A review on photovoltaic/thermal hybrid solar technology

A significant amount of research and development work on the photovoltaic/thermal (PVT) technology has been done since the 1970s. Many innovative systems and products have been put forward and their quality evaluated by academics and professionals. A range of theoretical models has been introduced and their appropriateness validated by experimental data. Important design parameters are identified. Collaborations have been underway amongst institutions or countries, helping to sort out the suitable products and systems with the best marketing potential. This article gives a review of the trend of development of the technology, in particular the advancements in recent years and the future work required.     

Hydrogen production through sorption-enhanced steam methane reforming and membrane technology: A review

With the rapid development of industry, more and more waste gases are emitted into the atmosphere. In terms of total air emissions, CO₂ is emitted in the greatest amount, accounting for 99 wt% of the total air emissions, therefore contributing to global warming, the so-called “Greenhouse Effect”. The recovery and disposal of CO₂ from flue gas is currently the object of great international interest. Most of the CO₂ comes from the combustion of fossil fuels in power generation, industrial boilers, residential and commercial heating, and transportation sectors. Consequently, in the last years’ interest in hydrogen as an energy carrier has significantly increased both for vehicle fuelling and stationary energy production from fuel cells. The benefits of a hydrogen energy policy are the reduction of the greenhouse effect, principally due to the centralization of the emission sources. Moreover, an improvement to the environmental benefits can be achieved if hydrogen is produced from renewable sources, as biomass.     

A review on bio‐hydrogen production technology

The progress of bio‐hydrogen technology has led to the development of new energy technologies and is significant for the sustainable use of energy. After summarizing current research results, this study discusses that the key to increasing the hydrogen production rate is to improve the activity of hydrogen producing bacteria under the conditions of anaerobic fermentation. Using waste to prepare hydrogen producing bacteria is the developmental trend. The primary factors influencing bio‐hydrogen production from plant straw fermentation are also pointed out, indicating the method to improve the hydrogen production rate from plant straw. In addition, application of artificial intelligence technology to a bio‐hydrogen production reactor is helpful to achieve automatic control of continuous bio‐hydrogen production and improve the rate of hydrogen production.     

太阳能裂解水制氢

在新能源领域中，氢能已普遍被认为是一种最理想的新世纪无污染的绿色能源，这是因为氢燃烧，水是它的唯一产物。氢是自然界中最丰富的元素，它广泛地存在于水、矿物燃料和各类碳水化合物之中。     

Hydrogen production through solar energy water electrolysis

Various methods of making hydrogen from water have been proposed, but at the present time the only practical way to make hydrogen from water without fossil fuel is electrolysis. The development of a new, advanced, water electrolyser has become necessary for use in hydrogen energy systems and in electricity storage systems. All the new possible electrolysis processes, suitable for large-scale plants, are being analysed, in view of their combination with solar electricity source. A study of system interactions between large-scale photovoltaic plants, for electrical energy supply, and water electrolysis, is carried out. The subsystems examined include power conditioning, control and loads, as they are going to operate. Water electrolysis systems have no doubt been improved considerably and are expected to become the principal means to produce a large amount of hydrogen in the coming hydrogen economy age. Thus, the present paper treats the subject of hydrogen energy production from direct solar energy conversion facilities located on the earth's oceans and lakes. Electrolysis interface is shown to be conveniently adapted to direct solar energy conversion, depending on technical and economical feasibility aspects as they emerge from the research phases. The intrinsic requirement for relatively immense solar collection areas for large-scale central conversion facilities, with widely variable electricity charges, is given. The operation of electrolysis and photovoltaic array combination is verified at different insolation levels. Solar cell arrays and electrolysers are giving the expected results during continuously variable solar energy inputs. Future markets will turn more and more towards larger scale systems powering significantly bigger loads, ranging from hundreds of kW to several MW in size. Detailed design and close attention to subsystem engineering in the development of high performance, high efficiency photovoltaic power plants, are carried out. An overall design of a 50 MWp photovoltaic central station for electricity and hydrogen co-generation is finally discussed.     

Hydrogen production from alcohols and ethers via cold plasma: A review

Hydrogen is one of the most promising energy and the fuel for fuel-cell-powered automobiles. Liquid fuels have been considered as the most suitable source for onboard hydrogen production, and cold plasma is proved to be a potential way to convert them. In this review, the conversion of methanol, ethanol and dimethyl ether (DME) using different types of cold plasma has been summarized. Hydrogen is the main product with different by-products depending on reaction conditions. The conversion of liquid fuels for hydrogen production via cold plasma has good prospects, and reaction conditions optimization and reactor design are very important for its future application onboard.     

A new solar based multigeneration system with hot and cold thermal storages and hydrogen production

A multigeneration system based on solar thermal energy associated with hot and cold thermal storage is designed and analyzed energetically and exergetically. The system produces electricity, a heating effect, a cooling effect, hydrogen, and dry sawdust biomass as outputs by means of organic Rankine cycles, a heat pump, two absorption chillers, an electrolyser, and a belt dryer. The intermittent behavior of the renewable energy source is addressed through the incorporation of hot and cold thermal storage systems to operate an organic Rankine cycle and provide cooling at night. The performance assessment indicates that the overall (day and night) energy and exergy efficiencies are 20.7% and 13.7%, respectively. The majority of the total exergy destruction is attributable to the sawdust belt dryer, at about 64.0%.     

A tutorial on reversed absorption cycles for solar applications

The absorption refrigeration cycle is already used in solar applications. The solar heat is either used to operate the vapor generator of the refrigeration units or, in the case of heat pumps, to load the evaporator. In the first case the solar heat is added to the high-temperature part of the unit; in the second, to the low-temperature part. In both cases the absorption unit is rejecting heat to the ambient at a mean temperature level. The present paper considers the addition of solar heat at the mean temperature level and the operation of a reversed absorption cycle splitting the solar heat into two parts. One part is rejected at a lower temperature level, and the other part, the output, is delivered for use at higher temperature levels. The thermodynamics of the reversed cycle is examined, and its theoretical behaviour is described.     

A critical review on integrated system design of solar thermochemical water-splitting cycle for hydrogen production

The development of clean hydrogen production methods is important for large-scale hydrogen production applications. The solar thermochemical water-splitting cycle is a promising method that uses the heat provided by solar collectors for clean, efficient, and large-scale hydrogen production. This review summarizes state-of-the-art concentrated solar thermal, thermal storage, and thermochemical water-splitting cycle technologies that can be used for system integration from the perspective of integrated design. Possible schemes for combining these three technologies are also presented. The key issues of the solar copper-chlorine (Cu–Cl) and sulfur-iodine (S–I) cycles, which are the most-studied cycles, have been summarized from system composition, operation strategy, thermal and economic performance, and multi-scenario applications. Moreover, existing design ideas, schemes, and performances of solar thermochemical water-splitting cycles are summarized. The energy efficiency of the solar thermochemical water-splitting cycle is 15–30%. The costs of the solar Cu–Cl and S–I hydrogen production systems are 1.63–9.47 $/kg H₂ and 5.41–10.40 $/kg H₂, respectively. This work also discusses the future challenges for system integration and offers an essential reference and guidance for building a clean, efficient, and large-scale hydrogen production system.     

A comparison of solar absorption system configurations

Solar thermal driven cooling systems for residential applications are a promising alternative to electric compression chillers, although its market introduction still represents a challenge, mainly due to the higher investment costs. The most common system configuration is an absorption chiller driven by a solar thermal system, backed up by a secondary heating source, normally a gas boiler. Heat storage in the primary (solar) circuit is mandatory to stabilize and extend the operation of the chiller, whereas a cold storage tank is not so common.This paper deals with the selection of the most suitable configuration for residential cooling systems with solar energy. In Spain, where cooling needs are usually higher than heating needs, the interest of a reversible heat pump as auxiliary system and a secondary cooling storage are analyzed.A complete TRNSYS model has been developed to compare a configuration with just hot storage (of typical capacity 40 L/m² of solar collector surface) and a configuration with both, hot and cool storages. The most suitable configuration is very sensible to the solar collector area. As the collector area increases, the advantages of a cool storage vanish. Increasing the collector area tends to increase the temperature of the hot storage, leading to higher thermal losses in both the collector and the tank. When the storage volume is concentrated in one tank, these effects are mitigated. The effect of other variables on the optimal configuration are also analyzed: collector efficiency curve, COP of the absorption chiller, storage size, and temperature set-points of the chillers.     

A review and new approach to minimize the cost of solar assisted absorption cooling system

Solar energy is an alternative energy source for cooling systems where electricity is demand or expensive. Many solar assisted cooling systems have been installed in different countries for domestic purpose. Many researches are going on to achieve economical and efficient thermal systems when compared with conventional systems. This paper reviews the past efforts of solar assisted-single effect vapour absorption cooling system using LiBr–H₂O mixture for residential buildings. Solar assisted single-effect absorption cooling systems were capable of working in the driving temperature range of 70–100 °C. In this system LiBr–H₂O are the major working pairs and has a higher COP than any other working fluids. Besides the review of the past theoretical and experimental investigations of solar single effect absorption cooling systems, some new ideas were introduced to minimize the capital and operational cost, to reduce heat loss from generator and thus to increase COP to get effective cooling.     

太阳能干燥技术概况及应用前景

阐述了太阳能干燥的国内外应用概况,指出太阳能干燥的优势、局限性与影响推广的原因。分析了我国太阳能干燥技术的应用前景,建议我国政府对太阳能干燥给予政策上的鼓励与扶持,并加大宣传力度。     

ITO-free wrap through organic solar cells—A module concept for cost-efficient reel-to-reel production

Organic solar cells have the potential to make cheap photovoltaic devices feasible. In order to achieve this, material and production costs have to be minimised by using device architectures, which are suited to tap the full potential of reel-to-reel production.The inversion of the layer sequence in organic bulk-heterojunction solar cells is motivated by the possibility to omit the commonly used expensive indium tin oxide electrode utilising the so-called wrap through concept. In this concept, the hole contact is formed by a highly conductive formulation of poly(3,4 ethylenedioxythiophene):poly(styrenesulfonate), which is led through via holes in the solar cell to the backside of the substrate in a regular pattern, where it is contacted with a metal layer with low sheet resistance. In this way, a scalable parallel connexion is realised. If higher voltage is desired, one can also connect several such cell segments in series monolithically. We will show that the inversion of the layer sequence is possible without loss of device performance. Using the results of small area inverted devices, we calculate the optimal dimensions of the wrap through solar cell module.First devices with active areas of 2-4 cm² with parallel and serial wrap through connexion will be shown as proof of concept.     

Process technology for mass production of large-area a-Si solar modules

The production of large-area (0.6 × 1.0 m²) modules takes place in a fully automated semiconductor line and a semi-automated panel finishing line. The a-Si deposition occurs in a multichamber reactor for parallel processing of p-, i- and n-layers which provides for flexibility in the cell design (single- and multijunction structures) without significant loss in throughput. Specific aspects of module construction, namely the properties of commercially available large-area TCO substrates, scale-up of the PECVD process, and patterning for color-neutral semitransparent modules, are discussed. The module production is now based exclusively on-a-Si/a-Si tandem structures. The average power output is initially 36 W, and stabilizes around 15% below that level.     

Revisiting solar hydrogen production through photovoltaic-electrocatalytic and photoelectrochemical water splitting

Photoelectrochemical (PEC) water splitting is regarded as a promising way for solar hydrogen production, while the fast development of photovoltaic-electrolysis (PV-EC) has pushed PEC research into an embarrassed situation. In this paper, a comparison of PEC and PV-EC in terms of efficiency, cost, and stability is conducted and briefly discussed. It is suggested that the PEC should target on high solar-to-hydrogen efficiency based on cheap semiconductors in order to maintain its role in the technological race of sustainable hydrogen production.     

A comprehensive review on bioinspired solar photovoltaic cells

Researchers have derived inspiration from the biophotosynthetic structures in nature and have started to synthesize the modified bioinspired solar cells copying the evolved organic and inorganic material properties. One of the highlighted examples of bioinspired photo voltaic (PV) cells is the astonishing achievement of an increase in the absorption of integrated sunlight waves in unpatterned solar cells simulated from the wings of the butterfly. Further, deployment possibilities of incorporating flexible cells on flat or curved surfaces for optimizing performance are also under progress. This article mainly discusses the recent concepts of bioinspired solar cells at the research and development level with the prospects and challenges that lie ahead in the upcoming field of photovoltaic renewable energy cell technology. Different potential materials found suitable for bioinspired solar cells construction are reviewed with their particular challenges.     

A review on long-term sorption solar energy storage

In the past decade, long-term sorption and thermochemical heat storage has generated lot of interest. This paper presents the state of the art in this field of research, materials used in these systems and technological difficulties that researchers are set against. An emphasis is put on recent demonstrative projects including absorption and adsorption for long-term solar energy storage. It emerges that considerable breakthrough have been made. Even though there is no mature long-term sorption or thermochemical energy storage yet, primarily due to the high cost of materials, the suitability of this technology to long-term storage remains its main power of attracting.     

A comparison of solar absorption air conditioning systems

A computer simulation of solar powered absorption air conditioning systems is discussed. The results of simulations of various systems composed of conventional flat plate or evacuated tube collectors, wet or dry cooling towers, lithium bromide-water or aqua-ammonia working fluids and hot water, chilled water or refrigerant storage alternatives are obtained over a common operating cycle. Performance of the lithium bromide-water working fluid is shown to be superior to aqua-ammonia. Relative performance gains realized with the evacuated tube collector and relative performance losses associated with the dry cooling tower are presented. Chilled water storage is shown to be advantageous for an evacuated collector, dry cooling tower, lithium bromide-water system.     

A new absorption refrigeration cycle using solar energy

A new type of absorption refrigeration cycle that is co-driven both by solar energy and electricity was evaluated. The principle of a heat transformer was applied to the absorption refrigeration system to increase its efficiency. In this paper, a thermodynamic model describing the performance of the new cycle was developed and a computer program was written to evaluate its performance. The COP, condenser heat load, the theoretical minimum evaporating temperature and refrigeration capacity for a typical daily load of the system were calculated and compared with those of traditional absorption refrigeration systems. The results show that the new cycle not only overcomes some shortcomings of the traditional absorption cycle with unsteady energy input from a variable source such as solar energy, but also increases the system’s coefficient of performance.