Combined steam based high-temperature heat and power storage with an Organic Rankine Cycle, an efficient mechanical electricity storage technology

Combined steam based high-temperature heat and power storage with an Organic Rankine Cycle, an efficient mechanical electricity storage technology

Journal of Cleaner Production xxx (xxxx) xxx Contents lists available at ScienceDirect Journal of Cleaner Production journal homepage: www.elsevier...

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Journal of Cleaner Production xxx (xxxx) xxx

Contents lists available at ScienceDirect

Journal of Cleaner Production journal homepage: www.elsevier.com/locate/jclepro

Combined steam based high-temperature heat and power storage with an Organic Rankine Cycle, an efficient mechanical electricity storage technology A. Arabkoohsar Department of Energy Technology, Aalborg University, Denmark

a r t i c l e i n f o

a b s t r a c t

Article history: Received 19 July 2019 Received in revised form 12 September 2019 Accepted 29 October 2019 Available online xxx

Today, mechanical energy storages are getting more important than before as the share of fluctuating renewable energies are dramatically increasing in the global energy matrix. Steam-based high-temperature heat and power storage is one of the very recent mechanical energy storage technologies introduced. This system stores electricity as heat in a packed bed of rocks and then, co-generates heat and electricity through a conventional Rankine cycle when discharging. This system presents an electricity and heat efficiencies of about 33e35% and 60e65%, meaning an overall efficiency in the range of 93e98%. As the major production of the system is heat, it is only appropriate for countries with district heating systems. As not all countries have heat networks, and according to the fact that, electricity is getting much pricier than heat everywhere, a modification of this technology in order for offering a better electricity efficiency could be highly advantageous. This study proposes the hybridization of a steam-based high-temperature heat and power storage with a small-scale Organic Rankine Cycle (with three different working fluids) to improve its electricity efficiency. The hybrid system is comprehensively analyzed and compared to its conventional design. The results prove the electricity efficiency of 42.6 e46.3% is obtained for the hybrid systems which are 24e35% higher than that of the conventional design. © 2019 Elsevier Ltd. All rights reserved.

Handling Editor: Kathleen Aviso Keywords: High-temperature heat and power storage Electricity storage Organic Rankine cycle Co-generation District heating

1. Introduction Today, the importance of renewable energy technologies is increasing all around the world, even in the countries supplying most of the globe’s oil and gas such as Iran, etc. (Tavana et al., 2019). Biomass, biogas, tidal, geothermal, wind and solar energy are of the most important sources of renewables, where there is a certain attention to the two latter sources (i.e. solar and wind) although  rawski their fluctuating availability is a serious challenge yet (Bo et al., 2019). The variable output profile of energy systems hiring these two renewables makes them difficult to synchronize with the energy distribution networks, especially power grids (Neuman et al., 2014). For overcoming this challenge in the electricity sector specifically, such energy technologies should be connected to either an electricity storage system or an auxiliary flexible-agile electricity supplier (Nami and Arabkoohsar, 2019). Regarding the hybridization of renewable electricity generation systems, many studies could be found in the literature proposing

E-mail addresses: [email protected], [email protected]

such solutions. For example (Arabkoohsar et al., 2016), proposed the combination of a PV plant equipped with an energy storage unit to a power productive gas station to improve the reliability of supply and thereby, modify the power sales strategy of the plant (Pantaleo et al., 2017). presented an innovative design of a hybrid CSP-biomass cogeneration plant for flexible generation and investigated the performance of their energy systems via a sort of data from a number of real power plants. They concluded that although their integration increases the efficiency, it does not result in positive profitability compared to a biomass-only cogeneration plant (Pantaleo et al., 2018). proposed and analyzed the performance of a combined Brayton-ORC (Organic Rankine Cycle) plant which is driven by a hybrid biomass-solar system accompanied with a thermal energy storage. Having optimized the ORC system performance and the size of the thermal energy storage unit, they observed the enhancement of the efficiency, the flexibility and the levelized cost of energy of the power plant (Pramanik and Ravikrishna, 2017). presented a thorough review of concentrated solar power plants combined with other renewable and conventional energy resources, e.g. biomass, wind, natural gas, etc. (Guo et al., 2018) published a thorough review article of hybrid

https://doi.org/10.1016/j.jclepro.2019.119098 0959-6526/© 2019 Elsevier Ltd. All rights reserved.

Please cite this article as: Arabkoohsar, A., Combined steam based high-temperature heat and power storage with an Organic Rankine Cycle, an efficient mechanical electricity storage technology, Journal of Cleaner Production, https://doi.org/10.1016/j.jclepro.2019.119098

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renewable energy systems in all energy sectors, including electricity (Suresh et al., 2019). proposed hybridization of solar thermal power plants with biomass heaters and investigated the thermodynamic performance of their proposed solution for stable power output (Sadi and Arabkoohsar, 2019). investigated the performance of a parabolic trough solar power plant combined with a waste incinerator as the secondary boiler to produce clean and dispatchable power. Combination of wind farms with hydropower reservoirs (Hamann and Hug, 2016), integrating solar power plants with hydropower systems (Farfan and Breyer, 2018) and hybridization of a solar-wind power plant with a hydropower plant (Wang et al., 2019) are some further examples of such hybrid systems. With respect to the electricity storage systems, there is no doubt that batteries have the most mature state-of-the-art and offer way better energy efficiency than any other technologies; however, the low storage capacity and too high cost of batteries make them not be appropriate for large-scale applications (Salim et al., 2019). Therefore, there should be other electricity storage solutions for large solar and wind power plants, where mechanical energy storage technologies have received much attention over the last decades (Guelpa et al., 2019). Among mechanical electricity storage technologies, pumped hydroelectric storage is the one which has a fully developed knowledge and technology, offers 85% net efficiency and is suitable for very large applications; however, the high cost and the special topographical needs are the two main drawbacks of that (Zakeri and Syri, 2015). Flywheel energy storage, which has pretty low maintenance costs, a long lifetime and the very interesting efficiency of about 90%, in addition to the large cost, suffers from the low storage capacity (Mousavi G et al., 2017). Compressed air energy storage system, based on the latest state-ofthe-art, might be available in i) isothermal-adiabatic configuration which offers an efficiency around 80% (Odukomaiya et al., 2016), or in ii) low-temperature design which is somewhat simpler and cheaper in design and presents an efficiency in the range of 60e65% (Wolf and Budt, 2014), or in subcooled configuration co-generating heat, electricity and cold at a coefficient of performance just above 150% (Arabkoohsar, 2018). Regardless of the configuration, all the CAES technologies suffer from the need of special geographical locations for the cavern. Pumped heat electricity storage is another mechanical electricity storage technology which has been recently introduced. This system performs like a high-temperature heat pump in the charging mode and somewhat similar to a gas turbine when discharging. The net efficiency of this system is claimed to be about 84%. The main deficiency of this technology is the lack of well-established knowledge and state-of-the-art yet, especially about the complicated technology of compressor and turbine it requires, and thus, is not commercially available yet (Benato and Stoppato, 2018). In addition to the above-discussed technologies, there is one more new mechanical electricity storage system that has very recently been launched to the market, i.e. high-temperature heat and power storage (HTHPS) (Arabkoohsar and Andresen, 2017c). Based on this concept, surplus electricity of a renewable power plant is given to a packed bed of stones via an electrical coil to be stored as high-temperature heat. Then, when needed, the stored heat is called to drive a conventional power cycle for co-generation of heat and electricity at high overall efficiency (“Stiesdal Electricity Storage, 2016”). Two power blocks have been proposed and investigated for this so far, i.e. i) an air-based multistage Brayton cycle (Arabkoohsar and Andresen, 2017a) which is a simpler and cheaper technology but offers a lower net efficiency, and ii) a steam-based Rankine cycle (Arabkoohsar and Andresen, 2017b) which requires a higher initial investment but leads to better overall efficiency. The Rankine based concept of this technology has just been demonstrated in pilot-scale in Germany and has resulted

in a power-to-power efficiency of about 35% and power-to-heat efficiency of 60% (overall ~95%) (“Siemens High-Temperature Heat and Power Storage Project,” 2016). The main drawback of this new electricity storage system is that although it has high overall efficiency, its major output is heat, not electricity. This is of importance from two aspects. One fact is that the HTHPS is only an appropriate solution for the countries with well-established district heating systems which are a limited number of lands (Arabkoohsar and Andresen, 2018), and the second fact is that not only electricity will be the dominant sector of energy with special importance in the future, but also even now electricity is much more priced than heat (Rashid et al., 2019). As of the most important reasons for this, one could mention the well-developed renewable based-power technologies (Diesendorf and Elliston, 2018), and the increasing penetration of electrical facilities in the other energy sectors, e.g. electrical vehicles (Kester et al., 2018), large-scale heat pumps (Arabkoohsar, 2019), etc. Having all these said, one could conclude that improving the design of the HTHPS system with the aim of higher electricity efficiency rather than a better heat output rate can be a wise choice. Therefore, this work proposes and invesstigates the combination of steam-based HTHPS technology with a small-scale ORC unit (with three different working fluids) in order to increase the power-to-power efficiency through the use of the rejected heat of the power block from its condenser. 2. Hybrid steam-based HTHPS-ORC system Fig. 1 illustrates the hybrid HTHPS-ORC system which mainly consists of the three parts of the steam-Rankine cycle, the packed bed of rocks as the heat storage unit and the small ORC unit connected to the condenser of the steam-Rankine cycle. In the conventional system of the HTHPS system, everything was just the same except the ORC unit which was not part of the design and instead, the condenser of the steam cycle would supply heat to the local district heating system. When the HTHPS is in the charging mode, the only operating component is the packed bed of stones which is charged via an electrical coil. For this, as Fig. 2 shows, a number of fans circulate air from the bottom of the packed bed to the electrical coil and from there to the top of the storage letting the hot air flowing through the rocks from the top to the bottom. During the discharging mode, the Rankine cycle starts operating. The heat required for the boiler is supplied by the thermal storage unit recovering the stored electricity as high-temperature heat. Naturally, a huge amount of low-grade heat is to be rejected from the condenser of the steam Rankine cycle. In the conventional system, the pressure of the condenser has been kept at a slightly higher level than regular Rankine cycles to be able to supply district heating. The required outlet temperature of district heating supply is 80e90  C; thus, the condenser temperature is set at 100  C to guarantee the required outlet temperature (Arabkoohsar and Andresen, 2017b). In this work, however, the condenser is coupled to an ORC unit to use it for electricity generation. Naturally, the size of the ORC unit will be smaller than the HTHPS system itself. The selection of an appropriate working fluid for the ORC system in accordance with the highest and lowest temperatures of the cycle is a key factor. Having the hot source temperature of 100  C, R123, R124 and R134a lie among the best choices of ORC working fluids. As the ORC condenser temperature is quite low, one needs a cold enough source for that. Having Denmark as a case study, the limitless source of underground water with a year-round temperature in the range of 5e7  C at the depth of 25 m is the best cooling option available. The ORC condenser could not have a pressure below the atmospheric level. While for the R123, the

Please cite this article as: Arabkoohsar, A., Combined steam based high-temperature heat and power storage with an Organic Rankine Cycle, an efficient mechanical electricity storage technology, Journal of Cleaner Production, https://doi.org/10.1016/j.jclepro.2019.119098

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Fig. 1. Schematic of the hybrid HTHPS-ORC system; HPT: high-pressure turbine, IPT: medium-pressure turbine, LPT: low-pressure turbine, P: pump, T: turbine, E: evaporator, C: condenser, red arrows: hot airflow of the thermal storage, orange arrows: working fluid of the main Rankine cycle, green arrows: ORC working fluid, blue arrows: secondary fluid of ORC condenser. (For interpretation of the references to colour in this figure legend, the reader is referred to the Web version of this article.)

Fig. 3 illustrates the diagram associated with the HTHPS (left) and the ORC unit using R124 (as a sample cycle among the three considered cases). The temperature of the condenser of the HTHPS is 100  C to be able to supply district heating (in the conventional design) and the ORC units (in the hybrid designs). 3. Material and methods Naturally, for the charging phase, one only needs to consider the packed bed of rocks into calculations. Here, Schumann’s onedimensional two-phase model is used to simulate the performance of the packed bed of stones (Attonaty et al., 2019). Based on this model, for the airflow through the rocks, one has:

rs cs ð1  εÞ ra ca ε

dTs d2 T s ¼ hv ðTa  Ts Þ þ k dt dx2

_ a cp;a dTa DpU m dTa ðTa  Tsoil Þ ¼ hv ðTs  Ta Þ   A dt A dx

(1)

(2)

in which, r is density, c refers to the thermal capacity, T points out _ is mass flow rate, ε represents the porosity of the to temperature, m packed bed, A is cross-sectional area, D refers to the diameter of the storage, and the subscripts a and s represent airflow and the stones, respectively. The three parameters hv, k and U are the volumetric heat transfer coefficient, the effective conductivity of rocks and the overall heat transfer coefficient through the packed bed to the surrounding soil which are, respectively, given by the following three correlations (Benato, 2017): Fig. 2. Circulation of airflow through the packed bed of rocks for charging the storage.

hv ¼ 700 atmospheric condenser pressure is quite affordable with the underground water source, to be able to use the other two working fluids, i.e. R124 and R134a, one needs to increase the pressure of the condenser. Considering the minimum possible pressure/temperature after the ORC turbines as well as setting a minimum achievable temperature at the condenser outlet based on the temperature of the cold source (assuming 5  C here), the pressures of R124 and R134a at this point are set at 210 kPa and 410 kPa, respectively. Table 1 presents information about the details of the hybrid HTHPS-ORC system being investigated in this study.

hm _ a i0:76 Ad

k ¼ ks ð1  εÞ þ ka ε  U¼

 1   1 R R þ dins R R þ dins þ R þ ln þ ln hin kins kr R þ dins R

(3) (4)

(5)

in these relations, d is the equivalent diameter of rock pieces, k is thermal conductivity, h refers to the convective heat transfer coefficient, d represents thickness, R is the radius and R is the thermal influential distance in the packed bed. The two subscripts in and ins

Please cite this article as: Arabkoohsar, A., Combined steam based high-temperature heat and power storage with an Organic Rankine Cycle, an efficient mechanical electricity storage technology, Journal of Cleaner Production, https://doi.org/10.1016/j.jclepro.2019.119098

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Table 1 Characteristics of the hybrid steam-based HTHPS-ORC system. Case

Parameter

Information

Steam-Based HTHPS System

Maximum power supply capacity Maximum charging/discharging time Maximum pressure of steam cycle (HPT inlet) Maximum temperature of the steam cycle (HPT inlet) IPT inlet pressure IPT inlet temperature LPT inlet pressure LPT inlet temperature Air-fluid heat exchangers nominal effectiveness factor Fluid-fluid heat exchangers nominal effectiveness factor Secondary fluid heat transfer of fluid-fluid heat exchangers Pressure loss of heat exchangers at nominal flow rate Pressure of secondary heat transfer fluid Turbines nominal isentropic efficiency Pump nominal isentropic efficiency Packed bed of stones volume Radius of the storage Height of the storage Porosity of the packed bed Heat capacity of stones Maximum allowable temperature of the storage Thickness of the insulation Insulation thermal conductivity Maximum allowable temperature for heat exchangers Working fluid(s) Turbine inlet pressure Turbine inlet condition Condenser pressure Turbine isentropic efficiency Pump isentropic efficiency Evaporator effectiveness factor Condenser effectiveness factor Condenser secondary fluid Condenser secondary fluid inlet temperature Condenser secondary fluid outlet temperature

5 MW 12 h 100 bar 550  C 30 bar 550  C 2.5 bar 350  C 0.95 (H. C. Guo et al., 2019a,b) 0.85 (Arabkoohsar et al., 2017) Industrial oil 0.2 bar (Guo et al., 2019a,b) 12 bar 0.85 (Zhao et al., 2016) 0.75 (Zhao et al., 2016) 608.2 m3 4.4 m 10 m 35% 826 J/kg.K (Esence et al., 2017) 950 K 0.5 m 0.023 W/m K 627  C R123/R124/R134a 652.2/1945/3247 kPa Saturated vapor 105/210/410 kPa 0.85 (Nami and Akrami, 2017) 0.75 0.85 0.85 Underground water 5 C 25  C

ORC Unit

Fig. 3. T-s diagram of the HTHPS system (left) and the ORC cycle with R124 (right).

represent the internal wall and insulation of the storage. Note that based on Schumann’s model, it is assumed that there is no heat conduction in the airflow, the rocks are uniform particles with small Biot numbers and the effect of pressure and viscosity changes are negligible. During the discharging phase, in the steam cycle, the turbine set comes in a triple-stage configuration. Using the marked numbers on Fig. 1, one could write the turbine model as below (Mohammadi and Mehrpooya, 2016):for the HPT:

_ _ st ðh1  h2 Þ ¼ his;hpt m_ st ðh1  h2s Þ W hpt ¼ m

(6)

for the IPT:

_ ¼ m_ st ðh  h Þ ¼ h _ st ðh3  h4s Þ W 3 4 ipt is;ipt m

(7)

and for the LPT:

_ ¼ m_ st ðh  h Þ ¼ h _ st ðh5  h6s Þ W 5 6 lpt is;lpt m

(8)

Please cite this article as: Arabkoohsar, A., Combined steam based high-temperature heat and power storage with an Organic Rankine Cycle, an efficient mechanical electricity storage technology, Journal of Cleaner Production, https://doi.org/10.1016/j.jclepro.2019.119098

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_ is the rate of work production of the turbines, h is specific where, W enthalpy, his is the isentropic efficiency, while the subscripts hpt, ipt, lpt and st refer to the high-pressure, medium-pressure and lowpressure turbines and the steam flow through the Rankine cycle. The summation of the work of the three turbines gives the total work production by the steam-cycle. The steam leaving the LPT enters the condenser of the steam cycle which acts as the evaporator of the ORC unit as well. For the stean cycle condenser one has:

. _ orcp ¼ m_ W orcf ðh13s  h11 Þ h

Q_ cond ¼ m_ st ðh6  h7 Þ

horc ¼

(9)

and for the ORC evaporator, the energy balance will be as:

Q_ orce ¼ m_ orcf ðh9  h13 Þ ¼ Q_ cond

(10)

in which, orc-f refers to the working fluid of the ORC unit. For the pump of the steam cycle, one could simply write:

_ p ¼ m_ st ðh  h Þ W 7 h 8s

(12)

Q_ blr is the heat supplied by the thermal storage to the boiler. Finally, the electricity efficiency (hel ) of the steam cycle will be:

_

.X tt

E t¼1 stcycle

t¼1

Q_ blr

(13)

Xtt

.X tt Q_ Q_ t¼1 cond t¼1 blr

(14)

where, E_ stcycle is the net rate of electricity production of the cycle and the term tt is the number of time-steps the cycle operates each discharging round. Having already known the supplied rate of heat to the ORC evaporator (Eq. (10)), for the ORC turbine, one has (Xi et al., 2019):

  h10 ¼ h9  his;orct ðh9  h10s Þ; Where : h10s ¼ horcf 

T¼90;x¼1

(15) _ orct ¼ m_ W ordf ðh9  h10 Þ

(16)

For the ORC condenser, one has:

m_ orcf ðh10  h11 Þ ¼ m_ ugw ðh14  h15 Þ; Where   : h10 ¼ hORCf  s¼s9

.X tt

_

E t¼1 orc

t¼1

(19)

Q_ orceva

where, E_ orc is the rate of electricity production of the ORC unit and Q_ orceva is the rate of heat supplied to the evaporator of the ORC unit by the steam cycle during tt time-steps of discharging. Having said all this, one could define the power-to-power efficiency of the conventional HTHPS design as:

Xtt

_

.X chgt

E t¼1 stcycl

t¼1

(20)

E_ chg

& x¼0 OR T¼10

hconvpth ¼

Xtt t¼1

. Q_ cond Xchgt E_ t¼1

(21)

chg

The global efficiency of the hybrid system will be obtained by:

hhybrid ¼

. Xtt  E_ stcycle þ E_ orc Xchgt E_ t¼1 t¼1

chg

(22)

where, hconvptp and hconvpth represent the power-to-power and power-to-heat efficiencies of the conventional system and hhybrid is the net efficiency of the hybrid system (which is pure electricity). E_ is the rate of electricity production of the steam cycle, E_ stcycle

chg

is the rate of electricity being stored during the charging phase, and chgt is the number of charging time-steps.

4. Results and discussion

While the heat efficiency (hh Þ of that is defined as:

hh ¼

Xtt

While its power-to-heat efficiency will be:

Q_ blr ¼ m_ st ðh1  h8 Þ þ m_ st ðh3  h2 Þ þ m_ st ðh5  h4 Þ

Xtt

in which, P is pressure and y is the specific volume of the organic fluid. Similar to the steam cycle, considering 5% losses for the electricity generator and gearboxes, 95% of the net rate of work of the ORC unit is converted to electricity. The efficiency of the ORC unit is defined as:

(11)

in which, his;p is the isentropic efficiency of the pump. Considering an overall loss rate of 5% for the electricity generator (including the losses of the gearbox etc.), 95% of the net work production of the cycle, which is the turbine set work minus the pump work, is converted to the electricity. For the boiler of the steam cycle, one has:

hel ¼

¼ m_ ordf yorcf ðP13  P11 Þ (18)

hconvptp ¼ is;p

is;orcp

(17)

where, the subscript ugw represents the underground water flow. For the ORC pump, the following equation applies:

Before presenting the results, one needs to validate the numerical method used for the packed bed of rocks. In this work, the validation is accomplished via the comparison of the numerical results with those reported by (Elouali et al., 2019) based on different methods of packed bed modeling. In order to do this, similar operation conditions as the reference work are applied here. The reference work investigates the charging process of a small packed bed of stones from the initial uniform temperature of 20  C by a uniform inlet airflow of 0.225 kg/m2s with a temperature of 550  C. The storage height, diameter and porosity are 1.2 m, 0.148 m and 40%, respectively. Stones filling the storage have an equivalent diameter of 0.02 m, density of 2.68 tonnes/m3, the thermal capacity of 1.068 kJ/kg.K and thermal conductivity of 2.5 W/m.K. Further details of the experimental conditions could be found in (Elouali et al., 2019). Fig. 4 compares the results of the numerical solution of the present study based on Schumann’s model with those of the reference study based on the three different models of Schumann’s model, single-phase model and continuous-solid-phase model. The storage is divided into 7 nodes with equal volumes along the height. According to the figure, expectedly, the results of the model developed in this work are most close to those reported for Schumann’s model in the reference study while there is acceptable accuracy of the calculations compared to the other two models as well. After validating the model, the hybrid system is taken into the

Please cite this article as: Arabkoohsar, A., Combined steam based high-temperature heat and power storage with an Organic Rankine Cycle, an efficient mechanical electricity storage technology, Journal of Cleaner Production, https://doi.org/10.1016/j.jclepro.2019.119098

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Fig. 4. Comparison of the numerical results with those of the reference work.

operating conditions to see how well it performs in terms of energy efficiency and how different parameters can affect its performance. As mentioned before, the energy storage system is supposed to be sized for 5 MW electricity storage for 12 continuous charging hours. Naturally, the size of the packed bed in both the conventional and hybrid systems should be the same. However, the size of the power blocks will be different because, in the former, it is the steam cycle that should supply the maximum energy output of 5 MW by itself, while in the latter, the summation of the steam cycle and the ORC cycle outputs should be 5 MW. The operation strategy of the packed is so that it is charged to the uniform temperature of 677  C during the charging time, and then, when discharging, it discharges until its top node reaches the minimum allowed temperature of 600  C. The temperature 677  C is set based on the maximum operating temperature of heat exchanger materials and the temperature 600  C is set because it is needed for generating the superheated steam at 550  C through the boiler. As the storage discharges, the bottom of the storage gets colder and the cold area of the storage expands upward while discharging process continues. Thus, for proper sizing of the storage, one needs to know what will be the temperature profile of the storage along the height at the end of a discharging phase. The stable format of this temperature profile is achieved after 3 rounds of full charging-discharging phases. Thus, the storage sizing and all the results of the simulations presented hereafter are associated with the fourth round of charging-discharging. Fig. 5 shows the profile of the storage temperature along the height, when the HTHPS is not connected to any ORC unit yet, at the end of the third discharging round. Fig. 6 presents the profile of the storage temperature along the height at the end of the 4th 12-h charging process with a continuous rate of 5 MW. Here, in all the cases, for the sake of good temperature stratification, the height of the storage is fixed at 10 m. As the figure shows, when the storage reaches the radius of 3.5 m, it can have the uniform temperature of 677  C and if its radius is enlarged thereafter, the temperature of the bottom-nodes get away from the maximum allowed value accordingly. Having the storage height for 10 m, with a radius of 3.5 m, the volume of the storage will be 384.8 m3. This sized packed bed is appropriate for both of the conventional steam-based HTHPS and the proposed HTHPS-ORC system. Table 2 details a report of the performance of the steam-based HTHPS

system when charging-discharging for a maximum of 12 h each at a constant rate of 5 MW. It is noteworthy that due to the losses of the power block, the packed bed will reach the minimum allowed top node temperature of 600  C much earlier. Thus, the discharging process is not taking 12 h long. As seen, the total rate of supplied heat from the storage to the boiler is about 14.5 MW when discharging. The electricity being generated when this cycle is performing is constantly 5 MW and the rate of heat given to district heating through the condenser is about 9.3 MW. Thus, the power-to-power and power-to-heat efficiencies of the conventional system will be, respectively, 34.4% and 63.7%. The marked value with * are associated with the case that the system is not supposed to supply any heat to the district heating system, rather it is only to produce electricity. In this case, the condenser pressure can be lower which means higher electricity production. Here, the LPT outlet pressure and temperature will be 9 kPa and 43.9  C, which results in 36.1% electrical efficiency and no heat output. Thus, the global efficiency will also be 36.1%. For having proper sizing of the steam and ORC cycles when combined, one needs to know how much net electricity could be delivered for every 1 MW of heat supplied to the ORC evaporator. As mentioned before, different organic working fluids will be considered. Although the supply temperature of the evaporator is constant (100  C), changing the working fluid changes the operation condition of the ORC unit significantly. Table 3 lists the values of important parameters of the ORC units with different working fluids and 1 MW supplied heat to the evaporator. According to the table, the ORC cycle employing R124 results in the best electricity output among all the three options with a net efficiency of 17.0%, while the cycle with R123 and R134a lead to 13.7% and 15.8% efficiencies, respectively. Fig. 7 presents a flow diagram of the energy stored in the packed bed of rocks in the form of heat and how it is lost, how it is used to drive the ORC unit and how it is converted to the electricity in both of the steam and ORC cycles. Having the efficiencies of the ORC unit in different cases, the electricity efficiency of the steam cycle, as well as the maximum available heat of the steam cycle condenser, one could simply size the hybrid system components. Table 4 presents information about the size of the ORC unit and HTHPS power block in the three different cases. In all the three cases, the summation of the ORC and

Please cite this article as: Arabkoohsar, A., Combined steam based high-temperature heat and power storage with an Organic Rankine Cycle, an efficient mechanical electricity storage technology, Journal of Cleaner Production, https://doi.org/10.1016/j.jclepro.2019.119098

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Fig. 5. Packed bed temperature profile at the end of the third discharging round.

Fig. 6. The storage temperature profile along the height at the end of the 4th charging phase for different volumes.

Table 2 Steam-based HTHPS system performance report. Parameter

Value (Unit)

Charging period Discharging period Heat losses from the heat storage during a round trip Work production rate of HPT Work production rate of IPT Work production rate of LPT Work consumption rate of Pump Heat supply rate of boiler for the main steam flow Heat supply rate of the first re-heater Heat supply rate of the second re-heater Heat production rate through the condenser (district heating supply) Steam/water mass flow rate Thermal storage efficiency over one charging-discharging cycle Power-to-power efficiency of steam-based HTHPS Power-to-heat efficiency of steam-based HTHPS Global efficiency of the system

720 min 249 min 427.5 kWh 1.2 MW 2.3 MW 1.6 MW 48.0 kW 12.1 MW 1.5 MW 0.8 MW 9.3 MW 3.95 kg/s 99.3% 34.4% (36.1%*) 63.7% (0%*) 97.4% (36.1%*)

steam units power outputs will be 5 MW. Fig. 8 shows the profile of the top and bottom nodes of the thermal storage in the three different hybrid systems during a full charging-discharging mode. As seen, there is very little difference between the temperature

Table 3 Operation conditions of ORC unit with different working fluids in the hybrid system. Parameter (unit)

R123

R124

R134a

Evaporator pressure (bar) Evaporator outlet temperature (oC) Turbine outlet temperature (oC) Turbine net produced work (kW) Condenser pressure (bar) Condenser outlet temperature (oC) Heat rejected from the condenser (kW) Pump outlet temperature (oC) Work consumption of the pump (kW) Net electricity production (kW) Efficiency of the cycle (%)

6.5 90 37.8 145.8 1.05 28.8 856.1 30.0 1.7 136.9 13.7

19.5

32.5

11.6 184.2 2.1 6.8 821.8 6.1 6.3 170.0 17.0

9.8 176.8 4.1 9.8 833.7 10.9 10.7 157.9 15.8

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Fig. 7. Flow diagram of the energy streams from storage to electricity production.

Table 4 Size of the ORC unit and the steam cycle for different hybrid cases. Cases

ORC unit size (MW)

Steam cycle size (MW)

ORC with R123 ORC with R134a ORC with R124

1.01 1.13 1.20

3.99 3.87 3.80

profiles of the different cases either in the charging mode or in the discharging phase. This is because not only the sizes of the ORC units in all the three cases are smaller than 1/3 of the steam cycle but also their sizes are so close to each other. According to the data of the above graphs, in the hybrid system, the packed beds of rocks stay in operation until the 326e335 min of the discharging process which means a longer discharging phase for approximately 35% compared to the conventional system of the steam-based HTHPS. Hereafter, for assessing the hybrid system performance under fluctuating energy profiles, the data of a real wind farm in Denmark is used. The real operational data comprises a 12-h surplus electricity of the wind farm followed by a 12-h demanded electricity profile of the farm (both in 5-min gaps). The data has been levelized to a maximum value of 5 MW. Fig. 9 presents these two profiles. Fig. 10 shows the variation of the top and bottom nodes of the packed beds in the different cases under the fluctuating conditions.

According to the figure, unlike the full charging mode (Fig. 8), in the real operation condition, the received surplus power is not enough to take the entire of the packed bed to the uniform temperature of 677  C. Here, the maximum temperature of the bottom node of the packed bed in all the three cases is below 570  C. The discharging process of the packed bed stops immediately after its top node temperature meets the minimum allowed level of 600  C. Fig. 11 illustrates the rate of heat supplied to the boiler by the packed beds of rocks over the discharging phase for the three different cases. This figure presents separate graphs for the heat flows coming to the main working fluid stream and that supplied over the reheaters. Expectedly, the rate of direct heat supply to the boiler is up to five times of the energy withdrawn by the reheaters. As such, due to being sized smaller than the other two cases as a result of better ORC efficiency, the steam-cycle associated with the ORC using R124 requires lower heat supply from the packed bed. Fig. 12 shows the trend of heat supplied to the evaporator of the ORC unit via the condenser of the steam-cycle in different cases. The graph only covers the times that the steam-cycle is in operation and the packed bed has not run out of stored heat yet. As seen, compatible with the previous results, there is not a big difference between the length of discharging phases in different cases. Here, the ORC units with R123, R134a and R124 are supplied for 91, 94 and 96 5-min time-steps.

Fig. 8. Top and bottom nodes temperatures of the packed bed in different systems over a full charging-discharging process.

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Fig. 9. Surplus and demanded electricity for charging and discharging of the packed bed of rocks.

Fig. 10. Top and bottom nodes temperature profiles of the packed bed in different hybrid systems in real conditions.

Fig. 13 gives information about the rate of power production by the steam turbines in different cases. According to the figure, in the peak discharging load, the steam turbine associated with the hybrid system employing R123 generates just below 3.3 MW electricity while the power output of the systems with R134a and R124, at the same time-steps, are just above 3.1 and 3.0 MW, respectively. Here again, as the systems stop discharging at the 91st, 94th and 96th time-steps due to the packed bed of rocks running out of the stored energy, the power outputs fall to zero thereafter. Fig. 14 presents information about the rate of work production/ consumption of the turbines/pumps in the ORC units in different cases over the discharging phase. Evidently, similar to any other Rankine cycle, the rate of work consumed by the pump is much lower than that produced by the turbine. This is seen for all the three cases where, for example, for the hybrid system with the ORC unit using R124, the maximum work production of the turbine is about 1.2 MW while the maximum pump work in the same period is below 70.2 kW. Note that the discharging phase never reached

the 5 MW electricity demand as that is somewhere around timestep 120 (see Fig. 9). Fig. 15 shows the trend of heat dissipation from the condensers of the ORC units in different cases to the underground water as the cooling source. Just as expected, the trend of fluctuations of these profiles is similar to those related to the work of ORC pumps/turbines presented in the previous figure. Here, the maximum amount of heat rejected from the ORC condensers for the cases with R123, R134a and R124 are, respectively, 5.6, 5.4 and 5.5 MW. Fig. 16 shows the share of the ORC and HTHPS electricity generators out of the demanded power of the wind turbine. According to the figure, the ORC unit with R124 makes a better contribution than the other two systems. For this case, the steam cycle maximum production comes up to 3.6 MW while the ORC production of this configuration is just below 1.1 MW. For the case with R123, these figures are 3.7 MW and 0.9 MW, and for the case with R134a, one has 3.5 MW and 1.0 MW, respectively. Summing the productions over the entire course of discharging, one could see

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Fig. 11. Rate of heat supply to the boiler by the packed bed of rocks in different cases.

Fig. 12. Rate of heat supplied to the ORC units in different cases.

that the ORC units employing R123, R134a and R124 make the overall contributions to power supply of 25%, 27%, and 31%, respectively. Finally, Fig. 17 compares the electrical energy efficiency of the hybrid systems in the three different cases with that of the conventional design of the steam-based HTHPS system. In addition, as the goal of the system is to increase the electricity production of the system, it is fair to consider a case that the HTHPS system does not supply any heat through the condenser and therefore, has a higher electricity production rate as well. According to the figure, the system with R124 offers an electricity efficiency of 46.3% which is almost 35% better than the conventional system (with a power-to-power efficiency of 34.4%), 28% better than the HTHPS with no heat production (with the electrical efficiency of 36.1%), 9% better than the system with R123 (with electricity efficiency of 42.6%), and 4% better than the system with R134a with 44.5% efficiency. Note that since the energy conversion efficiency of the electrical

coil is considered 100%, which is a logical assumption, the global energy conversion efficiency of the conventional design of the steam-based HTHPS cycle remains as that reported in Table 2 (i.e. 97.4%) while the values given in the above figure for the electrical efficiencies of the other four cases (i.e. 36.1% for the HTHPS with no heat output, 42.6% for the hybrid system with R123, 44.5% for the hybrid configuration with R134a, and 46.4% for the hybrid design with R124) will be the same as their global energy efficiencies. 5. Conclusion Hybridization of the novel co-generative concept of steambased HTHPS with an ORC unit, with the main aim of enhancing the power-to-power efficiency of the system, was proposed and investigated in this study. This hybridization is inspired by the fact that electricity will be much more valued than heat in the future smart energy systems due to the two main reasons of mature renewable electricity production technologies and the increasing

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Fig. 13. Rate of electricity output of the steam cycle during the discharging phase for different cases.

Fig. 14. Rate of work consumption/production of the ORC pumps/turbines over time in different cases.

penetration of electrical-driven energy systems in the other energy sectors, including heat sector, e.g. heat pumps. For this, the packed bed of rocks of the HTHPS system was designed and sized. Then, three different ORC cycles with different working fluids (R123, R134a and R124) were used to be coupled with the power block of the HTHPS unit. The power blocks of the hybrid systems, including the steam-cycle and the ORC units, were sized and designed based on the different operation conditions they face in each case. The hybrid systems were sized for a maximum power output of 5 MW. The investigations on the performance of these three hybrid systems were accomplished using the surplus/demanded electricity profiles of a real wind farm in Denmark, as the case study.

The results showed that for a steam-based HTHPS unit, the power-to-power efficiency does not exceed 34.4%, though owing to the high heat efficiency of 63.7%, an overall energy efficiency about 97% could be achieved. On the other hand, adding the ORC units allows for reducing the size of the power block of the HTHPS system as a big portion of the demanded electricity could be supplied by the added unit. The ORC systems with R123, R134a and R124 could offer electricity efficiencies of 13.1%, 15.8% and 17.0%, respectively. The electricity efficiencies of the hybrid systems with R123, R134a and R124 are better than the conventional system for 24%, 29% and 35%, respectively. The power-to-power efficiencies of the hybrid systems with R123, R134a and R124 will be 42.6%, 44.5% and 46.3%, respectively.

Please cite this article as: Arabkoohsar, A., Combined steam based high-temperature heat and power storage with an Organic Rankine Cycle, an efficient mechanical electricity storage technology, Journal of Cleaner Production, https://doi.org/10.1016/j.jclepro.2019.119098

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Fig. 15. Rate of heat dissipation through the ORC condensers in different cases.

Fig. 16. Steam cycles and ORC units’ contributions to covering the demanded electricity profiles.

According to the results of this study, the clear conclusion is that the proposed system can effectively pave the way for a secure penetration of renewable energy sources into the energy systems. Therefore, the technology will considerably contribute to pushing the existing electricity systems towards a cleaner yet more sustainable production chain. Although there is an argument that ORCs with different working fluids could have environmental impacts, the clear fact is that fluorinated gases (gases emitted by refrigerants) contribute far less than any other pollutants to the greenhouse gas emissions. Among the different systems with the three different refrigerants considered in this study, the system employing R123 is the most environmentally friendly case (the global warming potential index, GWP, of R123 is 77). The system using R124 is the second best case (R124GWP ¼ 609) and the worst case is the system employing R134a (R134aGWP ¼ 1430).

The perspective is that this solution will also be absolutely feasible economically because not only the steam-based HTHPS technology has already been proven as cost-effective solutions, but also the ORC system is addressed as an economically wise choice for heat recovery and power production. In addition to these, it was well discussed that how energy pricing will be different in the future where electricity will be an even pricier energy than today compared to cold and heat. The future works on this topic include the optimization of the processes and size of the components of the system considering energy market regulations, defining an optimal operating strategy for the system when coupling to a real renewable plant, etc. Finally, demonstrating the technology in lab-scale and then, pilot-scale, is necessary for commercializing that.

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Fig. 17. Comparison of the hybrid systems electricity efficiency with the conventional steam-based HTHPS system.

References Arabkoohsar, A., 2018. An integrated subcooled-CAES and absorption chiller system for cogeneration of cold and power. In: IEEE Xplore, Proceeding of SEST, pp. 1e5, 2018. Arabkoohsar, A., 2019. Non-uniform temperature district heating system with decentralized heat pumps and standalone storage tanks. Energy 170, 931e941. Arabkoohsar, A., Andresen, G.B., 2017a. Dynamic energy, exergy and market modeling of a high temperature heat and power storage system. Energy 126. https://doi.org/10.1016/j.energy.2017.03.065. Arabkoohsar, A., Andresen, G.B., 2017b. Thermodynamics and economic performance comparison of three high-temperature hot rock cavern based energy storage concepts. Energy 132. Arabkoohsar, A., Andresen, G.B.B., 2017c. Design and analysis of the novel concept of high temperature heat and power storage. Energy 126, 21e33. https://doi.org/ 10.1016/j.energy.2017.03.001. Arabkoohsar, A., Andresen, G.B.B., 2018. A smart combination of a solar assisted absorption chiller and a power productive gas expansion unit for cogeneration of power and cooling. Renew. Energy 115, 489e500. https://doi.org/10.1016/ j.renene.2017.08.069. Arabkoohsar, A., Machado, L., Koury, R.N.N., 2016. Operation analysis of a photovoltaic plant integrated with a compressed air energy storage system and a city gate station. Energy 98, 78e91. https://doi.org/10.1016/j.energy.2016.01.023. Arabkoohsar, A., Gharahchomaghloo, Z., Farzaneh-Gord, M., Koury, R.N.N., DeymiDashtebayaz, M., 2017. An energetic and economic analysis of power productive gas expansion stations for employing combined heat and power. Energy 133. https://doi.org/10.1016/j.energy.2017.05.163. Attonaty, K., Stouffs, P., Pouvreau, J., Oriol, J., Deydier, A., 2019. Thermodynamic analysis of a 200 MWh electricity storage system based on high temperature thermal energy storage. Energy 172, 1132e1143. https://doi.org/10.1016/ j.energy.2019.01.153. Benato, A., 2017. Performance and cost evaluation of an innovative Pumped Thermal Electricity Storage power system. Energy 138, 419e436. https://doi.org/10.1016/ j.energy.2017.07.066. Benato, A., Stoppato, A., 2018. Pumped thermal electricity storage: a technology overview. Therm. Sci. Eng. Prog. 6, 301e315. https://doi.org/10.1016/ j.tsep.2018.01.017.  rawska, A., Szyman  ska, E.J., Jankowski, K.J., Dubis, B., Borawski, P., Bełdycka-Bo Dunn, J.W., 2019. Development of renewable energy sources market and biofuels in the European Union. J. Clean. Prod. 228, 467e484. https://doi.org/ 10.1016/j.jclepro.2019.04.242. Diesendorf, M., Elliston, B., 2018. The feasibility of 100% renewable electricity systems: a response to critics. Renew. Sustain. Energy Rev. 93, 318e330. https:// doi.org/10.1016/j.rser.2018.05.042. Elouali, A., Kousksou, T., El Rhafiki, T., Hamdaoui, S., Mahdaoui, M., Allouhi, A., Zeraouli, Y., 2019. Physical models for packed bed: sensible heat storage systems. J Energy Storage 23, 69e78. https://doi.org/10.1016/j.est.2019.03.004. , J.-F., 2017. A review on expeEsence, T., Bruch, A., Molina, S., Stutz, B., Fourmigue rience feedback and numerical modeling of packed-bed thermal energy storage systems. Sol. Energy 153, 628e654. https://doi.org/10.1016/ j.solener.2017.03.032. Farfan, J., Breyer, C., 2018. Combining floating solar photovoltaic power plants and hydropower reservoirs: a virtual battery of great global potential. Energy Procedia 155, 403e411. https://doi.org/10.1016/j.egypro.2018.11.038.

Guelpa, E., Bischi, A., Verda, V., Chertkov, M., Lund, H., 2019. Towards future infrastructures for sustainable multi-energy systems: a review. Energy. https:// doi.org/10.1016/j.energy.2019.05.057. Guo, S., Liu, Q., Sun, J., Jin, H., 2018. A review on the utilization of hybrid renewable energy. Renew. Sustain. Energy Rev. 91, 1121e1147. https://doi.org/10.1016/ j.rser.2018.04.105. Guo, C., Xu, Y., Guo, H., Zhang, X., Lin, X., Wang, L., Zhang, Y., Chen, H., 2019a. Comprehensive exergy analysis of the dynamic process of compressed air energy storage system with low-temperature thermal energy storage. Appl. Therm. Eng. 147, 684e693. https://doi.org/10.1016/ j.applthermaleng.2018.10.115. Guo, H., Xu, Y., Zhang, Y., Liang, Q., Tang, H., Zhang, X., Zuo, Z., Chen, H., 2019b. Offdesign performance and an optimal operation strategy for the multistage compression process in adiabatic compressed air energy storage systems. Appl. Therm. Eng. 149, 262e274. https://doi.org/10.1016/ j.applthermaleng.2018.12.035. Hamann, A., Hug, G., 2016. Integrating variable wind power using a hydropower cascade. Energy Procedia 87, 108e115. https://doi.org/10.1016/ j.egypro.2015.12.339. Kester, J., Noel, L., Zarazua de Rubens, G., Sovacool, B.K., 2018. Policy mechanisms to accelerate electric vehicle adoption: a qualitative review from the Nordic region. Renew. Sustain. Energy Rev. 94, 719e731. https://doi.org/10.1016/ j.rser.2018.05.067. Mohammadi, A., Mehrpooya, M., 2016. Exergy analysis and optimization of an integrated micro gas turbine, compressed air energy storage and solar dish collector process. J. Clean. Prod. 139, 372e383. https://doi.org/10.1016/ j.jclepro.2016.08.057. Mousavi G, S.M., Faraji, F., Majazi, A., Al-Haddad, K., 2017. A comprehensive review of flywheel energy storage system technology. Renew. Sustain. Energy Rev. 67, 477e490. https://doi.org/10.1016/j.rser.2016.09.060. Nami, H., Akrami, E., 2017. Analysis of a gas turbine based hybrid system by utilizing energy, exergy and exergoeconomic methodologies for steam, power and hydrogen production. Energy Convers. Manag. 143, 326e337. https://doi.org/ 10.1016/j.enconman.2017.04.020. Nami, H., Arabkoohsar, A., 2019. Improving the power share of waste-driven CHP plants via parallelization with a small-scale Rankine cycle, a thermodynamic analysis. Energy 171, 27e36. https://doi.org/10.1016/j.energy.2018.12.168. Neuman, P., Pokorny, M., Weiglhofer, W., 2014. Principles of Smart Grids on the generation electrical and thermal energy and control of heat consumption within the District Heating Networks. IFAC Proc. 47, 1e6. https://doi.org/ 10.3182/20140824-6-ZA-1003.00553. Odukomaiya, A., Abu-Heiba, A., Gluesenkamp, K.R., Abdelaziz, O., Jackson, R.K., Daniel, C., Graham, S., Momen, A.M., 2016. Thermal analysis of near-isothermal compressed gas energy storage system. Appl. Energy 179, 948e960. https:// doi.org/10.1016/j.apenergy.2016.07.059. Pantaleo, A.M., Camporeale, S.M., Miliozzi, A., Russo, V., Shah, N., Markides, C.N., 2017. Novel hybrid CSP-biomass CHP for flexible generation: thermo-economic analysis and profitability assessment. Appl. Energy 204, 994e1006. https:// doi.org/10.1016/j.apenergy.2017.05.019. Pantaleo, A.M., Camporeale, S.M., Sorrentino, A., Miliozzi, A., Shah, N., Markides, C.N., 2018. Hybrid solar-biomass combined Brayton/organic Rankinecycle plants integrated with thermal storage: techno-economic feasibility in selected Mediterranean areas. Renew. Energy. https://doi.org/10.1016/ j.renene.2018.08.022.

Please cite this article as: Arabkoohsar, A., Combined steam based high-temperature heat and power storage with an Organic Rankine Cycle, an efficient mechanical electricity storage technology, Journal of Cleaner Production, https://doi.org/10.1016/j.jclepro.2019.119098

14

A. Arabkoohsar / Journal of Cleaner Production xxx (xxxx) xxx

Pramanik, S., Ravikrishna, R.V., 2017. A review of concentrated solar power hybrid technologies. Appl. Therm. Eng. 127, 602e637. https://doi.org/10.1016/ j.applthermaleng.2017.08.038. Rashid, K., Safdarnejad, S.M., Ellingwood, K., Powell, K.M., 2019. Techno-economic evaluation of different hybridization schemes for a solar thermal/gas power plant. Energy 181, 91e106. https://doi.org/10.1016/j.energy.2019.05.130. Sadi, M., Arabkoohsar, A., 2019. Modelling and analysis of a hybrid solar concentrating-waste incineration power plant. J. Clean. Prod. 216, 570e584. https://doi.org/10.1016/j.jclepro.2018.12.055. Salim, H.K., Stewart, R.A., Sahin, O., Dudley, M., 2019. Drivers, barriers and enablers to end-of-life management of solar photovoltaic and battery energy storage systems: a systematic literature review. J. Clean. Prod. 211, 537e554. https:// doi.org/10.1016/j.jclepro.2018.11.229. Siemens high temeprature heat and power storage Project [WWW Document]. https://www.siemens.com/press/en/pressrelease/?press¼/en/pressrelease/ 2016/windpower-renewables/pr2016090419wpen.htm&content%5b%5d%3WP. Stiesdal electricity storage [WWW Document], n.d. URL https://www.stiesdal.com/ energy-storage/. Suresh, N.S., Thirumalai, N.C., Dasappa, S., 2019. Modeling and analysis of solar thermal and biomass hybrid power plants. Appl. Therm. Eng. 114121 https:// doi.org/10.1016/j.applthermaleng.2019.114121. Tavana, A., Emami Javid, A., Houshfar, E., Mahmoudzadeh Andwari, A., Ashjaee, M., Shoaee, S., Maghmoomi, A., Marashi, F., 2019. Toward renewable and sustainable energies perspective in Iran. Renew. Energy 139, 1194e1216. https:// doi.org/10.1016/j.renene.2019.03.022. ~ o-Echeverri, D., Wang, H., 2019. Wang, X., Virguez, E., Kern, J., Chen, L., Mei, Y., Patin Integrating wind, photovoltaic, and large hydropower during the reservoir refilling period. Energy Convers. Manag. 198, 111778. https://doi.org/10.1016/ j.enconman.2019.111778. Wolf, D., Budt, M., 2014. Lta-caes e a low-temperature approach to adiabatic compressed air energy storage. Appl. Energy 125, 158e164. https://doi.org/ 10.1016/j.apenergy.2014.03.013. Xi, H., Li, M.-J., Zhang, H.-H., He, Y.-L., 2019. Experimental studies of organic Rankine cycle systems using scroll expanders with different suction volumes. J. Clean. Prod. 218, 241e249. https://doi.org/10.1016/j.jclepro.2019.01.302. Zakeri, B., Syri, S., 2015. Electrical energy storage systems: a comparative life cycle cost analysis. Renew. Sustain. Energy Rev. 42, 569e596. https://doi.org/10.1016/ j.rser.2014.10.011. Zhao, P., Gao, L., Wang, J., Dai, Y., 2016. Energy efficiency analysis and off-design analysis of two different discharge modes for compressed air energy storage system using axial turbines. Renew. Energy 85, 1164e1177. https://doi.org/ 10.1016/j.renene.2015.07.095.

Nomenclature A: Area (m2) c: Specific heat capacity (W/m2) D: Diameter (m) _ Rate of electricity (kW) E: h: Specific enthalpy (kJ/kg) hv: Volumetric heat transfer coefficient (W/m2.K)

k:

Thermal conductivity (W/m.K) Mass (kg) _ : Mass flow rate (kg/s) m P: Pressure (kPa or bar) Q_ : Heat transfer rate (kW) R: Radius (m) R: Thermal influential distance (m) o T: Temperature ( C or K) 2 U: Overall heat transfer coefficient (W/m .K) V: Volume (m3) w: Specific work (kJ/kg) _ Work Rate (kW) W: m:

Greek Symbols

h: Energy efficiency r: Density

ε: Heat exchanger effectiveness factor ε: Porosity d: Thickness (m) l: time-step counter Sub/superscripts a: Air blr: Boiler el: Electricity chg: Charging cond: Condenser dcs: District cooling supply line eva: Evaporator f: Working fluid (organic) g: Electricity generator h: Heat hpt: High pressure turbine in: Internal wall ins: Insulation ipt: Medium pressure turbine is: Isentropic process lpt: Low pressure turbine orc: ORC unit p: Pump pth: Power-to-heat ptp: Power-to-power s: Stones st: Steam t: Turbine tt: Timestep counter ugw: Underground water.

Please cite this article as: Arabkoohsar, A., Combined steam based high-temperature heat and power storage with an Organic Rankine Cycle, an efficient mechanical electricity storage technology, Journal of Cleaner Production, https://doi.org/10.1016/j.jclepro.2019.119098