PV cells marketing began with monocrystalline silicon.

Based on perfectly crystallized silicon sections, they have achieved yields between 16% and 20% (24.7% in laboratory).

Later, polycrystalline silicon appeared, more economical, less efficient, but with the advantage of being able to be manufactured in a square shape; in order to take advantage of the rectangular surface available in a module.

They are based on silicon bar disorderly structured sections in small crystals form.

They have a lower performance than monocrystalline (19.8% in laboratory and 14% in commercial modules) being their price generally lower.

Then appeared thin-film technologies with similar performances to silicon modules at high temperatures or under diffuse radiation conditions.

Following are detailed thin-film modules of different semiconductor materials:

– Amorphous silicon (TFS): also based on silicon, which in this case does not follow any crystalline structure.

Usually used for small electronic devices (calculators, clocks, etc.) and small portable modules.

Its maximum yield in laboratory has been of 13% being 8% in commercial modules.

– Gallium Arsenide (GaAs): highly efficient cells to be used in special applications such as satellites, space exploration vehicles, etc.

GaAs Tandem cells are the most efficient solar cells, reaching values of up to 39%.

– Cadmium telluride (CdTe): 16% laboratory yield and 10% in commercial modules.

The drawback is that cadmium tellurium is a toxic substance. That is why manufacturing companies are working on their modules recycling process.

The next step in this evolution is represented by so-called Tandem cells that combine two or more distinct semiconductors.

Because each type of material takes advantage of only a part of solar radiation electromagnetic spectrum, by combining two or more materials it is possible to take advantage of a greater part of it.

First Tandem solar cells slope are CIGS (copper-indium-gallium-selenium).

In this case bond is not p-n type like in silicon, but a complex heterounion with which yields of 11% are obtained.

The second Tandem solar cells variant are CIS (copper-indium-selenium). With yields of 11% in commercial modules.

Another Tandem solar cells are the CZTS (copper-zinc-tin-sulfur-selenium) with yields of 9.6%.

Finally we find plastic solar cells based on polymers.

They are a type of flexible solar cell that can come in many forms including organic solar cells.

They are lightweight, potentially disposable, inexpensive to manufacture (sometimes using printed electronics), customizable at molecular level and their manufacturing has less impact on the environment.

They have a yield of approximately 5% and are relatively unstable to photochemical degradation.

For this reason, the vast majority of solar cells are based on inorganic materials.

Polymer solar cells do not require sun optimum orientation as the plastic collects energy up to 70° from sun to sun axis outdoor (and in any orientation indoor).

Its application field is mainly mobile phones and laptops.

Currently underway tests to produce solar cells with new materials include colloidal quantum dots and halide perovskites.

Advances in solar energy are unstoppable and their use at a massive level depends a lot on these, as the space needed to capture a certain amount of energy will be reduced and the performance of the systems will increase.

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

Solar energy wherever you are with Sopelia.

The solar energy direct conversion into electrical energy uses the physical phenomenon called photovoltaic effect of light radiation with valence electrons interaction in semiconductor media.

In conventional crystalline silicon cell case, 4 of the normally silicon atom 14 electrons are valence atoms and therefore can participate in interactions with other atoms (both silicon and other elements).

Two adjacent pure silicon atoms have a pair of electrons in common.

There is a strong electrostatic bond between an electron and the two atoms it helps together hold.

That link can be separated by a certain energy amount.

If the supplied energy is sufficient, the electron is brought to a higher energy level (conduction band), where it is free to move.

When it passes to the conduction band, the electron leaves a “hollow” behind, that is to say a vacuum where an electron is missing. A nearby electron can easily fill the gap, thus exchanging space with it.

To take advantage of electricity it is necessary to create a coherent electrons movement (and voids) by an electric field inside the cell.

The field is formed with physical and chemical treatments that create an excess of positively charged atoms in one part of the semiconductor and an excess of negatively charged atoms in the other.

This is obtained by introducing small amounts of boron (positively charged) and phosphorus (negatively charged) atoms into the silicon crystalline structure, ie doping the semiconductor.

The electrostatic attraction between the two atomic species creates a fixed electric field that gives the cell the so-called diode structure, in which the current passage is obstructed in one direction and facilitated in the opposite one.

In phosphor doped layer, which has 5 outer electrons against the 4 silicon, a negative charge formed by a valence electron is present for each phosphorus atom.

In doped layer with boron, which has 3 outer electrons, a positive charge formed by the voids present in boron atoms when combined with silicon is created.

The first layer, negative charge, is denoted by N; the other, positively charged, with P; the separation zone is called P-N junction.

When the two layers are approached, an electronic flow is activated from the N zone to the P zone, which, when the electrostatic equilibrium is reached, determines a positive excess of charge in the N zone and an excess of negative charge in zone P.

The result is a device internal electric field that separates the excess electrons generated by the absorption of the light in the corresponding holes, pushing them in opposite directions (the electrons towards the zone N and the holes towards the zone P) so that a circuit can collect the current generated.

Therefore, when light hits the photovoltaic cell, positive charges are pushed in increasing numbers towards cell top and negative charges towards the bottom, or vice versa, depending on cell type.

If lower and upper part are connected by a conductor, the free loads pass through it and an electric current is obtained.

While the cell remains light exposed, electricity flows regularly as direct current.

Conversion efficiency in commercial silicon cells normally ranges from 13% to 20%.

Typical photovoltaic cell has a total thickness of between 0.25 and 0.35 mm.

It is generally square in shape, has a surface area between 100 and 225 mm² and produces (with a radiation of 1 kW / m² at a temperature of 25 ° C) a current between 3 and 4 A, a voltage of approximately 0.5 V and a corresponding power of 1.5-2 Wp.

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

Solar energy wherever you are with Sopelia.

Solar Layout is the App for collectors and solar modules on site positioning.

This is the most intuitive Solar App of the market.

To use it on field is not necessary to have an Internet connection because it works from place latitude, obtained by GPS.

Today we will see PV solar energy part.

To begin press right command represented by the figure of the house with the solar module and cable with the plug in the initial screen.

If our Smartphone GPS is not enabled, the App will ask us to activate it to locate our position.

Intermittent earth planet image immediately appear with the legend “Localizing”.

When our device GPS have located our position, the following screen appears to confirm it.

By confirming our location Solar Equipment Use Menu will display.

In the same we find 4 applications:

1- Winter use: represented by the snow image
2- All year use: represented by flower, sun, leaf and snow images
3- Spring / summer use: represented by flower and sun images
4- On-grid connection: represented by the plug image.

By selecting one of the 4 applications, Options Menu will display.

There are 3 variables in the Menu:

1- Inclination: represented by module and angle image
2- Orientation: represented by module and cardinal points image
3- Distance: represented by 3 modules rows image.

By pressing Inclination option, we get recommended inclination value for location and solar application selected, accompanied by some Tips considering losses to take into account.

Pressing Orientation option, we obtain procedure to fix modules orientation description and access to recommended compass App discharge, if we don´t have it.

Pressing Separation option, the Kind of Surface Menu is displayed for us to select the appropriate option (Horizontal / Non horizontal).

If the surface on which the modules will be placed is horizontal, we only must enter Collector Height in cm data.

If the surface on which the modules will be placed is non horizontal, in addition to Collector Height in cm data, we must enter Surface Inclination Angle data.

We will enter a positive value if it matches the modules inclination direction and a negative value if it is different.

In this way we obtain the Separation (distance) between modules rows in meters.

Pressing i button Tips related to shadows and singular locations (snow, desert and rain areas) are deployed.

Download Solar Layout and placed solar PV modules on site in the most intuitive way with Sopelia.

Sorry, this entry is only available in Español.

The profitability of a photovoltaic system must be analyzed with certain nuances.

The weightiest factor when deciding whether it is feasible or not, is the potential energy savings during their years of life.

In the case of an isolated photovoltaic system, economic factor is not the main determining factor in deciding whether or not installation (electrification of rural areas, marine signaling, energy demand in remote locations, etc.).

Isolated (Off-grid) Systems

Installation can be evaluated for 2 reasons:

1. A range of total supply needed

2. Power grid not reach where energy demand originates

In the latter case you can opt for laying a new distribution line from the nearest point of the overall grid or choose an autonomous system.

When great powers are not needed and consumption is moderate, the option of autonomous generator is more interesting. Obviously, the higher or lower placement solar radiation level is another determinative factor.

In abundant wind areas, a wind turbine or a wind combined with photovoltaic system may be the most convenient option.

In cases where is needed a fairly large power requiring a large number of solar modules while consumption was not high enough to justify the laying of a grid line, the diesel generator can be the best option.

If both budgets (solar isolated and line grid laying) are of similar magnitude (or even laying a grid line is slightly higher), it can be more interesting access to the electricity grid, which will ensure any consumer at any time of year.

Grid connected (On-grid) Systems

It consists of a module field and inverter which can convert DC generated into AC identical to that of the electricity distribution network, to inject energy produced by the modules into the grid.

In return, you can received a contribution (feed-in tariff) established by law for a period which generally ranges between 15 and 25 years.

To realize the economic study should first determine electricity production depending on the sunshine hours of installation location and installed peak power.

Annual electricity production is then multiplied by the contribution is allocated to the project.

Finally a cash flow is prepared detailing revenues (sale of electricity and taxes recovery) and expenses (initial investment, annual maintenance and insurance costs, administrative and financial annual expenses) for the entire period.

From the data obtained the recovery period and IRR of the investment is determined.

The other way is the net-metering.

In this case, the owner of the photovoltaic system can take power from the grid when their system can not provide enough to meet demand, and inject energy to the grid when their system produces above necessary to meet demand.

The solar module prices fell reaching the threshold of U$D 0.50/W Exworks for conventional crystalline silicon modules.

Simultaneously, the price of electricity generated from fossil fuels is increasing annually.

In fact, it is estimated that several European countries will reach grid-parity (equal price between PV and conventional electricity) in 2020.

In developing countries, photovoltaic systems connected to the grid will remain still an expensive option because of the high subsidies electricity generation and distribution receive; limiting their development.

The turnkey price of a fixed installation connected to the grid (modules, support structures, inverters, protections, measurement systems, project costs, installation and administrative permissions) ranges from U$D 2 and 5/W depending on the facility size and location.

You can access content like this in Spanish in the Manual Técnico – Comercial de Energía Solar Fotovoltaica de Sopelia.