**8. Phase change material into the solar water heating systems**

Solar radiation is occurred from the daylight and can be absorbed with solar collectors. These collectors are used for various applications; one of the solicitations is production of outlet hot water. The outlet of the hot water temperature is depending upon different types of collectors (**Figure 10**).

**Figure 10.** *Different types of solar collectors.*

*Phase Change Materials for Renewable Energy Storage Applications DOI: http://dx.doi.org/10.5772/intechopen.98914*

Generally, these solar collectors are mounted on walls for thermal management in the buildings. The thermal power output of the various solar collectors can be determined with product of conversion efficiency and intensity of solar irradiance [44]. The output of thermal power collector can be calculated using following Eq. (4)

$$\mathbf{Q\_{KN}} = \left(\mathbf{n\_0} - \frac{\alpha\_1(\theta\_\mathbf{K} - \theta\_\mathbf{u}) + \left(\theta\_\mathbf{K} - \theta\_\mathbf{u}\right)^2}{E}\right). \mathbf{E.A\_K} = \mathbf{m.C\_P.} (\theta\_\mathbf{K0} - \theta\_\mathbf{K}) \tag{5}$$

QKN Output of thermal power of collector (W), E solar irradiance intensity (W / m<sup>2</sup> ), AK Collector area (m<sup>2</sup> ). Where: n0: Zero-loss collector efficiency, α1: Basic heat loss coefficient (W/m2 K), θ K: Mean collector temperature (K), θ u: Ambient air temperature (K).*θ* KO: Collector outlet temperature (K), θ KI: Collector inlet temperature (K), m: HTF mass flow rate (kg/s), C p: heat capacity of HTF (J/kg K).

Among all the solar collector, the flat plate solar collector is discussed in detail owing to Manufacture process is easy, cost effective, maintenance is low and easy installation. This type of Flat plate solar water heater is suitable for urban households (**Table 2**).

#### **8.1 Flat plate**

Flat plate is one type of heat exchanger for solar collector that converts radiant energy from sunlight into heat energy. This plate is generally used for low and moderate temperature applications i.e. <80°C. This type of collector contains one is case, second is absorbers like copper or aluminum positioned in the heat exchanger owing to good conductors for heat, the heat transfer fluid and insulation materials. To improve thermal efficiency, need to be minimizing the thermal losses and integrate the superior thermal properties of PCM. The thermal storage materials can be integrated either in the collector or separate thermal storage tank. Flat plate collectors are used in hot water production and space heating, and air conditioning system [50, 51]. For solar water heating, the flat-plate collectors are installed at the optimum angle is Latitude +10°. Water is transport fluid in solar water heating and it has good thermodynamic properties such as high heat capacity, high energy density and incompressible.

Disadvantage of water as transport fluid is damage the collector when it is freeze in winter. The damage can be managed by positioning collector at low solar inputs and need to be add antifreeze mixtures to improve above mentioned problems. The usual antifreeze substances are ethylene glycol or propylene glycol. These chemicals are variegated with water and proper discarding due to toxicity. The durable of antifreeze chemicals is about 5 years [52].

In Flat plate solar water heater, PCM can be equipped in two ways (i) Flat plate integrated solar collector (ii) Flat plate non-integrated solar collector.


**Table 2.**

*Performance data for distinguish solar collectors [45].*
