High performance Carnot Batteries based on hybrid cycles

Pumped thermal energy storage (PTES) has seen a rapid increase in research interest and private investment during the last few years. A range of different concepts has been proposed, based on different thermodynamic cycles, and the most promising ones are already being turned into demonstration projects or small-scale storage plants. These include PTES systems based on the Joule-Brayton cycle, the Rankine cycle and the Liquid Air cycle, among others. This presentation will explore how hybridising some of these concepts can result in systems that are more flexible, cheaper, or have superior performance compared with the original cycles. More specifically, two examples will be shown where the Joule-Brayton cycle can be effectively used to support a Rankine battery and a Liquid Air battery. One general advantage of Brayton-PTES systems is that they can use molten salts as liquid storage media. Molten salts are cheap, safe and abundant, and have been used for concentrated solar power (CSP) applications in a large number of commercial plants. Employing the same storage material at similar temperature levels opens the possibility of hybrid “solar-PTES” systems that would require less capital investment than two separate plants. Such a hybrid system could charge the same hot stores using either solar energy or off-peak electricity, becoming both a power plant and an energy storage plant, therefore increasing the capacity factor while employing a single heat engine during discharge. A numerical model has been implemented to study a solar-PTES system where an existing CSP plant (based on the Rankine cycle) is retrofitted with a Brayton heat pump, and several strategies are explored to boost the overall performance. Similar configurations could be employed to transform other kinds of thermal power plant (such as coal power plants) into Brayton-Rankine batteries. In contrast to most PTES systems, liquid air energy storage (LAES) stores most of the available energy cryogenically, by liquefying atmospheric air and storing it at very low temperatures. This is advantageous because liquid air has a very high energy density - and is free. However, the difficulties in reaching full liquefaction during the charge process have a significant impact on the round-trip efficiency of the cycle. It has been found that these difficulties can be greatly minimised by employing the support of a Brayton cycle. A hybrid system was designed where a Brayton-PTES plant operates as a topping cycle and an LAES plant operates as a bottoming cycle. The cooling provided by the Brayton cycle allows the LAES side to achieve full air liquefaction, which translates into a significant boost in performance. Furthermore, the cold thermal reservoirs that would be required by the two separate cycles are replaced by a single heat exchanger that acts between them, therefore saving significant amounts of storage media per unit of energy stored. Results from a numerical study indicate that the hybrid cycle can increase round-trip efficiency by 5-10 percent points compared with the separate cycles, and achieve an even larger increase in terms of energy density

Progress and prospects of thermo-mechanical energy storage—a critical review

Abstract: The share of electricity generated by intermittent renewable energy sources is increasing (now at 26% of global electricity generation) and the requirements of affordable, reliable and secure energy supply designate grid-scale storage as an imperative component of most energy transition pathways. The most widely deployed bulk energy storage solution is pumped-hydro energy storage (PHES), however, this technology is geographically constrained. Alternatively, flow batteries are location independent and have higher energy densities than PHES, but remain associated with high costs and short lifetimes, which highlights the importance of developing and utilizing additional larger-scale, longer-duration and long-lifetime energy storage alternatives. In this paper, we review a class of promising bulk energy storage technologies based on thermo-mechanical principles, which includes: compressed-air energy storage, liquid-air energy storage and pumped-thermal electricity storage. The thermodynamic principles upon which these thermo-mechanical energy storage (TMES) technologies are based are discussed and a synopsis of recent progress in their development is presented, assessing their ability to provide reliable and cost-effective solutions. The current performance and future prospects of TMES systems are examined within a unified framework and a thermo-economic analysis is conducted to explore their competitiveness relative to each other as well as when compared to PHES and battery systems. This includes carefully selected thermodynamic and economic methodologies for estimating the component costs of each configuration in order to provide a detailed and fair comparison at various system sizes. The analysis reveals that the technical and economic characteristics of TMES systems are such that, especially at higher discharge power ratings and longer discharge durations, they can offer promising performance (round-trip efficiencies higher than 60%) along with long lifetimes (>30 years), low specific costs (often below 100 $ kWh−1), low ecological footprints and unique sector-coupling features compared to other storage options. TMES systems have significant potential for further progress and the thermo-economic comparisons in this paper can be used as a benchmark for their future evolution

Progress and prospects of thermo-mechanical energy storage—a critical review

Abstract: The share of electricity generated by intermittent renewable energy sources is increasing (now at 26% of global electricity generation) and the requirements of affordable, reliable and secure energy supply designate grid-scale storage as an imperative component of most energy transition pathways. The most widely deployed bulk energy storage solution is pumped-hydro energy storage (PHES), however, this technology is geographically constrained. Alternatively, flow batteries are location independent and have higher energy densities than PHES, but remain associated with high costs and short lifetimes, which highlights the importance of developing and utilizing additional larger-scale, longer-duration and long-lifetime energy storage alternatives. In this paper, we review a class of promising bulk energy storage technologies based on thermo-mechanical principles, which includes: compressed-air energy storage, liquid-air energy storage and pumped-thermal electricity storage. The thermodynamic principles upon which these thermo-mechanical energy storage (TMES) technologies are based are discussed and a synopsis of recent progress in their development is presented, assessing their ability to provide reliable and cost-effective solutions. The current performance and future prospects of TMES systems are examined within a unified framework and a thermo-economic analysis is conducted to explore their competitiveness relative to each other as well as when compared to PHES and battery systems. This includes carefully selected thermodynamic and economic methodologies for estimating the component costs of each configuration in order to provide a detailed and fair comparison at various system sizes. The analysis reveals that the technical and economic characteristics of TMES systems are such that, especially at higher discharge power ratings and longer discharge durations, they can offer promising performance (round-trip efficiencies higher than 60%) along with long lifetimes (>30 years), low specific costs (often below 100 $ kWh−1), low ecological footprints and unique sector-coupling features compared to other storage options. TMES systems have significant potential for further progress and the thermo-economic comparisons in this paper can be used as a benchmark for their future evolution

Position-dependent effects of locked nucleic acid (LNA) on DNA sequencing and PCR primers

Genomes are becoming heavily annotated with important features. Analysis of these features often employs oligonucleotides that hybridize at defined locations. When the defined location lies in a poor sequence context, traditional design strategies may fail. Locked Nucleic Acid (LNA) can enhance oligonucleotide affinity and specificity. Though LNA has been used in many applications, formal design rules are still being defined. To further this effort we have investigated the effect of LNA on the performance of sequencing and PCR primers in AT-rich regions, where short primers yield poor sequencing reads or PCR yields. LNA was used in three positional patterns: near the 5′ end (LNA-5′), near the 3′ end (LNA-3′) and distributed throughout (LNA-Even). Quantitative measures of sequencing read length (Phred Q30 count) and real-time PCR signal (cycle threshold, C(T)) were characterized using two-way ANOVA. LNA-5′ increased the average Phred Q30 score by 60% and it was never observed to decrease performance. LNA-5′ generated cycle thresholds in quantitative PCR that were comparable to high-yielding conventional primers. In contrast, LNA-3′ and LNA-Even did not improve read lengths or C(T). ANOVA demonstrated the statistical significance of these results and identified significant interaction between the positional design rule and primer sequence

Working to Increase Stability through Exercise (WISE): screening, recruitment, and baseline characteristics

Background The aim of this paper is to describe the utility of various recruitment modalities utilized in the Working to Increase Stability through Exercise (WISE) study. WISE is a pragmatic randomized trial that is testing the impact of a 3-year, multicomponent (strength, balance, aerobic) physical activity program led by trained volunteers or delivered via DVD on the rate of serious fall-related injuries among adults 65 and older with a past history of fragility fractures (e.g., vertebral, fall-related). The modified goal was to recruit 1130 participants over 2 years in three regions of Pennsylvania. Methods The at-risk population was identified primarily using letters mailed to patients of three health systems and those over 65 in each region, as well as using provider alerts in the health record, proactive recruitment phone calls, radio advertisements, and presentations at community meetings. Results Over 24 months of recruitment, 209,301 recruitment letters were mailed, resulting in 6818 telephone interviews. The two most productive recruitment methods were letters (72% of randomized participants) and the research registries at the University of Pittsburgh (11%). An average of 211 letters were required to be mailed for each participant enrolled. Of those interviewed, 2854 were ineligible, 2,825 declined to enroll and 1139 were enrolled and randomized. Most participants were female (84.4%), under age 75 (64.2%), and 50% took an osteoporosis medication. Not having a prior fragility fracture was the most common reason for not being eligible (87.5%). The most common reason provided for declining enrollment was not feeling healthy enough to participate (12.6%). Conclusions The WISE study achieved its overall recruitment goal. Bulk mailing was the most productive method for recruiting community-dwelling older adults at risk of serious fall-related injury into this long-term physical activity intervention trial, and electronic registries are important sources and should be considered