We can talk about two types of solar energy use: the one used to produce thermal energy (basically, sanitary hot water and heating) and the one that converts solar radiation into electricity through the so-called photovoltaic technology.
Finally, we must also consider the possibility of making a more global use of solar radiation in the construction of buildings. This way of taking advantage of solar energy is called bioclimatic architecture and takes into account natural light and the weather conditions of each location for the construction of new homes.
Solar thermal installations consist of a system for capturing the radiation that comes from the sun (the solar collector), a storage system for the thermal energy obtained (the accumulator tank), and a heat distribution and consumption system. The most widespread and well-known applications are low-temperature, that is, those that provide heat at temperatures below 100oC. The main components of this type of facility are described below.
Thermal solar energy
The thermal solar collector
The flat collector with a glass roof is the type of collector that, up to now, has been more widespread. Its operation is based on the greenhouse effect, that is, it captures solar radiation inside, transforms it into thermal energy, and prevents it from going outside.
The main elements that make up a solar collector with a glass roof are:
- Transparent cover
- Absorbent surface
- Circulation tubes
- Isolating material
As a general rule, the collectors must be installed facing south to capture maximum solar radiation, and their inclination concerning the horizontal plane must be equal to the latitude of the location.
Storage tank
It serves to accumulate energy at times of the day when it is possible and use it when demand occurs. In small installations, it is possible to incorporate the accumulator in the upper part of the collector: they are the equipment called thermosiphons, which take advantage of the circulation of the water due to temperature difference (convection).
Heat distribution system and consumption
It consists of a control and management system for the facilities, pipes, and ducts, pumps to circulate the fluids, air vents, and various valves.
Support system
To make up for possible periods without sun, solar thermal installations incorporate a conventional water heating system, which is only used when the energy received in the collectors is not enough.
Solar thermal installations can be made as open circuits or as closed circuits, depending on whether the same water that circulates through the solar collectors is drinking water or not.
Open circuit installations are simpler but have the drawback of the danger of frost, corrosion, or scale on the collector. In closed circuit systems there is no mixing between the liquid that circulates through the collectors (primary circuit), to which an antifreeze is added, and the water intended for consumption (secondary circuit).
Photovoltaic Solar Energy
Photovoltaic solar energy is the transformation of light into electrical energy through solar cells, providing economic and environmental benefits.
It is an inexhaustible, clean, silent, and environmentally friendly energy. Plus, it's available anywhere.
Solar cell
The solar cell is a semiconductor where, artificially, a permanent electric field has been created, with which, when the solar cell is exposed to the sun, the circulation of electrons occurs and the appearance of electric current between the two faces of it. . Among the various semiconductor materials used for the manufacture of photovoltaic solar cells, the most widely used is silicon (monocrystalline, polycrystalline or amorphous), which, doped (artificially contaminated) by a certain element, such as phosphorus, constitutes a semiconductor layer. called "n" (with an excess negative charge) or a layer called "p" (with an excess positive charge) if it is doped by another type of element, such as boron. The union of these two layers (p-n union), provided with the appropriate electrical contacts, which makes possible the appearance of electrical current when there is one that is illuminated (the n), forms a solar cell..
The nominal power of the cells is normally measured in watts peak (Wp), which is the power that the cell can provide with a constant radiation intensity of 1,000 W/m2.
For example, a 10 Wp installation would supply a power of 10 W, with radiation of 1,000 W/m2.
A normal single cell has a surface area of about 75 cm2 and a nominal power of 2.5 W, which means that, with radiation of 1,000 W/m2, it provides voltage values of about 0.5 V and a current of about 2 A.
To obtain usable power for medium power devices, a certain number of cells must be joined in what is called a photovoltaic panel. These plates usually contain between 36 and 72 cells to produce a direct current of 12 or 24 V and provide a power between 80 and 190 Wp.
To optimize the performance of the plates, they must be oriented to the south, with an inclination that depends on the latitude and the time of year.
