Design of photovoltaic systems: requirements and types of systems.
A photovoltaic system consists of a set of photovoltaic modules (panels), an electrical component (cables) and an electronics (inverter). The modules use incident solar energy to produce electricity through the photovoltaic effect.
The purpose of the photovoltaic system is to achieve significant energy savings for the structure served. The advantages that underlie the development of this technology are:
• Compatibility with architectural requirements and the protection of the environment
• No noise pollution
• An economy and alternative to fossil fuels
• Generation of electricity without polluting emissions
This article briefly describes the requirements and characteristics necessary for a correct design of a photovoltaic system.
The apparent position of the sun
Since the Earth turns on itself from west to east, and as we do not perceive this movement, we have the impression that it is the celestial sphere that rotates in the opposite direction, that is, It is to the west, dragging all the stars, included Sun.
As a result of the axis in relation to the plane of the Earth, you have that the Sun appears, from season to season, at different heights on the horizon.
This erroneous impression, which has influenced the vision of the world and the sky for thousands of years, however, is the most intuitive and remains the most used even today to designate, in a simple and intuitive way, what happens in The sky, also for the positioning of the sun.
The energy flow emitted by the Sun and absorbed by the Earth’s crust is defined as solar radiation, or more precisely for the design of the photovoltaic system, as the energy of the radiation of the sun exploitable in a horizontal plane.
The solar radiation that passes through the layers of the atmosphere is subject to different effects, a part is reflected in space, a part diffuses in all directions, a part is absorbed and, finally, a part called solar radiation. directly the surface of the earth.
The site of the installation
The size of the photovoltaic energy for the system connected to the network can be estimated taking into account, in addition to the economic availability, the following aspects:
• the availability of space in which to install the photovoltaic system (available surface)
• the availability of solar energy (solar radiation)
• Morphological and environmental factors (shading and albedo)
Identification of the space in which the photovoltaic system will be installed
The first operation to be carried out is to locate the spaces where to place the photovoltaic modules. In general, in the case of residential installations, it is about placing the panels on the sides of the roof. If possible, it is better to opt for an installation integrated in the cover. So we need to identify the faces with the best exposure to the south.
The optimal exposure is the one that coincides with the complete south; therefore, the maximum productivity in azimuth equal to 0 degrees.
In addition, it is necessary to identify the optimum inclination of the panels with respect to the horizontal plane; this value is set inclination.
As a general rule, the maximum productivity values are obtained with the following slope:
optimal slope = latitude of the site – 10 °.
The solar field and its effective exposure
In order to correctly evaluate the solar gains, it is necessary to calculate the direct and diffuse solar radiation that affects each surface of the solar fields (the surfaces of the panels exposed to radiation), taking into account the inclined plane, the direct, diffuse radiation, etc
Availability of solar energy
The availability of solar energy for the installation site must be verified using the data of the monthly average daily solar radiation in a horizontal way, taking into account the meteorological phenomena.
Azimuth and angle of inclination.
Morphological and environmental factors (shading and albedo)
The effects of mask due to the volumes on the horizon, due to natural elements (hills, trees) or artificial elements (buildings), determine the reduction of solar gains and, therefore, the recovery time of the investment.
The components of a photovoltaic system
Here are some basic components of the photovoltaic system that characterize the type of installation:
• photovoltaic modules:
Devices that provide the transformation of solar energy into electrical energy.
• charge controller:
Device for the protection of accumulators (regulates the charging and discharging of batteries).
Devices to store the energy of the photovoltaic system and be able to supply it to the users when the modules are not able to produce due to the absence of solar radiation.
Device for transforming direct current of modules into alternating current (220 volts). Note: if the equipment to be fed is of type CC, this component can be excluded
• electrical panel:
For electrical distribution. In case of high consumption or lack of power of the photovoltaic modules, the current is taken from the public network. Otherwise, the excess solar energy is reintroduced into the network. In addition, it measures the amount of energy supplied by the photovoltaic system to the network.
• photovoltaic cell:
The photovoltaic cell, the size of approximately 10 x 10 cm, is the basic device at the base of each photovoltaic system.
We can have different types of photovoltaic systems: systems connected to the network (connection to the network) and isolated installation of the network (autonomous).
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