A review of thermoelectric generators for waste heat recovery in marine applications

Sustainable Energy Technologies and Assessments 59 (2023) 103394
Available online 5 August 2023
2213-1388/Crown Copyright © 2023 Published by Elsevier Ltd. All rights reserved.
Review article
A review of thermoelectric generators for waste heat recovery in
marine applications
Manabendra Saha *
, Owen Tregenza , Jemma Twelftree , Chris Hulston
Power & Energy Systems, Platform Division, Defence Science & Technology Group, Department of Defence, Australian Government, Fishermans Bend, VIC 3207,
Australia
A R T I C L E I N F O
Keywords:
Waste heat recovery
Thermoelectric generator
Marine applications
Marine vessels
Challenges
A B S T R A C T
Due to the surging cost of fuel and stringent international regulations on greenhouse gas emissions, marine
industries are focussing on discovering alternative power sources to decrease fuel expenses and enhance engine
efficiency. To address future regulations, installed power generation will likely need to be complemented by a
mix of energy-efficient plants, waste-energy recovery technologies, smart-power system configuration and
network management, and energy-storage technologies.
Thermoelectric generator systems offer the potential of harnessing waste heat and energy from low to high
quality heat sources. Thermoelectric generator systems also offer many other advantages, including direct energy
conversion (i.e., heat to electricity), no moving parts, a long lifespan, and no maintenance. This makes the
thermoelectric generator system a perfect candidate for waste heat recovery from marine vessels. This study
performs a critical review of thermoelectric generator waste heat recovery technologies and addresses the
challenges for their potential application in current and future marine vessels.
A description of marine waste heat recovery systems using thermoelectric generators is presented, including a
cited energy-saving figure of merit or claimed benefit, such as fuel consumption reduction. Nonetheless, it is
noted that the metric definitions vary across different sources and should be considered in the context of the
literature source. This article also considers the challenges and prospects for thermoelectric generator waste heat
recovery in marine vessels. The main objective of this paper is to demonstrate the fuel and energy-saving po
tential of thermoelectric generator technology for marine vessels and to guide future research.
Introduction
The marine industry is facing challenges associated with rising fuel
costs and tightening emission legislation [1,2]. Bunker fuel prices have
climbed to the highest level since the beginning of 2020 [3], and fuel
expenses are now calculated to account for 43% to 67% of total vessel
operating costs [4], where the fuel expenditure was only for 13% in the
1970 s [5]. Furthermore, stricter environmental regulations apply extra
leverage on fuel costs [6,7]. This demands innovations and novel tech
nologies to enhance energy efficiency and reduce pollution.
The global shipping fleet can be categorised into five vessel classes,
namely: bulk carrier, oil tanker, container, chemical tanker, and general
cargo which account for 90% of the total deadweight tonnage (DWT)
[8]. As per the International Maritime Organisation’s (IMO) Fourth
Greenhouse Gas Study 2020 [8], these ships are consuming the major
portion of fuel used in marine industries and producing the majority of
emissions. Another category of shipping is the global naval fleet that can
be divided into a broad number of unique classes, such as aircraft car
rier, frigate, submarine, and coastal defence among others. Although,
the global naval fleet represents a significantly smaller proportion of fuel
consumers in comparing to commercial shipping fleet [9,10].
For current and future marine vessels, the power and energy
Abbreviations: AEs, Auxiliary engines; ABs, Auxiliary boilers; CFD, Computational fluid dynamics; DWT, Dead weight tonnage; EGB, Exhaust gas boiler; KC, Kalina
cycle; MPPT, Maximum power point tracking; MEs, Main engines; MW, Megawatt; ORC, Organic Rankine cycle; PGEC, Phonon-glass electron-crystal; RTG,
Radioisotope thermoelectric generator; SRC, Steam Rankine cycle; SCRC, Super-critical Rankine cycle; STEG, Solar thermoelectric generator; TCs, Thermocouples;
TE, Thermoelectric; TEG, Thermoelectric generator; IMDs, Implanted medical devices; WHR, Waste heat recovery; WTEGs, Wearable thermoelectric generators; ZT,
Dimensionless figure of merit.
* Corresponding author.
E-mail address: manab.saha1@defence.gov.au (M. Saha).
Contents lists available at ScienceDirect
Sustainable Energy Technologies and Assessments
journal homepage: www.elsevier.com/locate/seta
https://doi.org/10.1016/j.seta.2023.103394
Received 27 September 2022; Received in revised form 21 June 2023; Accepted 26 July 2023

2
demands and environmental constraints, are increasing for both com
mercial and naval ships. It can be distinguished as follows:
Commercial ships are being driven by volatile fuel price and
increasing environmental regulations by the IMO and MARPOL (the
international convention for the prevention of pollution from ships)
[11].
Naval ships are being driven by the growth of new capability and
equipment demands including sensors, effectors, and navigation systems
[12,13].
Auxiliary and propulsion power demands are generally met by diesel
engines and diesel-generator sets (~96% of commercial ships above 100
gross tonnage (GT) capacity) [14]. A large amount of heat dissipates
from the propulsion and auxiliary power plants of ships. In particular,
marine diesel engines waste almost 50% of fuel thermal energy to the
surroundings [15]. Effective utilisation of this wasted heat by inte
grating waste heat recovery (WHR) technologies will enhance plant ef
ficiency and reduce overall fuel consumption [16].
There is a growing base of knowledge on the application of WHR
technologies for internal combustion (IC) engines [17–21]. However,
the majority of the studies are focussed on thermodynamic cycle based
WHR systems. For instance, Song et al., [19] demonstrated the potential
of WHR from the jacket cooling water and exhaust of a marine diesel
engine by employing an organic Rankine cycle (ORC) system. The
experimental study pointed that the overall efficiency can be raised by
10.2% by employing an optimised ORC system. Yang et al., [20] sug
gested a system utilising a dual loop ORC for the purpose of recuperating
waste energy generated by a diesel engine and reported that up to 5.4%
waste energy recovery efficiency can be achieved under different engine
operating conditions. Lecompte et al., [22] reported an overview of ORC
architectures and evaluated their performance under a set of boundary
conditions for the WHR applications. Sprouse and Depcik [23] con
ducted a critical review on IC engine exhaust WHR systems focussing on
the ORC expander and working fluids to exploit energy from low-
medium grade exhaust heat. Bombarda et al., [24] compared Kalina
and ORC cycle based WHR systems (WHRS) from the exhaust heat of a
17.8 MW diesel engine. The study concluded that the cycle based WHR
system, in particular the Kalina cycle, is not economically justified for
low power levels and medium–high temperature heat sources.
Furthermore, corrosion issues (as a result of using organic fluids) de
mand the adoption of costly material [24].
Thermoelectric (TE) generator systems are emerging as an effective
technology for recovering waste heat and energy from low to high
quality heat sources [25]. They offer many attractive advantages such as
[26,27]:
• Direct energy conversion (i.e., direct thermal to electrical energy);
• No moving parts;
• A long lifespan;
• No maintenance;
• Can be integrated into existing plant (e.g. oil heat exchange);
• Robustness.
This makes the TE generator (TEG) a perfect candidate for the waste
heat recovery in marine vessels. The waste heat exploitation by TEG
systems can improve overall system efficiency and reduce fuel expen
diture [28]. Kim et al., [29] experimentally reported that 119 W can be
recovered from a 110 kW turbocharged diesel engine exhaust using only
40 TE modules with a thermal conversion efficiency of 2.8%. The energy
recovery increased with the increasing engine load. Riffat and Ma [30]
presented an overview of TEG applications for WHR systems. Champier
[27] exhaustively reviewed TEG applications in industrial and domestic
appliances for recovering waste heat and energy. Orr et al., [31]
reviewed the WHR system of an automotive car using TEGs and heat
pipes. They concluded that TEG WHR could improve the overall system
efficiency by 5% and reduce fuel consumption by 3%.
Marine WHR applications have some key differences compared to
other applications like vehicle engines or generators [15,32,33]. These
differences include:
• Operating environment: Marine WHR systems are designed to
operate in a harsh marine environment, with exposure to saltwater,
humidity, and potential vibrations.
• Energy Availability: Ships typically have a substantial quantity of
waste heat, which can be harnessed to provide significant energy
savings. This is not the case with most vehicles or small generators.
• Heat transfer medium: In marine WHR systems, the heat transfer
medium is often seawater, which can significantly impact the sys
tem’s design and operation due to bio-fouling issue. Although having
access to seawater can also be a great source for heat sinking.
• Maintenance and upkeep: Marine WHR systems must be designed to
withstand the harsh marine environment and be maintained
frequently to ensure they continue functioning correctly.
• Regulations: The marine industry is subject to strict international
regulations regarding emissions and energy efficiency, making the
design and implementation of WHR systems more complex, which
may not apply to other applications.
In summary, a marine WHR system must able to operate in a chal
lenging environment, with limited space and large amounts of waste
heat available, and be able to withstand harsh conditions while also
being maintained frequently.
For marine vessels, Singh and Pedersen [15] comprehensively
reviewed different WHR technologies and discussed the possible re
covery efficiencies and integration issues in ships. However, the work
was predominantly focused on thermodynamic cycle based WHR sys
tems fo000r marine engines. Similarly, Zhu et al., [34] compared WHR
systems of ships operating on different bottoming power cycles such as
SRC, KC, ORC and cycles using CO2 as a working fluid. The review
concluded that there is no simple solution for optimal WHR across all
kinds of ships and there are trade-offs between cycle configuration,
working fluid characteristics and WHR efficiency.
Liu et al., [17] aimed to harvest waste energy from a marine diesel
engine by employing a steam Rankine cycle and ORC combination. It
was reported that the system reduces fuel usage by 9322 tons per year
and improves the thermal efficiency by 4.42% (14 cylinder two-stroke
marine diesel engine at 100% engine load) [17].
Despite the numerous studies on thermodynamic cycle based WHR
technologies for marine diesel engines, there is no critical review that
addresses TEG based WHR systems in marine vessels.
To the authors’ knowledge, only one study by Kristiansen and Niel
sen [35] is available in literature which presented the potential of TEGs
in commercial ships. However, the study was confined to recovering
waste energy from the exhaust of a main engine and incinerator of a
single bulk carrier. Comparatively, the current work comprehensively
reviews TEG WHR for a broader range of marine vessels and highlights
the energy-saving figure of merit or claimed benefit.
To address the growing regulations and energy demands of the ma
rine industry, installed power generation on marine vessels will likely
need to be complemented by a mix of energy-efficient plants, waste-
energy recovery technologies, smart-power system configuration and
network management, and energy-storage technologies. This paper
performs a review of TEG WHR technologies and systems for their
application in current and future marine vessels. The overall aim of this
work is to conduct a systematic review of marine WHR systems utilising
TEG. This article also discusses the challenges and prospects for TEG
based WHR systems in marine vessels. The paper ends by highlighting
the challenges that evidently demonstrate the potential of TEG tech
nology to enhance marine vessels’ capability and guide future research
and concluding remarks.
M. Saha et al.

3
Waste heat recovery in marine vessels
This section conducts a brief literature review, evaluating the prin
cipal sources of waste heat and WHR technologies for marine vessels.
Energy analysis of marine systems
Baldi et al., [6] performed an analysis of the energy consumption of a
chemical tanker vessel, based on its operations over a one-year period.
All ship operations, including sailing, loading/unloading, manoeuvring,
and waiting period in port were considered in the study. The ship was
47,000 tonne of deadweight and it comprises a four-stroke main Diesel
engine of 7.7 MW capacity, an additional diesel generator system of 1.4
MW capacity and auxiliary boilers to generate steam at 28,000 kg/hr.
Table 1 represents the input and output energy flows of the chemical
tanker [6]. As expected, the propulsion related energy consumption is
the most significant and accounts for about 70% of the overall energy
expenditure.
Fuel energy is wasted to the surroundings through various heat
transfer and loss mechanisms, for example, heat losses through exhaust
gas [31]. The largest waste heat source of a diesel-powered ship is the
diesel engine. Fig. 1 shows the energy balance comparison between a
two-stroke marine diesel engine functioning at 100% specified
maximum continuous rating (SMCR) [37] and a four-stroke water-
cooled, direct-injected diesel engine operating at 80% of full load con
ditions [38]. Although larger commercial ships generally use large two-
stroke marine diesel engines owing to their slow speed operation, naval
ships and many coastal vessels such as ferries, use a four-stroke diesel
engine for their higher engine speed and compact size [39,40].
The Sankey diagrams in Fig. 1 demonstrate that almost 50% of the
total fuel energy in a two-stroke engine and around 63% in a four-stroke
engine are lost to the environment through different streams without
performing any useful work. These diagrams are generic and for com
parison purposes only.
Characteristics of marine waste heat
Marine waste heat refers to the excess heat generated by marine
transportation and shipping activities, such as from the propulsion sys
tems, generators, and auxiliary equipment on ships [2]. The amount of
waste heat generated through different streams varies on a quantity and
quality basis. Waste heat quality is regulated by its temperature and
categorised as high, medium and low quality according to its tempera
ture range, as shown in Table 2 [41].
For marine vessels, most of the wasted heat dwells between medium
and low quality temperature ranges. Table 3 lists the prime sources of
waste heat of a marine vessel and their associated temperature range
[31]. Although the waste incinerator exhaust supplies the highest
quality of heat, the quantity of heat is insignificant in comparison to the
exhaust of main engine. Quantitatively, the exhaust of the waste incin
erator generates 4.8% heat of the main engine, as reported by the 4762
h/year operations of a bulk carrier M/V Rosita [35]. The engine’s
exhaust presents the most significant potential for utilisation by a WHR
system, despite being the medium quality heat source. The moderate
temperature range of the scavenge air also makes it a potential
competitor. The cooling jacket water heat generated by the engine,
while considered a low-quality heat source, is abundant and continu
ously available throughout engine operation. With appropriately
selected WHR technology, it could be the right candidate for WHR ap
plications [2].
Some of the key characteristics of marine waste heat include
[2,7,16,34]:
• Availability: Marine waste heat is continuously generated during the
operation of marine vessels, making it a consistent and reliable
source of energy.
• Diversity: Marine waste heat can come in different forms, such as
low-pressure steam, hot water, or exhaust gases.
• Low/medium grade heat: The waste heat generated from the ship is
considered low/medium grade heat as it has low thermal energy
content compared to other heat sources.
• Energy intensity: The energy intensity of marine waste heat can vary
depending on the vessel’s type, its size, and its operation. For
example, cargo vessels can generate more waste heat than passenger
ships.
• Large quantity: The large size and high fuel consumption of marine
vessels result in the generation of a large quantity of waste heat.
These characteristics of marine waste heat pose challenges to its
effective utilisation. Nonetheless, they also offer opportunities for re
covery and reuse in several applications such as power generation,
heating and cooling, and desalination. Particularly, marine waste heat
can be a valuable resource for energy recovery and efficiency, with the
potential to supply a significant source of clean energy that can aid in
mitigating greenhouse gas emissions.
In naval ships, gas turbines are also utilised for their light weight,
high flexibility, high speed, and capability of generating power at a
higher propulsion load [44,45]. Although the application of marine gas
turbines in commercial shipping sectors is still limited to high-speed
ferries, and cruise ships, there is increasing demand. This is because of
IMO’s strict emission control regulation and gas turbines’ lighter weight
and compact footprint than diesel engines [46]. Despite the advantages
of low emissions and high power-to-weight and power-to-volume ratios,
marine gas turbine’s thermal efficiency is lower than a diesel engine
since excessive residual heat is ejected into the surroundings through
exhaust gas. The typical thermal efficiency of marine gas turbines varies
between 30% and 40% [44,47]. In this context, exploiting waste heat
from the marine gas turbine’s exhaust is an interesting topic of WHR
research.
Waste heat recovery technologies
WHR technologies can utilise waste heat for power generation and
consequently reduce the overall fuel consumption. The usable marine
waste heat energy dwells in the area between medium to low heat
quality. This is because the most significant quantities of marine waste
heat are in this temperature range [2,31]. For marine vessel integration,
the WHR technologies should have the following desirable attributes
[31]:
• High efficiency in utilising the medium to low quality waste heat;
• High power density;
• Able to manage transient heat sources;
• Flexible and adjustable to the vessel operational change, such as full
speed or slow steaming;
• Straightforward to incorporate with other power systems on the ship;
• High reliability;
• Negligible footprint due to onboard space and weight constraints;
• Safe in handling and operation.
It is worth mentioning that the listed characteristics are not all
mutually agreeable (e.g., high conversion efficiency will typically imply
system complexity, as in the case of cycle-based WHR systems). Addi
tionally, any particular WHR technology alone cannot achieve all
Table 1
Energy analysis of a chemical tanker [6,36].
Producers (Input) % Consumers (Output) %
Primary engines 88.4 Propeller 70
Auxiliary engines 9 Auxiliary power 14
Boilers 2.6 Auxiliary heat 16
M. Saha et al.

4
desirable attributes together.
Although many WHR technologies are currently available to exploit
medium and low quality waste heat, their application in marine vessels
has extra challenges [31]. The quantity and quality of marine diesel
engine waste heat varies significantly owing to nature of vessel
operations. For example, ambient conditions will vary with seasonal
change, sea conditions, and the ship location. A marine WHR system
should be able to adapt and adjust with such dynamic operation to
achieve optimum performance. Additionally, naval ships have signifi
cantly different operating profiles as compared to slow-steaming com
mercial ships. To be applicable for naval ships, WHR technologies must
be adaptable to highly dynamic operational profiles.
A WHR system must facilitate smooth power-sharing by integrating
with existing ship power systems. From an economical point of view,
any WHR systems must be technically viable and economically feasible
having a short payback period [5,31,34,48]. For marine vessels, the
WHR technology should have the capabilities to allow a certain per
centage of increase in energy savings. WHR systems are typically
Fig. 1. Heat balance diagram of a marine two-stroke diesel engine (redrawn from [37]) and four-stroke diesel engine (data from [38]).
Table 2
Classification of waste heat quality [15,41].
Quality Temperature range (◦
C)
Low Up to 232
Medium 233 – 649
High Above 650
Table 3
Main waste heat sources with their temperature range of a typical ship [18,31,42].
Source Temperature range (◦
C) Reference
Waste incinerator exhaust 850 – 1200 IMO [43], Singh et al., [15]
Engine exhaust gas 200 – 500 Heywood [42]
Scavenge air (compressor outlet) 100 – 160 Shu et al., [18], Singh et al., [15]
Engine cooling water, engine oil 70 – 125 Shu et al., [18], Singh et al., [15]
Fig. 2. WHR technologies applicable to marine vessels.
M. Saha et al.

5
associated with the prime mover or significant auxiliary power gener
ation systems. WHR technologies for a marine application are presented
in Fig. 2 [2,17,31,49,50].
Thermoelectric energy harvesting
Technologies such as thermodynamic cycles and gas expansion-
based systems have been explored to enhance fuel efficiency by utilis
ing wasted exhaust heat from marine engines [31,34,51]. Nevertheless,
the integration of thermodynamic cycle and gas expansion based WHR
systems can be challenging to scale efficiently due to space constraints.
Furthermore, the thermodynamic cycle based WHR systems require
continuous maintenance, increasing the overall operational costs.
Moreover, most cycles-based WHR systems have a minimum heat
requirement to be feasible.
Fig. 3 represents a diagram of WHR system architectures according
to installed propulsion power recommended by MAN Diesel and Turbo
[52]. Fig. 3 reveals that the WHR system based on Power Turbine
Generator (PTG) or Organic Rankine Cycle (ORC) unit suits a marine
vessel with installed propulsion power of less than 15,000 kW. The
Steam Turbine Generator (STG) or PTG unit-based WHR system fits
15,000 kW to 25,000 kW power capacity marine vessels. Above 25,000
kW propulsion-powered marine vessels require Steam Turbine - Power
Turbine (ST-PT) generator unit as a WHR system.
Cycle based WHR systems are typically part of (or highly integrated)
diesel engine or gas turbine system. This requires engine original
equipment manufacturer (OEM) investment to address engine integra
tion challenges such as system control and interfacing and class
approval. Specifically, for the case of turbo-compounding, incorrect
matching can degrade engine performance. TEG systems can be incor
porated into exhaust systems or heat exchangers and would not neces
sarily require OEM approval.
Waste heat harnessing by TEG is not a usual practice in the marine
industry. This is due to [53]:
• a deficiency of high-temperature thermoelectric modules (TEM),
• low energy conversion efficiency and
• high costs relative to conversion efficiency.
Despite these current drawbacks, thermoelectric materials could
potentially be used in myriad applications aboard ships, incorporated as
part of heat exchange processes or used to recover waste heat, increasing
overall plant efficiency [54,55]. The advantages of TEG are numerous
[27]:
1. Straight conversion of energy (i.e., TEG directly converts thermal
energy into electricity);
2. Solid-state and stationary parts inside the TEG without any working
fluids, therefore zero maintenance costs;
3. Prolonged life-time, particularly when operating with unchanging
heat sources;
4. No scale effects. TEGs are readily scalable for micro generation in
minimal spaces in electronic chip-size or to produce tens/hundreds
of kW units;
5. Silent operation;
6. Possible to install in any position which makes TEGs suitable for an
embedded arrangement.
Regardless of the numerous advantages, TEGs were confined to space
applications for a long time owing to their exceptional reliability
[27,56]. The application of TEGs in the automobile industry has been
investigated since early 2010; however, application in the marine in
dustry is still in the infancy stage [57]. Given the presence of multiple
potential WHR sites that exhibit consistent temperatures and have ac
cess to a reliable supply of seawater for cooling purposes, there is sub
stantial potential for employing TEG systems in marine vessels [31,58].
Thermoelectric generator technology
The principle of thermoelectric generation
A thermoelectric generator operates on the concept of the Seebeck
effect and is usually employed to transform heat energy into electrical
energy [59]. Conversely, when electrical energy is provided to a TE
generator, heat flows in a reverse direction that generates a cooling ef
fect and is regarded as a thermoelectric cooler (TEC) [60]. Which is
known as the Peltier effect. Fig. 4 depicts the thermoelectric effect of a
Peltier cooler and Seebeck thermoelectric generator. The
Figure demonstrates that entropy and heat move from one end to the
other end of the thermocouple using the charge carriers.
As shown in Fig. 4, a TE junction can be constructed by connecting P-
type and N-type semiconductors. P-type semiconductors have been
doped with electron acceptor atoms that carry electron holes (positive
charge carriers) in the crystal [61,62]. N-type semiconductors have been
doped with electron donor atoms that carry negative electrons in the
crystal [26,63]. An electromotive force is induced across the TE junction
with a temperature gradient, according to the Seebeck effect. The
induced electromotive force allows the flow of current when an elec
trical load is connected. Hence, TE junctions are recognised as genera
tors due to their ability to directly convert thermal energy into electrical
Fig. 3. WHR system architectures according to installed propulsion power
(data from [52]).
Fig. 4. An illustration of the TE effect in a Peltier cooler (left) and a Seebeck TE
generator (right).
M. Saha et al.

6
energy. [64,65].
When a temperature gradient is applied across the TE junction, the
electrical voltage, E(V), generated can be specified as [66]:
E = αΔT (1)
where, ΔT (K) is the temperature gradient across the TE junction, and α
(V/K) is the Seebeck coefficient. The Seebeck coefficient (α) is a material
property that varies with temperature and is defined as the ratio of a
potential difference (ΔV) across the junction to the temperature gradient
(ΔT) [66]:
α =
ΔV
ΔT
(2)
Material properties that promote high conversion efficiency among
the TE junctions are as follows:
• High electrical conductivity;
• Low thermal conductivity;
• High Seebeck coefficient.
Electron scattering can occur without good electrical conductivity.
Low material thermal conductivity eliminates heat backflow between
the cold and hot sides of the TEG under an applied temperature gradient.
Additionally, the Seebeck effect must be maximised. These three pa
rameters are affected by the materials’ electronic properties and thus
optimisations of all three are challenging. The working fluid (electrons)
conducts undesirable electric current and heat while the increasing
electrical conductivity decreases the Seebeck effect substantially, thus it
is crucial to balance these properties [60].
TE device efficiency depends on the TE materials’ performance. The
performance is embodied in a dimensionless figure of merit, ZT, which
can be formulated as [67]:
ZT =
α2
σ
k
T (3)
where α (V/K) denotes the Seebeck coefficient, σ (S/m) represents the
electrical conductivity, k (W/m-K) denotes the thermal conductivity,
and T (K) refers the temperature of the material. It is desirable to have a
larger value of ZT for optimum device efficiency. For commercially
available TE materials, ZT values are currently in the range of 1–2 [64].
When the ZT values of a TEG is increased to 2, overall fuel efficiency for
automotive vehicles was shown to be increased by approximately 10%
[68].
ZT values are temperature-dependent [56,64,69,70]. Fig. 5 illus
trates ZT values of different thermoelectric materials as a function of
temperature.
Waste heat sources in marine systems are dynamic. Therefore, it is
essential to consider the mean ZT of a TEG WHR system, throughout the
operating temperature range [55]. In addition, the ZT varies for mate
rials doped at different levels; thus the variable ZT values must be
considered during the TEG module construction.
TE efficiency is the ratio of the generated electrical energy (Welec) to
the heat flow (Qh) through the hot side of a TEG. TE efficiency (ηTE) can
be estimated by the following relationship [75,76]:
ηTE =
Welec
Qh
=
ΔT
TH
×
̅̅̅̅̅̅̅̅̅̅̅̅̅̅
1 + ZT
√
− 1
̅̅̅̅̅̅̅̅̅̅̅̅̅̅
1 + ZT
√
+ TC
TH
(4)
Here, TH refers the hot side temperature, TC refers the cold side tem
perature, and ΔT = TH − TC refers the temperature difference of the TE
modules. Noting that the expression ΔT/TH represents the Carnot effi
ciency and the theoretical upper limit of conversion.
Fig. 6 represents the TE conversion efficiency with temperature
gradients, for different values of ZT. Note that the value of TC was kept
constant at 30 ◦
C. It is found that the TE generation efficiency is a few
percent when comparing with Carnot efficiency. The most common TE
modules have a ZT ≈ 1 [27,64,65], which provides about ~9% thermal
to the electrical conversion efficiency at the temperature difference of
300 ◦
C. This is across the junction only and does not include losses due to
the system integration. Module fabrication and multi-module system
integration will introduce further parasitic heat and electrical resistance
conduction losses.
For TE materials with a ZT value of 3, conversion efficiency ap
proaches to 20%. As the low conversion efficiency is a hindrance to the
application of TEGs, researchers have attempted to address three pri
mary issues [27]:
1. Increasing ZT value;
2. Increasing material operating temperature with higher ΔT and,
3. The development of low cost materials.
Fig. 5. Variation of figure of merit values with temperature for different TE materials overlaid with the marine waste heat source. PbTe with SrTe (P-type PbTe
endotaxially nanostructured with SrTe) [71], Skutterudite Co23.4Sb69.1Si1.5Te6.0 [72], P-type FeNbSb half-Heusler [73], Polycrystalline Sn.95Se [74].
M. Saha et al.

7
Table 4 demonstrates the commercially available TEG materials and
their allowable operating temperature for waste heat recovery.
Thermoelectric materials
Since the discovery of the TE effect, the use of TE materials was
confined to thermocouples for measuring temperature owing to their
low conversion efficiency [81]. One of the earliest and most significant
applications of TE materials in power generation was in space explora
tion in the 1960 s, when NASA used TE devices to power the electrical
systems on its deep space probes, including the Voyager, Pioneer, and
Galileo missions [81,82]. In addition to space missions, TE materials
have also been utilised in power generation applications where waste
heat is available. For example, in industrial settings to recover waste
heat from furnaces and other equipment.
TE materials are attractive for power generation applications
because they are solid-state devices that have no moving parts and are
highly reliable. They can also be designed to operate at high tempera
tures, making them suitable for use in harsh environments. However,
their efficiency is relatively low compared to other power generation
technologies, and they are currently more expensive than traditional
power generation technologies. This section outlines some common
areas of TE material research and development. TE materials can be
categorised as traditional, nanostructured and novel materials.
Traditional thermoelectric materials
Traditional TE materials are mostly bulk-doped semiconductor al
loys. According to the operating temperature and performance, tradi
tional TE materials can be placed into three categories [54,83,84]:
1. Bismuth–Telluride (Bi2Te3) alloys for low-temperature applications
(less than 250 ◦
C)
2. Lead–Telluride (PbTe) based materials for intermediate temperature
(150 – 500 ◦
C) applications and
3. Silicon-Germanium alloys (Si1-xGex) for high-temperature (i.e., over
500 ◦
C) applications.
Common and commercially available TEG modules are made of
Bi2Te3 alloy based materials [59]. The Bi2Te3 material offers good per
formance with ZT values close to unity at ambient temperature. How
ever, they are not suitable for high-temperature applications as Bi and Te
are easily oxidised and vaporised [83]. Mamur et al., [85] summarised
the latest development and characterisation of nanostructured Bi2Te3.
The authors concluded that the ZT value increases from 0.58 to 1.16
when Bi2Te3 materials are produced in a nanostructured shape.
PbTe is an excellent TE material and it can be employed in appli
cations up to 500 ◦
C. PbTe has good thermal and chemical stability, low
vapour pressure and high mechanical strength [86]. A reasonably fair ZT
value, about 0.8, allowed for its application in multiple space missions
conducted by NASA. Advanced research reported that single-phase
PbTe-based materials can exhibit ZT values of around 1.4 and even
better ZT values up to 1.8 can be obtained for homogeneous PbTe-PbSe
materials [27,87].
Si1-xGex are among the best TE materials for the high temperature
applications. Furthermore, Si1-xGex alloys are one of the cheapest and
most non-toxic TE materials [88]. A significantly higher ZT value (i.e.,
ZT = 1.88) at 600 ◦
C is found for the nanostructured Si0.55Ge0.35(P0.10
Fe0.01) materials [89].
Fig. 6. Typical TE conversion efficiency for distinct ZT values.
Table 4
TEG materials and operating temperature for waste heat recovery.
TEG Material Operating Temperature Range (◦
C) Reference
Bismuth Telluride (Bi2Te3) < 250 Rodriguez et al., [64]
Bismuth Antimony Telluride (BiSbTe) 25–––250 Poudel et al., [77]
TAGs (Te-Ag-Ge-Sb) 150 – 500 LaGrandeur et al., [78]
Half-Heusler 400 – 600 Zhang et al., [79]
Lead Telluride (PbTe) 500 – 600 Rodriguez et al., [64]
Skutterudite 500 – 800 Rodriguez et al., [64] and Rogl et al., [80]
M. Saha et al.

8
Nanostructured thermoelectric materials
Nanostructured TE materials are produced by incorporating poly
crystalline structures and interfaces on a nanometre scale into bulk
materials [90]. By increasing phonon scattering, nanostructuring re
duces the lattice’s thermal conductivity, which in turn reduces the rate
of heat transfer [91].
The ZT value of TE materials improves significantly (from original TE
semiconductors) by employing nanostructure engineering [92] which
results in higher TE efficiency. It was theoretically and experimentally
explored that nanostructuring generates ultrahigh power density at the
module’s hot side and increases system performance significantly
[79,93].
Simultaneously, employing advanced synthesis and characterisation
techniques, common bulk materials comprising nanostructured com
ponents were designed to achieve higher yields [82]. Research by Sarbu
and Dorca [94] reveals that ZT can be improved in one of the following
ways:
• nanomaterial comprised bulk samples and
• nanomaterials themselves
Nevertheless, the production of nanostructured materials is beset
with challenges as a result of the substantial quantity of samples
required on the nanoscale [95].
Novel thermoelectric materials
Advances in understanding the relationship between thermoelectric
properties, structure, and chemical composition have resulted in the
emergence of several material development strategies that will lead the
exploration of novel high-performance TE materials. Table 5 shows
some advanced thermoelectric materials and their corresponding ZT
value.
Graphene has attracted significant interest due to its extraordinary
thermoelectric and thermal transport properties [101]. Olaya et al.,
[102] report a ZT value of graphene and carbon clusters (C60), syn
thesised by the chemical vapour deposition of up to 1.4.
The contribution of different materials to TE technologies is depicted
as a percentage in Fig. 7 [81]. It is not surprising that Bismuth Telluride
and Lead Telluride based TEM are the major area of research and cover
19% and 18% of TEM, respectively.
Numerical modelling and experimentation of TEG system
Numerical modelling and experimentation are important tools for
understanding and optimising the performance of TEG modules.
Numerical modelling involves using mathematical formulas to simulate
the behaviour of the module, while experimentation involves measuring
the actual performance of the module in a real-world setting [103,104].
A brief overview of numerical simulation and experimental exploration
using TEGs is presented in this section.
Numerical modelling of TEG
Numerical modelling involves using mathematical equations of heat
energy conversion and electric field conversion to simulate the behav
iour of TEG systems [103]. This can be done using commercial computer
software such as COMSOL [105], ANSYS [106], or MATLAB. The
modelling process typically involves creating a virtual representation of
the TEG module and using equations to describe the heat transfer,
electrical conductivity, and TE properties of the materials employed in
the device. This enables the prediction of the TEG module’s performance
under different operating conditions.
By taking into account the variation in internal energy, the numerical
model can be expanded to include transient states in addition to steady
states. Researchers have made significant advancements in the numer
ical models of TEG devices over the past few years. The proposed nu
merical models have become increasingly comprehensive, covering
various aspects such as TE module to TEG system, one-dimensional to
three-dimensional, and steady state to transient state. Luo et al., [103]
conducted a detailed assessment of TEG numerical models, with a spe
cific emphasis on the various modelling methods and their application in
different scenarios. They have concluded that thermal resistance based
one-dimensional models can rapidly determine the performance of both
the TEG module and its system under various parameters, but their ac
curacy is relatively low. Conversely, three-dimensional numerical
models offer high accuracy, but at the expense of longer computation
times.
Fraisse et al., [107] conducted a comparative analysis of one-
dimensional models, such as the thermal resistance model, analogy
model, and numerical model, to predict the performance of a TEG. They
used ANSYS finite element method to perform numerical simulations. As
per their findings, the outcomes projected by the numerical model are
consistent with those anticipated by the analogy model. However, the
thermal contact resistance model overestimated the output voltage and
power.
Meng et al., [108] reached similar conclusions by comparing the
simplified thermal contact resistance model with the three-dimensional
numerical model. Because of its high accuracy and ability to visualise
physical field distribution characteristics, the three-dimensional nu
merical model has emerged as the most frequently used model to
anticipate the performance of TEG devices. Nonetheless, accurate
Table 5
Peak ZT values of some novel thermoelectric materials.
Materials Type ZT Value Peak Temperature, ◦
C Reference
Pb0.98Na0.02Se + 3 %CdSe 1.4 650 Gayner et al., [96]
Pb 0.997Sb0.003Se 1.45 557 Gayner et al., [96]
Pb0.92Sr0.08Se 1.5 627 Gayner et al., [96]
Sn0.98Mg0.03In0.03Te 1.5 567 Bhat and Shenoy [97]
SnTe 1.6 650 Li et al., [98]
Sn0.99Ag0.01Se0.85S0.15 1.67 550 Lin et al., [99]
PbTe-4SrTe-2Na 2.2 642 Biswas et al., [71]
SnSe single crystals 2.62 650 Zhao et al., [100]
M. Saha et al.

9
numerical model development of TEG devices is not available due to the
unknown and challenging direct measurement of the TEG module’s
working temperature. Therefore, developing comprehensive models of
TEG systems that take into account the heat transfer mechanism from
heating/cooling sources to the hot/cold sides of TE modules is crucial to
anticipate their performance accurately.
In summary, both one-dimensional and three-dimensional modelling
of TEGs are important research areas, with a current focus on improving
the efficiency and reliability of TEGs. Further research is needed to
bridge gaps in the understanding of the thermal and electrical behaviour
of TEGs, and to develop accurate models for real-world applications.
Experimentation of TEG
Experimental testing of TEGs is essential for verifying the accuracy of
numerical models and characterising the performance of a TEG module.
The main parameters that are typically measured during experimental
testing of TEGs are the temperature difference across the module, the
electric potential generated by the module, and the current flowing
through the module. An experimental study of TEG involves investi
gating the performance of the device under different conditions to
optimise its efficiency and power output. A growing base of knowledge
on the experimentation of TEG has developed in recent years. A sum
mary of some experimental studies focussing on power generation using
TEG is presented in Table 6.
Both numerical modelling and experimentation can be used together
to optimise the design of a TEG module. The modelling can be used to
predict the performance of different design configurations, and experi
mental testing can be used to validate the models and identify any
Fig. 7. Contribution of various materials used in TE research and development (data from [81]).
Table 6
Summary of a selected experimental study on TEG based power generation.
Authors/Year TEG
Material
Operating Temperatures, Hot
side (Th) and Cold side (Tc)
Max Heat
Input, W
Max Power
Output, W
Remarks
Bottega et al.,
2023 [109]
Bi2Te3 Th = 160 ◦
C;
Tc = 40 ◦
C
148.5 4.10 The maximum TE conversion efficiency was achieved up to 2.8%.
Gharzi et al.,
2023 [110]
Bi2Te3 Th = 52 ◦
C;
Tc = 17 ◦
C
560.3 6.22 The generated electrical power by a series array 70 TEG module has a
0.96–1.11% contribution to increasing the overall hybrid solar system
efficiency up to 15.75%.
Qasim et al.,
2022 [111]
Bi2Te3 Th = 67.6 ◦
C;
Tc = 29.9 ◦
C
1404 29.49 The TEG panel made of 150 TEG modules produces an average energy of
1.435 kWh with a maximum TE efficiency of 2.1% using waste heat from
solar hot water system.
Xie et al., 2020
[112]
Bi2Te3 and
Sb2Se3
Th = 142 ◦
C;
Tc = 32 ◦
C
Not specified 5.6 With hydrothermal power generation as the heat source, the TE module
was pressurized at 40 MPa, resulting in a maximum power output of 5.6
W.
Goswami et al.,
2019 [113]
Not
specified
Th = 59 ◦
C;
Tc = 20 ◦
C
46.5 1.033 By utilising 48 TEG modules, it was possible to achieve a TE conversion
efficiency of 2.218% using waste heat from a 10 kW biomass engine.
Nararom et al.,
2018 [114]
Bi2TE3 Th = 69.6 ◦
C;
Tc = 31 ◦
C
30.5 1.03 Using solar radiation, the energy conversion efficiency of the single TEG
module is measured to be 1.81%, resulting in a power output of 1.03 W.
M. Saha et al.

10
discrepancies or areas for improvement.
Commercially available TEG systems
TEG systems are commercially available and widely used in a variety
of applications. TEGs are used in various industries, including automo
tive, aerospace, consumer electronics, and waste heat recovery. In
automotive applications, TEGs are used to convert waste heat from the
engine into electrical energy to improve fuel efficiency. In consumer
electronics, TEGs are used to power wearable devices, such as smart
watches and fitness trackers, using body heat as the source of thermal
energy. In waste heat recovery, TEGs are used to convert waste heat
from industrial processes into electrical energy to improve energy
efficiency.
A number of companies specialise in the production of TEGs and
offer a range of products with varying performance specifications, such
as maximum power output, thermal conversion efficiency, and oper
ating temperature range. Some of the well-known TEG manufacturers
and the feature of their products (i.e., TE cooler and generator) are
tabulated in Table 7.
These TEGs are used in a variety of applications, including waste
heat recovery, renewable energy systems, and temperature control
systems. They are available in different shapes and sizes to suit various
applications, and the selection of a TEG largely depends on the tem
perature difference, power output, and overall system design
requirements.
Applications of thermoelectric generators
The nature and quality of the waste heat sources and the conditions
in which they are used, are the two essential criteria for TEG applica
tions [27]. TEGs have various applications due to their inherently high
reliability and can be used to build generators with long, service-free
lifespans. Some typical examples include:
• In the space domain, radioisotope TEGs (RTGs) have been utilised by
NASA for over 50 years [122]. RTGs use a nuclear heat source and
can operate for many years after their launch. RTGs are well suited
with medium to low power demands in space because of their light
weight and high reliability [123].
• TEGs can be utilised for unmanned sites for isolated and off-grid
power generators [124]. TEGs are the most dependable power
source in such conditions as they are maintenance-free, operate
around-the-clock, perform under all atmospheric conditions, and
function without battery backup [27,124].
• Since human body heat is a constant energy source, it can as a heat
engine to power implanted and wearable medical devices [54,69].
Leonov et al., [125] developed different wearable thermoelectric
generator (WTEGs) based products that can produce 0.8 – 3 mW of
power using the body’s natural heat flow.
• A solar thermoelectric generator (STEG) was developed to exploit
heat from solar radiation [126].
Thermoelectric waste heat recovery systems
A TEG-WHR system generally consists of TE modules, a waste heat
source and heat sink [56]. Heat is shifted from a high-temperature zone
(e.g., the exhaust gas of the engine) to the TEM hot junction, and it is
discharged to a low-temperature zone (e.g., engine cooling water)
through the TEM cold junction.
A schematic of a TE module system is depicted in Fig. 8, highlighting
the arrangement of P-type (electron deficit) and N-type (electron excess)
doped semi-conductor elements which are thermally connected in par
allel and electrically in series.
Table 7
Summary of the commercially available TEG and TE coolers.
Company Name and
Model No.
Generator /
Cooler
TE Material Max Power
Output, W
TE Conversion Efficiency/
Coefficient of Performance (COP)
Operational Temperature Range (Th -
Tc)/ Temperature Gradient (ΔTmax),◦
C
Sources
Wellen Tech
(TEG-25–56)
TEG Bismuth
Telluride
9.6 4.8% 200–––30 [115]
AMS Technologies
(Mars 65)
TEG – 65 8% 500–––115 [116]
Everredtronics
(TEG241-60BA)
TEG Bismuth
Telluride
20.9 5% 330–––30 [117]
Europeran
Thermodynamics
(GM250-127–28-12)
TEG – 25.5 5% 250–––30 [118]
Laird
(ETX25-12-F1-6262-
TA-W6)
TE Cooler Bismuth
Telluride
192.05 COP 0.43 ΔTmax = 83.2
[119]
Ferrotec
(7004/031/240B)
TE Cooler Bismuth
Telluride
49.0 COP 0.47 ΔTmax = 72
[120]
Advanced Thermal
Solutions
(ATS-TEC50-38–008)
TE Cooler Bismuth
Telluride
133.3 COP 0.57 ΔTmax = 68
[121]
Fig. 8. Schematic of a simple TE module system.
M. Saha et al.

11
This section discusses various applications of TEG systems for WHR
systems.
Automobile waste heat
Various studies have evaluated TEG-WHR devices for automotive
vehicles. Typical units focus on the exhaust gas stream; a stack of
modules along a vehicles’ exhausting line is a common occurrence. Ef
forts from automotive manufacturers and allied companies are reviewed
in [127], with conversion efficiencies ranging from 2.9% through 6%. In
an experimental investigation, Haider and Ghojel [128] propose a TEG-
WHR system (5% conversion efficiency) to replace a vehicle alternator,
resulting in a 2% to 5% saving in engine fuel consumption. Agudelo
et al., [129] examined the energy recovery potential from an automobile
diesel engine exhaust and reported that about 8% to 19% fuel con
sumption can be reduced at different operating conditions. The US
Department of Energy funded the automotive TE-WHR project
[130–132] where different TEG architectures were attached in the BMW
X6 and the Lincoln MKT (Ford) passenger cars. For the BMW, the system
recovered about 605 W and 450 W of power for the design point and
dynamic test drive conditions, respectively. The TEG system attached to
the Lincoln MKT recovered 225 W for a high-speed highway driving and
80 W at a slow-speed city driving [130]. Nonetheless, considering the
techno-economic point of view, it is suggested that existing TEG-WHR
device efficiencies are quite low to be viable for application in com
mercial vehicle systems [27,31,128].
Industrial waste heat
A TEG for recovering industrial gas-phase waste heat in China was
proposed by Meng et al., [133]. The results demonstrate that about 1.47
kW/m2
can be recovered with a 4.5% conversion efficiency and a waste
gas temperature of 350 ◦
C. The payback duration for the system was
calculated as 4 years, considering the industrial waste energy and set-up
costs. Ma et al., [134] experimentally probed the WHR potential of an
industrial biomass gasifier using commercial Bi2Te3 based TEGs. The
results show that about 29.7 W electrical energy with maximum 10.9%
conversion efficiency can be recovered using TEG-WHRS at a tempera
ture difference of 505 ◦
C between TEG hot side and cold side. In Kaji
kawa [135], the onsite experiments of TEG-WHR units at various
locations throughout an incinerator system for industrial waste pro
cessing, is reported. Conversion efficiencies are in the 2% to 3% range.
Electronics and microprocessor waste heat
Many electronic devices such as microprocessors generate waste heat
during operation. The waste heat emitted from electronic devices could
be utilised to provide power to other parts in the device, such as a
cooling fan. About 1.5 mW of power was recovered from a semi
conductor circuit by placing a TEG between the heat sink and integrated
circuit [136]. A novel TEG-WHRS was proposed to extract waste heat
from a mobile phone where about 1.5% − 4.2% energy can be recovered
[137].
A list of common electronic waste heat sources are as follows:
▪ Batteries
▪ Power electronics (switching AC to DC/ DC to AC)
▪ Computers.
Marine vessel waste heat
Marine vessels generate a significant amount of waste heat from their
engines and exhaust systems, which can be utilised to power various
onboard systems such as lights, navigation equipment, communication
systems or to charge batteries. In a marine vessel, the hot exhaust gases
from the engine can be used as the heat source for the TEG. The cold
seawater can be used as the heat sink. The TEG can be installed in the
exhaust system or in the engine cooling system to capture waste heat and
transfer it into electricity. The use of TEGs in marine vessels can provide
several benefits, including:
▪ Increased energy efficiency: by utilising waste heat to generate
electricity, TEGs can increase the overall energy efficiency of
marine vessels, reducing their fuel consumption and emissions.
▪ Cost savings: TEGs can help reduce the operating costs of ma
rine vessels by providing an additional source of electricity
without the need for additional fuel consumption.
▪ Improved sustainability: TEGs can help reduce the environ
mental impact of marine vessels by reducing their emissions
and reliance on fossil fuels.
Overall, TEGs have the potential to be a useful technology for har
nessing waste heat in marine vessels and improving their energy effi
ciency. Section 5 presents a thorough evaluation of WHR systems
utilising TEGs in the marine industry.
Marine waste heat recovery systems using thermoelectric
generators
The main waste heat sources of marine vessels, ordered in decreasing
value, are combustion engine exhaust, scavenge air cooling, engine
jacket cooling, lubricating oil cooling, and incinerators [35]. Primary
engines (for propulsion and manoeuvring) are the main source of waste
heat onboard a ship and a significant portion of heat is lost through
exhaust and cooling water channels. Despite the substantial WHR po
tential, the application of TEG-WHRS is not common in the marine in
dustry. Nonetheless, it is anticipated that TEG-WHRS are likely to be
installed in new ships and existing ships in the future [16,31,35,55].
The integration of TEGs into ships is more favourable than other
transportation schemes (such as automotive vehicles) because of the
availability of sea water as a cooling medium. However, insufficient
research is available in the literature on the TEG-WHRS for marine
Table 8
Estimation of TEG power on a bulk carrier ship [35].
Source of Waste Heat Medium Hot-side Temp. (o
C) Flow Rate Calculated TEG
Power (kW)
Electrical generator Flue gas 340 0.69 m3
/s 10.0
Incinerator Flue gas 340 0.68 m3
/s 9.7
Main engine exhausts after the boiler Flue gas 210 14.18 m3
/s 42.4
The main engine scavenge air cooling Air 162 13.92 m3
/s 46.4
Excess steam from the boiler Sat. Steam 159 0.087 kg/s 5.9
Main engine cooling water Fresh water 83 18 kg/s 11.8
FW generator unit, boiling water Fresh water 61 8.3 kg/s 4.3
Lubrication oil cooler Lubrication oil 49 46 kg/s 2.1
Fresh water generator unit, condenser Sea water 37 25 kg/s 0.4
Total energy recovered 133 kW
M. Saha et al.

12
applications. This section discusses current research efforts exploring
the application of TEG-WHRS in the marine domain.
TEG-WHR on a bulk carrier ship
Kristiansen et al., [16,35] analysed the potential of integrating TEGs
in large ships such as container ships, cruise ships, oil tankers or ocean
liners, where the main engine(s) (~8 – 16 MW) is the principal energy
source [35]. A bulk carrier with 52,292 deadweight tonnage (DWT)
capacity, namely the M/V Rosita, was considered for WHR potential via
TEGs [35]. Its running hours were 4762 h/year, averaged over the last
four years. The bulker has a 7.8 MW primary engine and three auxiliary
engines of 480 kW for power supply.
The amount of recoverable TEG power was estimated using the
product of predicted TEG efficiency and the usable waste heat. This
estimate is shown in Table 8. In the calculation of power output, the
TEG’s hot-side temperature (Th) was considered as the mean tempera
ture of the flue gas and the cold-side temperature (Tc) was considered as
the actual sea temperature at summer or tropical conditions. Tc was kept
constant at 29 ◦
C. Values were collected from the official sea trial test
records at continuous service output (CSO), which is 85% load on the
primary engine at the normal running conditions.
The main engine was the primary waste heat source for the TEG-
WHR systems. However, scavenge air also shows a considerable
source of waste heat for the TEG-WHR systems due to the distinct outlet
temperatures. The analysis suggested that TEG-WHR systems can
recover ~ 6% of total energy from the ship and it can increase the overall
fuel energy efficiency up to 55% [35].
TEG-WHR from ship incinerator
Considering the oil incinerator higher temperature, Kristiansen et al.,
[16] selected it as the most promising heat source for TEG applications.
Furthermore, none of the energy released during combustion in the
marine incinerator is typically utilised for other heat exchange processes
[35]. A typical shipboard incinerator used for the study by Kristiansen
et al., [16] is presented in Fig. 9.
For maximum power output, TEGs are installed in the exhaust after
the incinerator. Fig. 10 illustrates the design of a TEG heat exchanger.
The modular cross-section provides the flexibility of the TEG heat
exchanger to be employed in different sized incinerators.
The hot exhaust gas passes through the SS316 stainless steel rect
angular channels. A copper layer was utilised on the steel as a thermal
spreader. A water-cooled copper channel was used as the TEG’s cold
side. Electrical insulation between the semiconductors of each side of
the TE module was provided by a ceramic substrate.
A cost analysis was conducted to calculate the maximum TEG power
output and relevant cost per unit. Fig. 11 shows a line graph of net TEG
power corresponding to cost per watt. An optimised maximum power
output can be obtained by increasing the unit price. At the bottom end of
the figure, a slight increase in cost contributes a significant difference in
generated power. While at the top end of the figure, a hefty price
increment gives only marginal power increase. The estimation shows
that 58 kWelectric power can be extracted from 850 kWthermal incinerator
for 6.6 US$/W at optimum TEG performance. However, minimising the
expense, about 25 kWelectric can be extracted for 2.5 US$/W. The ma
terial expenditure of the TEG accounts for 24% of the total expense.
When the onboard electric power demand remains constant, the addi
tional power output from the TEGs reduces the load on the diesel gen
erators and saves fuel. Although more up-to-date costings are required
for accurate predictions, the fuel savings can justify the additional cost
of integrating the TEG system with an incinerator.
TEG-WHR from marine engine
A numerical study has been conducted on a marine engine with a
rated power of 1.7 – 3 MW to evaluate the TEG performance using
Fig. 9. A typical shipboard incinerator (TeamTec OG200C) (redrawn
from [16]).
Fig. 10. Design of a modular cross-sectioned TEG heat exchanger (redrawn
from [16]).
Fig. 11. Net optimum power as a function of cost per unit (data from [16]).
M. Saha et al.

13
exhaust WHR systems [138]. A system-level simulation model of TEG
thermal contact resistance was developed and validated by experiments
to probe the feasibility of Mg2Sn0.75Ge0.25, Cu1.98Se and Cu2Se as po
tential TE materials to exploit waste heat from a small-sized MTU marine
engine of a yacht.
Fig. 12 depicts a schematic of the TEG-WHR arrangements on the
marine engine. The TEG-WHR set-up consists of hot exhaust gas, and a
cooling water supply, TE modules, insulation materials, with cold and
hot side heat exchangers [138]. The serial connected TE couples are
positioned between the cold and hot side heat exchangers. Straight fin
type heat exchangers were employed in this study to enhance heat
transfer between heat source/sink and TEM’s hot and cold side.
Although, the heat exchanger fins improve heat transfer, they also raise
the engine back pressure and this contributes to increased pumping
power which increases fuel consumption. Therefore, the proper design
of heat exchanger is crucial to balance between potential increased
pumping losses and the power recovered by TEG –WHR systems. Two
marine engines, M70-V12 and M73-V20, were taken as references in the
study, and the parameters of M70-V12 were used in the baseline model.
By comparing the Cu2Se and Cu1.98Se, it has been found that Cu1.98Se
performs better than Cu2Se for WHR from the marine engine. Engine
exhaust gas is used as the hot side fluid and sea water used as cold side
fluid of the TEG. The result shows that TEG-WHR systems can recover
2.45 kW from the 84.42 kW of exhaust heat for the V12 M70 4000 en
gine. The output results and input parameters for the specific TEG-WHR
systems are presented in Table 9.
The European funded ECOMARINE project conducted an experi
mental investigation of TEG-WHR to reduce the fuel consumption of
Fig. 12. Schematic of TEG WHR system (redrawn from [138]).
Table 9
Input parameters and results for the TEG WHR system (data from [138]).
Parameters Value
TE conversion efficiency (%) 2.91
TEG electrical power output (kW) 2.45
Heat input from exhaust (kW) 84.42
Hot side temperature (◦
C) 435
Cold side temperature (◦
C) 10
Exhaust flow rate (m3
/s) 5.7
Heat exchanger material Copper cartridge brass
TEM – N type Mg2Sn0.75Ge0.25
TEM – P type Cu1.98Se and Cu2Se
Ceramic substrate Al2O3
Fig. 13. A schematic diagram of TEG-WHRS implemented in ECOMARINE project (redrawn from [139]).
Table 10
Manufacturer’s performance parameters of marine TEG-WHR
systems of ECOMARINE project (data from [139]).
Operational Parameters Value
Output power (W) 28.3
Load resistance (Ω) 0.42 ± 15%
Open circuit voltage (V) 6.9
Output current (A) 8.2
Output voltage (V) 3.45
Module heat flow (W) 566
M. Saha et al.

14
marine engines [139]. Fig. 13 shows a schematic diagram of the TEG-
WHR system implemented by the project. A total of 750 TEG modules
(GM250-127–28-10) were used for the experimental design. Table 10
shows the manufacturer’s performance parameters. The heat exchanger
constructed is a tubular jacket of 500 mm diameter with a glycol-based
primary cooling medium, whereas the secondary cooling medium is sea-
water. However, the flow of exhaust gas does not create any turbulence
inside the tube to enhance heat transfer. Usually, effective heat transfer
is essential between the exhaust gas streams and the hot side of the TEG
module to achieve maximum TE power output and efficiency [139]. The
initial prediction suggested about 6.4% TEG conversion efficiency can
be achieved for a temperature difference of 220 ◦
C between the hot and
cold sides. However, the experimental results reveal that 20.3 KW of
electrical energy is generated (recovered) from a 1.7 MW marine diesel
gas engine using the TEG-WHRS and represents a conversion of 1.2%.
Eddine et al., [56,140] experimentally investigated the performance
of a TEG, replicating marine operating conditions and quantified the
effect of the heat source interface clamping pressure on the TE effi
ciency. The behaviour and characterisation of two types of commercial
TE materials, namely Bi2Te3 and Si80Ge20, were investigated. Fig. 14
depicts the TEG device and the experimental setup built for this work
[56]. The figure also shows a heat exchanger and clamping system. A
spreader individually cools each TEG to ensure an optimal heat transfer.
During the experiments, the cooling water temperature and flow rate
remained constant. The tests were conducted to optimise the perfor
mance of the TEG in a marine application.
The results show an optimum clamping pressure of 3.5 MPa for the
TEG device. Increased clamping force reduces thermal interface resis
tance, reducing temperature losses and increasing the recoverable waste
heat [141]. At the same operating conditions, Bi2Te3 TEM shows better
performance (power and conversion efficiency) than the Si80Ge20 TEM.
It was found that the potential TEG conversion efficiency using Bi2Te3
TEM was 0.6–1.3% and 0.2–0.9% when Si80Ge20 TEM was used. The
possibility of integrating these Bi2Te3 or Si80Ge20 TEMs in a marine
engine depends on the operating profile of the related ships. While the
Bi2Te3 TEM shows more eminent performance on low engine speed, they
demonstrate poor durability at higher temperatures (e.g., ~above
250 ◦
C). On the contrary, the Si80Ge20 TEM offers significant durability
and remarkable performance stability at higher working temperatures.
TEG-WHR for membrane desalination of ballast water
Ballast water treatment and management is an ongoing issue for
ships, including passenger or cruise ships, small and bulk carriers, and
cargo ships [142]. Numerous rules and regulations are enforced at local
and international levels to reduce the environmental consequences of
inappropriate disposition of polluted ballast water at ports [142,143]. In
recent work, Gude [143] proposed energy harvesting from the main
engine’s waste heat using a novel integrated TEG for a membrane
desalination reverse osmosis (RO) unit. This projected TEG system,
generating power from waste heat, can reclaim the ballast water in the
form of clean potable water providing fresh supply in ships.
A bulk carrier ship was considered to determine the TEG-WHR po
tential for desalination. The RO desalination process with a water re
covery efficiency of 45% was considered for Gude’s study [143]. The
energy requirements for the entire RO process can be shown as [144]:
ET = Ein + Ept + Ehp + EA − EERD (5)
where ET represents the total energy demand, Ein denotes the required
energy to draw the feed water, Ept denotes the required energy for pre
and post treatment, Ehp denotes the energy needed for the high-pressure
pump, EA denotes the required energy by other accessories and EERD
denotes the energy recovered by the energy recovery devices (ERD). By
considering the TEG’s ZT value of 0.25 at 125 K temperature difference
between the ambient sea-water and waste heat sources of the bulk
carrier ship, approximately 133 kW of electricity can be produced. It is
found that freshwater generation rates can be enhanced up to 25.6%
employing energy recovery devices. The proposed approach is a novel
solution addressing both issues of freshwater production and ballast
water treatment.
TEG-WHR from the boiler of marine power plant
Chen and Sasaki [145] investigated the potential of employing TEGs
in the boiler section of a marine steam turbine. The study was conducted
using computational fluid dynamics (CFD) modelling with the com
mercial software ANSYS Fluent, to simulate a TEG-WHR system incor
porated into a 300 kW natural gas-fired swirl-stabilised boiler
employing a multidimensional TEG model.
The three metre high boiler burner has an octagonal cross-section as
depicted in Fig. 15. TEG’s were installed on the bottom and top surfaces
of the boiler’s furnace. To generate a temperature differential across the
Fig. 14. Schematic diagram of TEG device and the experimental set-up (redrawn from [56]).
Fig. 15. Cross-section view of the boiler body and the TEG locations (redrawn
from [145]).
M. Saha et al.

15
TEG surfaces, the furnace walls were water cooled. Bismuth telluride
was used as the TE module material.
The simulation results reveal that the TEG model is capable of
operating alongside the fluidic thermal regime of the boiler system and
the heat exchanger geometry. The work quantified that more than 600
W power can be extracted from a 300 kW boiler’s waste heat [122].
TEG-WHR from the hull below the water line
Armenakis and Chatzis [58] reported an innovative approach to
generate electrical power on ships using extensive TE module arrays
attached to the ship’s hull below the waterline. The TEG’s hot side
temperature was maintained using the ship’s main engine exhaust or
auxiliary equipment (e.g., incinerators, burners, etc.) waste heat. The
available waste heat can be effectively extracted by employing suitable
ducts transporting hot flue gases into the TEG’s hot side.
The authors proposed a novel direct cooling method to maintain low
temperatures on the TEG module’s cold side. As the TE modules were
fixed to the hull’s inner side below the waterline, conduction heat
transfer directly cools the cold junction of the TE module arrays. The
cooling of the TEGs is sufficient, reliable, and immediate because the
hull temperature below the waterline is substantially lower than
ambient conditions owing to the direct contact with seawater on the
hull’s outer side. No pumping units or heat exchangers are necessary to
cool the TEGs which lead to a significant advancement of the overall
power factor. This improvement is almost linearly proportional with the
ship’s speed and inversely proportional to the seawater temperature.
The study was conducted on the bulk carrier “Desert Challenger”, a new-
built (2017) ship of 61,000 tons deadweight with a main engine capacity
of 8.86 MW [58].
An experimental setup was designed to replicate the bulk carrier’s
operating conditions on a smaller scale. The exhaust gases were supplied
by a 4 cylinder, direct injection Perkins-Sabre M92B marine engine with
rated power of 64 kW. The exhaust gas temperature was measured to be
240–265 ◦
C. The TEG array was comprised of 20 Bi-Te based TE modules
clamped on a hollow duct of 250 × 300 × 50 mm3
dimension.
Fig. 16 shows the TE module assembly attached to a piece of 12 mm
thick marine structural steel, imitating the ship’s hull. To simulate the
sea water movement, the wet plate was subjected to contact with a
continuous flow of fresh water, causing a gradual decrease in the tem
perature of its outer surface from 100 ◦
C to 30 ◦
C.
A high conductivity graphite sheet was attached with the ceramic
substrates on each side of the TEG module to ensure low thermal
interface resistance between TEG surface and heat source/sink. The
graphite sheets have high thermal conductivity and are able to with
stand at very high temperatures [58]. The average power output per TE
module was measured to be 12 W, and in total, 240 W was recovered
from the TEG array configuration.
TEG-WHR on the cooling system of a ship
Wang and Romagnoli [53] conducted an experimental and compu
tational study on a TE module-level device to explore the influence of
cold-side heat transfer mechanisms on the overall TEG performance of a
marine WHR system. Both thermal and electrical performance of the
TEM device with a conventional tubed cold-plate and optimised flat
groove cold-plate heat exchanger was investigated and compared in
detail.
A commercial Bismuth Telluride (Bi2Te3) TE module (TECTEG TEG1-
12611–6.0) with 126 TE pairs was examined in the research [53].
Fig. 17 illustrates the experimental set-up used to characterise the TEM
device.
A computational model was developed by employing ANSYS Multi
physics TE simulation to characterise the TE module device’s thermal
and electrical performance. Fig. 18 shows a schematic of the
Fig. 16. TEG arrays attached on the wet hull-plate (redrawn from [58]).
Fig. 17. A diagram of the TEM device test rig (redrawn from [53]).
M. Saha et al.

16
computational domain.
Results showed that output power increases linearly with a rising
temperature differential across the TEM device. The novel flat groove
heat exchanger demonstrated more efficient cooling than the conven
tional approach. Around 2.7% gain in maximum power output is ob
tained employing the new cooling system at the temperature gradient of
225 ◦
C. The newly designed TEG with an improved cold-side heat
dissipation system demonstrates significant potential to harnessing
waste heat from the marine vessels.
Discussion on marine TEG-WHR technologies and Figure of merit
The application of TEGs in marine vehicles, specifically for waste
heat recovery systems, has been explored in various research studies.
The comparative analysis provides insights into TEG-WHR applications
and discusses several research efforts and case studies related to the
integration of TEGs in different marine applications. TEG-WHRS has the
potential to recover a significant amount of waste heat from the various
heat sources in marine vessels and it can improve the overall fuel energy
efficiency of ships. While the potential for WHR in the marine industry is
significant, the use of TEG-WHRS is not yet common. However, it is
anticipated that TEG-WHRS will be installed in new ships and existing
ships in the future.
One study analysed the potential integration of TEGs in large ships
such as container ships, cruise ships, oil tankers, or ocean liners. The
TEGs were primarily installed to recover waste heat from the main en
gine exhaust, but scavenge air cooling was also identified as a consid
erable source of waste heat. The analysis estimated that TEG-WHRS
could recover approximately 6% of the total energy from the ship,
leading to an increase in overall fuel energy efficiency of up to 55%.
Another research effort focused on TEG-WHR systems utilising waste
heat from a ship’s incinerator. The study found that TEGs installed in the
exhaust after the incinerator could generate up to 58 kW of electrical
power from an 850 kW thermal incinerator. The cost analysis showed
that the additional power output from the TEGs could justify the inte
gration costs by reducing the load on diesel generators and saving fuel.
A numerical study investigated the feasibility of TEG-WHR systems
in marine engines, using exhaust waste heat. The results showed that
TEG-WHR systems could recover 2.45 kW from 84.42 kW of exhaust
heat from a marine engine. The study compared different thermoelectric
materials and found that Cu1.98Se performed better than Cu2Se for waste
heat recovery from the marine engine. Experimental investigations
conducted by the ECOMARINE project demonstrated the generation of
20.3 kW of electrical energy from a 1.7 MW marine diesel gas engine
using TEG-WHRS.
Additional research explored the performance of TEGs under marine
application conditions. It examined the effect of heat source interface
clamping pressure on the TE efficiency and compared the performance
of different TE materials. The study found that an optimum clamping
pressure of 3.5 MPa and certain TE materials, such as Bi2Te3 and
Si80Ge20, showed potential for TEG integration in marine engines.
A unique application of TEG-WHR was proposed for membrane
desalination of ballast water on ships. By utilising waste heat from the
main engine, a TEG system could generate power to support reverse
osmosis desalination. This approach not only addresses freshwater
production but also helps in the treatment and management of ballast
water.
Overall, these studies demonstrate the potential of TEG-WHRS in
marine platforms for recovering waste heat and generating electricity.
While further research and development are needed to optimise TEG
designs and materials for marine applications, the use of TEGs shows
promise in improving fuel efficiency and reducing environmental
impact in the marine industry. Table 11 summarises the discussed ma
rine waste heat recovery systems using TEG. A cited energy-saving
Fig. 18. Computational modelling of TEM device with conventional tubed cold-plate TEG device (redrawn from [53]).
Table 11
Tabulated summary of marine waste heat recovery systems using thermoelectric generators (TEG-WHRS) reported in the literature.
Location/ Application of TEG-
WHR
The Figure of Merit or Claimed Benefit Percentage of Energy
Recovery
References
Main engine, incinerator, and
boiler
133 kW recovery from 7.8 MW marine diesel engine. 1.7% [35]
Ship incinerator 58 kW recovery from 850 kW incinerator 6.8% [16]
Main engine 20.3 kW recovery from 1.7 MW marine diesel engine 1.2% [139]
Exhaust pipe 2.45 kW recovery from 84.42 kW of exhaust heat 2.9% [138]
Desalination of ballast water 133 kW of energy is recovered, and the freshwater production rates can be increased up to
25.6%
– [143]
Marine boiler 600 W recovery from 300 kW marine boiler 0.2% [145]
Hull below the waterline 240 W recovery from 64 kW natural aspiration marine diesel engine 0.38% [58]
Cooling system 2.7% energy recovered 2.7% [53]
M. Saha et al.

17
figure of merit, or claimed benefit, is also included. It is noted that the
energy saving definition varies across different sources and should be
considered in the context of the literature source.
Challenges and prospects of TEG-WHRS on marine vessels
Challenges
Although there is a great potential to utilise TEGs for WHR, there are
several challenges associated with the commercial application of TEG-
WHRS in marine vessels. The major challenges for TEG WHRS, as
identified from the literature, are discussed in the following subsections.
Low TE conversion efficiency
Low TE efficiency is the biggest challenge to utilising a TEG in ships.
The uttermost TE conversion efficiency of the available commercial TEG
is below 7% [146]. TE efficiency significantly depends on the ZT values
of the TE material. Currently, commercially viable thermoelectric ma
terials that are suitable for marine vessel integration have a figure of
merit around 1.0. However, new TE materials are under development
with significantly higher ZT values (up to 3.0), and these may be suitable
candidates for future marine vessel integration [59,82,96].
Non-Uniform temperature
Non-uniform temperature distributions on the hot and cold side of a
TE module decrease TE efficiency. In order to increase the heat recovery,
several strategies, including thermal interface resistance studies [141],
TE material development, and the design and optimisation of exhaust
heat exchangers, have been proposed and are under investigation. Based
on the concept of phase change heat transfer, heat pipes share the ad
vantages of offering low thermal resistance. Heat pipes have been
inserted to exhaust pipes to lower the effective thermal resistance
[70,147–149].
Heat dissipation
Inappropriate heat dissipation to the cold side of a TEG is another
challenge. The overall TE performance is greatly influenced by the
temperature differential between the hot and cold sides of the TEG.
Marine vessels can access the unlimited availability of sea water, which
can be used as the TEG cooling medium. Wang and Romagnoli [53]
examined the impacts of a cold-side heat dissipation system on a TEG
system’s overall performance for marine WHR. They reported that a TEG
with an improved cold-side heat dissipation system demonstrates sig
nificant potential for harnessing waste heat from ships [50,53]. Arme
nakis and Chatzis [58] proposed a direct method of cooling the TEG
modules in the marine application by conduction heat transfer as TEG
modules are attached to the inner side of the wet metal plates of the
ship’s hull below the waterline. More research on the utilisation of
seawater cooling for marine TEG systems is needed. In addition, the
effect of seawater biofouling should be considered and addressed, as this
has the ability to degrade heat dissipation effectiveness [150].
Space limitation
On board space limitations are another constraint to the integration
of TEG-WHR systems. The maximum rated power of a commercial TE
module is less than 40 W [64,132]. Therefore, a significant number of
TEGs are essential to produce kW levels of power, potentially creating a
WHR system with a high volume requirement. Owing to the limited area
of marine exhaust systems, it is essential to find an innovative installa
tion approach. To resolve this issue, heat pipes may be employed to
carry heat remotely because of low effective thermal resistance and high
conductivity, i.e., TEGs do not necessarily have to contact exhaust pipes
directly; TEGs can be installed in a place where enough space is avail
able [31,132,151]. In addition, the use of other thermal transport fluids
in conjunction with multi-loop heat exchange systems could be
considered.
Unsteady nature of flue gas
The unsteady nature of flue gas mass flow rate and temperature due
to varying operating profiles is another challenge. This can trigger two
problems [132]:
I. The power available for charging batteries varies with time; thus, the
power loss happens if appropriate methods are not employed to draw
the maximum value.
II. And under extreme operating conditions, such as high-speed vessel
emergency movement, TEGs may be subject to a higher temperature
than their maximum tolerance level. Consequently, TEGs may be
damaged, thus the safe operation of TEGs could be threatened.
To address the first problem, a DC/DC (direct-current) converter
employing a maximum power point tracking (MPPT) method can be
implemented [152]. At the same time, to resolve the second issue,
different approaches such as designing a thermal bypass [153], phase
change thermal storage [154], and using heat pipes [155] can be
applied.
Future prospects and potential future research directions
Previous research has demonstrated the viability of TEGs. Consid
erable progress has been made demonstrating TE power generation
technology as a feasible strategy for WHR and its potential to reduce fuel
consumption.
The commercial application of TEG-WHR systems in marine vessels
is very limited. Considering this status, more research is essential to
accelerate TEG-WHR systems in marine application. Both from the level
of:
1. TE materials and
2. TE device application and integration
The following sections outline some of the potential future research
directions needed to advance the application of TEG-WHR for marine
vessels.
Discovery of high ZT value TE materials
Expanding research on TE materials to raise the dimensionless ZT
value of the materials will strengthen the competitiveness of TEG-WHR
systems in the marine domain. By increasing the value of ZT, the effi
ciency gap between TEG and other WHR technologies (such as ther
modynamic cycle based WHR system) can be closed. When the ZT value
reaches 4.0, the efficiency of a TEG is said to be comparable to that of the
ORC and Kalina cycle [156].
Alternatively, reducing TEG material and manufacturing costs is
another viable path for increasing adoption and acceptance within
marine industries. Innovation of low-cost TE materials and novel TEG
manufacturing technologies will significantly reduce capital costs,
making TEG systems more attractive, even with comparatively lower
conversion efficiency.
Development of high-temperature TE materials
The development of high-temperature TE materials tailored to
operate at the exhaust temperature range of marine engine full-load
operation is needed. Currently, Bismuth-Tellurium (Bi-Te) based TE
materials are employed in TEG-WHR system owing to its durability,
chemical stability and extraordinary high performance at low operating
temperature (up to 250 ◦
C) [132,157]. Available Bi-Te based TEGs can
be employed for commercial ships which have a fairly constant slow
operating speed and relatively lower exhaust temperature. However, for
high speed marine vessels (e.g., naval ships), the engine exhaust tem
perature raises significantly and can reach 500 ◦
C [31]. Such high
exhaust heat cannot be fully utilized using available commercial Bi-Te
based TEGs because for high-temperature environments (e.g., high-
M. Saha et al.

18
speed ships), available Bi-Te based TEGs require separate design con
siderations to limit exposure to elevated temperatures. This trade-off
limits their thermal efficiency. Alternatively, the adoption of high-
temperature TE materials such as Skutterudite, Silicon Germanium,
etc., which are capable of operating above 500 ◦
C, would be beneficial
and allow for greater heat recovery.
Evolution of advanced heat transfer materials with low thermal interface
resistance
A focus on the heat exchanger materials and designs with high
thermal conductivity, low thermal interface resistance, high strength,
and low-cost. The parasitic temperature losses due to heat transport are
still high, despite design efforts [132,138,149]. Therefore, new studies
should be conducted to develop advanced strategies to reduce transport
losses such as interface resistance, enhance heat recovery, and improve
homogeneous surface temperature distribution at the TEG’s thermal
interfaces.
Development of cooling method of TEG
To increase the temperature gradient between the hot and cold sides
of the TEG, research should focus on the heat dissipation of the cold side.
So far, minimal research [53,58] has focused on the cooling methods for
TEGs in the marine application environment.
Optimal application of heat pipes in TEG
Research on the investigation of heat pipes in TEG should be stim
ulated for marine application. A heat-pipe assisted TEG-WHR system is
attractive to researchers because of its increasing heat removal ability,
abolishing space limitation (carrying heat into a location where
adequate number of TEGs can be installed) and protecting the TEGs from
high-temperature damage [147–149]. However, the varying operating
conditions (i.e., fluctuating exhaust temperatures) of the marine engine
impact the heat pipes performance. Additionally, heat pipes can increase
the pressure drop and resultantly raise the associated fuel consumption.
Thus, the application of heat pipes in marine TEG-WHR system demands
more attention and further research.
Development of novel TEG modules configurations
Research should focus on developing novel TEG module configura
tions, such as curved TE modules or tubular-shaped TEGs. The typical
flat-plate module arrangement requires thermal interfacing, introducing
interface resistances. To accelerate the commercialisation of TEG-WHR
systems in marine vessels, extensive studies need to be conducted on
annular or tubular-shaped TEGs, ranging from structure design to
parameter optimisation. Annular configurations may also allow TEG
integration into tube-bank styled heat exchangers, which are common
throughout marine vessels.
Expanding TEG-WHR system research for transient conditions
The majority of the research studies on TEG-WHR systems, mainly
numerical and theoretical investigations, have been carried out under a
steady-state conditions. However, a marine engine’s exhaust tempera
ture and mass flow rate fluctuates significantly in actual operation
(manoeuvring, cruising, loading/unloading, and waiting in port)
generating unsteady exhaust temperature. Consequently, more research
under transient states needs to be performed to precisely characterise
TEG performance and increase the life expectancy of TEG-WHR systems.
Conclusions
For current and future marine vessels, power and energy demands
are increasing. To address these demands, installed power generation
will likely need to be complemented by a mix of energy-efficient plant,
waste-energy recovery technologies, smart-power system configuration
and network management, and energy-storage technologies to meet
both existing and future marine vessel requirements. This paper has
presented a critical review of thermoelectric generators (TEGs) as a
waste heat and energy recovery technology, applicable to marine ves
sels, and to address the challenges faced by current and future ships.
Although this paper is not an exhaustive review, it has attempted to
cover the concept, recent advancement, and application of TEGs for
waste heat recovery (WHR) technologies and systems. Furthermore, this
literature review has highlighted challenges and prospects for the
application of TEG-WHR systems in marine vessels. This paper has
demonstrated the potential of TEG technology to reduce marine vessel’s
fuel consumption and enhance capability. The key findings of this study
are as follows:
▪ TEGs have proven to be a promising technology for converting
waste heat into electricity, offering potential applications in
various fields, including space missions, marine vessels, remote
power generation, medical devices, and waste heat recovery
systems.
▪ WHR systems incorporating TEGs have exhibited energy effi
ciency improvements and cost savings in various sectors,
including automotive, industrial, electronics, and marine
industries.
▪ TEG-WHR systems can be effectively integrated into marine
applications, such as bulk carrier ships, shipboard incinerators,
marine engines, membrane desalination systems, and marine
power plant boilers. The integration of TEGs into WHR systems
in the marine industry has shown promising results, enabling
the conversion of excess heat into electricity.
▪ TEG-WHR systems can recover approximately 6% of total en
ergy from a ship and increase the overall fuel energy efficiency
by up to 55%. Further research and development are needed to
optimise TEG performance and increase their efficiency in this
specific application.
▪ Continued efforts in TEG research should focus on enhancing
material properties, exploring new thermoelectric materials,
improving system design, and increasing the efficiency of heat-
to-electricity conversion. These advancements will contribute
to the wider adoption and commercialisation of TEG technol
ogy in various sectors, promoting sustainable energy practices
and reducing environmental impact.
CRediT authorship contribution statement
Manabendra Saha: Conceptualization, Methodology, Formal anal
ysis, Investigation, Data curation, Project administration, Visualization,
Writing – original draft, Writing – review & editing. Owen Tregenza:
Conceptualization, Resources, Writing – review & editing, Supervision.
Jemma Twelftree: Writing – review & editing, Visualization. Chris
Hulston: Supervision, Writing – review & editing.
Declaration of Competing Interest
The authors declare that they have no known competing financial
interests or personal relationships that could have appeared to influence
the work reported in this paper.
Data availability
Data will be made available on request.
Acknowledgments
The authors express their sincere gratitude to the reviewers for their
invaluable assistance and support in improving the quality of this paper.
Their thoughtful feedback, insightful suggestions, and meticulous
attention to detail have significantly contributed to enhancing the
overall clarity and coherence of our work. The authors also would like to
M. Saha et al.

A review of thermoelectric generators for waste heat recovery in marine applications

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