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Power, Fresh Water Generation and Heating

Reasonable water and electricity supply policies are of vital importance for the development of locations where there is inadequate water. Solar photovoltaic systems or diesel generator systems using reverse osmosis (RO) for fresh water generation are commonly used for a few kV to a few MW, capacity plants, for simultaneous generation of electricity and fresh water. For dispatchable (on demand) electricity and fresh water generation in isolated regions and on islands, diesel generator-based systems are used. With respect to CSP-based electricity and fresh water generation systems, steam Rankine cycle power systems (Palenzuela et al., 2015), organic Rankine cycle power systems (Astolfi et al., 2017), or supercritical carbon dioxide Brayton cycle power systems (Sliarau et ah, 2019) can be used for power generation, and reverse osmosis systems (El-Emam and Dincer, 2018) or thermal energy-driven desalination systems (Astolfi et ah, 2017) can be used for fresh water generation. Simplified schematics of a typical concentrated solar thermal energy-driven organic Rankine cycle-based electricity system with reverse osmosis-based desalination system and thermal energy-driven desalination systems are shown in Figures 3 and 4, respectively. A summary of previous works on concentrated solar power-based cogeneration systems using the ORC technology and desalination system (reverse osmosis or thermally driven) is given in Table 3.

Sunplified schematic of a typical concentrated solar thermal energy-driven orgamc Rankine cycle-based electricity

Figure 3. Sunplified schematic of a typical concentrated solar thermal energy-driven orgamc Rankine cycle-based electricity

and reverse osmosis-based desalination system.

Authors

Solar

Held

Storage

ORC capacitv/working fluids

Max.

temperature of ORC/HTF

Desalination

system

Remarks

Delgado and Garcia (2007)

PTC

100 kVe (Toluene, Octa- methylcyclotetrasiloxane, MM)

365 °C (HTF)

RO

Toluene is a promising working fluid, based on thermodynamic analysis of the system.

Bruno et al. (2008)

FPC,

ETC,

PTC

11.72 kWe and 27.82 kWe (Isopentane, n-propilbenzene, tribromomethane, dibromomethane, ethylbenzene, and other)

400 °C (ORC)

RO

Solar thermal energy-based fresh water generation cost: 4.32 €/mJ to 5.5 & m5. PV-RO-based fresh water generation cost: 12 83 €/m! to 14 85 6/m Isopentane and n-propilbenzene are promising working fluids.

Nafey and Sharaf (2010)

FPC,

CPC,

PTC

99S kV to 1131 kW (Toluene, dodecane, nonane, octane)

300 °C (HTF)

RO

System with direct vapor generating solar collectors.

Toluene is a promising working fluid for РТС-based plants (with fresh water generation cost: 0.903 S/m!).

Nafey et al. (2010)

PTC

-

347 kVV to 662 kW (Toluene)

340 °C (HTF)

RO

Fresh water generation cost (seawater desalination): 0.59 S/m! to 0.S9 S/m!.

Sharaf et al. (2011)

PTC

394 kV to 1123 kW (Toluene)

350 °C (HTF)

MED-TVC,

MED-MVC

Plant using a multi-effect distillation system with thermal vapor compression (MED-TVC) is better than the mechanical vapor compression (MED-MVC).

Karellas et al. (2011)

PTC

-

250 kV (R134a)

113.5 °C (ORC)

RO

Hybrid system integrating solar PV and CSP-ORC. Minimum cost of fresh water production is about 6.52 €/m! for Chalki Island, Greece

Sharaf (2012)

PTC

Not mentioned (Toluene)

350 °C (HTF)

RO, MED,

MED-TVC,

MED-MVC

A CSP-ORC-system with RO desalination is the best alternative (with fr esh water generation cost: 0 57 S.W)

Li et al (2013)

PTC

100 kV (MM)

400 °C (HTF)

RO

Supercntical ORC-systems have higher thermal efficiency than a subcntical ORC-system.

Mathkor et al. (2015)

PTC

1 MW (Cyclopentane)

189 °C (ORC)

Single effect desalination

Hybrid system by CSP and biomass energy using an ORC-unit (1 MWJ, single absorption chiller (682.3 kW and a single effect desalination unit (234 mVday). Exergy efficiency: 41.7%.

Astolfi et al. (2017)

PTC

Thermo- clme

Up to 5 MW (n-pentane)

300 °C (HTF)

MED

Hybrid system powered by a CSP-ORC, solar PV, and DG-set with RO and MED-units. Fresh water generation cost: 1.43 S/m5 to 2.15 S/mJ.

El-Emam and Dincer (2018)

PTC

Two-tank indirect

200 kW to 500 kV (n-octane)

340 °C (ORC)

RO

Polygeneration using an ORC-unit, vapor absorption cooling unit, desalination unit, and electrolyzer. Optimum exergy efficiency and cost rate: 30.3% and 278.9 S/h.

Desai et al. (2019b)

Foil-

based

Two-tank indirect

1 MV (n-pentane, MM, cyclopentane, isopentane, toluene)

238 °C (ORC)

MED

Lowest LCOE for cyclopentane (0.17 t/kWh^) and lowest levelized cost of water for MM (0.91 €/m3).

Toluene (Delgado-Torres et al., 2007), R134a (Karellas et al., 2011), isopentane (Bmno et al., 2008), MM (Li et al., 2013), and n-octane (El-Emam and Dincer, 2018) were proposed as promising organic working fluids for CSP-driven ORC systems with RO desalination. For concentrated solar thermal energy-driven ORC-systems with a thermal energy-driven desalination system, n-pentane (Astolfi et al.,

2017), toluene (Sharaf, 2012), and cyclopentane (Mathkor et al., 2015; Desai et al., 2019b) were proposed as promising organic working fluids.

The parabolic trough collector is the most widely-used CSP technology for ORC-based cogeneration systems (El-Emam and Dincer, 2018). Recently, a nanostmctured polymer foil-based concentrated solar collector technology was analyzed as a promising alternative compared to a РТС-based system for ORC power systems integrated with a multi-effect distillation (MED) desalination system (Desai et al., 2019b). The assumptions related to the solar irradiation, capital cost of the sub-systems and electricity consumption significantly influence the techno-economic performance of the cogeneration system. The concentrated solar thermal energy integrated MED-system is less expensive than a RO-based desalination system (Ghobeity et al., 2011; Sharan et al., 2019). Depending on seawater salinity, membrane configuration and efficiencies of components, the specific electricity consumption for reverse osmosis systems is about 3.5 kWh(/m3 to 5 kWhe/m3 (IRENA, 2012; Sharan et al., 2019). For multi-effect seawater distillation systems, the specific electricity consumption is about 1 kWhe/m3 to 1.5 kWly'm3 (Alfa Laval, 2018).

Power, Cooling and Heating

Conventional vapor compression refrigeration systems (VCRS) powered by electrical energy are widely used for cooling applications. Such systems can be powered by electrical energy produced by a concentrated solar thermal energy-based organic Rankine cycle power system. A low-grade thermal energy-driven vapor absorption refrigeration system (VARS) can also be integrated as a bottoming cycle to an organic Rankine cycle power system. A simplified schematic of a typical concentrated solar thermal energy-driven organic Rankine cycle-based vapor compression or absoiption refrigeration system is given in Figure 5. A summary of previous works on CSP-driven ORC-based cooling and/or heating systems is given in Table 4.

Authors

Solar collector

ORC capacitv/working fluids

Cooling system/ refrigerants

Remarks

Al-Sulaiman et al. (2011a)

PTC

500 kW# (n-octane)

VARS (LiBr-H,0)

Exei'gy efficiency of tngeneiation system: 20% for solar mode, 7% for storage mode, and 8% for solar-storage mode.

Al-Sulaiman et al. (2011b)

SOFC-Biomass- solar thermal

500 kW< (n-octane)

'ARS (LiBr-H,0)

Energy efficiency of tngeneration system: 90% for solar mode, 90% for biomass mode, 76% for solid oxide fuel cell (SOFC) mode.

Buonomano et al. (2015)

Solar thermal and geothermal

6 kV (R245fa)

VARS (LiBr-H,0)

Cooling capacity: 30 kW, heating capacity: 87 kWfc

System efficiency: 69.4% for tngeneration mode, 6.4% for only power mode. Payback penod range: 2.5 у to 7.6 y.

Karellas and Braimakis (2016)

PTC and biomass

1.42 kWs (R134a, R152a, R245fa)

VCRS (R134a, R152a, R245fa)

Cooling capacity: 5 kW, heating capacity: 53.5 kVib.

Solar-ORC thermal, electrical and exergy efficiency: 6%, 3%, and 7% COP of VCRS: 3.88, payback penod: 7 y.

Patel etal (2017)

PTC/LFRdish and biomass

10 kV (n-pentane, Toluene, R245fa)

Cascade YARS-YCRS

Fully biomass-based system better than solar-biomass system LFR as a solar field and n-pentane as an ORC working fluid are the more appropriate choices

Bellos and Tzivanidis (2017)

PTC

  • 89.3 to 177.6 kW •
  • (Toluene, n-octane, MDM, MM, etc.)

ARS (LiBr-H,0)

Toluene is the more suitable woridng fluid with exergy efficiency of 29.42%. For toluene, net power output: 177.6 kVe, heating capacity: 398.8 kVlh, cooling capacity: 947.2 kW,

Bellos et al. (2018a)

PTC and biomass

S.2 kW (Toluene, n-octane, MDM, MM, n-heptane, cyclohexane)

YCRS (R141b, R 600, R161, R600a, and other)

Cooling capacity: 5 kW, low-temperature (50 °C) heating capacity: 7.91 kV]h, high temperature (150 °C) heating capacity: 5 kVlh. Toluene is the more suitable refngerant Payback period: 5 13 y.

Bellos et al. (2018b)

PTC and waste heat

146.8 kW (Toluene, n-octane, MM, n-pentane)

ARS (LiBr-H,0)

Simple payback period: 4.86 y. Cooling capacity: 413.6 kW, heating capacity: 947.1 kVft. Toluene is the more suitable refrigerant

Villanm et al. (2019)

LFR, CPC

25 kV (NO'EC 649)

ARS

Cooling capacity: 17.6 kW. Energy perfomiance of LFR-ORC-system very sensitive to location compared to CPC-ORC-system.

Bellos and Tzivanidis (2019)

PTC

10 kV to 15 kV (Toluene, n-octane, MM, n-pentane)

VARS (LiBr-H,0)

Toluene and n-octane are the preferred refrigerants when the heat rejection temperature is about 125-135 °C.

Sunplified schematic of a typical organic Rankine cycle-based electricity and cascaded vapor compression and absorption refrigeration system (Adopted from Patel et al., 2017)

Figure 6. Sunplified schematic of a typical organic Rankine cycle-based electricity and cascaded vapor compression and absorption refrigeration system (Adopted from Patel et al., 2017).

A bottoming VARS using lithium bromide-water (LiBr—H,0) as a refrigerant is limited to space cooling at a commercial level (Tassou et al., 2010). Vapor absoiption refrigeration systems with ammonia- water (NH,-H,0) are less advisable for food applications due to toxicity, flammability, low boiling point temperature difference of refrigerant and absorbent, low coefficient of performance and incompatibility with materials (Deng et al., 2011). Integrated systems based on adsorption cooling and liquid desiccant cooling technologies are still at the research and development phase (Jradi and Riffat, 2014).

Concentrated solar thermal energy-powered organic Rankine cycle systems integrated VARS, which works on thermal energy, are typically limited to space cooling. On the other hand, ORC-integrated VCRS, which works on electrical energy, can be used for refrigeration applications. Patel et al. (2017) proposed a concentrated solar thermal energy and biomass energy-powered ORC unit with a cascaded refrigeration system, as shown in Figure 6. In such a system, the electricity and heat duty requirements of the VCRS and VARS are fulfilled by the ORC-unit, combining the advantages of both systems. The cascaded system achieves low temperature (up to -20 °C) cooling and requires much lower electricity compared to the vapor compression refrigeration system (Patel et al., 2017).

Design Considerations

The key aspects of designing CSP-integrated ORC-imit-based multi-generation systems optimally are briefly covered in this section.

Solar irradiation data

The duration and intensity of the solar irradiation affect the performance, capacity factor, and economic viability of the system significantly. The sizing and configuration of the system also depend on the solar irradiation. Local factors like fog and pollution level, dust/sand storms, wind speeds and their variations also need to be considered when selecting the place of installation.

Solar collector field and thermal energy storage

Concentrated solar collector type and size and thermal energy storage type and size need to be carefully selected, as both these systems har e major shares in the capital cost of the complete system. Optical efficiency and overall heat loss coefficients are crucial parameters for concentrated solar collector fields and improvements in these parameters often increase the solar field cost. The use of thermal energy storage facilitates delivery of the utilities according to the need by absorbing the variations due to fluctuations in the solar irradiation. For off-gr id locations, where there are no available central gr ids, integr ation of other energy sources, fossil fuel based or biomass based, may be needed to meet the utility demands.

Organic Rankine cycle power system and other sub-systems

The selection of cycle configuration, component types and designs, and working fluid is important for efficiently converting solar thermal energy into multiple products. All these parameters are dependent on the application type and maximum capacity requirement. The other products (cooling, heating, fresh water) should be selected based on the needs of the region. The primary need (electricity, cooling, heating or fresh water) of the place is of vital importance for successful implementation. The cooling and desalination systems can be thermal energy driven or electrical energy driven, and the selection depends on the techno-economic analysis. Integration of thermal energy driven systems with an organic Rankine cycle power system enables a high energy utilization factor and high overall system efficiency. However, in such a system, the net power output is lower compared to only power generating systems with a condensing turbine. Therefore, the selection of an ORC power system and other sub-systems should be done carefitlly.

Load characteristics

The system design needs to be based on a detailed analysis of the part-load characteristics of the components of the multi-generation systems. Due to the mismatch between supply and demand, the major challenge is to provide a dilute and variable nature of solar energy input to the various demands. Moreover, it needs to be addressed that the actual system performance may differ from that of the design predictions due to the system inertia causing delays during the start-up and shut-down phases.

System configuration and control

For optimal system configuration, all of the aforementioned parameters need to be considered carefiilly. The process controls of the CSP-driven multi-generation systems based on the ORC technology should be designed as a subset of the overall plant control strategy. A proper system configuration and control provide desired products to the consumers cost-effectively and reliably.

Cost

Concentrated solar collector powered medium-scale dispatchable multi-generation energy systems with thermal energy storage are typically more costly than fossil fuel based and biomass based systems. However, factors like availability of fossil fuels and biomass as well as high carbon footprints for the former and high water footprints for the latter are the major drawbacks of these technologies.

 
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