In the design of photovoltaic systems, regardless of the topology that is selected, there are some keys that must be taken into account to design this type of systems properly.The solar resource is the most important parameter for its sizing, it tells us how much energy we have available per square meter in a certain place for its later use. Currently, there are free databases, specialized software or even paid web pages to access this information: among them SolarGis, widely used worldwide, as well as the data center of surface meteorology and solar energy belonging to NASA. or the meteorological software Meteotest Meteonorm.All these tools have reliable information with different sampling periods that provide complete information to quantify the resource. In Colombia we have information from the IDEAM and the Solar Atlas published by the UPME in 2005. Even if this information exists in secondary databases or in first category software, it is insisted on making measurements in the field to have even more reliable data.For the selection of the system we can question ourselves in the following way: what do we want ?, what kind of system? These questions can be answered knowing that energy needs are met, if we want to have support or if we simply want to take advantage of the daytime generation. In some areas of the country, hybrid systems can be considered, in addition to solar energy, for example using a support generator or even another non-conventional renewable source, such as wind. The main goal according to the objective is to calculate a system to provide the expected energy.Another key aspect, equally important to the irradiation, is to determine the energy consumption of the site to which we are going to connect the system. In systems on roof we evaluate the load curve in a period of time and with this we determine the size of the arrangement. As is the regulation today in Colombia, the surpluses can not be injected into the network, so it is very important that this arrangement provides an energy that is below the load curve of the day with less movement, for example on a Sunday .In isolated systems the recommendation is to tabulate the user's energy habits because that is the energy that must be guaranteed during the days of autonomy established. In systems connected to the "utility" type network, the purpose is to produce as much energy as possible, the design of the project is based on activities that guarantee the evacuation of the energy produced (connection to the SIN), selection of properties taking in account socio-environmental risks for subsequent acquisition, topography and access routes. The recommendation is that the selected properties be insured in the early stages of the project.From the technical point of view, the temperature is a very important parameter due to the significant effect in the electrical response of the photovoltaic module, critical in the selection of the inverter. The voltage ranges of the inverter must be wide enough to withstand the changes produced by this parameter. Additionally, mitigating or reducing the shading on the photovoltaic surface can avoid the irreversible damage of the cells that make up the modules by the generation of hot spots.Other parameters besides temperature and shading limit the production of energy and are basically summarized in: orientation and inclination of the modules, efficiency of the selected equipment, manufacturing tolerances and particulate matter of the environment.