los Angeles, CA. By implementing thermal energy storage, the mill could decouple electric and heat production. The mill could take advantage of time-of-day pricing while producing the constant heat required for paper processing. This paper focuses on plant economics in 2012 and 2015, and suggests that topping cycle industrial CHP plants could benefit from the addition of high temperature (400–550°C) energy storage. Even without accounting for the California incentives associated with implementing advanced energy storage technologies and distributed generation, the addition of energy storage to CHP plants can drastically reduce the payback period below the 25 year expected economic lifetime of a plant. Thus thermal energy storage can make more CHP plants economically viable to build.

Active Fluidized Bed Technology Used for Thermal Energy Storage

A higher number of research institutions work on solutions for energy storage systems. Therefore a large number of differing approaches in competition among each other to develop storage technologies. At the TU-Wien, Institute for Energy Systems and Thermodynamics a novel thermal energy storage concept based on an active fluidized bed technology — the so called sandTES-heat exchanger technology — has been developed. The present paper describes the basic idea behind the key technology and the design methodology of a test rig in semi-industrial scale. In addition the results of selected preliminary experimental and numerical investigations are presented and discussed.

Considerations for the Design of a High-Temperature Particle Reoxidation Reactor for Extraction of Heat in Thermochemical Energy Storage Systems

In an effort to increase thermal energy storage densities and turbine inlet temperatures in concentrating solar power (CSP) systems, focus on energy storage media has shifted from molten salts to solid particles. These solid particles are stable at temperatures far greater than that of molten salts, allowing the use of efficient high-temperature turbines in the power cycle. Furthermore, many of the solid particles under development store heat via reversible chemical reactions (thermochemical energy storage, TCES) in addition to the heat they store as sensible energy. The heat-storing reaction is often the thermal reduction of a metal oxide. If coupled to an Air-Brayton system, wherein air is used as the turbine working fluid, the subsequent extraction of both reaction and sensible heat, as well as the transfer of heat to the working fluid, can be accomplished in a direct-contact, counter-flow reoxidation reactor. However, there are several design challenges unique to such a reactor, such as maintaining requisite residence times for reactions to occur, particle conveying and mitigation of entrainment, and the balance of kinetics and heat transfer rates to achieve reactor outlet temperatures in excess of 1200 °C. In this paper, insights to addressing these challenges are offered, and design and operational tradeoffs that arise in this highly-coupled system are introduced and discussed.