Chapter 1
Basics of photovoltaic cells
In 1887 Hertz observed that the spark jumps more easily between two spheres of different potentials when their surfaces were strongly illuminated by the light of another shock, and later found that a negatively charged zinc sheet and attached to an electroscope, was rapidly losing its load to illuminated by an electric arc. In all, it concluded that, under the action of light, zinc, and in general all metals emit negative charges
The experimental results obtained were as follows:
• The photoelectric effect is instantaneous, ie the radiation occurs without retardation (the time is about 3 x 10 E-9 seconds)• The number of photoelectrons emitted, ie the intensity of the current produced is proportional to the radiation received• On the speed issue has no influence on light intensity, and its polarization state, but if their frequency or wavelength• For each metal there is a minimum frequency of light radiation, below which no effect picture shows the electric• The photoelectric cells are devices based on light radiation action on certain metal surfaces. The effect of this radiation can be of three types:
- Effect photoemission or fotoexterno: in the metal causes a burst of electrons with their release- Or fotointerno photoconductive effect: it changes the electrical conductivity of metal- Photovoltaic Effect: creates an electromotive force in the metal
In this last section is where they are integrated photovoltaic cells that generate a current proportional to the step of receiving luminous flux. These cells have the advantage over the other types that do not require auxiliary voltage, or vacuum, which is why they are used for converting solar energy into electrical energy
Chapin, bellows and Perarson developed in 1954 the first solar cell capable of converting, in an efficient, sunlight into electricity. Used mainly for food of artificial satellites for certain electronic equipment photosensitivity and feeding small loads in remote or difficult to access.
Physical principles
As we all know, matter is made up of atoms, which in turn are composed of two distinct parts: the core, equipped with a positive electrical charge, and electrons orbiting in different energy bands, electrically charged negative offset of the nucleus, thus forming an entirely stable and electrically neutral
The electrons in the last layer has been given the name of the valence electrons and have the ability to interact with other similar forming a crystal lattice
By division, we can say that there are three types of materials, electrically speaking, and they are:
• Drivers: have a little valence electrons bound to the nucleus and can move easily within the crystal lattice in response to a small external agent• Semiconductors: their valence electrons are bound to nuclei in the drivers, but simply provide a small amount of power to behave like them, releasing their outermost electrons• Insulation: have a very stable configuration, which is difficult to change, since the valence electrons are strongly bound to the nucleus, and to supply energy to the atom jump would be too large
The materials used for photovoltaic cells are semiconductors, since the energy that binds the valence electrons with the nucleus is similar to the energy of the photons that make up the solar energy. When impact is on the semiconductor (usually silicon), its photons provide the energy necessary for the valence electrons so that the links are broken and are free to move in the semiconductor
The place left by the absence of the electron released is called hollow and has a positive electrical charge (equal to the one with the electron but of opposite sign). These holes also shift as the electron released is likely to fall into a hole next, then produces a movement of these "absences of electrons." The fact that the electrons occupy gaps left by other electrons is called recombination
These free electrons and holes created in these points where the light tends to diffuse dark areas, thus losing its activity. However, both particles move in the same direction, do not produce electricity, and recombine before or after restoring the broken link. However, if somewhere near the region where these pairs of electrons and holes are created to form an electric body inside the semiconductor field to separate electrons from holes, making each circle in the opposite direction and, consequently, leading to an electric current in the direction of that electric field.
Creation of the electric field
In conventional solar cells the electric field is achieved by joining two regions of a silicon crystal chemically treated differently
One of the two regions is called n-doped (doped) with phosphorus. Phosphorus has five valence electrons, one more than silicon, so that the phosphorus-doped region shows a greater affinity for electrons than pure silicon
The other region, called p, has been doped with boron. Boron has only three valence electrons, one less than the boron-doped silicon has an electron affinity lower than pure silicon. Thus, the pn junction thus formed has a potential difference Vc causes the electrons have less energy in the zone in the area n p. consequently, an electric field directed in the area to the area p n tends to send the electrons to holes near the area p and n.
The constitution of a conventional silicon cell of crystalline silicon bar doped with boron, which is cut into disks with a thickness of 0.3 mm. One side is heavily doped with phosphorus by diffusion at high temperature in a gaseous atmosphere rich in it, so that this element enters the silicon more concentrated than that it contained boron to a depth of approximately 0.3 microns. Above this layer is deposited conductive wire rack in the back a continuous layer. Both serve to facilitate making electrical contact with the two regions
When photons impinge on the top layer of the cell, some links are broken, then generating electron-hole pairs
If this generation is produced at a distance of less than unity so-called diffusion length before or after these carriers will be separated by the strong electric field that exists in the union, moving the electron to the p and the gap area to the ny area leading therefore to a stream from the area the area na p
If the diffusion length is very short, this means that in a short distance, the electron and hole recombine and light energy that was absorbed to create the pair is recovered as heat, which in our case is not desirable
The electrical current produced, being employed in useful work, develops a voltage drop that makes the area more negative p. As this area was the lowest potential energy of electrons (ie, the highest potential or most positive), the effect of external load is to reduce the potential of the area p, ie, narrow the field separator that appears on the union
The current given by each solar cell for a given illumination varies depending on the voltage drop produced abroad, according to what is shown in the figure below
The power delivered is nearly constant, until it reaches a voltage value for which the union field decreases significantly. Then the current tends to zero quickly.
The maximum power that can give a cell corresponds to a voltage slightly lower than the open circuit Vac
The maximum current Icc cell can supply occurs when there is no external voltage, but in this case provides no power at all. The maximum current value Im is also somewhat lower than the short circuit current Icc
Given the above, to obtain a good performance in solar cells, they must be made of a material in which the binding energy of electrons is not too low, you would loose much of the energy of photon, or too high, because only the most energetic photons of the solar spectrum could break the links. Silicon, with 1.1 eV, is the most widely used material. Gallium arsenide with the 1.4 eV, is theoretically the best features but is more expensive. The copper sulfide with 1.3 eV, is a promising material.
Performance of photovoltaic cells
Performance is defined as the ratio between the maximum electrical power that can provide a photovoltaic cell and the light power incident on the surface
The yield obtained in the laboratory on monocrystalline silicon cells is 22-24% but once mass production going on this fall to a value of approximately 15%, which means that for every 100 watts we receive from the sun, only 15 are used for our use.
Chapter 2
Photovoltaic cells and panels
The photovoltaic cell is the one device capable of converting light into electricity in a direct and immediate. Normally, the most widely used photovoltaic cells are formed by the pn junction and built of monocrystalline silicon. However, there are different procedures and types of materials used for building cells, which then summarize the most suspect and the most used.
Gallium arsenide cells
Photovoltaic cells are perhaps the most suitable for manufacturing of panels, as its theoretical performance limits reached close to 27-28% in its single crystal. The main problem is that this material is rare and abundant, for which fact has not begun handling until relatively recently, with its low technology and high costs.
Monocrystalline silicon cells
As mentioned at the beginning of the most widely used photovoltaic cells are currently the single crystal silicon. This may be due in large part to the industry that is mounted on silicon as the basis for all transistors, integrated circuits and other electronic active components. On the other hand we can not forget that the silicon is the second most abundant material on earth after oxygen
After these data, one may ask why the photovoltaic cells are expensive. The answer to this question has several aspects. First, silicon is not found in pure state and there are certain elements difficult to eliminate. On the other hand, it has to melt and be grown to form a single crystal, as will be seen later, a stage which invests much time and energy. Another important aspect is that, for now, its use is somewhat limited and can not be manufactured in quantities that could significantly bring down the cost of the product
A monocrystalline silicon solar cell is nothing more than a pn junction diode that is especially sensitive to light, generating electricity. The following figure shows the equivalent circuit of a photovoltaic cell, which shows the current source, diode, a small capacitive effect (expressed by a capacitor) and two typical resistance of manufacture, serial and one parallel or shunt, which are formed by the materials themselves
The intensity curve voltage (IV) which defines the behavior of a photovoltaic cell is represented in the figure below
Here you can see the typical steps that define a cell. They are:
• Short-circuit current Icc
It is that which occurs at zero voltage and can be measured directly with an ammeter connected to the solar cell output. Its value varies depending on the surface of the light radiation to which the cell is exposed
Normally, cells and 100 mm in diameter, its value is close to 2.5 amps of 100mW/cm square.
• Open circuit voltage Vac
It can measure the tension in the absence of a load and represents the maximum voltage that can give a cell. Its measurement is done by simply connecting a voltmeter between terminals, and its value varies depending on the type of construction inside the cell, around 0.5V.
• Peak Power Wp
Is the maximum electrical power that can supply a cell and is defined by the point of the IV curve where the product of intensity and the maximum voltage produced. All other points on the curve generated by lower values of the product.
• Form factor FF
Is defined by the following expression:
FF = OP.VP / Icc.Vca
Clearly, the FF will always be a value smaller than unity, and the solar cell will be much better the closer the value of the form factor to this figure. Typically, the FF commercial cells is between 0.7 and 0.8, having the monocrystalline silicon, generally better value than those made with polycrystalline silicon
The form factor turns out to be a parameter of great practical use, since being evaluated with that of another cell type gives us an idea of the quality of this device, comparatively speaking.
• Conversion efficiency, performance
Finally, another parameter that defines the quality of a photovoltaic cell performance or conversion efficiency (n), represented by the following formula:
N = Wp / Wr
Where WP (peak power) is the product of the peak intensity (PI) for the peak voltage (VP), represented in the figure by the dashed rectangle, and the WR radiation power incident on the solar cell surface
To be familiar with the operation of a photovoltaic cell must bear in mind two fundamental concepts:
a) The terminal voltage of a pn junction varies with temperature, but at a certain temperature this tension is constantb) the current supplied by a solar cell to an external circuit is proportional to the intensity of radiation and cell surface
The graphs clearly show these concepts, as we observed that if we maintain a constant light and vary the temperature, the initial curve is shifted while the open circuit voltage becomes more small
In another graph we see that if the cell to maintain a constant temperature and decrease the incident radiation, we obtain a short-circuit currents dwindling, but are related proportionally with highlights
It can also be seen that the open circuit voltage has not changed significantly, which shows stability against illumination increases
If we now observe the behavior of the voltage, current and aunándolas our cell performance in a single graph, we get very interesting deductions, such that the temperature increases the voltage drops, while the curve corresponding to the intensity increases its value to a lesser extent , which translates into a decrease in performance. We say, therefore, that as the temperature at which the cell is increased, decreased performance, producing the opposite effect, ie an increase in performance in terms of lower temperatures.
Chapter 3
The photovoltaic module
Logically, and with very few applications (toys, educational equipment, etc..), The cells are grouped into what is called module or photovoltaic panel, which is nothing more than a set of cells connected properly, so having a optimal conditions for their integration into power generation systems, being compatible (both tension and potential) with the needs and standard equipment on the market
Normally speaking panels 6, 12 and 24 volts, although their voltage is above these, ranging powers
Normally it comes to panels of 6.12 and 24 volts, although their voltage is above these, ranging powers produced between 2.5 and 80 W
The cells that make up a photovoltaic panel must be within a narrow range in their electrical parameters, to prevent decompensation that would occur inside the module when a generate more current neighbors. Precisely for this reason are very important final testing of the cells within the manufacturing process
The world PV consists of several layers that coat the cells above and below, in order to give mechanical protection, since they also protect them against atmospheric agents, especially water, which can be causing the oxidation of the contacts, which would be useless for cell energy production
The photovoltaic modules have structures and a variety of forms according to different manufacturers. We could make a general division saying that a module can consist of:
- Cover- Encapsulating layer above- Photovoltaic cells- Rear encapsulant layer- Back protection- Setting Support- Output electrical contacts
Briefly describe the main qualities required to submit the materials used in the manufacture of photovoltaic modules
• Outer sheath
It has a protective function essentially as it is the one to suffer the action of atmospheric agents. For this reason, glass is often used instead of silicon as a few years ago, since no durability problems. The tempered glass especially, has some qualities that give the photovoltaic module advantages over other types of materials, which has good impact protection while having excellent transmission to solar radiation spectrum
The glass used to manufacture photovoltaic modules and panels should be, on the outside, extremely smooth and able to give or retain dirt. Not so usually in the back, which is in contact with the encapsulant, and is rough in order to improve the penetration of radiation and adherence to this, which embeds the cells.
• Layers encapsulants
They are responsible for protecting the solar cells and interconnect contacts. The materials used (silicones, polyvinyl butyral, or etilvinilo EvA acetylene, etc..) Must have above all an excellent solar radiation transmission and a no degradation against UV radiation, because if not, can decrease performance of the module. The encapsulant should give further the mission to protect and cushion the possible changes and impacts that may occur as well as act of adhesive between the back and bottom covers
• further protection
Its mission is primarily to protect against atmospheric agents, exerting an insurmountable barrier against moisture, some manufacturers use glass, but usually are used acrylics, silicones, TEDLAR or EVA. These materials, increasingly used, provide unique characteristics because they are up to 2300 times less moisture absorbing silica
They usually have white as this increases performance panel
• Support Framework
It is the party providing mechanical rigidity to the assembly and allow insertion into structures covering more modules
The frame is usually anodized aluminum or stainless steel, and sometimes can apply special treatment to make it more resistant to marine environment, which is so detrimental to the materials
The support frame must keep the necessary holes for attachment to a rack, eliminating the need to be handled after a framework should not be drilled in any way, since the vibrations can pop the glass, have a ground that should be used if the number of units will be installed is large
• Electrical contacts
Are those that will allow access to the energy produced by all cells. The forms and methods are varied. Some manufacturers offer one or two meters of cable that runs inside the panel, others have positive and negative terminals, which are sometimes in a weatherproof junction box or simply are protected once the connection is made with a rubber sleeve . Anyway, should be convenient for wiring and allow the connection of a large number of modules is difficult.
• Regulations on PV modules
Given the development of photovoltaic solar energy is growing, for years have established a set of rules governing the quality
These rules are mandatory in some countries and recommended in others, in any case be an advantage for users of these systems
In Spain, there is an established norm that regulates the 8/11/1985 tests to be performed to obtain approval from the ministry of industry and include:
- Visual inspection- Mechanical tests:
Electrical terminals (tensile, bending, torque)
Resistance to torsion module
Shock resistance module Ice Ball- Electrical characteristics:
Open circuit voltage
Voltage at maximum power point
Short circuit current
Current at maximum power point
Power at maximum power point- Testing electrical insulation (leakage)- Proof of durability:
Temperature cycles
Wet-temperature cycles
Resistance to saline environments
Resistance to ultraviolet radiation
Life test
Chapter 4
Charge Regulators
As seen above, PV modules have an output voltage exceeding the rated voltage of the batteries or accumulators on the premises. This is due mainly to two causes:
- The panel voltage must be higher to compensate for the decline that may occur due to the number of temperature- The PV panel voltage must always be greater than the battery voltage in order to load properly. As discussed, to achieve full state of charge in a battery of 12 V nominal, we need a minimum voltage of 14 V (2.34 V for battery cells)
The mission of the regulator, therefore focuses on avoiding that, due to excessive tension provided by the panel, this can eventually overload the battery, resulting in damage that can lead to a battery life
In short, the charge controller is a device able to avoid overloading the battery while the voltage limits appropriate values for maintenance in a state of flotation, the battery pack
The mission of the charge controller is of paramount importance in most cases, since we are working with a fully variable power source and seasonal. Suppose, for example, a fixed consumption for every day of the year. If we calculate the number of solar modules required, we must logically be based winter radiation to ensure the proper functioning of the system at the worst time. But this gives us to the view that, when summer arrives, the value of radiation can be duplicated, so that production will double to that calculated in the winter season and, on the contrary, consumption is the same. In the absence of a regulatory system would lead to an excess current that would be able to boil the electrolyte with the consequent loss of water and deterioration of the storage group, the tension is not limited
Typically, the control of the state of battery charge is done by measuring the line voltage, using data provided by different manufacturers, as there is a relationship between these two parameters. Thus, the control circuit of the charge controller knows when it must begin to act by limiting the voltage and current supplied by the PV group
There are essentially two groups of regulators: the shunt or parallel type and series type. The mission of both is the same and differ in the way of work and performance of each of these elements. Then we discuss the performance of these basic types of regulators.
shunt regulator
The traditional method of controlling the charging of the batteries in electric power systems is regulated shunt. Devices of this type placed in parallel with the solar group and the battery system detects the voltage of the battery terminals, and when the potential reaches a value set in advance, creating a low resistance path through the solar group , thereby deriving the current and away from the batteries
A diode in series, between the regulator and battery shunt prevents the return current of the battery through the regulator or the solar group. As the system that is powering the battery outlet, the terminal voltage down until you disconnect the shunt regulator and resume the load
Shunt regulators are to dissipate full output current when the group's solar battery system reaches the state of full load. This is a reasonable task when solar electric systems are small, but large systems require large heat sinks or sinks lower multiple. What leads to reliability problems and high cost
Then you can say that these regulators are cost-effective approach when the power module is not too big and can match the price then type series regulators with higher performance and able to handle more current from the PV group
Series regulator
Today you can find a type of charge controller that virtually no energy dissipates and is termed type serial
These devices are based on the concept of regulation series, in which the solar group is disconnected from the battery system when it attains a state of full load. In short, this team is equivalent to a switch connected in series providing a path of low resistance (milliohms) from the solar group to the battery system during loading and an open circuit between the solar and battery group when it is is fully charged
In the series regulator does not dissipate any energy in either state, because when in the closed position there is no voltage drop across the switch, and when in the open position there is no current flow. The only power consumed is required within the equipment for detection and control circuits
In many cases, this single unit can run on any system whose nominal operating voltage is between 12 and 48 Vdc
A simple threshold control setting allows for the proper functioning of any tension, because what you do is open or close a relay which does not depend on the system voltage
These teams consist of:
- A mechanical relay whose contacts provide a low resistance path for current that flows into the battery- Detection and control circuitry to determine the appropriate state relay- Tours to protect relay contacts degradation due to interruption of the connection and strong currents
The built-in relay should be a high quality component characterized by large areas of low resistance contact. You must also meet for a short period of performances secured a minimum, as this defines the life of the regulator and be fully protected against environmental influences
The control circuits perform various functions including, screening potential of the battery to determine whether this is fully charged, temperature compensation to enable accurate automatic adjustment of the temperature coefficient of the battery and measuring the power of the solar group.
Operation
When the voltage at the terminals of the battery reaches, during loading, the level preset threshold, the control circuit opens the relay and allow you to remain open for some time, after which closes the relay to resume charging
Synchronized with this cycle, the control circuit opens the relay for a short period of time (usually one second), during which, we measure the output voltage of the solar panels. If the voltage of the PV group is lower than the potential of the battery, the relay will remain open. This condition occurs every night, when the output power drops to zero solar group
This feature of the control circuitry eliminates the need for blocking diode and the voltage drop for its use provides. In some models, also provides terminals for temperature sensing element, sensor, which can adhere to the casing of the battery is charging, the potential end of the load is a function of temperature, this characteristic feature resets threshold point automatically to ensure full battery charge at any temperature. This gives a correction compensation threshold point-3mV / ° C / cell, ideal for batteries used in solar energy systems. Sensor using a temperature-controlled environment is irrelevant, since the threshold voltage can be adjusted at the beginning in connection with the temperature going to be accumulators
The circuitry to protect the relay contacts consist of solid state devices in parallel with the contacts to reduce tension to 6V, ensuring safe behavior and long-term regulators getting into a longer life with fewer circuits accessories and a greater reduction in the price
The great advantage of regulators series is its small space and the absence of heat which makes them optimal for use in completely airtight cabins, working in harsh conditions.
Chapter 5
Support structures for photovoltaic panels
The support structure is another important aspect of these facilities ensures a good anchorage at the same time not only provides necessary guidance to the solar generator, but the ideal angle for better utilization of radiation
These elements are responsible for making the modules are resistant to the action exerted by the elements. In this chapter will be studied various ways to put photovoltaic modules
Suppose you have an area of 1m square panels, and the installation area can produce winds of 200 km / h. the formula for the maximum wind pressure is:
P = F / S
Where:
F = force of the windV = air velocity in m / sS = surface area in meters squared receivingP = wind pressure on KP / sq m
This example demonstrates the great effect that can make the wind on a group of solar modules and make us think of the serious consequences of poor anchorage or a wrong design of the structure that supports all
Not only is the action of wind, the problem of support and structure, we must also beware of the snow, rain, frost, etc.. In fact, some of the actions described above (snow, rain) affect the shape of the support site of lift, while frost or certain environments (eg near the coast), they affect the type of materials used for construction structures
As mentioned above, the photovoltaic panel support has a dual mission. On the one hand, mechanical, to provide and ensure the perfect assembly and consolidation, and second, to provide precise guidance as well as the angle or angles suitable torque advantage of the maximum radiation or more interesting for the application to which it is intended. The orientation must always be south (if in the Northern Hemisphere), it is the only direction in which we take, in a total radiation emitted by the sun. Only in very special circumstances can change the direction slightly to the west or the east, such as the event of a natural barrier (mountains, etc.). For a short period to prevent direct sunlight
In the accompanying figure are clearly represented the paths of the sun in different seasons, and we see his short tour in the winter, while we see that the path of the radiation is more horizontal than in summer. It is the cause for which the slope of the PV panels is usually larger, so that make the most of the low winter radiation Shining its rays normally. As a result, there is a loss in summer than could be offset, if you design the support, varying the inclination of the set at an angle of less value going to affect the sun at an angle as close to 90 degrees on the surface solar panel
Types of structures
We do various media classifications to speak, but we make the distinctions more interesting in terms of the form of situation. In the accompanying drawing representing four typical ways of putting a group of photovoltaic modules, which will be discussed below
1) is the classic way to install large arrays of photovoltaic modules, as another method would result in significant inconvenience for assembly. This type of structure is very robust, and we must not forget that this provision the wind is less because, as we all know, at the higher altitude of the air force, as in the lower layers is more attenuated. It also has this way of mounting a great facility for installation of both the support structure itself as photovoltaic panels, since you work at ground level. A drawback is the easy accessibility and the increased likelihood of partial shading that may occur
Most of these installations are protected by a metal enclosure to prevent the passage of people and animals that could bring an action detrimental to the smooth operation of the facility
The assembly of this type of support the solar array is not too good for applications in the mountains, where it can cause the presence of snow, as this, fall in large quantities, could partially or completely cover the solar panels. However, this drawback can be remedied by the creation of a higher seat, according to the height you can reach the precipitation as snow
2) The support system is mainly used in installations where it already has a mast, but is not ruled out the possibility of a special assembly, given the ease and simplicity it presents. The facilities for which it is recommended this type of implementation should not be overly large, with little more than a square meter modules, and that if this surface is exceeded, would require us to exaggerate and even braced the mast, which might be possible that another system could be cheaper and easier installation. This system is widely used in facilities with repeaters, which already has an antenna that can act as a mast, so that just enough to make the support frame and hardware modules of union with the tower3) Another way, more and more used primarily in domestic installations, is to match the structure of the walls of the enclosure where it will install photovoltaic solar energy. Obvious advantages of this method, not only in security due to the height that can be installed, but the lightweight structure that is used as the base has a good anchor point also being built. Can this system be adapted by expansion bolts or making a small site where the structure is inserted. Wind action is drastically reduced because it can not practically affect the back, and a headwind will only exert direct force on the support points. This option only has the drawback that it is mandatory that one of the south facade. Any variation present problems complicate the structure accessories, having to give it a side angle for perfect orientation4) The installation on the roof of a building is one of the methods used at the time of making the installation of solar equipment, since we usually always have the right place to ensure perfect orientation, plus enough space. He mentioned the case of installation on the ground, about the problems with snow, must be taken into account here too. The anchor usually does not present problems, but we must ensure the perfect restoration of impermeability and not allow water reservoirs may occur that may impair later. A fast and safe houses that is applicable to telecommunications facilities, telemetry, etc.. , Which are usually flat roof, the roof is to drill introducing a threaded stud with nuts and washers, both below and above, leaving the anchors firmly secure the structure. To make the set perfectly waterproof, sealed with silicone all joints to prevent the passage of water.
Types of materials used
The materials used for construction of support structures can vary depending on the type, environment which are under strength, and so on. The main materials used are as follows:
aluminum
This material is widely used for small structures (one to six modules usually) because it has a great advantage because of its easy machining, light weight and high strength. It is very convenient, almost essential, to use the aluminum is anodized, so your life can expand to large periods of use
The supports made of aluminum tubes can be formed either with or angular dimensions and thicknesses appropriate to the forces to be subjected by the wind. It is recommended that all hardware is stainless steel
Iron
It is the material commonly used for large installations or panels must withstand high winds, as it is in a range of sizes, shapes and thicknesses wide. In all cases, the structures built with iron support should be subject to a galvanized corrosion properties are conferred for many years. This plating bath surface should incorporate a thickness of not less than 100 microns, to ensure complete protection
We should note that all cutting, welding, etc.., Must be executed prior to galvanizing, as any subsequent amendment would lose the protection in place where. However, taking into account that it may be that when the facility is required to make any necessary adjustments are available in the market for a product for small touches of galvanized cold that, when applied to the site of damage, will protect against all the corrosive action
As in the previous case, it is recommended that all hardware used is stainless steel to lengthen its life and allow any time to change some of the elements that compose
Stainless steel
It is the perfect material that can be used for building structures, impervious to almost all s external actions and types of environments. Stainless steel is widely used in facilities that are located in a saline environment, which as you know, are altana corrosive. The game against the use of stainless steel for the construction of metal supports stowage in its high price and special handling that makes expensive welding cost. However, this drawback can be absorbed by the quality and long life to provide use
When using stainless steel for the construction of support structures must take into account that if the PV module frame is aluminum, you should avoid direct contact of these materials, through an insulator, since these two elements produce a corrosion galvanic high, especially in saline environments. The installation of galvanic corrosion inhibitors, in this case, mandatory use
Fiberglass
For some time, new synthetic materials being established in some applications to traditional materials. This is the case of fiberglass or composite, which has some excellent physical and mechanical properties, coupled with a considerable weight reduction over steel. Its no corrosion make it particularly suitable in solar applications, and presents an electrical insulation, in some cases, we can avoid the whole ground
Fiberglass can be in different colors and profiles, while the "L" or tube, so that fits a multitude of applications and types of support structures, either using only the material
Support Points
One of the most important aspects to consider regarding the structures are the points of support, because on them depends the strength of the whole. It is useless to calculate an angle to support very strong winds if not securely fastened to the floor structure, deck or anywhere else. In the case of using mast must brace think the possibility of this and provide it with a solid base
The figure shows four different types of floor seats or deck structures. Drawing A represents a concrete slab with perimeter base, it must be reinforced at the ends with straps around the perimeter and through the center of the slab
In Schedule B you can see the foundations of classical layout with wooden beams, faster to install but shorter. Similar to this kind, but much stronger, is shown in Figure C, which shows the outline of a structure using concrete blocks, it is advisable to be strengthened with ¼ inch shoulder straps along the block
Finally, if D has an arrangement with metal foundation. This type of foundation should be firmly anchored to the ground, as it has enough mass to withstand high winds.
Effects of atmospheric conditions on solar photovoltaic and some tips to avoid
We must not forget that the solar modules and connections and support structures are completely in the open, and this represents a careful selection of materials used in each and every one of the facilities, especially as the conditions are tougher weather that occur
The first rule for sizing and define each and every one of the elements that form the PV array is to obtain as much data from the area in question, winds (frequency and intensity), temperature (both maximum and minimum), rainfall, presence of snow at certain times of year, type of environment (if corrosive), fog, etc.. These factors will be very useful also for the calculation of results of photovoltaic modules, as well as the battery capacity
If the winds are strong, the support structure of the modules must be provided in order to leave a gap between modules, so that air can circulate between them exert less pressure than if the PV panels are glued to each other. This distance may be about two inches
As mentioned earlier, we must take into account the possibility that, if any precipitation falls as snow, they can get to cover the solar modules. To avoid this raises the base of the structure enough to allow snow to pile up without harming the surface sensor. It is advisable in all cases, the insertion of straps between the legs of the structure to get more support strength
In the case of marine environments, the choice of the metallic material be held no expense spared, and that eventually all will give better results if you perform the installation with inferior materials. This is because, as we all know, the high corrosive power that has the environment in marine areas. Logically, if the structure is in contact with sea water (marker buoys, platforms, etc..), The problem becomes more acute and should be used in this case or stainless steel with dual hot-dip galvanized to give it thickness much higher than typically is provided for installations with more benign environments
The rain on the metal components in itself represents nothing more than the possibility of accelerated oxidation. However, as mentioned above, the installation further comprises other components such as the electrical connections, wiring, etc.. These elements must be completely sealed in order to avoid possible short circuits caused by rainwater
It is advisable that the solar modules have sealed junction box, or if you are naked terminals, can be protected after connecting via a rubber sleeve. All electrical conductors must be properly insulated, and even may recommend the use of wires in the outer parts of double-layer hose under a sturdy plastic tube, since it has been shown that in a time not too long hose wire is finished fourth, starting from the time a rapid and progressive deterioration, with consequent risks involved
We think that the solar photovoltaic installations are not always final and unchangeable. For this reason we must pay careful attention to the parts of mooring (both panels-structure and structure-based support), since in a given time may be necessary to replace a module or expansion in photovoltaic media size , having increased power demand. For this reason we have to use good materials in hardware, preventing corrosion between rings and nuts can do to delay a job that in principle it is easy
As a final tip must never forget the use of silicone all the joints or weaknesses against water and moisture sealing through the use of these electrical connections, boxes, boards, etc..
Graphic examples of various types of supports
As has often been said that a picture is worth a thousand words, here are gathered a number of drawings and photos depicting a more graphical various solutions adopted. For outdoor installation of photovoltaic modules and panels.
The problem of corrosion and its treatment
Most metals are found in nature in form of oxide or sulfides and only be obtained of these natural compounds by contribution of large amounts of energy. However, the metals thus obtained are in an unstable situation and when they enter again into contact with the environment (atmosphere, water, etc.). Tend to regain its natural state. This trend is what is known as corrosion.
Chapter 6
Installation of photovoltaic panel
As seen in previous chapters, the sun's rays strike the earth at different angles of inclination, variables, or only by the position of the observer, but by the time of year. Indeed, for facilities located in the northern hemisphere (for Spain), the orientation of the solar array will be south, while if it is found in the southern hemisphere the orientation is north (as in South America and Africa). Of any shape, such as panels produce maximum power when solar rays perpendicular to the panel surface, we find the angle of inclination angles to the panel surface, we find the angle of inclination such that we produce the maximum electric current oriented once in position. Logically, this angle will vary throughout the months of the year, as the inclination of these rays will be greater the closer the summer and vice versa. Therefore, and for Spain, the angles vary between 20-25 ° to 55-60 ° to the horizontal, as summer or winter respectively
Always best to get maximum production angle would vary month to month, but as this is quite annoying, in most installations choose the most suitable angle depending on the time in which to be used more often or by giving a large inclination to maximize the winter sun if consumption is equal for all months of the year. In some cases it is possible, and not particularly bothersome to two inclinations a year, winter (55-60 °) and a summer, that is around (25-30 º)
Once we have the ideal angle for the best use of radiation, we will describe the electrical connection between panels. As we all know, the interconnection between the modules can be of two types: in series (to increase voltage) or parallel (thus increasing the intensity produced). However, all too often has to have a mixture of the two types of connections in order to get the current and voltage suitable for each particular case
It is well known that the two modules connected in parallel the resulting voltage is the same as one, but, on the contrary, the electric intensity is twofold. If instead the two modules are connected in series, the voltage will double, while the electric current produced corresponds to that of one of them. In the charts below you can see some examples that illustrate the above, being the common denominator of all the use of a module whose nominal voltage is 12V and current of 2 amperes, which is a prerequisite for connecting panels in series, parallel and mixture of these two forms
It is obviously important to good electrical connections to ensure high reliability, in anticipation of possible failures with respect to voltage drops produced in the joints. This fault, which is generally more common than we think in principle, be eliminated by providing the appropriate terminals for each type of connection, so that we can escape from the driver on the winding terminals so little security that we can offer
Nor should we forget the protection from the elements of the electrical conductors, especially those interconexionan modules and that bind to the regulatory system. These are precisely those who most directly suffer inclement weather, so your choice should not raise doubts, since in any case, install the best quality about their external insulation. A good habit is to introduce them in conduit, at least in the section to be found in the open
Installation of regulation and control
The teams will be the system of regulation and control (charge controllers, alarm systems, voltmeters, ammeters, switches, etc..) Must fit into a small control box that meets all the necessary information for a stroke of view we know the general condition of the components forming the photovoltaic system. As essential elements are the charge controller and a voltmeter or other reference element we approximate charge state which is the battery. This measurement can be done with a densitometer if the battery is maintenance-type and therefore accessible to the electrolyte
Usually, these control panels are usually constructed for each editor, adapting to the needs of the installation. As a rule we can differentiate two broad types of facilities, or where there is often inhabited staff, and those that are remote and lack of care or people who use them directly. The first involve a mix of all those teams that give us details of your operation, such as voltmeters, ammeters, low voltage disconnect switches, fuses or thermal magnetic protection, etc.., Which of course will be fully in line with the size and importance of the facility . By contrast, in all those applications where the computer is unattended, it would be completely absurd to have a large number of devices for signaling data that no one will see. We recommend in such cases the use of the regulator as an essential element and a low voltage disconnect able to protect the battery in case of excessive discharge
There are some very interesting equipment such as ampere-hour meters, which allow us to control the amount of Ah well, that flow from the solar panel to the battery, the battery to the load, or both. These measures are useful, especially if we take the accounts monthly or weekly, can give us real data of the solar system or even the consumption of connected equipment. Using the amp-hour meter can make an analysis of production-expenditure balance during all seasons, which is useful for installations where there is no evidence of radiation or in other occasions where the use is unknown will perform on a specific computer and can make interesting findings of these elements
The amperihorimetros have usually four digits that can jump in steps of 1 or 10 amps, can be extended by connecting shunts. Consumption is very low (= 0.6mA maximum) and does not represent major obstacle to its use.
Installing converters
Everything mentioned in the previous sections corresponds to all solar PV, but once located in terminals of the storage battery, which remains corresponds to a conventional electrical current
The converters or inverters, both sine and square wave must always be installed as close to the batteries as possible. This statement is justified by the large voltage drop may occur if the drive away from the batteries too. Consider that once made the transformation, working with high voltage (220V) and low current, minimum losses brings us even using a small driver section
To illustrate the above statement, we calculate the difference section of thread that should be incorporated into a converter dc / ac to 12 V input 500W, if situáramos to 2 meters or 20 meters accumulators of these, and admit a fall 0.2 voltage V
If we recall the formula for calculating a driver section for the first case we have:
S = 2IL/56 (Va-Vb)S = (2x500W/12V x 2m) / 56 x 0.2 V = 166.4 / 11.2 = 14.85 mm2
For example 20 m 14.85 x 10 = 148.5 mm2
Obviously, the cost differential between a conductor and another case fully justified placing it close to the accumulators, as in the first instance would use 2x2 meters 14.85 mm2 conductor and the other 2 x 20 m of a section 148.5 mm2, while the section in both cases we should put the AC line would be around 1.5-2.5 mm2
If the installation of converters out instead of AC / DC, DC / DC, we could make two distinctions, the first if the input voltage exceeds the output voltage (eg 24/12). In this case, it is desirable to have the converter closer to the receiver for the same reason that exposed on the voltage drops. Conversely, if the input voltage is lower than the output (eg 12/24), the DC / DC converter must be as close to the accumulators
Summary of practice standards for installation of photovoltaic systems
- Have the modules facing south with the ideal angle for better utilization of solar radiation- Avoid partial shading on cells or modules produced by obstacles
Chapter 7
Maintenance of a photovoltaic system and performance testing
Is usually understood as the combination of PV modules by, regulation and control systems and batteries, the rest being a conventional electrical installation, where the integrated teams will have a more or less particular maintenance
Based on the above, we will focus on three basic elements, then describe brief guidelines to take into consideration regarding the care of the components:
PV Panel
Indeed, although the most important element of the entire system, is the least maintenance work is going to produce. Indeed, the maintenance required for a photovoltaic solar module is minimal as to be reduced to a surface cleaning with abrasive Something, since dirt can be observed. Normally, in the facilities in the field, there will be no common dirt deposits unless it can be with any industry that eliminates waste by fires, in which case the need arise for more continued maintenance
Is precisely the point where maintenance is important is the need to provide the module of a crystal that does not present a rough surface can more easily keep dirt and present more resistance to cleaning. The crystals of the solar modules must be extremely smooth in order to foster the self-cleaning action of air and water naturally
There are some cases where it presents a major problem, and are where the PV system is located by the sea or in this (case of marine buoys, optical signals, etc..). It happens very often that the gulls often alight on the top of the support structure, defecating on panels and producing very persistent stains alter the functioning of the solar group, as a result of partial shading on the cells. For these cases, the inclusion has been devised in the top of the structure, a flexible antennas which do not allow the bird sift, avoiding the effects they produce.
Regulation and control box
I really do not need any special maintenance, except for their visual check to verify the proper functioning of the various teams that comprise
It is very convenient, if this box is installed in a place where there is moisture (near the sea, tropical countries, etc..), Protect the various devices such harmful action, for which there are some sprays that preserve the electronic components and electrical contacts of their effects by a simple spray
Accumulators
Apart from the precautions to be observed when installing a set of accumulators, as mentioned in the previous chapter, these elements are perhaps the most attention required of all components of a solar installation, especially those who have maintenance and which we will focus
The filling of the electrolyte is one of the typical operations of the maintenance of storage batteries, action to carry out water free of impurities and keep the electrolyte level within limits. The water to be used shall be of demineralized or distilled
It should be noted that the filling of the battery elements always be done with water and with acid, which is intended only for those rare cases where a leak may have occurred electrolyte
The main cause of the loss of water in an electrolysis tank is the same, produced by the load current, since the action of the evaporation occurs at a very small extent. Therefore, if a particular battery usually requires the addition of water, is a telling sign that is producing an overload, for which they take care to reduce the voltage regulator setting
If the level of electrolyte in a battery element is low enough to expose the plates of the same, they do leak when in contact with air, and consequently their destruction will occur. Conversely, if the level is too high, can reach the vent plugs and be pushed out by the action of the gases evolved during the last phase of the battery
In short, we can say that the correct level of electrolyte for different types of batteries, is:
- Batteries plant: ten millimeters above the top edge of the spacers- Tubular Batteries: If you are in opaque containers, usually supplied with level indicator cap. If containers are transparent, have two upper and lower marks printed on the housing
The practice regular maintenance work to the benefit of battery life, and it must follow some basic points, such as:
- Check the electrolyte level in each month of the elements- Visually inspect the battery so the container as the plates (if items were transparent), noting if the plates are bent or formed elements in the background come to short out these- Keep the terminals and connections free of sulphate, vaseline applied each time you need.
This defect occurs hopelessly poor contact and, consequently, a large voltage drop.
- Batteries plant: ten millimeters above the top edge of the spacers- Tubular Batteries: If you are in opaque containers, usually supplied with level indicator cap. If containers are transparent, have two upper and lower marks printed on the housingThe practice regular maintenance work to the benefit of battery life, and it must follow some basic points, such as:- Check the electrolyte level in each month of the elements- Visually inspect the battery so the container as the plates (if items were transparent), noting if the plates are bent or formed elements in the background come to short out these- Keep the terminals and connections free of sulphate, vaseline applied each time you need. This defect occurs hopelessly poor contact and, consequently, a large voltage drop.- Batteries plant: ten millimeters above the top edge of the spacers- Tubular Batteries: If you are in opaque containers, usually supplied with level indicator cap. If containers are transparent, have two upper and lower marks printed on the housingThe practice regular maintenance work to the benefit of battery life, and it must follow some basic points, such as:- Check the electrolyte level in each month of the elements- Visually inspect the battery so the container as the plates (if items were transparent), noting if the plates are bent or formed elements in the background come to short out these- Keep the terminals and connections free of sulphate, vaseline applied each time you need. This defect occurs hopelessly poor contact and, consequently, a large voltage drop.
Testing and troubleshooting of the different components
It is necessary, both during assembly and during operation ever, review the different and more unusual elements of the photovoltaic array. For this reason we will describe some basic steps to help us know if any element may be in poor condition.
Measurements on the PV panel
The great advantage of a photovoltaic panel resides mainly in the near absence of faults. Basically, you can stop producing power for only two reasons: one, the possible penetration of moisture that can corrode materials that make up the circuit, and another break, usually for external action, the top cover (glass) module solarIn both eventualities should be replaced by another, although in the case of glass breakage may be the fact, quite common, that the module continues to provide energy, but will be reduced by the reflections that produce tears
To determine in a straightforward and fairly accurate if a panel amperage provides us in the manufacturer catalog, just to have a small solar radiation meter that tells us the mW/cm2 of radiation incident on the surface of the panel and an ammeter was connected to terminals of the module to measure the short circuit currentSince we know that for monocrystalline silicon panels there is a direct ratio between the received light intensity and the short circuit current produced a simple enough rule of thumb to know if the panel produces what we actually announced. As a clarifying example, suppose you have a photovoltaic module which features indicate a short circuit current 3 rd to 100 mW/cm2 and 25 ° CWould be quite difficult to expect to have a similar radiation at that time, to see if its output gives the short 3 A above. In order to save this, we will have radiation meter parallel to the surface of the module, noting both the radiation and the electrical current that would flow between its terminals. Suppose the radiation recorded out of 60 mW/cm2. The theoretical intensity is calculated should give us:3 A 100 mW/cm260 mW/cm2 XX = 60x3/100 = 1.8 AIf this value is close to that obtained, we can ensure the effectiveness of the panel, but on the contrary, if you leave too (taking into account the precision of the apparatus and the temperature), we doubt the manufacturer's controls. A margin of +10% if the temperature is around 25 ° C, may be acceptable
To measure the intensity provided by the module to an external circuit (either the slider, battery or any load connected to its terminals), simply insert an ammeter in one of his lines to get the desired value. Often, we see that this value may fluctuate due to the passage of clouds or variations in ambient lightIf the measure you want to do is to find the tension, we use a voltmeter inserted in parallel with positive or negative line, reading the value offered in its scale. Except for very special cases, this measure is common for the panel and the battery, since the two met interconnected in an actual installation.Charge controllerChecks and adjustments of regulators should be made before inserting them into the PV array and will vary depending on the type of circuits used. As seen above, there are two large blocks of regulators, series and the shunt or parallel. The former have a readily ascertainable, because if we measure the current passing between the regulator and the battery, this is exactly what the panel can provide at that time. The circuit court is given when the voltage acquired by the battery equals the previously set on the regulator, voltage on the other hand it can be easily measured by a voltmeter between output terminals of the regulator. In the event that this voltage is high or low, or has no passage of current from battery panels, the regulator must be substituted and taken to repair
The other major regulators block corresponds to the shunt or parallel. To verify correct operation proceed to separate the drummer-regulatory panel, measure the voltage across the regulator output to the battery. This tension must be previously adjusted to avoid the overhead (approximately between 14 and 14.5 volts for 12 V facilities)This should be done when the sun is high on the horizon, and we observe the heating of the power transistors or elements responsible for the dissipation of excess power, if this occurs and the tension is around 14-14.5 V , as discussed above (28-29 V or 56-58 V for systems 24 and 28 volts nominal, respectively), we say that the regulator is in perfect working condition
If you want to check the regulator load current or reverse current absorbed by the photovoltaic module, etc.., We cover the panel with a very opaque blanket or wait for night to insert an ammeter, which will direct the current absorbed for the item and determine its value. These measures can be very useful if you suspect high leakage through the modules, excessive consumption of the regulator, failure of the blocking diode, etc..
Accumulation system
As already mentioned, and all we know, how to measure the passage of current between the panels-or battery-consumption will be inserting the ammeter in series between these elements. These data will be released on current input panels and actual consumption in ampere equipment or receiving equipment
However, the measures and controls that can be made to the accumulation system from merely measuring the open circuit voltage of each element and the density of these (in the case of a battery maintenance, since in those that did not required, the electrolyte is not accessible)
To determine the proper status of each item, whether or monoblocs 2 V, shall be separated electrically by measuring the tensions in these terminals and the density of the electrolyte with a hydrometer
In all cases measures should be similar, and if given the coincidence of any significant variation, the item must be given a more particular study we determined the cause of their variation
Not admissible under no circumstances have parallel or serial accumulators of different model, capacity or time to use different (union of old and new batteries and used, etc..), And that this would bring us current internal steps between element and another, leading to deterioration of the battery newest
