Impact of energy fluctuation on permeate quality in autonomous and directly coupled renewable energy powered nanofiltration and reverse osmosis systems

Autonomous membrane systems provide a unique opportunity to overcome challenges of lacking or dysfunctional water supply, sewage and electricity infrastructure which is the case in many rural areas worldwide1. Membrane technology provides a unique advantage where water is available yet through predominantly dissolved contaminants such as TDS, fluoride, arsenic, uranium, nitrate and many other inorganic as well as organic contaminants not usable. Coupling membrane processes directly to renewable energies such as wind or photovoltaics is important to realise robust and decentralised systems for remote areas. However this poses particular challenges in terms of system operation, maintenance, as well as water quality2. Following several years of laboratory studies as well as field work with real waters the impact of such fluctuation has been studied for short term operation with a unique system3,4. To do so, the nature of fluctuations for both wind and solar resources was investigated to understand the impact on the membrane system5,6. This information was then transferred into suitable experimental protocols to study the amplitude, frequency and intermittency of fluctuations in a systematic manner7. In the process the resulting operation – and the safe operating window – was determined as a function of minimum power requirements2. Short term energy buffering was investigated via super-capacitor banks8. Please click Additional Files below to see the full abstract

Luminescent solar concentrators for building integrated photovoltaics: opportunities and challenges

This review examines the application of luminescent solar concentrators (LSCs) for building integrated photovoltaics (BIPV), both in terms of opaque façade elements and as semi-transparent windows. Many luminophores have been developed for LSC applications, and their efficiencies examined in lab-scale (<25 cm$^2$) devices. This analytical review illustrates, using ray-tracing simulations, the technical challenges to maintaining efficiency when scaling these energy conversion devices to pilot- (1000 cm$^2$) and commercial-scale (100 000 cm$^2$) modules. Based on these considerations, ambitious but feasible target efficiencies for LSCs based on ideal quantum dot (QD) luminophores are suggested as follows – for opaque and semi-transparent (50% average visible transmission), respectively: (i) 11.0% and 5.5% for lab-scale devices; (ii) 10.0% and 5.0% for pilot-scale modules; and (iii) 9.0% and 4.5% for commercial-scale modules. It is worth noting though, that the QD design requirements – particularly with regard to the overlap integral between the absorption and emission spectrum – become very critical as the LSC area increases. Whereas it is difficult to see opaque LSCs successfully competing against standard flat-plate photovoltaic modules for building integration, the application of semi-transparent LSCs as power-generating window elements has potential. Therefore, an economic analysis of the inclusion of LSCs into commercial glazing elements is presented and the potential for novel technologies – such as down-conversion (quantum-cutting) and controlling the direction of emitted light – to move this technology towards application is also discussed

Quantifying barriers to monovalent anion transport in narrow non-polar pores

The transport of anionic drinking water contaminants (fluoride, chloride, nitrate and nitrite) through narrow pores ranging in effective radius from 2.5 to 6.5 Å was systematically evaluated using molecular dynamics simulations to elucidate the magnitud

Photonic crystal-driven spectral concentration for upconversion photovoltaics

International audienceThe main challenge for applying upconversion (UC) to silicon photovoltaics is the limited amount of solar energy harvested directly via erbium-based upconverter materials (24.5 W m(-2)). This could be increased up to 87.7 W m(-2) via spectral concentration. Due to the nonlinear behavior of UC, this could increase the best UC emission by a factor 13. In this paper, the combined use of quantum dots (QDs)for luminescent down-shiftingand photonic crystals (PCs)for reshaping the emissionto achieve spectral concentration is shown. This implies dealing with the coupling of colloidal QDs and PC at the high-density regime, where the modes are shifted and broadened. In the first fabricated all-optical devices, the spectral concentration rises by 67%, the QD emission that matches the absorption of erbium-based upconverters increases by 158%, and the vertical emission experiences a 680% enhancement. Remarkably, the PC redshifts the overall emission of the QDs, which could be used to develop systems with low reabsorption losses. In light of this, spectral concentration should be regarded as one of the main strategies for UC photovoltaics

Renewable Energy Powered Water Treatment Systems

There are many motivations for choosing renewable energy technologies to provide the necessary energy to power water treatment systems for reuse and desalination. These range from the lack of an existing electricity grid, particularly in remote areas, to securing future energy and water supplies, to purely financial incentives. While many renewable energy technologies exist the two dominant ones used for powering desalination systems are PV modules and wind turbines. While wave power devices are a less mature technology, there are definitely synergies for desalination if these systems can be demonstrated to last 20 years in the harsh marine environment. Wind energy exhibits the lowest cost of electricity produced, while solar electricity is the highest. However, PV modules have a definite advantage as they contain no moving parts, thus enabling them to operate well in harsh conditions for over 20 years

Limitation of room temperature phosphorescence efficiency in metal organic frameworks due to triplet-triplet annihilation

The effect of triplet-triplet annihilation (TTA) on the room-temperature phosphorescence (RTP) in metal-organic frameworks (MOFs) is studied in benchmark RTP MOFs based on Zn metal centers and isophthalic or terephthalic acid linkers (ZnIPA and ZnTPA). The ratio of RTP to singlet fluorescence is observed to decrease with increasing excitation power density. Explicitly, in ZnIPA the ratio of the RTP to fluorescence is 0.58 at 1.04 mW cm(−2), but only 0.42 at (the still modest) 52.6 mW cm(−2). The decrease in ratio is due to the reduction of RTP efficiency at higher excitation due to TTA. The density of triplet states increases at higher excitation power densities, allowing triplets to diffuse far enough during their long lifetime to meet another triplet and annihilate. On the other hand, the shorter-lived singlet species can never meet an annihilate. Therefore, the singlet fluorescence scales linearly with excitation power density whereas the RTP scales sub-linearly. Equivalently, the efficiency of fluorescence is unaffected by excitation power density but the efficiency of RTP is significantly reduced at higher excitation power density due to TTA. Interestingly, in time-resolved measurements, the fraction of fast decay increases but the lifetime of long tail of the RTP remains unaffected by excitation power density. This may be due to the confinement of triplets to individual grains, leading decay to be faster until there is only one triplet per grain left. Subsequently, the remaining “lone triplets” decay with the unchanging rate expressed by the long tail. These results increase the understanding of RTP in MOFs by explicitly showing the importance of TTA in determining the (excitation power density dependent) efficiency of RTP. Also, for applications in optical sensing, these results suggest that a method based on long tail lifetime of the RTP is preferable to a ratiometric approach as the former will not be affected by variation in excitation power density whereas the latter will be

From concept to commercialisation: student learning in a sustainable engineering innovation project

An interdisciplinary sustainable design project that combines membrane technology with renewable energy to provide water for remote communities and developing countries was offered to students for voluntary participation. Through continuous design stages and improvements on several prototypes, laboratory testing and several field trials in Australia, and interactions with industry partners and funding agencies, the project has offered very important experience to students and contributes significantly to graduate attributes that are difficult to gain during traditional coursework education. Such initiatives offer an exciting addition to the environmental engineering curriculum and can be adapted to various teaching frameworks and topic areas. In addition to acquiring technical skills, the students gained skills in the areas of teamwork and interpersonal skills, project management, interdisciplinary skills, and confidence in interacting with non-engineers. A number of the students involved who have now graduated as well as peers were subsequently surveyed to evaluate student learning using critical incident questionnaires. One student felt that involvement in the project was more important than the entire engineering degree. Students also reported a boost in confidence, motivation, inspiration, pride of involvement, high degree of engagement, especially during field trips. One drawback was negative team experiences, caused by students who thought they should have been selected as project managers. However, this was described by a student (now in the workforce) as a representation of later office politics and as a good opportunity to develop character strength. Poor communication, team-building tools and lack of institutional support were additional issues needing addressing, as well as concerns from other academics that such activities could be to the detriment of other, more traditional, coursework-based learning activities. Significantly enhanced employment opportunities and extremely positive industry feedback were also noted. Industry emphasised the need for more project and time management skills