CONWAY TWITTY ON MITIGATING CLIMATE CHANGE WITH TECHNOLOGY STILL IN DEVELOPMENT

MITIGATING CLIMATE CHANGE WITH THERMAL ENERGY INNOVATIONS

CITATION: Henry, A., Prasher, R. & Majumdar, A. Five thermal energy grand challenges for decarbonization. Nat Energy (2020). https://doi.org/10.1038/s41560-020-0675-9, Published10 August 2020, DOI https://doi.org/10.1038/s41560-020-0675-9

ABSTRACT:  Roughly 90% of the world’s energy use today involves generation or manipulation of heat over a wide range of temperatures. Here, we note five key applications of research in thermal energy that could help make significant progress towards mitigating climate change at the necessary scale and urgency.

PART-1: WHAT THE HENRY ETAL 2020 ARTICLE SAYS

TO MITIGATE CLIMATE CHANGE WE MUST LIMIT GLOBAL WARMING TO LESS THAN 2C SINCE PRE-INDUSTRIAL:  Advancing our ability to transport, store, convert and efficiently utilize thermal energy will play an indispensable role in avoiding a greater than 2 °C rise in global average temperature. Even though this critical need exists, there is a significant disconnect between current research in thermal sciences and what is needed for deep decarbonization. Here, we highlight five thermal science and engineering grand challenges that we believe could have a meaningful impact on global emissions. These were identified based on estimations of the size of their potential impact (that is, by assessing the fraction of global greenhouse gas (GHG) emissions that could be abated if the technology was maximally successful), as well as our own opinions and qualitative assessments of the magnitude of the opportunities for scientific advancement and technological breakthroughs. For example, improving the efficiency of heat engines in the stationary power sector is not highlighted here, despite the fact that it could be impactful, because current heat engines already operate very close to their thermodynamic limits.

THE PROBLEM WITH RENEWABLES: As solar and wind electricity penetration has increased, its intermittency has hastened the need for low-cost storage over a wide range of time scales, from seconds to days, and even seasonal storage. THE RENEWABLE SOLUTION DOES NOT WORK WITHOUT STORAGE BUT THERE IS NO PRACTICAL STORAGE SOLUTION. Pumped Hydro is geographically limited and Lithium-Ion Batteries are too expensive. These technologies will not fully decarbonize the grid. It is necessary to solve this problem to fully decarbonize the grid.

THE ANSWER IS THERMAL STORAGE: Solving this problem could enable full decarbonization of the grid, thereby reducing global GHG emissions by ~25%. To do that, the storage problem must be solved and to do that we must address this thermodynamics issue:  It is easy to convert electricity to heat but there is a large efficiency penalty when converting the heat back to electricity.

PART-2: PROPOSED SOLUTIONS TO THE THERMAL STORAGE PROBLEM

(1) Amy Caleb 2017: Pumping liquid metal at high temperatures up to 1,673 Kelvin: [LINK] ABSTRACT: Heat is fundamental to power generation and many industrial processes, and is most useful at high temperatures because it can be converted more efficiently to other types of energy. However, efficient transportation, storage and conversion of heat at extreme temperatures (more than about 1,300 kelvin) is impractical for many applications. Liquid metals can be very effective media for transferring heat at high temperatures, but liquid-metal pumping has been limited by the corrosion of metal infrastructures. Here we demonstrate a ceramic, mechanical pump that can be used to continuously circulate liquid tin at temperatures of around 1,473–1,673 kelvin. Our approach to liquid-metal pumping is enabled by the use of ceramics for the mechanical and sealing components, but owing to the brittle nature of ceramics their use requires careful engineering. Our set-up enables effective heat transfer using a liquid at previously unattainable temperatures, and could be used for thermal storage and transport, electric power production, and chemical or materials processing.

The full text of the Amy Caleb paper is available for download in PDF format from this site. Here is the link: CALEB2017PDF  ….  WARNING: Clicking on this link will cause a large pdf file to  be downloaded to your device.

(2) Robert Laughlin (2017) Pumped thermal grid storage with heat exchange [LINK] ABSTRACT:  A thermal heat-pump grid storage technology is described based on closed-cycle Brayton engine transfers of heat from a cryogenic storage fluid to molten solar salt. Round-trip efficiency, computed as a function of turbomachinery polytropic efficiency and total heat exchanger steel mass, is found to be competitive with pumped hydro. The cost per engine watt and cost per stored joule based are estimated based on the present-day prices of power gas turbines and market prices of steel and nitrate salt. Comparison is made with electrochemical and mechanical grid storage technologies.

The link provided above is to the full text of the Laughlin paper. If the link fails, the full text PDF may be downloaded from this site. Here is the link: LAUGHLIN2017PDF  WARNING: Clicking on this link will cause a large pdf file to  be downloaded to your device.

PART-3: SUMMARY 

1. The traditional solution to intermittency of renewable energy from wind and solar in the form of fossil fueled backup contains the contradiction of a need for fossil fuels in the climate action effort to replace fossil fuels with renewable energy. Therefore, from the anti fossil fuel position of climate science, it is necessary to find alternative solutions to the intermittency issue in wind and solar renewable energy.
2. Although pumped hydro has been traditionally used for this purpose, this solution is location specific and is not a global solution. In the papers reviewed above and those listed in the bibliography below, are described new technologies currently under development that may offer a purely renewable energy storage solution to address intermittency in wind and solar without the contradiction of the need for fossil fuels to move the global energy infrastructure away from fossil fuels in a climate action effort to limit the temperature rise in anthropogenic global warming to 2C since pre-industrial.
3. Foremost among these energy storage technologies proposed in the the last decade, 2010-2020, are Thermal Energy Storage (TES), Pumped Heat Electricity Storage (PHES), and thermal energy storage with Phase Change Material (PCM). These alternatives to pumped hydro are currently under development with pumped hydro being currently the only storage technology available to address the intermittency issue in renewable energy.
4. The Henry (2017) paper presented above addresses two TES technologies citing the Caleb (2017) and Laughlin (2017) where energy storage is envisioned in molten metals and in molten salt. Advances in TES technology and engineering as well ongoing developments in PCM and PHES are described in the bibliography below over the period from 2011 to 2020. Advances in the science, technology, and engineering of such energy storage systems are encouraging and may one day lead to a solution to intermittency of wind and solar power in the absence of pumped hydro.

PART-4: CRITICAL COMMENTARY

1. In the history of energy that drove human progress since the Neolithic Revolution from human power, animal power, the invention of the wheel, water wheels, windmills, the combustion of carbon based fuels, and nuclear power, the evolution of energy technology was orderly and progressive. These changes were driven by ideas and innovations in a market economy. The dynamics of a market for energy that selects winners and losers is the evolutionary process gave us the fossil fueled economy we live in.
2. However, certain downsides to fossil fuels were identified in the 1960s when smog, oil spills, acid rain, and other environmental issues emerged as serious downsides to fossil fuels from both human welfare and ecology points of view. The 1960s hippie movement against fossil fuels, described in a related post [LINK] was a product of these weaknesses in fossil fuel energy.
3. These environmental weaknesses of fossil fuels spearheaded the renewable energy movement more than 50 years ago with innovations in wind, solar, tidal, and geothermal energy. However, in the market for energy, even as renewable energy was being developed and implemented, fossil fuels regained the upper hand with technological innovations needed to overcome environmental laws enforced by the newly formed Environmental Protection Agency (EPA). The acid rain story, presented in a related post [LINK] , is instructive in this historical context.
4. These innovations by the fossil fuel industry solved the smog, the acid rain, and oil spill problems and weakened the case against fossil fuels. At the same time, the widespread implementation of renewables revealed their operational weaknesses in terms of intermittency, and power output variability not under human control, the need for fossil fueled backup power, and high maintenance cost. As a result, renewables could not compete with the new improved fossil fuel energy product free of smog and acid rain. Wind, solar, tidal, and geothermal waned and retreated into a near death experience. This left the large and growing environmental movement against fossil fuels in shock because it had seemed for a time that the war against fossil fuels had been won and that clean green renewables were the future of energy.
5. The rise of fear based climate change environmentalism is best understood in this context. As described in the related post [LINK] , fear based climate change is preached by climate scientists and activist with horrific predictions of extreme heat, the collapse of polar ice sheets, catastrophic sea level rise, extreme weather in terms of storms, droughts, floods, heat waves, forest fires, mass extinctions, and the collapse of civilization. Even the phraseology to describe global warming and climate change turned into global heating and climate crisis or climate emergency. The fear is then further extended to the whole of the planet with the assessment that if we continue to burn fossil fuels it will be the end of life on earth and the end of the the planet itself.
6. At issue is the use of fossil fuels because all of these fearful things are described as the effect of burning fossil fuels. We are told that burning fossil fuels creates CO2 from very old carbon from under the ground that does not belong in today’s atmosphere. And that when this old CO2 is released into the atmosphere it causes atmospheric CO2 to rise [LINK]  and that in turn causes warming (or heating) by way of the greenhouse effect of CO2 . And that therefore, the only solution to the global heating crisis is to take “climate action” and that means to stop using fossil fuels and move the world’s energy infrastructure to wind and solar renewables.
7. We propose that the interpretation of this argument as a rationale for moving the world’s energy infrastructure from fossil fuels to wind and solar renewables is that there was no rational case for renewables because of their operational drawbacks particularly in terms of intermittency and unreliability. The theory of catastrophic climate change was needed to force the issue with fear based activism against fossil fuels having failed to compete in the market for energy.
8. Belatedly, after more than two decades of forced implementation of a flawed energy model with fear based activism against fossil fuels, climate science now boasts that the technologies such as TES, PCM, and PHES are currently in development and that these technologies hold the promise of solving the unreliability and intermittency problem of wind and solar renewable energy.
9. In the context of the history of the cart before the horse forced implementation of wind and solar renewables with fear based activism, the promising developments for reliable wind and solar renewables after the fact reveals the fallacy of forced fear based activism as a method for promoting renewables. A technology still under development and not ready for the market was thus imposed with activism.
10. This grotesque history of the attempt to force an energy transition with an incomplete and yet undeveloped technology is revealed as yet another criminal failure in a poorly thought out activism against fossil fuels before the alternative energy technology development was complete and before the technology was at hand.
11. The admission at this late stage in the climate movement that technologies for reliability of renewables are still in development in addition to the fear mongering lies needed to push that incomplete technology discredits the climate movement. There should be criminal charges or at the least lawsuits against the perpetrators of this scam.

SOME IMPLEMENTATION ISSUES FOR RENEWABLES

SOURCE: JAN SMELIK, THE NETHERLANDS COURTESY OF PAUL HOMEWOOD OF NOTALOTOFPEOPLEKNOW THAT.WORDPRESS.COM

WHAT JAN SAYS

1. First, biomass was thought to be renewable green energy but the logical flaws in that assessment is now widely recognized so that biomass is no longer either renewable or green.
2. With regard to solar: the amount of space it takes is such that it cannot be used on a large scale and what makes that worse is that solar requires exclusive use of the land it is on and the absence of shade.
3. The absence of sunshine at night these facilities can generate power only during the day. Also, at extreme latitudes, the solar energy available from the sun during the three winter months is essentially zero. To use this technology under those conditions, it would be necessary to store enough power for the months of no sunshine – an impossibility.
4. The Netherlands has 2,300 windmills installed on land and in the ocean for renewable energy as part of their climate action policy. The question is how many do we need to replace fossil fuels?  We take the current consumption of energy in the Netherlands of 2,440 petajoules. Of that, electricity accounts for 379 petajoules. or 106 billion kw-hours.
5. Wind turbines on average yield 5 megawatts per wind turbine.  5 megawatts = 5,000 kilowatts. At continuous production every hour of the day and every day of the year, one wind turbine can deliver 5000*24*365 = 43.8 million kw hours. For the 106 billion kw hours needed we require 2,420 wind turbines.
6. Wind turbine installation requires a minimum distance between them to avoid wind-shadow interference among them. This distancing requirement implies that the distance between wind turbines should be at least 5 times the height of the turbines.
7. Typically, wind turbines are about 200 meters tall. This means that they should be spaced 1km apart. Therefore, to install 2,420 wind turbines in the sea off the coast of the Netherlands, we need 2,500 square km. If a square, it will be 50km by 50km.
8. The computations above are based on the maximum power output continuously year round from each of these turbines. This output is available only between wind speeds of 10 to 15 meters per second. . Above 15 m/s they have to turn off the turbines to protect them from the wind. Most of the time the winds speed is below 10m/s with  correspondingly lower power output.
9. A good rule of thumb is that on average, we get 25% of the power output under ideal wind conditions of 10-15m/s. This means that the number of turbines we need are 4*2420 or 9,680 turbines. So instead of 2500 sqkm we will need 10,000 sqkm or 100km by 100km.
10. Yet another consideration is that the average we computed above is the average between very high and very low output with the very low output frequently zero. When the wind velocity is too low we don’t have power. This means that to use wind turbines, we must be able to store power for those times when the turbines are not delivering.
11. The amount of energy that must be stored for this function is enormous and so battery storage is not an option. What is being proposed is hydrogen. When there is too much power, the excess power is used to electrolyze sea water and make hydrogen. When there is insufficient wind and insufficient power, liquid hydrogen combustion generates and delivers power.
12. Although the liquid hydrogen option looks good on paper, the hidden complexity of this solution is that these back and forth energy conversions are not efficient but suffer enormous inefficiency losses. In the conversion to hydrogen and back to electricity 2/3 of the energy is lost to inefficiencies such that only 1/3 of the energy generated at high wind speed can be delivered at low wind speed.
13. To compensate for these inefficiency losses, we need more than 9,680 wind turbines. To compensate for a 75% efficiency loss, we need 2.5*9680 = 24,200 wind turbines. The area of ocean needed now goes up to 150km by 150km or 22,500 sqkm. 
14. It is noted that the analysis above is just for providing the electricity currently being consumed in the Netherlands that account for 16% of the total energy consumed by the country – as for example energy for transport (cars and trucks), home heating, and other direct uses for fossil fuels. 
15. To supply the total energy needs of the Netherlands, we will need 157,000 wind turbines. The area needed now explodes to 400km by 400km or 160,000 sqkm – compared with 41,453 sqkm for the country of the Netherlands. The North Sea region accessible and usable by the Netherlands for wind turbines does not contain sufficient area for the number of wind turbines needed. Add to that the eletrolysis and and hydrogen storage tanks. 
16. Now consider that wind turbines cost about 5 million Euros each (installed). The wind turbine energy system described above will cosgt 800 billion Euros – not including the facilities needed to store and use hydrogen. Also not included is the additional cost of modifying the electricity grid to deliver the wind energy involving hundreds of billions of Euros of investment needed. 
17. But the worst news of all is yet to come. It is that the life span of wind turbines in the salty sea environment is 20 years although they last about 30 years on land. That cost is not a one time investment but an ongoing maintenance cost to keep the facility in operation. 
18. In his September 2020 video, Jan adds the ecological damage caused by renewable energy along the lines of the presentation made in the Michael Moore film Planet of the Humans. He says as follows: 
19. Many of the measures taken to save the planet from climate change are made at the expense of the environmental. The advantages of Green technologies are exaggerated. Here are some drawbacks of green energy that are not widely known or appreciated. 
20. Biomass is already under fire now that it has become clear that forests are being felled on a large scale for the production of biomass. Greens vehemently oppose deforestation in Amazonia for agricultural purposes but ironically supported deforestation elsewhere for biomass until recently. Currently, global energy consumption is about 13.5 gigatons of oil equivalent =5.67E20 Joules per year. The total amount of wood in our forests worldwide is 536 gigatons of wood in the world’s forests. The thermal value of wood is 18 megajoules per kg of wood. Thus the available heat energy in the world’s forests is 9.5E21 Joules.  If we use forests for all our energy needs, we will use them all up in 17 years not counting planting and re-growth.
21. Another form of agricultural renewable energy is biofuel as for ethanol and palm oil. The problem here is that energy production competes with food production for agricultural land. A dramatic example is the millions of acres of forest lands burned and cleared for palm oil in Indonesia. The climate movement that once pushed for biofuels has now backed off from biofuels.  [RELATED POST ON BIOFUELS] . 
22. There are similar drawbacks to solar energy. Fields of solar panels compete with agriculture for land. The use of solar panels also raise serious environmental issues. The mining of rare earths needed to make solar panels is environmentally destructive and a greatly increased scale of this operation will wreak ecological destruction oon a grand scale. The ecological issues with these materials in solar cells re-appear at the end of their useful life in their disposal.  At the end of their lifespan, solar panels are shredded. Only the glass and metal are recycled. The rest of the solar cell is discarded. The toxic substances that were mined in the DRC now end up in the environment of the renewable energy consumers. Recycling is too costly because the toxic minerals are baked into the solar cells. 

DUGGAN FLANAKIN OF CFACT PROVIDES DETAILS ON THE WASTE DISPOSAL ISSUE IN WIND TURBINES.  [LINK TO CFACT WEBSITE]

1. At the end of the useful life of wind turbines of 20 to 30 years, they must be removed, discarded, and replaced. The waste disposal issue involves the concrete and rebar foundations and the very large blades that are up to 107 meters (351 feet) long. No part of these waste items is recyclable.
2. The volume of this waste disposal issue is enormous. Blade disposal alone is estimated to be 43 megatons by 2050, approximately 1.4 megatons per year on average equivalent to dumping a million cars a year. 
3. This dumping problem is made worse by the toxic nature of the the material. The toxicity issue is described by Flanakin as “a toxic amalgam of composites, fiberglass, epoxy, polyvinyl chloride foam, polyethylene terephthalate foam, balsa wood, and polyurethane coatings”. 
4. The blades are so large and heavy that a tractor trailer can haul only one blade at a time to the landfill at a cost of $400,000 per blade. The volume of this disposal is 8,000 blades a year in the USA alone (. That’s 8,000 fossil fueled tractor trailer trips to the landfill every year in addition to the pollution of the soil with the blade materials. The total annual cost in the USA for blade disposal alone is $3.2 billion. At the same time blade disposal is using up US landfill disposal capacity. A blade disposal environmental crisis lies in wait. And then there are those solar panel and battery wastes to be disposed of as well. 
5. Yet another issue with wind turbines not well known is that wind farms create unsafe flying conditions because the rotational force of turbines creates turbulence that makes flying overhead and landing close by dangerous. This feature of wind farms is known to affect air ambulance services. 
6. This analysis by Duggan Flanakin was provided by the wuwt website. For details please visit this wuwt post at this link:  [THE REFERENCE WUWT POST BY FLANAKIN] 

PART-5:  PHES. PCM, AND TES BIBLIOGRAPHY

1. Thess, André. “Thermodynamic efficiency of pumped heat electricity storage.” Physical review letters 111.11 (2013): 110602.  Pumped heat electricity storage (PHES) has been recently suggested as a potential solution to the large-scale energy storage problem. PHES requires neither underground caverns as compressed air energy storage (CAES) nor kilometer-sized water reservoirs like pumped hydrostorage and can therefore be constructed anywhere in the world. However, since no large PHES system exists yet, and theoretical predictions are scarce, the efficiency of such systems is unknown. Here we formulate a simple thermodynamic model that predicts the efficiency of PHES as a function of the temperature of the thermal energy storage at maximum output power. The resulting equation is free of adjustable parameters and nearly as simple as the well-known Carnot formula. Our theory predicts that for storage temperatures above $400°C$ PHES has a higher efficiency than existing CAES and that PHES can even compete with the efficiencies predicted for advanced-adiabatic CAES.
2. Howes, Jonathan. “Concept and development of a pumped heat electricity storage device.” Proceedings of the IEEE 100.2 (2011): 493-503.  This paper addresses the early conceptualization of a system for reversible heat/work conversion based upon the heat engine cycle, developed in 1833 by John Ericsson, in combination with utility scale thermal energy storage in particulate mineral (e.g., gravel) and the development and test of the first prototype. Using these test results, mathematical modeling of the engine/heat pump has yielded improved second and third prototypes. Design of the second prototype and its behavior under test is discussed. Extant test results are used to extrapolate to the predicted performance of utility scale equipment.
3. Ni, Fan, and Hugo S. Caram. “Analysis of pumped heat electricity storage process using exponential matrix solutions.” Applied Thermal Engineering 84 (2015): 34-44.  Pumped heat electricity storage (PHES) is a recently proposed competitive energy storage solution for large scale electrical energy storage (EES). It is especially valuable for regions where specific geological structures are not available. The performance of PHES depends on two factors: the operations of turbomachines and the thermal storage system. The former is characterized by pressure ratio, polytropic efficiency and gas heat capacity ratio. The latter contains the parameters of heat regenerators that can be summarized into two dimensionless numbers: length Λ and step time π. The overall process operation can be described by temperature difference representing the energy stored per unit heat capacity, the storage bed utilization ratio and the turn-around efficiency. Exponential matrix solutions are obtained for a discretized heat transfer model of a typical pumped heat electricity storage process. Using the cyclic steady state and transient state solutions, we are able to analyze how dimensionless length and step time affect the storage bed utilization ratio as well as the turn-around efficiency. This model provides basic guidance for further development of such processes.
4. Roskosch, Dennis, and Burak Atakan. “Pumped heat electricity storage: potential analysis and orc requirements.” Energy Procedia 129 (2017): 1026-1033.  The rising share of renewable energy sources in power generation leads to the need of energy storage capacities. In this context, also some interest in thermal energy storages, especially in a concept called pumped heat electricity storage (PHES), arises. One possible design of such a PHES system consists of a compression heat pump, a thermal storage and an organic Rankine cycle (ORC). The present work analyses the general thermodynamic potential and limits of such a system and deals with the unusual requirements for the ORC. The potential analysis starts with the optimal case of combining two Carnot cycles with irreversible heat transfer. It is found that the efficiency of the entire process increases with increasing storage temperature and in general roundtrip efficiencies up to 70 % are predicted. Afterwards the cycles are transferred to cycles that are more realistic by considering technical aspects and a hypothetical working fluid which is optimized by an inverse engineering approach. This leads to lowered roundtrip efficiencies, which now, decrease with increasing storage temperatures. In a second step the specific ORC requirements as part of a PHES are considered, emphasizing the working fluid parameters. Especially, the use of a latent thermal energy storage leads to an ORC design differing from common (e.g. geothermal) applications. It is shown that the efficiency of the ORC and of the entire process strongly depends on the superheating at the expander inlet; here, the superheating must be held as small as possible, contrary to ORCs using common heat sources. [FULL TEXT PDF]
5. Dietrich, Axel, Frank Dammel, and Peter Stephan. “Exergoeconomic Analysis of a Pumped Heat Electricity Storage System with Concrete Thermal Energy Storage.” International Journal of Thermodynamics 19.1 (2016).  Within the last 25 years the share of renewable energy sources in electrical energy production in Germany has been rising considerably. The volatility of renewable energy sources results in an increasing mismatch between supply and demand of electrical energy creating the need for storage capacities. The storage of electrical energy via the detour of thermal energy can be realized by a relatively new technology known as Pumped Heat Electricity Storage systems. This paper examines the exergoeconomic performance of such a storage system. A sample system comprising a concrete thermal energy storage is introduced; unsteady operations are simulated and analyzed. Although the achieved efficiencies are reasonable economical operations of the analyzed Pumped Heat Electricity Storage System are currently not possible. For the analyzed operation scenario the exergetic system efficiency, electrical energy output to electrical energy input, amounts to 27:3%. Considering the storage capacity and the lack of geological requirements the Pumped Heat Electricity Storage system can compete with pumped hydro and compressed air energy storage. However, prices of the order of 60 ct/(kWh) are not competitive considering current energy prices. Based on improved system designs as well as rising energy prices we assess Pumped Heat Electricity Storage Systems as a potential alternative to established storage technologies.
6. Levelised Cost of Storage for Pumped Heat Energy Storage in comparison with other energy storage technologies, AndrewSmallbonea, VerenaJülchb, RobinWardlea, Anthony PaulRoskillyaa.  Sir Joseph Swan Centre for Energy Research, Newcastle University, Newcastle upon UK, Fraunhofer Insitute for Solar Energy Systems ISE, Freiburg, Germany. 2017.  ABSTRACT:  Future electricity systems which plan to use large proportions of intermittent (e.g. wind, solar or tidal generation) or inflexible (e.g. nuclear, coal, etc.) electricity generation sources require an increasing scale-up of energy storage to match the supply with hourly, daily and seasonal electricity demand profiles. Evaluation of how to meet this scale of energy storage has predominantly been based on the deployment of a handful of technologies including batteries, Pumped Hydro, Compressed Air Energy Storage and Power-to-Gas. However, for technical, confidentiality and data availability reasons the majority of such analyses have been unable to properly consider and have therefore neglected the potential of Pumped Heat Energy Storage, which has thus not been benchmarked or considered in a much detail relative to competitive solutions. This paper presents an economic analysis of a Pumped Heat Energy Storage system using data obtained during the development of the world’s first grid-scale demonstrator project. A Pumped Heat Energy Storage system stores electricity in the form of thermal energy using a proprietary reversible heat pump (engine) by compressing and expanding gas. Two thermal storage tanks are used to store heat at the temperature of the hot and cold gas. Using the Levelised Cost of Storage method, the cost of stored electricity of a demonstration plant proved to be between 2.7 and 5.0 €ct/kW h, depending on the assumptions considered. The Levelised Cost of Storage of Pumped Heat Energy Storage was then compared to other energy storage technologies at 100 MW and 400 MW h scales. The results show that Pumped Heat Energy Storage is cost-competitive with Compressed Air Energy Storage systems and may be even cost-competitive with Pumped Hydroelectricity Storage with the additional advantage of full flexibility for location. As with all other technologies, the Levelised Cost of Storage proved strongly dependent on the number of storage cycles per year. The low specific cost per storage capacity of Pumped Heat Energy Storage indicated that the technology could also be a valid option for long-term storage, even though it was designed for short-term operation. Based on the resulting Levelised Cost of Storage, Pumped Heat Energy Storage should be considered a cost-effective solution for electricity storage. However, the analysis did highlight that the Levelised Cost of Storage of a Pumped Heat Energy Storage system is sensitive to assumptions on capital expenditure and round trip efficiencies, emphasising a need for further empirical evidence at grid-scale and detailed cost analysis. [FULL TEXT PDF]
7. Arce, Pablo, et al. “Overview of thermal energy storage (TES) potential energy savings and climate change mitigation in Spain and Europe.” Applied energy 88.8 (2011): 2764-2774.  Thermal energy storage (TES) is nowadays presented as one of the most feasible solutions in achieving energy savings and environmentally correct behaviors. Its potential applications have led to R&D activities and to the development of various technologies. However, so far there is no available data on a national scale in Spain and on a continental level in Europe, to corroborate the associated energetic and environmental benefits derived from TES. This is why, based on a previous potential calculation initiative model performed in Germany, this work intends to provide a first overview of the Spanish TES potential as well as an European overview. Load reductions, energy savings, and CO₂ emissions reductions are tackled for the buildings and industrial sector. Results depend on the amount of implementation and show that, in the case of Europe for instance, yearly CO₂ emissions may get to be cut down up to around 6% in reference to 1990 emission levels.
8. Zhou, Zhihua, et al. “Phase change materials for solar thermal energy storage in residential buildings in cold climate.” Renewable and Sustainable Energy Reviews 48 (2015): 692-703.  Heating accounts for a large proportion of energy consumption in residential buildings located in cold climate. Solar energy plays an important role in responding to the growing demand of energy as well as dealing with pressing climate change and air pollution issues. Solar energy is featured with low-density and intermittency, therefore an appropriate storage method is required. This paper reports a critical review of existing studies on thermal storage systems that employ various methods. Latent heat storage using phase change materials (PCMs) is one of the most effective methods to store thermal energy, and it can significantly reduce area for solar collector. During the application of PCM, the solid–liquid phase change can be used to store a large quantity of energy where the selection of the PCM is most critical. A numerical study is presented in this study to explore the effectiveness of NH₄Al(SO₄)₂·12H₂O as a new inorganic phase change material (PCM). Its characteristics and heat transfer patterns were studied by means of both experiment and simulation. The results show that heat absorption and storage are more efficient when temperature of heat source is 26.5 °C greater than the phase transition temperature. According to heat transfer characteristics at both radial and axial directions, it is suggested to set up some small exchangers so that solar energy can be stored unit by unit in practice. Such system is more effective in low density residential buildings.
9. Zhou, Dan, Chang-Ying Zhao, and Yuan Tian. “Review on thermal energy storage with phase change materials (PCMs) in building applications.” Applied energy 92 (2012): 593-605. Thermal energy storage with phase change materials (PCMs) offers a high thermal storage density with a moderate temperature variation, and has attracted growing attention due to its important role in achieving energy conservation in buildings with thermal comfort. Various methods have been investigated by previous researchers to incorporate PCMs into the building structures, and it has been found that with the help of PCMs the indoor temperature fluctuations can be reduced significantly whilst maintaining desirable thermal comfort. This paper summarises previous works on latent thermal energy storage in building applications, covering PCMs, the impregnation methods, current building applications and their thermal performance analyses, as well as numerical simulation of buildings with PCMs. Over 100 references are included in this paper.
10. Soares, Nelson, et al. “Review of passive PCM latent heat thermal energy storage systems towards buildings’ energy efficiency.” Energy and buildings 59 (2013): 82-103.  This paper aims to explore how and where phase change materials (PCMs) are used in passive latent heat thermal energy storage (LHTES) systems, and to present an overview of how these construction solutions are related to building’s energy performance. A survey on research trends are firstly presented followed by the discussion of some physical and theoretical considerations about the building and the potential of integrating PCMs in construction elements. The different types of PCMs and main criteria that govern their selection are reviewed, as well as the main methods to measure PCMs’ thermal properties, and the techniques to incorporate PCMs into building elements. The numerical modeling of heat transfer with phase-change and heat transfer enhanced techniques are discussed, followed by a review of several passive LHTES systems with PCMs. Studies on dynamic simulation of energy in buildings (DSEB) incorporating PCMs are reviewed, mainly those supported by EnergyPlus, ESP-r and TRNSYS software tools. Lifecycle assessments, both environmental and economic are discussed. This review shows that passive construction solutions with PCMs provide the potential for reducing energy consumption for heating and cooling due to the load reduction/shifting, and for increasing indoor thermal comfort due to the reduced indoor temperature fluctuations.
11. H Abedin, Ali, and Marc A Rosen. “A critical review of thermochemical energy storage systems.” The open renewable energy journal 4.1 (2011).  Thermal energy storage (TES) is an advanced technology for storing thermal energy that can mitigate environmental impacts and facilitate more efficient and clean energy systems. Thermochemical TES is an emerging method with the potential for high energy density storage. Where space is limited, therefore, thermochemical TES has the highest potential to achieve the required compact thermal energy storage. Thermochemical TES is presently undergoing research and experimentation. In order to develop an understanding of thermochemical TES systems and to improve their implementation, comprehensive analyses and investigations are required. Here, principles of thermochemical TES are presented and thermochemical TES is critically assessed and compared with other TES types. Recent advances are discussed.