Tag Archives: energia solar en latinoamerica

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.

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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.

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Mexico Solar Thermal

As in most Latin American countries, in Mexico, statistics in solar thermal energy field are not up-to-date and renewable energies prospects do not include this source of generation.

In Mexico, in 2010, solar systems to heat water were installed in an equivalent area of 272,580 m2, reaching an accumulated area of 1,665,502 m2.

According to estimates, in next 4 years almost double the production area by solar thermal energy.

Although we do not find data about current installed capacity in Mexico, we can conclude that this type of energy has had a great growth in recent years and that it is likely that the installed capacity has doubled again.

Due to country average radiation levels, a solar thermal installation for domestic hot water has become a very profitable investment in Mexico, since water heating causes the greatest gas consumption and with this application, gas use is reduced by up to 80% in regions with higher radiation.

Recently there has been a noticeable decrease in prices of solar equipment for domestic hot water.
The factors that allow this to happen are imports, easy manufacturing, technology maturity and competitiveness between national and international companies that offer this type of equipment.

In Mexico, there are important companies that manufacture low temperature thermal solar energy equipment. The first began in 1940 in Guadalajara.

Several government programs have promoted low cost acquisition of solar heaters by residents of areas where the gas network does not reach.

Other solar thermal energy applications that have increased considerably are swimming pools conditioning and water heating for industrial processes.

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Hermosillo was one of the first states to adopt this type of technology for industrial processes in Mexico.

A cement company uses a thermal 291 KW equipment to operate a 75 tons of single effect cooling system. This was the first air conditioning system based on renewable energy in Latin America. The parabolic cylindrical collectors are located on the roof and on one side of corporate building; it operates in a range from 70 ° C to 95 ° C.

Other systems have been installed for generating heat purpose.

Mexican companies have commercially developed parabolic-linear solar concentrators to generate thermal energy between 50 ° C and 200 ° C. These systems are used mainly in food sector.

Some of the companies that currently have this alternative energy generation in the country are:

– Food company: installation of 80 solar concentrators for process heat generation and absorption chiller supply.

– Dairy company: installation of 70 solar concentrators for direct heat input in dairy products processing.

– Egg producing company: installation of 80 solar concentrators for boiler preheating.

Imagen relacionada

Despite advances, there is still much room for solar thermal technology development in Mexico.

The final impulse could come from special financing lines implementation, since for a large population sector initial system investment is still very high.

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The Solar Converter

They are equipment capable of altering voltage and characteristics of electric current they receive to transform it into suitable for specific uses.

Those that receive direct current and transform it into direct current with a different voltage are called DC-DC converters. They are not widely used in photovoltaic systems.

Those that receive direct current and transform it into alternating current are called DC-AC converters or inverters. The function of an inverter is to change a DC input voltage to a symmetrical AC output voltage, with the magnitude and frequency desired by user.

They allow to transform 12V or 24V direct current that modules produce and store batteries, in 125V or 220V alternating current.

This allows use of electrical devices designed to work with AC.

A simple inverter consists of an oscillator that controls a transistor, which is used to interrupt incoming current and generate a square wave. This square wave feeds a transformer that softens its shape, making it look like a more sinusoidal wave and producing the necessary output voltaje.

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The voltage output waveforms of an ideal inverter should be sinusoidal.

This gives rise to different types of inverters:

1) Square wave inverters: they are cheaper, but less efficient. They produce too many harmonics that generate interference (noise). They are not suitable for induction motors.

Recommended if you want AC power only for a TV, a computer or a small electrical device. Inverter power will depend on device nominal power (for a 19 ” TV a 200 W inverter is enough).

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2) Modified sine wave inverters: they are more sophisticated and expensive. They use pulse width modulation techniques.

Wave width is modified to bring it as close as possible to a sine wave. Harmonics content is less than in square wave.

They are the ones that offer best quality / price ratio for lighting, television or frequency inverters connection.

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3) Pure sine wave inverters: with a more elaborate electronics, a pure sine wave can be achieved.

Until recently these investors were large, expensive and inefficient; but lately, has been developed equipment with 90% or more efficiency, telecontrol, energy consumption measurement and battery selection.

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Since only induction motors and most sophisticated devices or loads require a pure sine wave form, it is usually preferable to use modified sine wave inverters; which are cheaper.

Inverters must be dimensioned from two variables.

First is considering electrical power wattages that inverter can continuously supply during its normal operation.

Inverters are less efficient when used at a low percentage of their capacity. For this reason it is not advisable to oversize them and they must be chosen with a power as close as possible to that of load consumption.

Second is starting power. Some inverters can supply more than their nominal capacity for short time periods. This capacity is important when using motors or other loads that require 2 to 7 times more power to start than to stay running once they have started (induction motors, high power lamps).

Incorporating an inverter is not always the best option from energy efficiency point of view. It may seem an easy solution to convert all solar system output to a standard AC power but it has several disadvantages.

First is that it increases system cost and complexity.

An inverter also consumes energy (in addition to 15% for performance loss) and therefore decreases overall system efficiency.

For a small house electrification (light points, TV and a small appliance) it is possible and profitable to do without the inverter.

For lighting it is better to invest in low voltage lights instead of investing in an inverter.

Laying of 2 lines can be interesting: one connected to batteries to feed points of low consumption lighting or LED and devices that consume DC and another connected to inverter to power appliances that consume AC.

The advantage of the inverter is that operating voltage is much higher and therefore the use of thick cables can be avoided. Especially when wiring is extremely long it may be economically feasible to use an inverter.

A feature that incorporates most modern converters is possibility of operating as battery chargers, taking alternating current from a generator or grid.

This is an extract of contents included in Technical-Commercial Photovoltaic Solar Energy Manual and Sopelia e-learning training.

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Solar Collectors Clamping And Anchoring

Proposed solution must comply, in order of importance:

– That it’s enough safe .
– That its cost be as low as possible.
– Speed and simplicity in assembly.

A method currently used is anchoring by chemical plug.

There are structures are of different materials. The most commonly used are aluminum and stainless steel.

Manufacturers usually sell the collector with its structure, although you can always design your own structure.

It is not advisable to transfer building cover with the anchor (it can cause leaks).

In case of large installations, a pre-assembly work can be carried out to make assembly on roof faster and cheaper.

In near coast areas, structure must be hot dip galvanized.

Screws should be made of stainless steel or corrosion resistant material.

Anchoring type will be based on:

1) Wind forces that must endure. If collector is South oriented (we are in the Northern Hemisphere), wind that represents a risk is that coming from North (it is the inverse if we are in the Southern Hemisphere), which will exert tensile force on the anchors. The South wind will exert compressive force, not so dangerous. Wind force on a surface is:

f = P. S. sen2α
f = Weight to counteract wind strength.
P = wind load (Kg / m2).
S = collector surface (m2).
sin2α = angle of inclination sine.

Wind force is decomposed into f1, which incites perpendicularly to collector surface and in f2, which does it in parallel.

f1 force is at the end what counts and what is obtained from previous formula.

2) Collectors orientation and inclination. Collectors are oriented towards Ecuador. Normally, if we are in Southern hemisphere, they are oriented towards North and vice versa. Deviations of up to 20% with respect to optimal orientation do not significantly affect system performance and thermal energy contributed.

Collector’s inclination angle will depend on solar equipment use. Orientates inclinations:

• All year use (H.W.S.): inclination angle equal to geographical latitude.

• Winter preferably use (heating): inclination angle equal to geographical latitude + 10º.

• Summer period preferred use (outdoor pools heating): inclination angle equal to geographical latitude – 10º.

Variations of ± 10º with respect to optimum inclination angle practically do not affect performance and useful thermal energy provided by solar equipment.

3) Collecting surface must be free of shadows. In the most unfavorable day of use period, installation must not have more than 5% of useful surface area covered by shadows.

Projected shadows practice determination is made observing environment from collector´s lower edge midpoint, taking the North-South line as a reference.

By making an angular sweep on both sides, we will try to locate nearby obstacles with an angular height greater than 15º / 25º.

A more accurate determination of possible shadows can be made using system sizing software based on simulation methods.

4) Minimum distance between collectors. Separation between collectors rows must be established so that at solar noon of most unfavorable day (minimum solar height) of use period, the shadow of upper edge of a row will be projected, at most, on lower edge of following row.

The formula of minimum distance between collectors is:

DT = L (senα / tan H + cosα)
H is the minimum solar height, which is:
H = (90º – latitude place) – 23.5º
L is collector´s height

If collector’s rows were arranged on a non-horizontal surface, expression would become:

DT = L ((sin (α – β) / tan (H + β) + cos (α – β))

α is still collector inclination angle respect to horizontal.

β is roof inclination angle respect to horizontal. It is positive if cover inclination angle direction coincides with that of collector; and with a negative value otherwise.

5) Finally, calculations must be carried out to ensure that cover or support will be able to support collectors weight, and that of the tank in case of thermosiphon and compact systems.

The R + D + I area of Sopelia has developed Solar Layout, the mobile app that allows collectors and modules to be optimally located at installation site.

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Free Solar Tools (IV)

On Internet we can find free tools for basic or low complexity solar systems dimensioning and for certain components or accessories estimation.

Sopelia research team has carried out an exhaustive search and testing from which a new corporate website section called Free Solar Tools has been created.

Selected tools were classified into 4 categories.

Today we will analyze the fourth of them: Solar Photovoltaic.

In the first category we have already analyzed tools to obtain data about solar resource and other variables to be considered in energy estimation solar system will provide in our location.

In the second category we have analyzed tools to calculate the “load”, ie the energy demand to be met.

In the third category we have analyzed tools for solar thermal systems dimensioning and system accessories estimating.

Now we are going to analyze tools for solar photovoltaic systems dimensioning and to estimate others individual components of a system.

The order of the tools is not random. We have prioritized the most intuitive, the most universal and those that can be used online without download.

For this fourth category our selection is as follows:

1) Solar Calculator

Approximate calculation tool from which budget, production data and system performance study is automatically obtained.

A Navigation Guide and Manuals can be found at page bottom.

Resultado de imagen de sistema solar fotovoltaico

2) Off-grid Solar Systems Calculator

Free online application for off-grid solar systems calculation.

It allows users to introduce new components from any manufacturer and product datasheets to be considered in the calculation.

Resultado de imagen de sistema solar aislado

3) Off-grid Systems Scale Calculator

Solar basic estimation of off-grid systems. Solar modules, batteries, controller and inverter calculation.

Resultado de imagen de sistema solar aislado

4) Solar Water Pumping Calculator

Calculator to obtain approximate energy needs figures for solar water pumping.

Resultado de imagen de bombeo solar de agua

5) Solar & Wind Energy Systems Calculation

Tool which determines requirements to meet solar and / or wind contribution for electrification and pumping needs.

Resultado de imagen de sistema eólico solar

6) Grid Connected System Online Simulation

Online application to estimate production and economic income of a grid-connected system.

Resultado de imagen de sistema solar conectado a red

7) Battery Bank Capacity Calculator

Calculator to estimate battery bank size needed to keep consumption by solar operation.

Resultado de imagen de banco de baterías solares

8) Wire Section Calculator

Tool in JavaScript format for copper and aluminum DC wire calculation.Resultado de imagen de cable solar

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The Solar Charge Controller

Charge controller is a device located between photovoltaic modules and batteries as an element of an isolated solar system.

Modules output voltage is set some volts higher than voltage battery needs to charge. The reason is to ensure that modules will always be able to charge the battery, even when cell temperature is high and generated voltage decreases.

This causes the drawback that once battery reaches its full charge state, module continues to try to inject energy producing an overload that, if not avoided, can destroy battery.

Charge controller is responsible for extending batteries life protecting them from overload situations, controlling load phases depending on their status and even reaching the cut depending on load needs of them.

Charge controllers may be working in one of the following situations:

Equalization status: equalization of batteries charge, after a period of low charge.

Deep charging state: regulation system allows charging until reaching final load voltage point.

Float state: battery has reached a charge level close to 90% of its capacity.

State of final charge and flotation: regulation system zone of action within Dynamic Flotation Band (range between final load voltage and nominal voltage + 10%).

To know which regulator to incorporate into a photovoltaic system it is necessary to know some elementary parameters.

First, one is isolated solar system nominal voltage. Batteries voltage and photovoltaic solar field define this voltage. Typical values are 12, 24, 48 and up to 60 volts.

The other parameter is photovoltaic modules system load current. It is recommended to multiply short circuit current Isc under standard conditions by 1.25 so that charge controller is always able to withstand current produced by modules.

Known system voltage and determined current value, we can choose the right charge controller. If there are still doubts, we can consult with provider technical department.

The simplest design is one that involves a single stage of control. Charge controller constantly monitors battery voltage but controls charge or discharge, never both. They are the cheapest and the simplest.

This can be achieved by opening the circuit between photovoltaic modules and battery (serial control) or by short-circuiting photovoltaic modules (shunt control).

Resultado de imagen de regulador de carga solar una etapa

In case of controllers that operate in two control stages, the two functions are controlled, both charge and discharge of battery. They are more expensive, but they are the most used.

Current charge controllers introduce microcontrollers and control 3 and up to 4 control stages.

Resultado de imagen de regulador de carga solar

During last years a new generation of charge controllers has been developed, whose main characteristics are to make photovoltaic field work at maximum working point and to always render it optimally.

These charge controllers are known as power maximizers or MPPT.

Another advantage of these devices compared to conventional controllers is the possibility of working with a different voltage in the generator field (solar panels) and batteries.

This directly influences in being able to put several modules in series, elevating system tension.

Working with lower currents we can reduce considerably voltage drop losses and use smaller cable sections and therefore of lower price.

For the choice of a conventional controller or an MPPT, we have to assess cost overruns that these systems have compared to benefits that it gives us due to system performance increase. In some cases, annual power increase can reach up to 30% compared to conventional controller.

Resultado de imagen de regulador de carga solar MPPT

Charge controller may not be essential in installations where the ratio between modules power and battery capacity is very small (eg: oversized batteries for safety reasons) so that charging current can hardly damage battery.

If modules field power in W is less than 1/100 battery capacity in W / h, charge controller may not be incorporated.

It can also be dispensed with a charge controller if system has self-regulated solar modules (not recommended for extreme climates).

This is an extract of contents included in Technical-Commercial Photovoltaic Solar Energy Manual and Sopelia e-learning training.

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

Free Solar Tools (III)

On Internet we can find free tools for basic or low complexity solar systems dimensioning and for certain components or accessories estimation.

Sopelia research team has carried out an exhaustive search and testing from which a new corporate website section called Free Solar Tools has been created.

Selected tools were classified into 4 categories.

Today we will analyze the third of them: Solar Thermal.

In first category we have already analyzed tools to obtain data about solar resource and other variables to be considered in energy estimation solar system will provide in our location.

In the second category we have analyzed tools to calculate the “load”, ie the energy demand to be met.

Now we are going to analyze tools to solar thermal system dimensioning and others to estimate individual components of a system.

The order of the tools is not random. We have prioritized the most intuitive, the most universal and those that can be used online without download.

For this third category our selection is as follows:

1) Solar Thermal Calculator

Approximate calculation tool from which budget, production data and system performance study is automatically obtained.

A Navigation Guide and Manuals can be found at page bottom.

Resultado de imagen de calculadora solar térmica

2) Simulation for Solar Thermal System Pre-design

Online application based on the TSOL software that allows solar energy system simulating to ACS and ACS + heating contribute.

Available in German, English, Spanish and French.

Resultado de imagen de simulación solar térmica

3) Solar Fraction Calculation

Free download program developed by IDAE (Institute for Energy Diversification and Saving) and ASIT (Solar Thermal Industry Association) that allows to define a wide variety of solar systems introducing a minimum of project parameters, associated to each system configuration; and in this way, obtain solar system coverage on ACS and pool conditioning energy demand.

Resultado de imagen de fracción solar térmica

4) Solar Expansion Vessel Calculation

Tool developed to calculate solar expansion vessel volume.

Volume values (total circuit, solar collectors, pipes), Maximum system temperature (ºC), Glycol concentration (%), Height between expansion vessel and system highest point (minimum value 1 Bar) and safety valve Pressure setting must be introduced.

Resultado de imagen de cálculo vaso expansión solar

5) Thickness Insulation Pipes Calculation

Calculator that allows to estimate minimum and more economical water pipes insulation thickness.

Pipe Grade and Size, Insulation Material, Humidity and Temperature (Internal and Ambient) must be entered.

Resultado de imagen de aislamiento tubería solar

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