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Solar Wiring

Cables, both direct current (DC) and alternating current (AC), if correctly sized, will minimize energy losses and protect the installation.

For a photovoltaic system, DC cables must meet some requirements:

* Have grounding line and protection against short circuit.
* Be resistant to UV rays and adverse weather conditions with a wide range of temperatures (approximately between -40ºC and 110ºC).
* Possess a wide voltage range (more than 2000 V).
* Be simple and easy to manipulate.
* Be non-flammable, of low toxic level in case of fire and without halogens.
* Have a very low conduction loss (up to 1%).

Photovoltaic installation cables must have certain characteristics that differentiate them from conventional cables, although many argue that differences are not very large.

Since voltage in a photovoltaic system is low DC voltage, 12 or 24 V, currents that will flow through the cables are much higher than those in systems with 110 or 220 V AC voltage.

Power amount in Watts produced by the battery or photovoltaic panel is given by the following formula: P = V. I

V = voltage in Volts
I = current in Amperes

This means that to supply a power at 12 V current will be almost 20 times higher than in a 220 V system. It implies that much thicker cables must be attached to prevent overheating or even a fire.

Following table indicates recommended cable section according to power and for different voltage levels.

For very low voltages and low power demands, very thick cables must be used. For example, to reach a power of approximately 1 Kw at 12 V we would need a 25 mm2 section cable. The same as to supply 20 Kw at 220 V.

This increases system price drastically because thicker cables are more expensive.

That is why it is very important that the lengths of DC wiring are as short as possible.

When designing large systems, a cost / performance analysis must be performed to choose most suitable operating voltage. It would be advisable to gather small groups of modules and if possible to make operating voltage higher than 12 or 24 V.

To verify cable section values recommended in tables, maximum voltage drops compared to voltage at which you are working should be below the 3% / 5% limit.

To calculate the relationship between conductor section and its length we can apply following formula:

S = 2 r. l. i / ΔV

Being:

r Conductive material resistivity (0.018 in case of copper conductors)
l Cable section length
i Current intensity
ΔV Voltmeter reading difference

Let’s see an example:

Battery terminals output voltage is 13.1 V. The main line between it and a device, which consumes 60 W, measures 12 m of 6 mm2 cable.

We must find the voltage value at device input to verify that we are within maximum recommended values of voltage drop.

The intensity i = P / V = 60 / 13.1 = 4.6 A

S = 6 = 2. 0.018. 12 4.6 / ΔV

ΔV = 0.33 V

Therefore, voltage at device input will be: 13.1 – 0.33 = 12.8 V

Voltage drop is 2.34% (maximum recommended value: 3%).

It is normal to use tables to select recommended section and use the formula to calculate the voltage drop and perform the verification.

In case that voltage recommended maximum values drop are exceeded, we will select section immediately above and we will carry out verification again.

Cables for photovoltaic applications have a designation, according to regulations, which is composed of a set of letters and numbers, each with a meaning.

Cables designation refers to a series of characteristics (construction materials, nominal voltages, etc.) that facilitate the selection of the most suitable to the need or application.

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.

Heat Transfer Fluid

Heat transfer fluid passes through absorber and transfers energy to thermal utilization system (accumulator or exchanger).

Most used types are:

* Natural water: can be used in open circuit, when sanitary water passes directly through collectors, or in closed circuit (independent consumption circuit).

In first case, circuit can only be constituted by materials allowed for drinking water supply. In some countries this system is not allowed.

It will be necessary to consider water characteristics, especially its hardness (calcium and magnesium amount), which when heated produces a hard crust or tartar.

This crust accelerates corrosion, restricts flow and reduces heat transfer. The values start to be problematic from 60 mg / l. Very soft waters can also cause problems due to their corrosivity.

* Water with antifreeze: to avoid drawbacks of freezing and boiling of heat transfer fluid, use of antifreezes called “glycols” is the most widespread.

Mixed with water in certain proportions prevent freezing to a limit of temperatures below 0 ° C depending on their concentration.

On the other hand the boiling point rises making heat transfer is protected against too high temperatures.

Choice of concentration will depend on historical temperatures of the area where installation is located and on characteristics provided by manufacturer.

Most commonly used glycols are ethylene glycol and propylene glicol.

Resultado de imagen de tabla anticongelante solar

Fundamental characteristics of antifreeze:

• They are toxic: their mixing with drinking water must be prevented by making secondary circuit pressure greater than that of primary, for prevention exchanger possible breakage.

• They are very viscous: factor to take into account when choosing electric pump that is usually more powerful.

• Dilates more than water when heated: as a safety standard, when we use antifreeze in proportions of up to 30%, when sizing the expansion vessel, we will apply a coefficient of 1.1 and 1.2 if proportion is greater.

• It is unstable at more than 120ºC: it loses its properties so it stops avoiding freezing. There are some that withstand higher temperatures, but they are expensive.

• The boiling temperature is higher than that of water alone, but not too much.

• Specific heat is lower than that of water alone, so it must be taken into account in the flow calculation, conditioning pipe and pump dimensioning.

To calculate antifreeze amount that must be added to an installation, you must first consult the table of historical temperatures which is the minimum temperature recorded in that city or location.

Once it is known, goes to glycols graph supplied by manufacturer and value is transferred to indicate what percentage is.

* Organics fluids: there are two types, synthetic and petroleum derivatives.
Precautions mentioned in case of antifreeze regarding toxicity, viscosity and dilation are applicable to organic fluids. Additional risk of fire should be mentioned, but also that they are chemically stable at elevated temperatures.

* Silicone oils: they are stable and of good quality products. They have the advantages that they are not toxic and that they are not flammable, but current high prices mean they are not widely used.

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

Solar Energy Wherever You Are

Many times the purpose of incorporating solar energy to our professional skills, scope of business or personal life has hovered in our head.

We have almost always run into the same barrier: time.

We are working or studying and we find it very difficult to have even a few hours a week.

It is rare to find training offerings that are not too short (few hours workshops) or too long (one or more years) and which in turn have an affordable price.

If we add the difficulty of having to move, because most are taught in presence way, finally we ended up postponing again and again this purpose.

In 2014 Sopelia gave, in collaboration with the Technology National University of Mar del Plata (Argentina), the Technical – Commercial Solar Energy Course in tele-learning (distance + presence) methodology.

In 2016 Sopelia updated and divided that training action in 2 specific courses:

* Technical – Commercial Solar Thermal Energy

* Technical – Commercial Photovoltaic Solar Energy

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Sopelia rode them on a Moodle 3.1 platform and the result is 2 courses in e-learning methodology.

This means you can receive Solar Energy training with the best market value wherever you are.

You only need a computer, smartphone or mobile device and Internet.

Being the 1st edition there is a 50% off list price.

These two courses provide technical and commercial training in solar energy domestic applications with the aim of spreading the technology and develop human resources for incorporation into work and business world.

You will identify the most relevant aspects of solar energy within the current energy landscape.

You will define, describe and analyze the most important features of solar energy.

You will know the composition, understand the operation, design and maintenance of facilities to implement thermal and photovoltaic solar energy projects.

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It is a training aimed at students and technical careers graduates, technical schools graduates, engineers, architects, professionals and installers of related sectors (air conditioning, electricity, rural), people with experience in renewable energies, environmental professionals and individuals interested in incorporating solar energy into their lives.

The 2016 edition starts on September 19th and ends on November 25th.

You can register until 16 September inclusive in www.energiasrenovables.lat

If you are under 30 years old and live in Latin America, with the course completed, you can apply to be Sopelia Country Manager in your country of residence.

And if you are under 25 and live in Latin America, you can get a 50% scholarship and finished the course, apply to become Sopelia Trainee.

If you speak Spanish you have no excuses, Solar Energy wherever you are with Sopelia.