*3.1. Location and Detailed Demand Analysis*

The simulation tool considers the Meteonorm [35] weather database to determine solar and meteorological resources, such as GHI, ambient temp, and wind speed. The thermal and electrical demands change with different categories of buildings, i.e., single and multifamily houses, tertiary buildings (such as hospitals, hotels, and gyms, etc.), and can be selected individually within the tool interface. Specific key parameters are included, such as load profiles, the current auxiliary source of

electricity, and energy system details. The simulation engine assesses the total monthly and annual total demand depending on inputs for each application. The monthly energy load (L) needed to raise the temperature of supply water to the desired hot water temperature is calculated using Equation (6):

$$L = m \times \mathbb{C}\_p \times N \times \left(T\_d - T\_s\right) \tag{6}$$

where '*m*' indicates the amount of hot water required per person in a day (in liters), '*Cp*' is the specific heat capacity (J/kg·K), '*N*' is several days in a month (days), '*Td*' is desired water temperature (◦C), and '*T<sup>s</sup>* ' cold supply water temperature in (◦C). The monthly demand can also be customized based on consumer utilization in that specific month. For a single-family house, the amount of DHW for one person in a day is considered as 28 L/person/day at 100% occupancy. The demand is kept constant to minimize the variables in the overall system and, thus, to have a fair comparison of collector performance for various locations. The fraction of occupancy can be parameterized to meet the specific thermal demand for the individual location. For tertiary buildings (such as industrial applications), tools consider a different consumption depending on process characteristics.

This simulation tool offers to choose an auxiliary heating system to meet the load demand. This tool also accommodates for the fact that the total collector electricity generation can be utilized for self-consumption or if there is excess electrical energy, it can be sold to the electricity grid in the context of a positive-energy building.

#### *3.2. System Variables*

This simulation tool consists of several PVT collectors and also recommends the number of collectors that would be required based on optimization of total demand and the storage tank capacity. The specific volume capacity (v/a), which is ratio of tank volume (liter) to collector gross area (m<sup>2</sup> ) can be changed depending on the number of storage duration hours.

The shading loss fraction on PVT modules can be adjusted manually. There is the provision to integrate PV and PVT collectors in a scenario if the thermal demand is first fully met by PVT modules, and electrical demand is not fully covered.

### *3.3. Working Principle of the Simulation Tool*

The simulation tool also optimizes the collector and installation parameters based on the demand, availability, and metrological conditions for a particular location. Simulation results highlight essential parameters such as GHI, irradiation on a tilted surface, thermal demand, thermal production, thermal solar coverage, electrical production, total electric and thermal savings, and environmental impact. The maximum power point P<sup>m</sup> (in kW) generated by the PV cells is obtained using Equation (7) depending on the global irradiation on the surface of the module G (W/m<sup>2</sup> ), ambient temperature *T<sup>a</sup>* ( ◦C), cell temperature *<sup>T</sup><sup>c</sup>* ( ◦C), nominal power of photovoltaic collector *<sup>P</sup><sup>n</sup>* (kW), *<sup>G</sup>STC* irradiance under STC (W/m<sup>2</sup> ), i.e., 1000 W/m<sup>2</sup> , and the temperature variation coefficient of power (γγ) (%/ ◦C) [36].

$$P\_m = P\_n \times \frac{G}{G\_{STC}} (1 - \gamma(T\_c - 25)) \tag{7}$$

The cell temperature *T<sup>c</sup>* is linked to the temperature of the absorber plate, which is dependent on the temperature of fluid going in and out of the module. Cell temperature is calculated for each simulation time step based on inlet and outlet temperatures, and electrical output is then calculated depending on the temperature coefficient of the module.

The instantaneous thermal efficiency of the collector is calculated based on Equation (8)

$$\eta\_{\rm th} = \eta\_o - a\_1 \left(\frac{T\_m - T\_a}{G}\right) - a\_2 \left(\frac{\left(T\_m - T\_a\right)^2}{G}\right) \tag{8}$$

where η*<sup>o</sup>* is optical efficiency, *a*<sup>1</sup> is first order heat loss coefficient (W/m<sup>2</sup> ·K), *a*<sup>2</sup> is the second order heat loss coefficient (W/m<sup>2</sup> ·K<sup>2</sup> ), *<sup>T</sup><sup>m</sup>* is the average fluid temperature (◦C), and *<sup>T</sup><sup>a</sup>* is ambient temperature ( ◦C). The various characteristics of the simulated module are listed in Table 1 and are validated by real measurements as explained in [25].

The temperature leaving the PVT module *T<sup>o</sup>* is determined using Equation (9)

$$T\_o = T\_i + \left(\frac{m \cdot C\_p}{G \cdot \eta\_{th}}\right) \tag{9}$$

where *T<sup>i</sup>* , *<sup>m</sup>*, and *<sup>C</sup>p*. represents inlet temperature (◦C), fluid mass flow rate (kg/s), and fluid specific heat (kJ/kg·K), respectively. Thermal solar coverage (Tsolar) is calculated using Equation (10) in this simulation tool

$$T\_{\text{solar}}\left(\%\right) = \frac{\text{Total collector thermal production (kWh)}}{\text{Total thermal demand (kWh)}} \times 100.\tag{10}$$
