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.

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).

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.

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.

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.

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

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.

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.

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

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).

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.

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.

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.

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.