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Basics of photovoltaic systems

How does a photovoltaic installation work?
 
General information  

The solar energy received globally is approx. 1,540,000,000,000,000,000 kWh/year (1,540 peta kWh/year). This is 15,000 times more than the worldwide energy consumption. Congratulations on your decision to actively use this largest energy pool worldwide. By the way, did you know that solar energy was first discovered in 1839 by the physicist Alexandre-Edmond Becquerel? The somewhat strange-sounding term "photovoltaics" originates in the driving force behind this technology, the light beam. A light beam consists of unimaginably tiny particles, the photons.

Generating power on the roof    

To simplify matters, let's start by explaining a pure silicon solar cell. If we recall what we learned in our physics lessons, silicon features 4 electrons in the outer electron shell of the atomic nucleus, the so-called valence electrons. The photons, i.e. the sunlight, bombard the solar cells and enrich the valence electrons with energy. The electrons are finally knocked off the silicon atom and leave a positive atom behind. For the free electrons to move into the right direction and to allow current to be generated, the front surface and the back surface of the cell need to be polarized differently. So the silicon atoms at the front surface are doped with a minor quantity of phosphorus atoms featuring an extra valence electron. On the back surface of the cell, however, boron atoms with only three valence electrons are added to the silicon atoms. This establishes a voltage difference between the positive and negative pole and allows electrons to flow, that's how current is generated. A large number of these solar cells put together and encapsulated with glass will then form one of your solar modules.

Converting power under the roof     

DC generated in the solar modules can be used in the household or fed into the utility transmission grid, provided it is first converted into AC. This is the core task of the Fronius inverter. Your Fronius inverter is a solar inverter of the most recent generation. It represents a highly complex link between the solar modules and the utility transmission grid. It is therefore expected to fulfill a series of highly demanding tasks.  

Conversion of DC into AC       

The Fronius inverters convert DC, generated in the solar modules, into AC. Synchronized with the supply voltage, this AC is then either fed into the circuit of your home or into the utility transmission grid. The Fronius inverter were developed exclusively for application in utility interactive PV installations. For more information on circuit diagrams, please turn to the installation and service instructions.  

Fully automated operation   

Fronius inverters operate in a fully automated manner. After sunrise, as soon as there is sufficient output generated by solar modules, the control unit starts monitoring the utility line voltage and frequency as well as the energy offer. Once enough sunlight is received, the solar inverter starts feeding the utility transmission grid. Depending on the type of installation, a few watts of solar power will be enough do the job!

The Fronius inverter will now continue to work in a way to always draw the maximum of power from the solar modules. This function is called MPPT (Maximum Power Point Tracking) and is carried out with a rate of accuracy of more than 99%. After dark, when the energy offered is no longer enough to feed the utility transmission grid, the Fronius inverter automatically cuts the connection to the grid and stops operating, of course with all settings and data being conserved.

Voltage transformation and galvanic separation  

The Fronius inverters are designed to be used in solar modules with a wide range of input voltage, which allows to use the most varied types of solar modules. Consider that the indicated values for the maximum DC voltage (total voltage of all solar cells connected) must never be exceeded. Thanks to its structure and its way of working, a Fronius inverter provides a maximum of safety, from installation and mounting to operation. The Fronius IG inverter is the first solar inverter to feature a HF transformer (HF = high frequency) that ensures a galvanic separation of the DC side from the utility transmission grid. In addition, the HF conception allows a radical reduction of the transformer's size, it therefore needs a lot less space and weighs much less. Despite the complete galvanic separation, Fronius inverters accomplish a high level of efficiency thanks to innovative circuit conceptions.

Grid monitoring

Inverters from Fronius also assume the task of monitoring the grid. This term includes all measures required for the protection of people and devices in case of a utility outage. Fronius inverters are programmed to immediately stop operating in case of irregular grid conditions (e.g. utility outage, interruption) and to interrupt feeding the grid. There is a series of possibilities for Fronius inverters to identify a utility outage:

  • Voltage monitoring
  • Frequency monitoring
  • Measuring the line resistance (only with the Fronius IG featuring ENS)
  • Intended feeding of a slightly modified frequency or voltage


In this context it is important to know that the Fronius inverters are able to carry out the monitoring procedures applicable in each country by theirselves, without additional electronic measuring devices. This considerably reduces installation work and all related costs.

Display and data communication

The high technical complexity of novel solar inverters requires a perfect display design, which is actually the "interface" with the user. It is uncompromisingly designed for easy operation and permanent availability of the system data. Fronius inverters already feature a fundamental logging function for recording data on minimum and maximum values directly on the display - on a daily, yearly and a total basis.

As an option feature, the display also allows indicating the following weather related data:

  • 2 different temperature values (e.g. temperature near the solar modules, outside temperature in the shade)  
  • Insolation
  • Wind velocity
  • Atmospheric pressure
  • Relative atmospheric humidity


In addition to the functions implemented in the Fronius inverters, a wide range of elements for data communication offered provides a large number of possibilities for data recording and visualizing. Required system expansions are easy to install. The appealing box provides space for a large number of system expansions, with a focus on easy connection to all current and new media, such as remote inquiry via modem, e-mail, internet, SMS, fax, etc.

Your benefit

The more of the above tasks the photovoltaic inverter is able to do itself, the easier and cheaper the installation will be as there are no more additional peripherals needed. Thanks to our experience and highly innovative technologies, the Fronius inverters can handle all these tasks simultaneously. It furthermore meets a series of requirements for the protection of people, household appliances and the inverter itself.
Some of these requirements are:

  • Grid monitoring
  • The type of current fed into the grid
  • Response to interferences (e.g. mobile phones)
  • Intended feeding of a slightly modified frequency or voltage