Display omitted
•Original thermal and cost analysis of a new solar power tower concept.•Potential for renewable, dispatchable electricity at low cost.•Modularity opens concentrated solar power to new ...markets.•In-depth comparison to alternative technologies.
In this paper, we present performance simulations and techno-economic analysis of a modular dispatchable solar power tower. Using a heliostat field and power block three orders of magnitude smaller than conventional solar power towers, our unique configuration locates thermal storage and a power block directly on a tower receiver. To make the system dispatchable, a valved thermosyphon controls heat flow from a latent heat thermal storage tank to a Stirling engine. The modular design results in minimal balance of system costs and enables high deployment rates with a rapid realization of economies of scale. In this new analysis, we combine performance simulations with techno-economic analysis to evaluate levelized cost of electricity, and find that the system has potential for cost-competitiveness with natural gas peaking plants and alternative dispatchable renewables.
Display omitted
•First prototype to combine Al-Si as a PCM with heat pipes and a Stirling engine.•Heat pipe and engine performance investigated at varied power levels.•Maximum efficiency of 18.5% in ...converting stored heat to electricity.•Promising system for modular concentrating solar power.
In this work, we present the design and experimental results of a prototype latent heat thermal energy storage system. This prototype used 100 kg of aluminum-silicon as a phase change material with embedded heat pipes for effective heat transfer, a valved thermosyphon to control heat flow out of the thermal storage system, and a Stirling engine to convert heat to electricity. We tested this system for 11 simulated days of operation; each day included charging of the thermal storage tank, simultaneous electricity generation with heat input, and electricity generation from stored heat alone. On each simulated day, we set the engine to a different power level, allowing us to investigate the response of heat pipes and our valved thermosyphon to part-load conditions. The prototype demonstrated a maximum efficiency of 18.5% in converting stored heat to electricity, at a maximum power output of over 1kWe. Extending these results to a commercial scale system with solar heat input, our modeling indicates that a discharge efficiency of over 30% and an annual efficiency of 18% could be achieved. This performance represents an advancement in established efficiency for any system that combines latent heat storage with electricity generation, and demonstrates that this system has potential for future commercial development.
•Design and construction of a dispatchable latent heat thermal storage system.•Heat transfer near uniform temperature via heat pipes and aluminum-silicon PCM.•On/off heat flow control using a valved ...thermosyphon.•Integration of subsystems with small temperature drops at interfaces.
In this work, we present the design, construction, and experimental results of a prototype latent heat thermal energy storage system. The prototype consists of a thermal storage tank with 100 kg of the aluminum-silicon eutectic as a phase change material, a valved thermosyphon that controls heat flow from the thermal storage tank to the power block, and thermoelectric generators for conversion of heat to electricity. We tested the prototype over four simulated days, where each day consisted of four phases of operation: charging, discharging, simultaneous charging and discharging, and storage. Our results show three major conclusions. First, the thermal energy storage system was able to receive and distribute heat with small temperature gradients – less than 5 °C throughout the thermal storage tank. Second, the valved thermosyphon was able to effectively control heat transfer, demonstrating an on/off thermal conductance ratio of 430. Third, the interfaces between subsystems had small temperature drops: of the ∼ 560 °C temperature drop from the thermal storage tank to the heat rejection system, ∼ 525 °C occurred across the power block. This work overcomes the challenges of integrating previously-developed subsystems together, providing a proof-of-concept of this system.
In this paper, polymer-based flat heat pipes (PFHPs) with a thickness on the order of 1 mm have been successfully developed and tested. Liquid-crystal polymer (LCP) films with copper-filled thermal ...vias are employed as the case material. A copper micropillar/woven mesh hybrid wicking structure was designed and fabricated to promote evaporation/condensation heat transfer and the liquid supply to the evaporator of the PFHP. Water was selected as the working fluid because of its superior thermophysical properties. An experimental study was conducted to examine the PFHP performance. The test data demonstrated that the PFHP can operate with a heat flux of 11.94 W/cm 2 and results in effective thermal conductivity ranging from 650 to 830 W/m · K, with the value varying with the input heat flux and the tilt angle. With the employment of flexible LCP as casing material, the PFHP could potentially be directly integrated into a printed circuit board or flexible circuits for thermal management of heat-generating components.
The recent development and commercialization of microelectromechanical systems (MEMS)/nanoelectromechanical systems (NEMS) has brought the related challenge of independently powering such systems. ...The concept of the nanogenerator (NG) has shown potential for harvesting energy from the ambient environment to power MEMS/NEMS. Kinetic energy harvesting NGs based on the piezoelectric properties of ZnO nanowires have attracted much interest. In this paper, we have fabricated hydrothermally synthesized ZnO-based NGs following the procedures standardized in the published literature. Likewise, reference NGs without ZnO piezoelectric material were fabricated in parallel with the ZnO NGs. The voltage output of both the ZnO NG and the reference NG was measured given a 10-Hz cyclic vertical load. Unexpectedly, both the ZnO and the reference NG were found to produce 3 mV with 0.451 N of load. A finite-element model was created to determine that the voltage potential of the NG should be about 1 mV with the given load. A possible explanation for this unexpected behavior is that the measured signals are not entirely piezoelectric in nature. Rather, the signals recorded from the NGs may be some alternate phenomenon, such as the triboelectric, flexoelectric, or electret effect.
•Solution to problem of passive dispatchable PCM heat extraction.•Stainless steel thermosyphon-based thermal valve with sodium working fluid.•Experimentally demonstrated high “on/off” thermal ...resistance ratio of 280.•Operation at 600 °C operating temperature.•Cycled more than fifty times showing reliability with no degradation.
Latent heat thermal energy storage systems have the advantages of near isothermal heat release and high energy density compared to sensible heat, generally resulting in higher power block efficiencies. Until now, there has been no highly effective and reliable method to passively extract that stored latent energy. Most modern attempts rely on external power supplied to a pump to move viscous heat transfer fluids from the phase change material (PCM) to the power block. In this work, the problem of latent heat dispatchability has been addressed with a redesigned thermosyphon geometry that can act as a “thermal valve” capable of passively and efficiently controlling the release of heat from a thermal reservoir. A bench-scale prototype with a stainless steel casing and sodium working fluid was designed and tested to be reliable for more than fifty “on/off” cycles at an operating temperature of 600 °C. The measured thermal resistances in the “on” and “off” states were 0.0395 K/W and 11.0 K/W respectively. This device demonstrated efficient, fast, reliable, and passive heat extraction from a PCM and may have application to other fields and industries using thermal processing.
Conventional concentrated solar power (CSP) is a reliable alternative energy source that uses the sun’s heat to drive a heat engine to produce electrical power. An advantage of CSP is its ability to ...store thermal energy for use during off-sun hours which is typically done by storing sensible heat in molten salts. Alternatively, thermal energy may be stored as latent heat in a phase-change material (PCM), which stores large quantities of thermal energy in an isothermal process. On-sun, the PCM melts, storing energy. Off-sun, the latent heat is extracted to produce dispatchable electrical power.
This paper presents the design of a thermosyphon-based device with sodium working fluid that is able to extract heat from a source as demand requires. A prototype has been designed to transfer 37kW of thermal energy from a 600°C molten PCM tank to an array of 9% efficient thermoelectric generators (TEGs) to produce 3kW of usable electrical energy for 5h. This “thermal valve” design incorporates a funnel to collect condensate and a central shut-off valve to control condensate gravity return to the evaporator. Three circumferential tubes allow vapour transport up to the condenser.
Pressure and a thermal resistance models were developed to predict the performance of the thermal valve. The pressure model predicts that the thermal valve will function as designed. The thermal resistance model predicts a 5500× difference in total thermal resistance between “on” and “off” states. The evaporator and condenser walls comprise 96% of the “on” thermal resistance, while the small parasitic heat transfer in the “off” state is primarily (77%) due to radiation losses.
This simple and effective technology can have a strong impact on the feasibility, scalability, and dispatchability of CSP latent storage. In addition, other industrial and commercial applications can benefit from this thermal valve concept.
Using vertically grown hydrothermal ZnO nanowires, we demonstrate the assembly of fully functional piezoelectric energy harvesters on plastics substrates. A seedless hydrothermal process is employed ...for the growth of single crystalline vertically orientated ZnO NWs at around 100oC. Flexible NG are assembled using ∼7μm thick PDMS polymer matrix on a 3x3cm substrate. A representative device with an active area of 4cm2 is characterised revealing average output voltage generation of ∼22mV (±1.2) and -32mV (±0.16) in the positive and negative cycles after 3-4mm periodic deflection at 20Hz. A power density of ∼288nW/cm3 is estimated for the device. It is envisaged that such energy scavengers may find potential applications targeting self-powered systems, sensors and on-body charging of electronics.
PDF
