Tag Archives: solar energy

Solar Exchanger

In solar thermal energy systems, heat exchanger is in charge of transmitting the heat energy collected by solar collectors to medium that needs to be heated.

Depending on type of heat transfer system used, they can be classified into:

Direct: Domestic hot water for consumption circulates through primary circuit and, therefore, will circulate through collectors. This system is suitable for small systems located in areas where there is no freezing danger. The trend is towards the restriction of its use, not being admitted in several countries.

Indirect: Domestic hot water for final consumption circulates only through secondary circuit, which means that heat transfer liquid only flows through the primary circuit and is never in contact with domestic hot water. In this case, an exchanger is needed to pass the heat collected in first to second circuit.

The selected exchanger will withstand the maximum working pressure of the system.

According to section HE-4 of Spanish CTE:

In case of an independent heat exchanger, the minimum power of heat exchanger P will be determined for working conditions in day central hours, assuming a solar radiation of 1,000 W / m2 and a performance of solar energy conversion to heat of 50 %, fulfilling the condition:

P = 500. A

Being:
P = minimum power of the exchanger [W]
A = the collector area [m2].

In case of an exchanger incorporated into the accumulator, the ratio between useful exchange surface and total collection surface shall not be less than 0.15.

In each of water inlet and outlet pipes of the heat exchanger, a shut-off valve will be installed next to the corresponding sleeve.

The heat exchangers used in sanitary water circuits will be made of stainless steel or copper.

The design head loss in the heat exchanger shall not exceed 3 m / ac, both in primary and in secondary circuit.

Solar exchangers type:

Plate heat exchanger: This type of heat exchanger is made up of a series of corrugated metal plates, joined together in a frame by pressure and sealed by a gasket. Plates form a series of interconnected corridors through which working fluids circulate. These fluids are powered by pumps.

In order to choose correct plate heat exchanger for the system, it is necessary to consult the manufacturer’s guidelines. However, it is recommended that the thermal power to be transferred (in Kw) is equal to 2/3 of the collecting surface (in m2).

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Double wrap exchanger: this system consists of a tank in which the secondary fluid (hot water) is accumulated and which has a double wall through which heat transfer fluid circulates, giving heat to domestic hot water.

Exchanger’s operating conditions dictate the choice of its material, which is usually carbon steel or alloy steels. Minimum exchange surface must be between 1/4 and 1/3 of useful collectors surface. However, there is a geometric limit to its use, which is given by housing dimensions. For a certain range of measurements, exchange surface can become less than a quarter collector surface. For volumes greater than 750 liters, the necessary exchange surface (which is the accumulator wall) is increasing and could result in very high accumulators for which it would be necessary to have a suitable machine room.

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Coil exchanger: is made up of a tube that is submerged in a tank where the secondary fluid accumulates. The primary or heat transfer fluid circulates inside the tube, giving heat to the secondary fluid.

According tube shape they are distinguished:

Helical coil exchanger. The spiral wound tube that carries heat transfer fluid is submerged inside accumulator at the bottom.

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Tube bundle coil exchanger. They are commonly used to obtain ACS. Primary fluid circulates through several tubes, not one as in the helical. Liquid flows inside coil by forced circulation, while outside the fluid in contact with coil is renewed by natural circulation.

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To know if a coil heat exchanger is suitable for use in solar applications, its minimum exchange surface must be between 1/4 and 1/3 of collectors useful surface.

The exchange surface of a helical coil or tube bundle will be the lateral surface of a cylinder based on outer section of the tube used and by height total length of the same. With this criterion it will be easy to size a tubular exchanger.

Some recommendations:
– The coil must be placed in the lowest part of accumulator.
– If it is helical, distance between turns should be equal to 2 times outer diameter of the tube.
– If we use antifreeze in a proportion of up to 30%, exchange surface must be increased by 10%.

This content was extracted from the Solar Thermal Energy Technical-Commercial Manual and is part of Solar e-learning.

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Solar Energy Panama

Panama’s National Energy Plan 2015-2050 suggests that up to 70% of country’s energy supply could be renewable in 35 years.

The generation matrix is highly dependent on hydroelectric resources (46% of installed capacity) and fossil fuels (42%) making Panama highly dependent on oil price evolution (it is a net importer) and rainfall regime, affected by the El Niño weather phenomenon that in recent years has caused significant droughts, causing a shortage of hydroelectric supply.

In addition, Panama’s National Interconnected System (SIN), which is the backbone of the electricity sector, is highly conditioned by the enormous distance between generation centers (province of Chiriquí, in the western zone) and consumption (Panama City and canal hub).

The energy matrix diversification need, guaranteeing supply and reducing price volatility, as well as complying with international commitments acquired by Panama in the Paris Agreement, has led to renewable energy sources slight introduction (wind and solar) and introduced natural gas into generation matrix.

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The Public Services Authority (ASEP) regulated in 2012 the connection of clean private plants to national electricity grid, with bi-directional meters and the energy “netting” to satisfy electrical consumption of each participant and sell the surplus.

Distributed rooftop solar generation delivers real-time power during the day with an unproductive asset (the roofs) to achieve a minimum fixed cost of own power for 25 years, with proven technology and reliable supply during peak demand and nights, because user is not disconnected from network.

The growth potential in the country is evident, as individual and business decisions to generate clean and renewable energy accelerate.

Reality is that solar energy participation in national energy matrix is not relevant. It currently represents only 2% of electricity generation.

A report from the International Renewable Energy Agency (IRENA) in May 2018 suggests the following recommendations for Panama:

o Evaluate regulatory and financial incentives for solar and wind energy development;

o Develop a national strategy to improve planning and modeling of electrical systems with greater RE penetration;

o Identify new operating practices to increase network flexibility and reliability with a greater RE participation;

o Evaluate the regulatory interfaces between National Electricity Market (MEN) and Regional Electricity Market (MER);

o Examine how to develop the capabilities of Panama’s workforce to achieve 2050 renewable energy target;

o Develop a long-term plan for electric mobility and sector coupling.

By referring to this post you will get a 50% discount on Sopelia E-learning training that begins on April 20 next.

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Solar Tracking Systems

To harness as much solar energy as possible, collection surface must always be perpendicular to the sun’s rays and this can only be achieved if modules are equipped with a solar tracking mechanism.
Using these mechanisms, total energy received in a day can be up to 35% higher compared to that received by a static module.

This difference in performance is reduced in cases of frequent cloudy days and in all those weather conditions in which the relationship between energy received by direct radiation and that received by diffuse radiation tends to decrease. That is why it is only recommended to use it in areas of low cloudiness.

A detailed analysis must be carried out to verify that performance increase achieved more than compensates for energy consumption and the cost and maintenance of monitoring mechanisms.

The two types of movement are:

1. Single axis: only allows rotation around a horizontal, vertical or inclined axis. You can track sun azimuth or height, but not both at the same time.

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2. 2-axis: in addition to the east-west rotation movement, a second rotary movement on a horizontal axis is also possible by varying the module angle with respect to the horizontal plane. They can be monopost (a single central support) or carrousel (several supports distributed along a circular surface).

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We can find different solar tracking systems. The most common are:

1. Passive tracking systems: These devices do not use electricity or have a motor. There are two North American patents. The first (Robbins Engineering) is based on Freon gas pressure expansion and contraction contained in two cylinders located on each side of the structure. The second (Zomeworks) is a gravity system based on the variation of the weight of a fluid contained in a container that when evaporated passes to another.

2. Tracking by sensors: the sensor is the element that allows the detection and measurement of the lack of direction between the sun vector and the normal to capture surface. The sensor is usually made up of pairs of photosensitive elements mounted on the module and moving in solidarity with it.
The photosensors use direct solar radiation to detect sun position. Tracking impossibility when sun occultations occur and need to spend time recovering address when sun reappears are inherent characteristics of all systems of tracking based on photosensors.
Deviation detected by the photosensors transmits an actuation signal that controls motors operation to achieve module movement. Constant speed motors are often used that operate intermittently so that the addressing error is kept within a tolerance band.
Systems using photosensors are used for small and medium systems.
Between one day’s sunset and the next day’s sunrise, the module must be placed in the sunrise position because once the sun has risen, much time would be lost in the 180º turn necessary to regain direction. For this, a clock is used that generates the appropriate order.

3. Tracking by calculated coordinates: this system follows sun position by calculating its astronomical coordinates and does not require solar rays physical presence. This circumstance renders coordinate systems immune to cloudy days and other circumstances that can produce addressing errors in a photosensor, as happens for example with flashes.
The use of computer controlled systems has the additional advantage that certain changes can be made at software level only.
It can also include additional functions such as bringing the modules to a position of maximum security against inclement weather or the return at night.

Sopelia has developed Solar Layout, the Android App that allows to obtain the inclination, orientation and distance between rows of photovoltaic modules at the installation site.

This content was extracted from the Commercial Technical Manual of Photovoltaic Solar Energy and is part of Sopelia Solar e-learning.

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Solar Accumulator Tanks

Accumulator is responsible for storing the thermal energy generated by the solar collectors.

It is essential in solar systems since periods of solar radiation and energy transfer do not usually correspond to periods in which hot water consumption takes place.

Storing energy using hot water is cheap, easy to handle, has a high heat capacity and is at the same time the consumption element in case of DHW (domestic hot water).

Accumulator type depends on the application: domestic hot water, air conditioning, heating or industrial use.

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Most common are:

Domestic hot water accumulators: they must be able to withstand high levels of pressure and expected working temperatures, not suffer deterioration due to corrosion phenomena and compulsorily comply with requirements for storing drinking water.
They are generally offered with capacities of 100 to 5,000 liters of accumulation.

Inertia accumulators: they are used as a heat accumulator for heating systems or for large DHW installations. They fulfill the function of buffer for heat or cold storage. They act as hydraulic memory between heat production and release.
They are generally offered with capacities of 500 to 5,000 liters of accumulation.

Combined accumulators: they combine accumulation of DHW and accumulation of heating.
In the same accumulator, for example, 175 liters of DHW accumulation and 600 liters of heating accumulation are combined.
They are generally offered with capacities from 175 to 250 liters for DHW accumulation and 500 to 2,000 liters for heating accumulation.

The most used materials accumulators’ construction are:

Steel: it needs internal treatments based on epoxy or vitrified to avoid corrosion.

Stainless steel: it is without a doubt the best material.

Galvanized steel: accumulation temperature must not exceed 65º C.

Reinforced fiberglass: resists corrosion, weighs little and is easy to maintain, but withstands low temperatures (60º C maximum).

Plastics: it has similar qualities to fiberglass.

Aluminum: it is not advisable due to corrosion problems.

In addition to interior treatments, accumulators incorporate corrosion protection devices.

One of the problems caused by corrosion is that rust and sediments favor the legionella development.
It is essential to avoid it by building accumulators with noble materials such as some type of stainless steel and / or combination of some inner lining and a cathodic protection system.

Accumulators are usually cylindrical in shape and have a vertical dimension greater than horizontal one to favor thermal stratification of the inside water.
Hottest water from top will be located in the extraction zone towards consumption or towards conventional support system. Coldest water is in the lower part of the tank, which will be from where it will be pushed towards solar collectors.
In this way, we operate the collectors at the minimum possible temperature, increasing their performance.

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Accumulation volume size depends mainly on three factors:

1 • Installed collectors surface

As a general criterion for DHW, an accumulation volume between 50-100 liters per m2 of solar collector is recommended.
Higher values do not lead to a significant increase in solar energy use, and accumulator cost increases.
In contrast, smaller sizes increase the temperature, thus decreasing collectors’ efficiency.
For small DHW systems production, solar tank capacity should be equal to daily hot water consumption.

2 • Operating temperature

This will determine type of stratification device, as well as insulator thickness to be used, depending on maximum losses that are admissible considered.

3 • Offset between collection – storage and consumption

Accumulation volume will be a function of lag between collection – storage and consumption period, which can be:

* Coincidence between collection period and consumption period (case of preheating a boiler in a continuous process).
In this case, accumulator specific volume will be 35-40 liters / m2.

* Offsets between collection and consumption not exceeding 24 hours (heating of sanitary water in multi-family homes, hotels, etc.).
In this case, volume will be 60-90 liters / m2.

* Offset between usual and periodic collection and consumption for more than 24 hours and less than 72 hours (heating of domestic hot water in industrial processes, etc.).
In this case, volume will be 75-100 liters / m2.

* Offsets between collection and consumption greater than 72 hours (heating of sanitary water in second home, on weekends.).
In this case, volume will be determined by balancing energy losses and gains and insulation optimizing.

This content was extracted from the Solar Thermal Energy Technical-Commercial Manual and is part of Solar e-learning.

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Nicaragua Solar Thermal

Undoubtedly, the emblematic project, in terms of thermal solar energy, is the system inaugurated on October 9, 2018 at the Doctor Alejandro Dávila Bolaños Military Hospital in Managua.

With an investment of US $ 4.3 million financed through a soft loan from Oesterreichische Kontrollbank and Raiffeisen Bank International and with the United Nations Agency for Industrial Development (UNIDO), and the National Production Center more Clean from Nicaragua support; This system provides 30% of the demand required for air conditioning and 100% of the demand for hot water (used in various hospital operational functions, such as: personal, patients and doctors hygiene, food cleaning and preparation in the kitchen, for laundry area, among others).

The solar system was installed in a 4,450 square meters area, is composed of 338 thermal solar panels and will have an environment positive impact eliminating more than 1,100 tons of dioxide carbon emission each year.

It is the second largest system in the world, the largest in hospitals and unique in Latin America.

Resultado de imagen de energía solar hospital militar nicaragua

Despite the increase in systems number, solar energy only represents 1% of Nicaragua’s energy matrix.

There is a feeling that decision making is more market focused and not as a development issue.

The key is to associate the solar technology development with economic activities, establish a relationship between water resources, renewable energy and food security and base on renewable energy the climate change adaptation.

Currently solar energy provides energy security in contrast, for example, to energy supply via hydroelectric dams that depends on rains that are varying more and more throughout the region due to climate change.

Resultado de imagen de energía solar térmica nicaragua

Energy sources diversification becomes indispensable and has led to a solar energy investments growth.

This has been possible due to public resources contribution to support this technology development, the political commitment and the role carried out by the private initiative.

In this sense, it is worth highlighting the work that the BID is doing in the region.

In spite of advances, the pending subject continues being the regional energetic integration.

An energy networks extension at regional level would help lower costs and a energy supply diversification would guarantee greater energy security.

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Architectural Solar Integration

Photovoltaic solar energy is the one that best integrates into the urban environment. For this reason, architectural solutions that incorporate it have emerged. Some are listed below.

In homes with a tiled roof, these can easily be replaced by same type photovoltaic tiles, since it is not necessary to change canning or slats and roof structure remains the same.

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Aluminum facades integrating photovoltaic cells are an alternative for new buildings or renovation projects.

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Photovoltaic modules with transparency together with aluminum profiles can be easily integrated into vertical walls, ceilings and roofs. These transparent modules are available in a wide range of applications, shapes and opacity.

Photovoltaic cells are embedded in the laminated safety glass. By varying glass weft position and density, it is possible to adjust light transmission and shadow effect inside the building.

For opaque solar modules in walls it is necessary to incorporate insulating materials that are behind to provide the necessary thermal barrier. The opaque and transparent modules can be combined on the same facade, improving building energy, thermal and acoustic efficiency.

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In addition to producing clean electricity, ventilated photovoltaic facade system incorporates benefits in building thermal and acoustic insulation. The thermal envelope can cause savings of between 25-40% of the energy consumed in the building.

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A photovoltaic skylight, in addition to photovoltaic generation, provides bioclimatic properties of thermal comfort inside the building due to the insulating glass air chamber. It also facilitates natural lighting and prevents UV rays and infrared radiation from penetrating into the building (improving comfort and avoiding premature materials aging).

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A photovoltaic canopy constitutes a constructive solution that combines electrical energy generation with solar protection properties and against adverse weather conditions.

The orientation, the minimum slope, the dimensions or the wind and snow loads are important factors to take into account when designing the structure.

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A photovoltaic car park consists of a structure that, in addition to protecting the vehicle, guarantees the in-situ energy generation for its grid discharge, self-consumption or electric car batteries supply.

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The first photovoltaic ceramic floor has also been released. It consists of photovoltaic solar glass integrated in high ceramic pavements, these being fully passable. It can be integrated into any project and environment without this giving up the design or aesthetics of it.

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Buildings, by integrating photovoltaic modules, create a world of possibilities. The great variety, shapes, colors and structures of photovoltaic cells, glass and profiles allow a modern architectural approach and also an innovative design combining elegance and functionality.

Sopelia has developed Solar Layout, the Android App that allows to obtain the inclination, orientation and distance between rows of photovoltaic modules at the installation site.

This content was extracted from the Commercial Technical Manual of Photovoltaic Solar Energy and is part of Sopelia Solar e-learning.

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Solar Thermal Pipes

Connection of different components of the solar system is carried out with pipes, until the necessary hydraulic circuits are formed.

Normally, materials used for primary circuit pipes are copper, black steel and plastic materials

The cross-linked polyethylene pipes can be used without problems, provided that manufacturer guarantees their use above 120º C.

Galvanized steel should not be used in primary circuits (from collectors to storage) due to the strong deterioration that zinc protection undergoes with temperatures above 65º C.

In general, the fluid velocity must not exceed 1.5 or 2 m / s in the primary circuit.

Pipes diameter can be selected so that fluid flow velocity is less than 2 m / s when pipe runs through inhabited places and at 3 m / s when the route is outside or by uninhabited places.

When steel is used in pipes or fittings, working fluid pH should be between 5 and 9.

Pipes dimensioning will be carried out in such a way that the load unit loss in pipes never exceeds 40 mm of water column per linear meter.

The circuit load total loss must not exceed 7 m of water column.

The maximum load loss is applicable to primary circuit and secondary circuit. If it were larger, we would be obliged to choose the immediately superior pipe diameter.

For pools heating, PVC pipes are used, which can have large diameters without a significant additional cost.

All piping networks must be designed in such a way that they can be emptied partially and totally, through an element that has a minimum nominal diameter of 20 mm.

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For pipeline selection, following aspects must be taken into account:

1º Fluid compatibility:

Materials to be used for ACS circuits may be:

• Metallic:

– Galvanized steel, UNE-EN 10.255 M series (only in cold water).
– Stainless steel, UNE-EN 10.312, series 1 and 2.
– Copper, UNE-EN 1.057.

• Thermoplastics:

– Non-plasticized polyvinyl chloride (PVC), UNE-EN 1.452.
– Chlorinated polyvinyl chloride (PVC-C), UNEEN ISO 15,877.
– Polyethylene (PE), UNE-EN 12.201.
– Crosslinked polyethylene (PE-X), UNE-EN ISO 15.875.
– Polybutylene (PB), UNE-EN ISO 15.876.
– Polypropylene (PP) UNE-EN ISO 15.874.
– Multilayer polymer / aluminum / polyethylene (PE-RT), UNE 53.960 EX.
– Multilayer polymer / aluminum / polyethylene (PE-X), UNE 53.961 EX.

Aluminum tubes and those whose composition contains lead are expressly prohibited.

2º Work pressure:

A minimum pressure of 1 bar and a maximum of 5 bar must be guaranteed at all points of consumption; so you can take 5 bars as pressure for series selection.

Although tanks safety valves are usually set at 8 bar this is a more appropriate design pressure.

3º Working temperature:

Hot water and heating pipes should remain stable with system working temperatures, sporadically be able to reach temperatures close to 95 ° C and continue to resist with a life expectancy of at least 50 years.

4º Charge loss:

When a liquid circulates inside a straight tube, its pressure decreases linearly along its length, even though it is horizontal.

That pressure drop is called charge loss.

Valves, constrictions, elbows, direction changes, derivations, etc. they cause load local or singular losses that must also be taken into account.

Total load loss, which is the sum of linear load loss and singular load losses, must be determined.

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5º Pipe size:

To calculate pipe size we start from the flow data.

We must determine pipeline minimum diameter (ie the most economical) without load loss exceeding a reasonable limit, so as not to be forced to use a higher power pumping group with the consequent energy waste.

We know from experience that fluid circulation speed maximum recommended is approximately 1.5 m / s if it does so continuously (primary circuits) and 2.5 m / s if it does so at intervals (secondary consumption circuits).

It is also recommended (or required) that pressure drop for each tube linear meter does not exceed 40 mm ca.

These 2 conditions impose a lower limit on pipe diameter.

It is usual to start from an estimated diameter based on experience in similar systems and verify that choice implies values of load loss and speed lower than recommended maximums.

If this is not the case, verification should be repeated for an immediately larger diameter.

If on contrary, we can select a smaller diameter than initial one, we will save on material; especially if circuit has a considerable length.

As a first approximation, we can resort to following formula:

D = j C 0.35

Being:
D diameter in cm
C flow in m3 / h
j 2,2 for metal pipes and 2,4 for plastic pipes.

Initial estimation, whatever method used, must be verified by using load loss tables or abacuses.

There are tables and specific abacuses for each type of material (copper, steel, plastics) that allow to determine load loss due to friction and fluid speed in the tubes.

This content was extracted from the Solar Thermal Energy Technical-Commercial Manual and is part of Solar e-learning.

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PV Modules Support Structure

Regarding situation of photovoltaic modules, there are the following general possibilities:

Flooring: It is the most usual way of installing modules groups (especially in solar farms) and has great advantages in terms of wind resistance, accessibility and ease assembly.
However, it is more susceptible to being buried by snow, flooding or being broken by animals or people.

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Pole: very used in small dimension systems, if it has a mast. It is the typical assembly type of isolated communication equipment or lampposts feeding.

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Wall: good anchor points must be available on a built building. Accessibility can present some problems.

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Roof: one of the most common because generally enough space is available. It also presents problems of snow cover and risks in roof fasteners waterproofing.

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If system is located in an urban area, most common is to place the module on the roof.

In structure assembly, roof sealing must be ensured by waterproofing elements use.

A study must also be carried out to determine if ceiling will support modules and support structure weight.

However, main factor when fixing the structure is wind strength. Structure must withstand winds of at least 150 km / h.

On terraces or floors, the structure should allow a minimum height of the module of about 30 cm. In mountain areas or where there is abundant snowfall, it must be higher.

The structure and supports should preferably be anodized aluminum, stainless steel or galvanized iron and stainless steel fasteners.

Anodized aluminum is lightweight and highly resistant.

Stainless steel is suitable for very corrosive environments and has a longer useful life but its cost is high.

Galvanized iron structures offer good protection against external corrosive agents with the advantage that zinc is chemically compatible with lime and cement mortar, once these are dry.

Structures come in kits or standard profiles that are on the market and a specific system structure can be built.

Supports designed for a specific solar module are usually cheaper than those manufactured in order to be able to hold any type of module. However, it will surely be the latter that will end up developing in greater numbers in near future.

Normally, a solar modules support has the following characteristics: it has a plate provided on its upper face with quick coupling means for modules and one or more holes for the screws to be introduced and thus join the plate to the support. The support also has fastening means attached to plate lower face for fastening to lower structure.

Orientation will always be towards the equator and the following inclinations are recommended:

Systems with priority function in winter (eg: mountain lodge): 20º higher than place latitude.

Systems with uniform operation throughout the year (p.e .: home electrification): 15º greater than place latitude.

Systems with priority operation in spring and summer (p.e .: campings): same as place latitude.

Systems whose objective is to produce the greatest amount of energy throughout the year (eg: connection to the grid): 85% of place latitude.

The reason for inclination increasing, compared to that recommended for solar thermal collectors, is that generally in the case of photovoltaic systems there is no auxiliary energy system and it is necessary to capture all the energy possible in the most unfavorable period (winter).

Sopelia has developed Solar Layout, the Android App that allows you to obtain the inclination, orientation and distance between rows of photovoltaic modules at the installation site.

This content was extracted from the Solar Photovoltaic Energy Technical-Commercial Manual and is part of Solar e-learning.

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Solar Thermal System Protection

The correct design of a solar thermal system involves foreseeing all the circumstances that may damage it and applying strategies that can prevent breakdowns that shorten its useful life.

There are basically 5 aspects to keep in mind:

I-Frost protection:

Protection method will depend on the heat transfer fluid used and specific weather conditions of system site.

It is not enough to protect only the collectors. Outer pipes must also be protected.

As anti-frost protection systems, following could be used:

1. Antifreeze mixtures: it is the most used solution to system protection from freezing danger.

2. Water circuits recirculation: this system is suitable for climatic zones in which periods of low temperature are of short duration.

3. Automatic drainage with fluid recovery: this system requires the use of a heat exchanger between collectors and accumulator to maintain hot water supply pressure in it. This solution is not recommended in case collector absorber is made of aluminum.

4. Outdoor drainage (only for prefabricated solar systems): this system is not allowed in custom solar systems.

5. Total system shutdown during winter: this solution is advisable for systems that are only used in summer and it should be taken into account that empty circuits are subject to greater corrosion risks.

6. Collectors heating by an electrical resistance.

7. Collectors capable of withstanding freezing: there are collectors on the market that have sufficient elasticity to withstand volume increase due to freezing.

8. Introduction in absorber circuit of elastic and watertight capsules containing air or nitrogen. By increasing pressure due to freezing, they are compressed avoiding failure due to breakage.

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II-Overheating protection:

An excess of heat in solar thermal systems occurs when there is too much solar uptake in relation to energy obtained consumption. When this happens, collectors retain the heat that has not been evacuated and raise its temperature to levels that can be dangerous for system.

It is estimated that a heat transfer fluid e temperature xceeding 90 ºC becomes dangerous for the system.

Problem arises when, for reasons already mentioned, temperature rises too high in collectors and the heat transfer fluid circulating inside primary circuit begins to boil, expand and emit steam.

Both dilation and vaporization raise the pressure inside the primary circuit.

On the other hand, when heat transfer fluid begins to boil in the primary circuit, scale builds up on surfaces of the various components that deteriorate equipment.

In collectors overheating, 3 cases can occur:

1. Closed circuit with outdoor expansion vessel: steam produced goes outside. This can cause scale and risk of emptying part of circuit, forcing it to be filled before it is put into service.

2. Open circuit (consumption water passes through collectors): if boiling pressure exceeds network pressure, the produced steam will discharge into network contaminating the water.

3. Closed circuit and closed expansion vessel: when temperature rises, pressure rises and safety valve will open when it reaches a certain predetermined value.

Overheating risk in storage is lower and it can be said that it could only occur if system has high performance collectors (eg, vacuum tube collectors) and lacks a dissipation mechanism.

When water is hard (content of calcium salts between 100 and 200 mg / l), necessary precautions shall be taken so that working temperature of any point of consumption circuit does not exceed 60 ° C, without prejudice to necessary requirements against legionella application.

In any case, necessary means will be available to facilitate circuits cleaning.

In addition to safety elements there are other mechanisms to avoid overheating dangers:

• Use an organic fluid with a high boiling point.

• Angle of inclination of collectors higher than optimal to capture solar radiation preferably in winter. This ensures that the most perpendicular rays of summer fall with greater inclination on collector and take less advantage.

• Excess heat poured into the pool.

• Eaves. Through arrangement of strategically placed eaves it is possible to reduce the solar radiation that solar collectors support in summer.

• Cover collectors with covers.

• Heat sinks. These devices circulate superheated liquid through ducts to dissipate its heat in the air.
Some direct all the superheated flow of primary circuit to a unit where heat is dissipated with the help of fans (air heaters).
Others, however, are structures that are placed in each collector or battery of collectors and that dissipate only heat generated by the unit they are on. This type of heatsink works by gravity, without electronic components and is activated by means of thermostatic valves. It has the advantage that it continues to work in the event of a power cut.

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III-Pressure resistance:

In case of closed systems, maximum working pressure of all components shall be taken into account. The component that has the lowest maximum working pressure is the one that will set the pattern for entire system.

In case of open consumption systems with network connection, maximum pressure of the same shall be taken into account to verify that all components of the consumption circuit support said pressure.

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IV-Reverse flow prevention:

System installation must ensure that no relevant energy losses due to unintentional inverse flows occur in any hydraulic circuit of the system.

The natural circulation that produces the reverse flow can be favored when the accumulator is below the collector, so it will be necessary to take, in those cases, the appropriate precautions to avoid it.

In systems with forced circulation, it is advisable to use a non-return valve to avoid reverse flows.

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V-Legionellosis prevention:

It must be ensured that water temperature in hot water distribution circuit is not lower than 50 ° C at the furthest point and before the necessary mixture for protection against burns or in the return pipe to accumulator. System will allow water to reach a temperature of 70 ° C. Consequently, the presence of galvanized steel components is not admitted.

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This content was extracted from the Solar Thermal Energy Technical-Commercial Manual and is part of Solar e-learning.

All you need is Sun. All you need is Sopelia.

Mexico Solar PV

Mexico is part of the solar belt, an area that considers countries with the highest solar radiation in the world.

The country set itself the goal of generating, by 2024, 35% of electricity with clean energy (currently 80% is generated with hydrocarbons).

It is estimated that solar energy will represent 13% of all energy for next year, and that their participation will gradually grow.

However, solar technology development, as in all Latin American countries (and almost entire world), presents a huge imbalance between large-scale projects and distributed generation.

As far as large-scale projects are concerned, with 37 solar power plants under construction and an estimated investment of US$ 5,000 million, Mexico aims to become a solar power thanks to regulatory support and enviable geographic conditions.

In Coahuila is the largest solar park in Latin America with an investment of US$ 650 million generates about 754 MW.

By the end of 2020, the country will have 5,000 MW of installed capacity.

This impulse is due to the Energy Reform that opened the sector to private initiative, the Energy Transition Law and the three electric auctions held to date.

Average price obtained in the third solar auction (in which contracts were assigned to 9 projects) represented a downward world record for all energies.

In sector, presence of foreign actors stands out, winning approximately 90% of the bids.

The other side of the coin is that of distributed generation.

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Although since 2007 it is possible to install solar panels in homes, shops and industries and connect them to the electricity grid; until 2017, necessary conditions distributed generation development were not created. It represents less than 0.3% of total electricity generation in Mexico.

Before Energy Reform, distributed generation could only be used for self-consumption (and surpluses were lost after 12 months), without it being possible to buy or sell photovoltaic solar energy.

Regulations approved in March 2017 regulate the following compensation models: 1) Net metering; 2) Net billing; 3) Total sale.

In addition, due to ignorance advantages of using solar energy, which could supply a home with high electricity consumption, with only 16 square meters of photovoltaic panels, are lost in Mexico.

Most people are unaware that installing a renewable technology system based on solar panels in their homes is legal, simple and accessible,

Another challenge to face trained personnel lack both technically, to install panels, and engineering, for systems design.

Betting only on large-scale projects is an absurd and non-logical proposal that makes renewables a financial product and not an energy policy tool that promotes employment and technological and industrial development at national level.

It favors macro projects and deepens energy sector convcentration.

Low prices concentration in auctions, with the consequent creation of a dominant position in a few actors (usually foreign companies), will in long term dilute the advantages of low short-term prices.

If we consider auctions as the only tool to increase renewables participation, we will be maintaining an obsolete energy matrix paradigm and committing a very serious error.

The future energy matrix is based on 3 pillars:

1) Energy efficiency

2) Renewable energies

3) Distributed generation

The path of energy revolution and citizen empowerment goes through prosumer figure development and energy cooperativism.

The way of concentration and centralization involves only changing fossils for renewables to maintain the “status quo” for benefit of those who always will continue to act as a collection agency in collusion with political party in government.

All you need is Sun. All you need is Sopelia.