5. Conclusions

energy produced from renewable sources. The refrigerators powered by renewable sources may work in stand-alone of off-grid connection. To connect a thermoelectric refrigerator to the

• the refrigerator is directly powered by the PV panel (the main components are the PV panel, the battery bank, the battery charge controller and the refrigerator); and

• the refrigerator is indirectly powered by the PV panel (the main components are the PV panel, the battery bank, the inverter for AC grid connection and the AC-supplied refrig-

Solar-driven thermoelectric refrigerators are of two types, namely, PV-battery thermoelectric systems and PV-PCM thermoelectric systems. The performance of the PV-battery thermoelectric systems depends on the intensity of solar radiation and temperature difference at the hot and cold sides of the TEC. In the case of PV-PCM thermoelectric systems, the PV is directly connected to the TECs having PCMs fixed at the cold side to replace the battery. Thermal storages have generally restricted capacity, and to improve this in some applications, the

Table 1 presents the technical characteristics of some selected thermoelectric refrigeration units with data available from the literature. The selected cases represent various applications with

COP Heat sink at

the hot side

Power supply Applications

vaccine, foodstuffs and drinks in remote areas, and outdoor off-grid applications

Grid Camping vehicles, buses, and special transports for electro

medicine

Grid Laboratory

DC Vaccine carrier

Electrical power input (W)

[63] 3.6 40 18 (DC) 1.44 12 0.12 With fan PV Medicine storage [64] 40 11.6 110 (AC) 25 13.75 0.69 With fan Grid On-grid applications

— 20 13 (DC) 12 52 0.23 Finned PV Cold storage of

20/30.9/40 0.26/0.21/ 0.22

10 (DC) 15.6 52 0.3 With fans Grid Domestic refrigerator

15.3 95.6 0.16 With fan PV Off-grid areas

with two phase

Finned with fan

fan

PV module in off-grid mode, the possibilities are [8]:

thermoelectric units use PCM integrated with thermal diodes [62].

Cooling capacity (W)

[65] 225 18.9 12 (DC) 11 48.1 0.23 Thermosiphon

5.2/6.5/ 8.8

[67] 0.83 17.6 18 1.5 15.4 0.1 Finned with

Table 1. Technical characteristics and performance of thermoelectric refrigeration units.

erator).

240 Bringing Thermoelectricity into Reality

Ref. Volume (litres)

[10] 115/115/ 40

[66] 21.9 40.5

[57] 13 22 12÷24

/48.5/ 54.2

[55, 56]

ΔT (

C) Voltage (V)

(DC)

8/8/10.3 /11.56

Thermoelectric refrigeration solutions are gaining relevance because of a number of positive aspects, such as long duration, noiseless operation, limited maintenance needs, absence of flammable or toxic refrigerants, possibility of being used in different positions and in movable solutions as well as flexibility of usage through optimized control. This chapter has summarized the principles of thermoelectric refrigeration, by presenting the analytical formulations determining the heat flow rate, cooling capacity and COP of a TEC, illustrating the methods to enhance the TEC performance and indicating the current applications of thermoelectric refrigeration. The future improvement of the TEC performance, together with the operational flexibility of the TEC driven by appropriate control systems, will increase the variety of the applications of thermoelectric refrigeration in different contexts, from single units to their inclusion into integrated energy systems.
