## 1 Introduction  
Our society's consumption of electrical energy is increasing worldwide. To help satisfy this demand, every year a big quantity of energy from non-renewable sources limited and harmful to the environment is generated [1]. In Europe, the building sector has the most energy demand spending around 70% of the total demand [2], making energy efficiency and renewable energy generation in buildings a hot topic. The energy efficiency subject has been tackled by building energy standards, namely nZEBs (nearly Zero Energy Buildings), with the requirements for nZEBs in Europe being defined locally [3] and also by associations such as Passivhaus [4] and ASHRAE (American Society of Heating, Refrigeration and Air Conditioning Engineers) [5], that develop guidelines and legislation in order to create more efficient buildings with adequate building envelope, that makes use of solar energy passively and to impose that the equipment installed is more energy efficient. With the energy efficiency in mind, renewable energy generation has been a target of research and development, namely the technologies related solar, wind, geothermal bio fuels and hydro power (mini hydro for local generation), which have the advantage of being clean and sustainable to the environment [6]. Out of the many renewable sources, solar has attracted great attention, not only because of solar thermal technology for domestic hot water (primary use) and water heating, but also for electrical energy generation with the photovoltaic (PV) panels [7]. However, due to the low energy efficiency of the PV panels (not higher than 23% [8,9]) and high installation costs [10], much of the research centers around improving these points [6]. The maximum power point tracking (MPPT) is one of the technologies studied in order to help improve the low energy efficiency of the PV panels, its main objective is to maximize the power generated by the PV system in continuously changing environment conditions. The PV characteristic are nonlinear and weather dependent, namely solar irradiation and temperature. Both in the I-V and P-V curves of a PV panel, there is a unique point for each set of environment conditions called the maximum power point (MPP), in which the generated power is maximized. Many researchers have studied different MPPT techniques to achieve the MPP, each with different efficiency values, complexities, speeds, costs and range of effectiveness [11]. The most commonly used MPPT algorithm in commercial products is the Perturb and Observe (P&O), because it is easy to implement and enables a very high energy conversion [12]. In this algorithm at a time \"n\" the power is measured and compared to the measured power in the previous measurement, if the power is increased the duty cycle will be affected so that the power continues to be increased in the same direction until MPP is reached, otherwise it is moving away from the MPP and the duty cycle will be affected in the opposite direction, unless it is equal and if it happens it is not changed. The Incremental Conductance is the most popular alternative and even offers lower oscillations at MPP, however it is more computationally intensive [13]. This algorithm is based on the knowledge of the value of the incremental conductance \(I/V\) and its increment to reach the MPP, if the increment is greater than \(-I/V\) the duty cycle is reduced, if the opposite is true the duty cycle is increased, if the increment isn't changed the duty cycle remains the same. Due to their fixed step size there is a trade between steady state and dynamic weather conditions, a large step size leads to a faster response to changing environment conditions but bigger oscillations in the steady state, while low step size enables lower oscillations in steady state conditions but slower response to changing environment conditions. Another very documented drawback of this method is the multiple maxima, that occurs when they are partially shaded and multiple MPP are detected [14].