In figure 2, we present the temperature distribution in the ICS and the solar irradiation over the time.

) and temperature distribution at the interface absorber/polymer (o), at the interface PCM/polymer (A) and on the polymer (□)

The maximum useful efficiency (MUE) was first defined by Faiman[5], as the ratio of the maximum extractable energy to the total solar incident energy upon the collector during the heating period. This definition has been extended to ICS-PCM by Tey et al[1], and can be written in our case as (eq 2):

In this equation, the numerator (or EICS) represents the amount of energy stored by the composite and the polymer. This expression takes into account the sensible heat of the PCM in solid and liquid form, the latent heat of the PCM and the sensible heat of the polymer envelope.

According to the raw data illustrated in figure 2, the MUE was found to be 0.26. Considering that the efficiency of the absorber, defined by equation 1, at the working temperature of 320-350 K is approximately between 0.3 and 0.4, the relative amount of energy transmitted from the absorber to the composite and the polymer envelope ranges from 0.67 to 0.89. This means that between 67 to 89% of the solar energy captured by the absorber is charged in the storage media.

During the discharge phase, the energy extracted from the storage media by the fluid flow is:

‘% • (eq 3)

Ef = |m. Cpf.(To — Tt)

The ratio between Ec and Ef describes the efficiency of the ICS to release the store energy, ^discharge — In our case ndischarge is equal to 0.98.

Figure 3 presents the power and energy released to the fluid over time. After 2000s, the composite has released 71% of the solar energy initially stored in more than 10,000s. This result illustrates the high potential of the composites materials to deliver the stored energy at a high power level.

Fig. 3: Power (o) and energy (A) released to the fluid over the time