On the basis of a five-parameter photovoltaic (PV) mathematical model, a multipeak output model of a PV array under partial shading conditions (PSCs) is obtained by MATLAB simulation. Simulation and experimental results demonstrate that the model can simulate the performance curves of the PV array under the PSCs. Optimized particle swarm optimization (OPSO) is used to control the multipeak output model that can quickly and accurately track the global maximum power point (GMPP) of PV modules under PSCs. Its main idea is to determine the initial position of particles and remove the acceleration factor and random number in traditional particle swarm optimization (PSO) algorithm. Additionally, according to the distance between two consecutive peak points, the maximum value of velocity is obtained. The advantages of the OPSO include the following: compared with the traditional PSO algorithm, the computing time is greatly shortened; and it is easy to achieve the MPPT with a low-cost microprocessor. In addition, a PV optimizer is designed to improve the output power of PV modules under PSCs, and simulation and experimentation have compared the output characteristics of PV modules in traditional control mode and optimized control mode under PSCs. The experimental results show that the PV optimizer improves the output power of the PV modules by 13.4% under the PSC.

The solar water heating system (SWHS) is one of the main ways to utilize solar energy. In this study, the design, transient performance and techno-economic analysis of a hotel SWHS in Shanghai are carried out. Three distribution strategies are considered for the SWHS, which are small-scale distributed system (System I), medium-scale system (System II) and large-scale centralized system (System III). Transient performance simulation results show that starting frequency of the auxiliary heater is much lower in summer than that in winter. System III holds the highest annually average daily obtained heat per person (13.021 MJ/person) and the lowest annually average heat loss percentage (2.10%). System I has the highest annually average thermal efficiency, which is 48.05%. Cost of the collector accounts for more than 70% of the total investment of three types of systems. Payback period of the three types of systems is System I > System II > System III. When constructing the SWHS in Shanghai, the large-scale centralized system is suggested. This research provides a theoretical basis for the design, selection and construction of the SWHS in China.