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Mechanical energy storage

Mechanical energy storage (or electromechanical energy storage) systems are devices which convert electrical energy into kinetic or potential energy which can be reconverted into electricity at a later stage. Mechanical energy storage systems can be used in the grid to balance peak periods and to provide ancillary services including frequency, primary and voltage control to the power grid. The main technologies include pumped hydro energy storage (PES), flywheels, compressed air energy storage (CAES), and liquid air energy storage (LAES).  

 

PES: This technology comprises two reservoirs at different elevations connected by either pipes or tunnels and exploits the potential energy of water to store energy. In those systems, water is pumped to the upper reservoir during periods of low electricity demand when there is an excess of electricity available and released to power turbines when more electricity is needed. The efficiency of this system is estimated to be between 70-85% [1]. 

 

Flywheels: they store kinetic rotational energy through a rotor which is charged and discharged electrically using a dual-purpose motor/generator. Flywheels are characterized by fast response times, long cycle life, and high power density. The most common applications include transportation, frequency regulation and stability in electric grids, balancing fluctuations in renewable generation and peak management. The storage capacity of the flywheel is proportional to the mass of the rotor, which requires making these systems very heavy (e.g., metallic or composite materials) [2]. 

Source: https://en.wikipedia.org/wiki/Flywheel_storage_power_system 

Source: https://arena.gov.au/ 

 

CAES: this technology stores electrical energy in the form of compressed air during periods of excess electricity or low energy demand. In these systems, air is stored in underground mines or caves created inside salt rocks. To reconvert the pressurized air into electricity two main technologies can be used which differentiate the two main CAES typologies: diabatic CAES (D-CAES) and adiabatic CAES (D-CAES) [3]. In systems belonging to the first typology, the pressurized air is fed into a combustion chamber using natural gas or fuel and then expanded into a turbine to generate electricity. The efficiency of these systems can be estimated around 55% [1]. On the other hand, in A-CAES systems no combustion chamber is used. In this case, the heat produced during the compression is recovered and stored as thermal energy and used to increase the temperature of the air before the expansion in the turbine. Because of the heat recovered, the efficiency of these systems can exceed 70%. CAES is a technology suitable for peak shaving, load shifting, or for stabilising the grid through frequency regulation, contingency reserves, voltage support, or black start [4]. 

Source http://www.apexcaes.com/technology-overview 

 

LAES: this technology is similar to the concept of an adiabatic CAES yet, in this case, the pressurized air (or nitrogen) is liquefied using a Linde or Claude process and then stored in an unpressurized vessel. The main advantage compared to CAES is the higher energy density of the liquefied air (or nitrogen) which is then evaporated and expanded in a turbine when electric power is needed. LAES can be also combined with waste heat and waste cold sources to increase the process efficiency. However, also in a stand-alone configuration, the heat of compression and the cold released before the expansion in the turbine can be recovered to improve both the liquefaction and discharging process reaching a round trip efficiency of around 60%. LAES can be integrated into the grid with the same functionality as CAES with the ability to provide also cold thermal energy in a co-generation asset [5].  

Source Borri E, Tafone A, Zsembinszki G, Comodi G, Romagnoli A, Cabeza LF. Recent Trends on Liquid Air Energy Storage: A Bibliometric Analysis. Applied Sciences. 2020; 10(8):2773. https://doi.org/10.3390/app10082773 

 

Another technology is pumped heat electrical storage (PHES) which is similar to PES, but in this case, heat is pumped between two thermal storages at different temperatures using a reversible heat pump/heat engine. However, this technology is in the development stage. 

 

MATURITY:  

Each technology has a different level of maturity [1,3,5]: 

 

PES is already a mature technology with TRL9 and more than 170 GW already installed worldwide. 

 

Flywheel is a technology already available on the market (TRL9). Nevertheless, some improvements are needed to reduce the cost of manufacturing and be competitive with other storage solutions.   

 

CAES: Diabatic CAES can be considered mature at TRL9 with two plants already operative, one located in McIntosh, US (110 MW) commissioned in 1991, and another in Huntorf, Germany (320 MW) commissioned in 1978. Regarding adiabatic CAES, two commercial facilities were launched in 2019 in Feicheng, Shandong, China (1250 MW) and in Goderich Ontario Canada (1.75 MW). 

 

LAES: unlike the CAES, this technology is at commercial/demonstration stage (TRL 7-8). In 2018, Highview Power [6] started to operate a grid-scale 5MWe/15 MWh LAES plant located in Bury in the UK. Nevertheless, commercial plants are currently being developed by the company in UK and other countries. 

CO-BENEFITS
PRE-CONDITIONS & ENABLING CONDITIONS
DRAWBACKS/ADVERSE IMPACTS OF THE SOLUTIONS after implementation
EXTERNAL LINKS
IMPACTS (Indicators + DNSH)
INSTRUMENTS/Processes for implementation
EXAMPLES

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Grey water treatment (including Nature Based Solutions) and reuse

Greywater is the wastewater generated in households or office buildings without serious contaminants, such as water from baths, sinks and washing machines. Greywater can be separated from blackwater (water from toilets or kitchens) and then treated on-site for direct reuse in toilets recharge or irrigation. Greywater is a relevant secondary source of water and nutrients. Many studies have analysed the environmental, economic, and energetic benefits of the reuse of greywater [1][2][6][7]. Greywater treatment systems can be introduced in new buildings or in existing buildings with retrofitting measures. There are different greywater treatment systems: diversion and filtration, diversion and treatment (using chemicals), or nature-based solutions (NBS). 

 

Traditional greywater treatment 

Greywater treatment by mechanical systems is typically based on filtration or treatment with chemicals. In filtration, the aim is to remove impurities using filters, with typically a few or several filters in a row in order to guarantee good results. In a purifying process done with chemicals, the aim is to add chemicals that bind impurities, which are then removed from the water, for example, by filters. The mechanical treatment can start with a settlement tank, where coarse particles settle in the bottom of the tank and are then removed. After that, the greywater flows through filters, typically first gravel and sand and then biological filters like wood or peat. Last, if needed, ultraviolet light or chemicals are used to remove potential bacteria. 

Green roof and greywater treatment [7] 

 

Grey water recovery system [10] 

The first filter is a biofilter, which removes the fats and oil. The sand and gravel filter removes small particulates and other impurities. 

 

NBS-based greywater treatment 

Nature-based solutions (NBS) applications are typically constructed wetlands, green roofs, and green walls [1][2][3]. 

 

Several studies have shown that NBS-based greywater treatment has high removal performances [1][5], indicating the suitability of these systems in treating domestic greywater. Planning and design parameters should be carefully considered when implementing NBS; high residence time of water can be especially important for grey water treatment efficiency (see e.g., [1]). To optimize the removal processes in NBS, appropriate plant species and substrates (as growing material), optimal hydraulic parameters, and suitable operating conditions are needed.  

 

The decentralized process consists of several stages: (i) greywater separation, (ii) storage, (iii) treatment by innovative NBS as multi-level green walls/green façades, or by mechanical systems as multi-layer filters and activated carbon, and (iv) final disinfection using commercial O3/UV systems (Ozone and Ultraviolet).  

MATURITY:  

 

Some building-level solutions for grey water treatment and reuse (including nature-based) are commercially available, for example:  

 

  • Aqua Gratis is a technology to capture and reuse the bath and shower water for flushing toilets. The solution is at the stage of initial market commercialisation. The technology development of Aqua Gratis was funded by the EU. 

  • REDI gives a solution for single-family houses, where the treated greywater can be used for watering the garden. 

  • Disinfection can be done with commercially available solutions, e.g. with ozone and ultraviolet (UV) light. 

 

Some examples of pilots are: 

 

  • Greywater treatment with nature-based solutions for indoor or outdoor modules in multi-level green walls/green façades was carried out in Houseful. The project tested also ozone and ultraviolet light for disinfection.  

  • Water management systems and how to monitor and collect water condition information for urban water management platforms were piloted in UNaLab. 

  • Green walls and constructed wetlands were piloted in NAWAMED, with a focus on grey water treatment from a public building, a parking area, and a refugee camp. 

  • A service model for grey water treatment with NBS was tested in Houseful. The service model considers a leasing contract and a payment fee per m3 of water treated and reused. 

 

The nature-based grey water systems have been tested in a rather short period of time (e.g., some months to 1–2 years). Since the operating time of grey water treatment should be closer to 15-20 years, a further full-scale testing is still needed. [1]. 

Passive building design strategies: building orientation, passive heating and cooling

Passive building design means providing passive heating, passive cooling, and natural ventilation to maintain comfortable indoor conditions with no need for energy, by taking advantage of location (climate), orientation, massing, shading, material selection, thermal mass, insulation, internal layout and the positioning of openings to allow the penetration of solar radiation, daylight, and ventilation in the desired amounts [1–8]. When duly applied, passive design strategies are a designer’s first opportunity to increase a building’s energy efficiency, without adding much less front-end cost to a project as compared to active design strategies. Efficient passive design results in smaller heating and cooling loads (so that the building’s mechanical system – if any – can be downsized) and smaller electric loads for lighting through the use of daylighting design strategies.  

 

Beyond local climate, building orientation is a key aspect for passive design. The most energy-efficient designs are facing south or north to allow better solar energy management and better quality of daylighting. Building shape is also very relevant in the design, as an elongated and narrow plant (with south or north facing façade) allows for more of the building to be receive daylight. Shading strategies properly combined with other passive design strategies are also required, especially in hot climates [9,10]. Since the main difficulty in designing natural ventilation systems driven by buoyancy and wind is the simultaneous estimation of ventilation airflows and indoor temperatures, solar chimneys are used [11,12]. A solar chimney is a vertical shaft utilizing solar energy to enhance natural ventilation. 

 

Passive heating can be achieved by capturing the heat from the sun inside the building. Tweaking the window-to-wall ratio and the building exposure to the sun, all the while controlling for the thermal mass, heat flows and insulation allows to effectively store, distribute and retain the heat. The thermal mass defines the capacity to absorb, store and release heat. Heavyweight construction materials like concrete, brick and stone exhibit large thermal mass that can be used to effectively store the heat over peak hours and release it overnight. 

Passive building design. Figure from

 

Passive cooling is a set of design strategies to reduce heat gains and favour heat dispersion. Many methods exist and include using solar shadings as well as designing openings in such a way to allow good ventilation (such as solar chimneys). Shading can either be operable (external louvres, blinds, and deciduous trees) or fixed (e.g. eaves, overhangs, fences and evergreen trees). 

 

 '

Shading devices for north-facing openings. 

Figure from https://www.yourhome.gov.au/passive-design 

 

Passive design strategies are rated in different standards, such as PassivHaus (Passive House), BREEAM, LEED or WELL. 

 

The literature shows that today there are many net-zero, nearly-zero energy, and certified Passive House buildings worldwide, in different climate or geographic regions. Most are in Europe and North America, followed by New Zealand, Kore, Japan, China, and India [1]. Literature also shows that is it possible to achieve at least the Passive House energy standard of performance in all climate zones [13]. 

 

MATURITY:  

 

Although individual passive techniques are already commercial, their holistic implementation in buildings is still at TRL=4-6. 

Citizen Participation Platforms

E-participation [1][2][3][4][5] enables citizens to use digital technologies or platforms, e.g., combination of geographic information systems (GIS), Web 2.0 and mobile technologies (including video, mobile messaging and Internet access), for communication, engagement and deliberation on policy or planning challenges.  

 

Engagement and participation are vital tools in climate adaptation and environmental decision making as these entail increased community acceptance, support for climate actions, and provide new insights based on local knowledge [12]. Citizens can be consumers as well as producers of useful data for policy development and decision making (WeGovNow, Smarticipate, AI4PublicPolicy). 

 

There are multiple degrees of citizen participation ranging from passive, i.e., being simply informed, to responsive, i.e., contribute to consultation, to active, i.e., being fully empowered by having final decisions delegated to them (see Arnstein’s ladder [6]) [7]. In e-participation initiatives, both top-down (i.e., issues identified by public authority) and bottom-up (i.e., citizens led initiative) approaches can be applied. As multiple actors (i.e., different departmental units) are involved in the provision of e-participation, cross-organizational issues related to ownership and accountability may arise [3].  

 

Technologies supporting government processes (GovTech) can add great value to participatory processes (e.g., access to sensor kits, web portals and data), as shown by examples of Madrid (Decide Madrid), Bristol (Bristol Approach to citizen sensing – e.g., air quality, solid fuel burning etc.) [7], and Brussels (Curieuzenair). E-participation is usually considered part of e-government [5]. 

 

E-Government (or Electronic-Government) [1][2][8] refers to the application of Information and Communication Technologies (ICT) to government functions and procedures with the objective to increase efficiency of government agencies, enhance delivery of public services, and facilitate low cost and faster public engagement with public authorities. A comparative survey [8] of global e-government performance of municipalities highlights the best e-governance practices. It uses five categories of measures: privacy and security, usability, content, service and citizen and social engagement. For citizen and social engagement category Shanghai, Auckland, Seoul, Madrid, Paris, and Lisbon are ranked top cities for year 2018-19. 

 

Open Governance [9] is about transparency of and access to government data and decision making process so that innovative forms of collaborative actions (i.e. bottom-up and top-down) can be applied to solve policy problems, raise awareness, increase public participation, change behaviour, promote e-democracy, and revolutionise traditional service provision [10][11]. It is closely associated with open government data that can provide new insights about issues and services as well as offers the opportunities to participate, comment and influence plans and policy agenda to foster greater citizen participation. 

 

 

E-participation solutions range from responding to planning e.g., top-down to bottom-up urban regeneration [Smarticipate] or policy challenge [WeGovNow] or reporting a local problem (e.g., Bristol’s FixMyStreet); or bottom-up budget planning (e.g., Helsinki’s participatory budgeting) or accessing open data (e.g., Hamburg’s Transparency portal).  

 

There are several e-participation initiatives where various ICT tools are used to deliver different public services. For instance,  

Cross border e-governance initiatives such as [ACROSS], [DE4A] and [GLASS] go beyond one city’s public administrative level (even at EU level and beyond [iKaaS]) and deal with cross-border interoperable, mobile [mGov4EU] and privacy-aware public services.  

MATURITY: 

 

Many e-government and e-participation tools are available at higher TRL and are already being used by municipalities for public services and e-participation, e.g., open source Consul platform is being used in 35 countries by 135 institutions; Similarly, Organicity tools are used for over 35 experiments in various cities. 

 

Some of the example solutions fall under validation and demonstration category such as DUET and Smarticipate.  

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Last update: June 15, 2023

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