Ferritic-Martensitic steel welds typically require post weld heat treatment (PWHT) to restore toughness and high temperature performance. This off-line thermal process reduces disparities between weld and base metal, but can cause distortion, cracking, or simply be impractical due to assembly size and joint non-uniformity. Here we show integrated welding and thermal processing applied to modified 9Cr-1Mo (Grade 91) steel, favored for advanced power generation applications, performed in real time through the addition of a secondary heat source near the primary weld head. Optimal integrated processing reduces weld fusion and heat affected zone hardness by 125 HV, approaching performance of conventional 730 degrees C, 60 min PWHT processing. Microstructures and mechanical performance are compared for mechanized GTAW welds, with equivalent lifetimes noted in cross-weld creep rupture tests up to 234 MPa at 550 degrees C, and up to 104 MPa at 650 degrees C. The integrated process was validated on a Grade 91 pressure vessel with multipass cold wire feed GTAW. After 550 degrees C, 71.4 bar thermomechanical cyclic testing, the maximum weld hardness is <350 HV.

We present design optimization and pilot implementation of a building integrated hybrid Concentrated Photovoltaic-Thermal (CPV/T) system for cogeneration of electricity and process heat. A multijunction solar cell module is used in conjunction with a two-stage thermal receiver to achieve high efficiency solar energy transfer to an existing building system. The sunflower-like CPV/T system has the PV/T module mounted at a 60mm distance from the focal point of a 500-sun concentrator. This recessed mounting allows for a 60-40% split of thermal-PV module energy collection, resulting in an overall system efficiency of >70%.

Hybrid concentrator photovoltaic-thermal (CPV/T) systems generate both electricity and process heat by splitting concentrated sunlight onto CPV cells and a thermal receiver utilizing a heat-transfer fluid. Such energy co-generation increases total conversion efficiency and reduces system costs to compete with more widely used electricity and heat-generation methods in target markets. Here, we design and prototype a sunflower-like CPV/T system that collects a portion of the incoming sunlight using triple-junction CPV cells operating with an average temperature of <85°C. In the same receiver, thermal output >245°C may be generated from both waste heat from the CPV cells and a spatially separated fraction of the incoming concentrated light illuminating a heat-exchanger coil. In total, >65% of incident sunlight is converted to electricity or process heat. On-sun field tests validate this model and guide future development, and a techno-economic model demonstrates a US average levelized cost of heat of 2.5 ¢/kWth.

Concentrating solar power (CSP) with thermal energy storage (TES) presents the major advantage over solar photovoltaics of dispohability. High thermodynamic efficiencies achieved by collecting and storing heat at higher temperatures, and recent maturing of the technology, are making molten-salt central receiver plants the preferred option for CSP. To explore potential further improvements in CSP efficiency and cost the world's first direct absorption molten salt volumetric receiver/storage system was built at pilot scale, commissioned and monitored. In this demonstration a 100 kWth beam-down tower directs solar radiation through a final concentrator into the open aperture of a 1.94 m high and 1.25 m internal diameter tank receiver situated near the ground. The receiver tank is filled with 3,800 kg of 60-40 wt% NaNO3-KNO3 and serves as a stratified or mixed single tank thermal store that can satisfy evening peak loads or provide baseload power through the night. Compared to the parasitic loads of a conventional tower-receiver plant, the energy needed for salt transport from receiver to TES and morning preheat is negligible for this new system. The hot-spot problem of tubular receivers is eliminated and. the combined receiver/storage tank reduces component costs. In-situ initial melting was accomplished using solar energy as the primary input. Thermal stratification was maintained by daily cycling of a divider plate and occasional mixing plate actions and hot spots were never observed during several months' operation between 250 and 500 C. Three cycles of complete salt freezing and in-situ on-sun re-melting were tested with no operational difficulty and no discernible damage.

Hybrid concentrator photovoltaic-thermal systems can cogenerate electricity and heat by beam-splitting incoming concentrated light onto photovoltaic cells and a thermal receiver to increase total conversion efficiency and potentially reduce system cost. To demonstrate this, we have designed and prototyped a transmissive spectrum-splitting concentrator photovoltaic module that maximizes solar energy conversion by utilizing the entire solar spectrum. Visible light is collected using infrared-transmissive triple-junction photovoltaic cells to achieve an in-band module efficiency of 43.3% for light of wavelength lambda < 873 nm, while 44.2% of out-of-band light with lambda > 873 nm is transmitted through for collection by a thermal receiver. During testing on a dual-axis tracked parabolic concentrator dish at up to 166 suns, cell temperatures were maintained at 119 degrees C or below via a novel active cooling method. This cooling system strictly flows silicone oil directly across both sides of the cells, without inhibiting optical transmission, as verified through experimentation and simulation. The module was validated outdoors for 572 sun?hrs, and achieved a maximum thermal receiver temperature of 180 degrees C. 86.1% of incident solar power is collected at 166 suns average concentration collectively among the electrical, cooling, and thermal receiver subsystems. The remaining 13.9% is lost to mirror reflectivity, dish shadowing, receiver reflection, and thermal losses. The ability to directly cool the cells with an inert silicone oil offers the potential for reduced system cost relative to previous transmissive hybrid concentrator photovoltaic-thermal systems, including microfluidic-cooled designs. This solar cogeneration capability is valuable in a wide range of commercial and industrial applications.

本文重点介绍了近年来电网级聚光太阳能(CSP)中央接收器、传热流体和热能存储(TES)研究方面的最新进展.综述的目的是突出可替代的设计和系统结构,强调不同于传统解决方案的方法.为了提高效率和与高温热力循环的兼容性,推动了利用各种集热介质的先进概念接收器的开发.已发布的工作可分为三种技术,如美国能源部第三代高温聚光太阳能发电的途径:液体接收器、气体接收器和固体接收器,每种接收器的热能存储(TES)方法都非常适合系统集成.大多数实验研究都集中在材料性能的研究上,很少进行有实际规模的系统级验证.创新型解决方案利用了先进的设计、材料和制造技术,目的是实现先进的CSP-TES系统.在这些概念构建和测试过程中,演示方案已经表现出了发展前景,并且仍然在积极开发中.随着不断的开发,CSP-TES系统可以为低成本、可调度的电力生产提供替代途径.

This paper highlights recent developments in utility scale concentrating solar power (CSP) central receiver, heat transfer fluid, and thermal energy storage (TES) research. The purpose of this review is to highlight alternative designs and system architectures, emphasizing approaches which differentiate themselves from conventional solutions. The push for increased efficiency and compatibility with high-temperature power cycles has driven the development of advanced receiver concepts utilizing various heat collecting media. Published work can be grouped into three technologies like US Department of Energy Gen3 CSP pathways: liquid, gas, and solid receivers, each with TES approaches ideally suited for system integration. Most experimental work has focused on material property investigation, with few system-level validations at meaningful scales. Innovative solutions utilizing advances in design, materials, and manufacturing are being pursued to realize advanced CSP-TES systems. Of those concepts built and tested, demonstrations have shown promise and remain topics of active development. With continued development, these systems can offer alternative pathways towards low-cost, dispatchable electricity production.

Side-by-side installations of flat plate photovoltaics and parabolic trough collectors consume significant space and have high system losses; by using an all-in-one, spectrum-splitting hybrid receiver, electricity and high-temperature heat can be generated with a single efficient system. Here, the performance of a transmissive concentrator photovoltaic/thermal (tCPV/T) system is demonstrated on-sun, with a total energy efficiency of 85.1% +/- 3.3%, 138 W electric power at 304 suns (with average cell temperatures <110 degrees C), 903 W hot water output (average 34 degrees C and 1.7 bar, peak temperatures to 56 degrees C), and 1,139 W high-temperature steam output (average 201 degrees C and 45 bar, peak temperatures up to 248 degrees C). The spectrum-splitting hybrid receiver uses a sparse array of III-V triple-junction solar cells on GaAs substrates contained within a transparent microchannel water cooling stack, followed by a structured flow path thermal receiver cooled with pressurized water. System economics based on a 2.72-m(2) prototype performance is shown to be at or near market competitiveness to natural-gas-produced process heat for a variety of locations, with a levelized cost of heat of 0.03 $/kW(t)h for an installation in San Diego, California.

Hybrid photovoltaic-thermal systems can decouple IR light from visible light, allowing it to be collected separately by spectrum-optimized mechanisms for increased total efficiency. To demonstrate this, we have designed and prototyped a transmissive spectrum-splitting concentrator photovoltaic module that maximizes solar energy conversion by utilizing the entire solar spectrum. The system first collects visible light using IR-transmissive triple-junction photovoltaic cells to achieve an in-band module efficiency of ηmIB = 34.7% for light of wavelengths λ < 870 nm. Simultaneously, 58.8% of light with λ > 870 nm is transmitted through the cells for collection by a thermal receiver. By combining electrical and thermal power collection, 75% of incident solar power is collected, far surpassing the collection capability of only photovoltaics. The module was tested on a dual-axis tracked parabolic concentrator dish at up to 160 suns for 60 cumulative on-sun hours while maintaining photovoltaic cell temperatures at an average of 50 °C via active cooling. The system performed as expected based on modeled values, and represents a cost-effective path forward for dual-generation of electricity and high-temperature heat with increased total efficiency. The capability is valuable in a wide range of commercial and industrial cogeneration applications.

A hybrid receiver composed of a concentrator photovoltaic (CPV) module and a thermal receiver is developed for a photovoltaic-solar thermal (CPV/T) cogeneration system. The receiver has the appearance of a flower and is referred to as a sunflower receiver. The unique nature of this design uses both waste heat from the CPV cells and intentional spillage of a large fraction of the concentrated solar energy to generate very high temperature thermal output (up to 250°C) from a single heat transfer fluid, while the temperature of the cells is maintained below 110°C as they convert part of the solar spectrum into electricity. The exit temperature of the heat transfer fluid is adjustable according to the requirements of commercial or industrial process heat application. Early prototype results are discussed.

We present the design, fabrication, characterization, and field testing of transmissive active cooling for use in a point-focus spectrum-splitting hybrid concentrator photovoltaics/thermal (CPV/T) system. Seven parallel-path 100 mu m thick microchannels are made using polydimethylsiloxane and attached to a CPV module containing a 6 x 6 array of 5.5 mm transmissive CPV cells on a sapphire substrate. Water is flowed through the micro-channels to actively cool the CPV cells. The total transmittance of the CPV module reduces by 5.2% with the addition of the active cooling microchannels, relative to the module transmission with no microchannels. The peak cell temperature is measured as 69 degrees C with a thermal resistance of 9.351 K/W at 157 suns, well below the 110 degrees C maximum allowed temperature. A maximum flowrate of 16.7 g/s is achieved from a 13 psi pressure drop across the microchannels and manifold assembly. The flow characteristics within each microfluidic channel show maximum fluid velocity of 4.3 m/s (Re = 953) with a calculated convection coefficient of 1.7 x 10(4) W/m(2)K (Nu = 5.36). The CPV/T module and cooling system performance was validated during week-long outdoor tests under varying solar conditions up to 250 suns using a 2.7 m(2) parabolic dish collector mounted to a two-axis tracking system.

A spectrum-splitting photovoltaic module is developed for hybrid photovoltaic-solar thermal energy conversion using direct fluid cooling (DFC) of partially transmissive concentrator photovoltaic cells. The waste heat generated in photovoltaic cells can be more efficiently extracted by flowing a heat transfer fluid in direct contact with both sides of the cells. The module also acts as a beam splitter, dividing the incident light into two parts. Photons with higher energy than the bandgap of the cells are absorbed in cells, while photons with lower energy are passed through the infrared-transmissive module to a thermal receiver. Optical modeling (experimental) shows 63.2% (34.3%) out-of-band transmittance through the cell regions and 90.4% (89.0%) full spectrum transmittance through the surrounding bypass region. Thermal modelling verifies the direct cooling fluid method is an effective way to maintain cell temperature <; 110°C. Electrical power conversion efficiency in a first prototype module is 79% of the bare cell efficiency. Fluid flow characterization shows laminar flow. The modules are currently undergoing field testing.

A hybrid solar energy conversion system has been developed for converting sunlight into electricity and thermal energy. The system increases efficiency and reduces cost by utilizing a transmissive, spectrum-splitting concentrator photovoltaic module featuring triple junction III-V solar cells. This enables cell temperatures to be maintained below 100 degrees C while thermal temperatures may rise as high as 600 degrees C. The presentation will discuss module and system design, a series of prototype iterations, and multi-day outdoor field testing. Techno-economic analysis will be presented in a variety of locations and industrial process heat contexts.

We present three-dimensional numerical simulations to quantify the design specifications of a directed thermoplate expanded channel heat exchanger, also called dimpleplate. Parametric thermofluidic simulations were performed independently varying the number of spot welds, the diameter of the spot welds, and the thickness of the fluid channel within the laminar flow regime. Results from computational fluid dynamics simulations show an improvement in heat transfer is achieved under a variety of conditions: when the thermoplate has a relatively large cross-sectional area normal to the flow, a ratio of spot weld spacing to channel length of 0.2, and a ratio of the spot weld diameter with respect to channel width of 0.3. Experimental results performed to validate the model are also presented. (C) 2018 Elsevier Ltd. All rights reserved.

A three-dimensional ANSYS-FLUENT Computational Fluid Dynamics (CFD) model of the central receiver in a compact hybrid solar-thermal collector is presented. The small scale cavity receiver is conical in shape, laser welded from Inconel 625 with a 38 mm entrance aperture, and uses pressurized water as the Heat Transfer Fluid (HTF) within a thermoplate serpentine flowpath. The coupled thermofluidic CFD model examines a simplified unrolled version of this dimpleplate heat exchanger, representing the laminar flow within 10 x 1 mm expanded flowpath serpentine channels complete with intrachannel spot welds and non-uniform concentrated solar irradiance heating. The computational model is validated against experimental results with the receiver at the focus of a 2.7 m(2) parabolic dish, two-axis tracking rooftop solar collector. For steady state conditions with the outlet HTF reaching temperatures in excess of 200 degrees C, the HTF temperature rise predicted by the computational model is in agreement with the experimental data. In order to accurately capture the heat losses from the heat exchanger to its surrounding, we present an additional three-dimensional CFD model including the heat exchanger and surrounding thermal insulation. Contours of temperature and velocity at the midplane of the dimpleplate receiver heat exchanger are presented. (C) 2018 Elsevier Ltd. All rights reserved.

Concentrator photovoltaic (CPV) systems have been unable to keep up with the plummeting cost of flat plate PV for large scale power generation. New markets must be explored in order to maintain a robust CPV industry. Solar thermal offers a large potential market but has issues competing with conventional, cheap fuels such as natural gas. Hybrid CPV/T systems are capable of producing heat at prices competitive with natural gas when the electricity produced by high efficiency CPV units is used to subsidize the cost of the thermal energy delivered.

A new modular, hybrid solar power system is designed to generate both electrical and thermal energy by utilizing the full solar spectrum. The key element, an infrared-transparent concentrator photovoltaic (CPV) module, acts as a spectrum splitter, dividing solar radiation into two parts. The ultraviolet and visible light (“in-band”) are converted to electricity with high efficiency in CPV cells, while the infrared light (“out-of-band”) is transmitted directly to a thermal receiver, where thermal power may be converted to electricity by a suitable heat engine or used directly for industrial process heat applications whenever needed. Here, we describe the optical design, modeling, fabrication, and performance validation of this novel spectrum splitting CPV module. A transfer matrix style approach, cumulative transmission model, is built to study the reflection, absorption, and transmission in each layer of the CPV module. To optimize the optical performance, different materials for module superstrate/substrate, encapsulant, cell substrate, and cooling fluids are compared in order to enhance the transmission of out-of-band light through the CPV module by minimizing absorption. Six antireflection coatings along with front and backside electrical contact grids are designed to maximize transmittance of in-band light to the cell and out-of-band light to the thermal receiver. The final design, currently being prototyped, predicts out-of-band light transmission to the thermal receiver of 74.1% (for the passively cooled version) and 65.3% (for the actively cooled version). When epitaxial liftoff technology is applied, the transmission will change to 80.8% (passively cooled) and 71.9% (actively cooled). Experimental prototypes show good agreement with modeled optical performance.

The current concept of commercial concentrated solar power (CSP) plants, based on the concept of a solar field, receiver, storage and power block, experienced significant growth in the past decades. The power block is the most well know part of the plant, while solar field depends on the receiver technology. The dominant receiver technologies are parabolic troughs and central towers. Most thermal energy storage (TES) relies on two tanks of molten salts, one hot and one cold serviced by pumps and piping systems. In spite of the technical development level achieved by these systems, efficiency is limited, mainly caused by thermal losses in piping, parasitic losses due to electric tracing and pumping and receiver limitations. In order to mitigate the these issues, a new concept called Concentrated Solar Power on Demand (CSPonD), was developed, consisting of a direct absorption Solar Salt CSP receiver which simultaneously acts as TES tank. Currently, in the frame of the flagship collaborative project between the Masdar Institute (UAE) and the Massachusetts Institute of Technology (USA) a 25 kW demonstrative prototype is in its final building phase at the Masdar Institute Solar Platform. The present paper, explains the demonstration prototype based on the CSPonD concept, with emphasis on the planned start-up process for the facility.

Process heat applications make up a large potential market for renewable energy. Concentrated solar thermal (CST) systems are capable of reaching temperatures necessary for a wide variety of industrial and commercial applications but are often overlooked due to the difficulty of competing with natural gas. Novel hybrid photovoltaic/thermal systems (PV/T) are capable of simultaneously generating electricity and heat. The electricity produced is of higher value and offsets the lifetime cost of the system by producing a cost savings to the facility, ultimately making solar heat competitive with natural gas, propane, coal, and other fuels. An economic model that utilizes the electricity savings as part of the cash flow within the levelized cost of energy equation is presented here. We further determine the sensitivity of PV/T system costs to technical, financial, and geographical parameters. A dish concentrator PV/T (CPV/T) system with a transmissive CPV array is used as a reference system for sensitivity analysis. Through design choices informed by this new modeling approach, the levelized cost of heat (LCOH) is shown to be competitive with natural gas in up to 6 states within the United States and can be reduced to a minimum of -1.4 cent/kWh(th) in Hawaii by factoring in the electricity savings from additional energy generated by the transmissive CPV module. Competitiveness in select global regions is also considered. Further examination of several other geometries of PV/T systems with this model, for an installation in California, shows that flat plate collectors with waste heat recovery result in the lowest LCOH of 1.23 cent/kWh(th).