## 1 Introduction  
The European Directive (EU) 2015/1513 amending Directive 2009/28/EC on the promotion of the use of energy from renewable sources sets a binding target of 20% final energy consumption in EU from renewable sources by 2020 [1; 2]. One of the renewable energy systems (RES) is solar energy which can be utilized in photovoltaic (PV) systems that are non-polluting and do not generate greenhouse gases or wastes which have to be stored. This kind of system has no moving parts, so the maintenance cost is very little [3; 4]. Due to its advantages, photovoltaic (PV) energy production has experienced a rapid growth all over the world in recent years, and, according to the policies of particular countries, a number of photovoltaic (PV) power plants increases [5; 6; 7; 8; 9]. Producers of PV modules provide characteristic parameters measured under Standard Test Conditions (STC) which are defined as follows: solar irradiance \(G=1000\) W/m\({}^{2}\), module temperature 25 \({}^{\circ}\)C, AM 1.5, and wind speed less than 5 m/s. The testing measurements are usually made in laboratories with the use of solar simulators. Under real conditions, the results of PV performance can be different because of the influence of specific environmental parameters in the given location [10], such as global solar radiation intensity and spectrum [11], ambient temperature, relative humidity, wind speed, and dust concentration in the air [12; 13; 14; 15; 16; 17]. All these factors strongly depend on meteorological conditions, characteristic for given climate [18; 19]. Moreover, it is important that the influence of environmental conditions is complex and final energy production depends on the overlapping of several effects, which are difficult to analyze individually [20]. In general, the most important factors are solar irradiation and temperature, since they directly influence the energy production, and PV modules temperature, which affects modules efficiency. For this reason, outdoor analysis of daily and seasonal variations of PV module performance allow the energy production to be realistically estimated and also limit the over or under sizing in prospective plants. In recent years much research on outdoor measurements of PV systems has been done, but the majority of them refer to warm climate conditions [21; 22; 23]. Nonetheless, spreading of PV technology all over the world implies the need for this kind of study also in locations characterized by lower insolation level such as temperate climate [24; 25]. It is also worth noting that most of work on outdoor photovoltaic (PV) performance is devoted to the investigation of pc-Si technology, since this is the one which is the most popular on the PV market. However, the dropping price of thin film technology (e.g., a-Si, CdTe, CIGS) is a motivation to testing of various kinds of thin film solar modules under real external conditions. The following types of PV technologies were studied experimentally under different climatic conditions:  
* a-Si, HIT, mc-Si--India [26],
* a-Si, HIT, pc-Si--India [27],
* a-Si, c-Si, CdTe--Turkey [5],
* mc-Si--Greece [2],
* mc-Si, pc-Si, a-Si, CIGS, CdTe--Italy [28],
* c-Si, a-Si, HIT--Italy [29],
* mono-Si, CIS--Turkey [30],
* a-Si, c-Si, CIGS--United Kingdom [11],
* a-Si, c-Si, CIGS, CdTe--Germany [31],
* mono-Si, poli-Si, a-Si, CIGS, CIS, CdTe--Netherlands [20]. All these investigations add new knowledge about the influence of external conditions on solar modules built with different semiconductor materials and allow for selecting the best technology type in the given location. At present, there are no published results of this kind of comparative study carried out in the Polish climate. Thus, the goal of this work is to characterize the solar conditions in Poland and evaluate the outdoor performance of three different PV technologies at the same location. This paper presents the comparison of traditional polycrystalline silicon (pc-Si) PV technology and two thin film technologies: cadmium telluride (CdTe) and copper-indium-gallium-diselenide (CIGS).