Without batteries, off-grid PV systems (except some cases such as water pumping) would be meaningless, because their functionality depends on electrical energy storage.

The battery is an electrochemical device that transforms chemical energy into electrical energy, whose presence is necessary because solar modules only generate energy when light hits them.

In addition, sometimes battery provides an instantaneous power higher than that of modules (eg: for starting motors) and provides stable and constant voltage regardless of light incidence.

The battery determines modules operating voltage. Therefore a safety margin is required which will mean a small loss (about 10%) with respect to maximum power that module could provide at higher voltages.

There is no ideal battery. The choice is a compromise between economy and suitability starting from a minimum quality that provides reliability and long life to the system.

In a battery, we have to take into account 3 technical considerations:

1º The discharge capacity

It is the maximum amount of electrical energy that can be supplied from its full charge to its complete discharge. Measurement unit is the amp hour.

The loading and unloading ratio and the battery and environment temperature are factors that can make vary its capacity.

2º The discharge depth

In renewable energy systems, only deep discharge batteries are used (we refer to capacity percentage that is used in a cycle of loading and unloading).

Deep discharge batteries have an average discharge of 25%, and can reach 90%.

3” Cycles of a battery

It is the time from complete charge to discharge.

Battery life is measured in number of cycles it can handle.

Auto-discharge should also be considered as an additional consumption that daily demands a certain percentage of stored energy.

As damaging as excessive discharge is for a battery to too much load. Way to prevent this is by introducing a charge controller.

Every time battery is recharged, does not completely regenerate, resulting in a degradation that will determine battery life.

If discharge depths are respected and maintenance is correct, battery service life should be approximately 10 years.

For PV systems, batteries used are:

1. Lead-Acid: Characterized by their low cost and maintenance they require (need to be in a cool place and periodically check electrolyte amount).

Lead-antimony are the most used in medium and large systems and lead-calcium are mainly used in small systems.

There are also 2 types of sealed lead-acid batteries: Gelled (incorporating an electrolyte gel type) and Absorbed Electrolyte (electrolyte is absorbed into a microporous glass fiber or a polymer fiber web).

These batteries don´t require maintenance in water aggregate form nor develop gases, but both require less deep discharges during their service life.

2. Nickel-cadmium: offer better performance, but have a higher price.

The electrolyte they use is an alkaline, have a low self-discharge coefficient, good performance at extreme temperatures and the discharge they support is around 90% of their rated capacity.

They are recommended for isolated or dangerous access places.

They can´t be tested with same reliability as lead acid. Therefore, if it is necessary to control charge state, they aren´t the best option.

3. Lithium: they take up little space, they weigh less, they do not emit gases, they can be put anywhere, loading time is the fastest, total discharges can be made without affecting their useful life in a relevant way.

What is the disadvantage? Its very high price.

The manufacturer who can optimize them will have found the solar sector Holy Grail.

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.

Cells are silicon in the most used modules, element which is the main component of the silica, the material of the sand.

The regional production capacity distribution differs significantly depending on product type and its value chain position.

Solar grade silicon production capacity is headed by the US; followed by Europe, China, Japan and the rest of Asia.

Silicon cells and modules production capacity is dominated by Chinese and Taiwanese manufacturers; followed by Europeans, Japanese and the US.

Thin-film manufacturers must still optimize production to reach optimal cost structure to be competitive.

A difficult task with much lower prices for polysilicon, resulting in a significant decrease in silicon modules prices.

In order to avoid scarcity or oversupply cases, it is of utmost importance to guarantee supply, demand stability, based on a sustainable market so that the industry can foresee the growth of the same and plan its capacities.

Photovoltaic systems demand depends to a large extent on general economic climate and, most importantly, on governments policies to support their development.

Tariffs, along with administrative procedures and grid connection simplification, as well as priority grid access are policies aimed to guaranteeing sustainable demand.

A silicon cell provides a voltage of about 0.5 V and a maximum power of between 1 and 2 W.

In module manufacturing process, a certain number of cells must be in series connected to produce voltages of 6, 12 or 24 V indicated for most applications.

To produce a 12 V module, you need between 30 and 40 cells.

Cells connecting process is done by a special welding that joins the back of a cell with the front face of the adjacent one.

After electrical interconnections are completed, cells are encapsulated in a sandwich structure (tempered glass laminate – EVA – EVA – polymer cells).

The structure varies by manufacturer.

Subsequently a vacuum sealing is carried out, introducing it in a special furnace for its lamination, making tight the assembly.

If they have a metallic support frame, module perimeter is first surrounded with neoprene or some other material that protects it.

Once positive and negative connections are mounted, following controls are performed to ensure a 20-year service life with acceptable performance levels:

– Thermal cycles (-40 ° to 90 ° C)
– Humidity cycles.
– Freezing cycles.
– Wind resistance.
– Mechanical strength.
– High electric shock resistance.
– Saline atmosphere test (for marine environments).

Manufacture, performance, electrical and mechanical characteristics of photovoltaic module are determined in product technical specifications provided by the manufacturer.

As in solar cell, following parameters are important:

– Module maximum power or peak power PmaxG.
– IPmax: Intensity when power is maximum or current at maximum power point.
– VPmax: voltage when power is also maximum or voltage at maximum power point.

Other parameters are:

– IscG short-circuit current.
– Open circuit voltage VocG.

These parameters are obtained under standard conditions of universal use according to EN61215. Established as follows and the manufacturer must specify:

* Irradiance: 1000 W / m2 (1 Kw / m2)
* Incident radiation spectral distribution: AM 1.5 (air mass)
* Normal incidence
* Cell temperature: 25ºC

Modules working conditions may be very different once installed, so it is advisable to know variations that can occur, in order to make calculations relevant corrections.

In practice, module power decreases by approximately 0.5% for each cell temperature increase degree cell above 25 ° C.

To avoid having to calculate radiation average intensities, we can assume that cell average working temperature is 20º higher than ambient temperature.

For this concept, yield drops to 90%. In not based on crystalline silicon technologies, yield lower is smaller.

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.

Sorry, this entry is only available in Español.

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 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.

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.

3) Off-grid Systems Scale Calculator

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

4) Solar Water Pumping Calculator

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

5) Solar & Wind Energy Systems Calculation

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

6) Grid Connected System Online Simulation

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

7) Battery Bank Capacity Calculator

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

8) Wire Section Calculator

Tool in JavaScript format for copper and aluminum DC wire calculation.

Solar energy wherever you are with Sopelia.

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.