Solar Power » Technologies

Photovoltaic Systems

In order to benefit from the electricity generated in solar modules, either by consuming it instantly on the premises or by feeding it into the grid, the module must be wired up with a few other electrical components. The exact combination depends on the size of the installation and whether it is connected to the grid or not.

Grid-connected, small-scale installation


PV in Building


In a small-scale, most likely residential, installation, the pv- module has to be connected to an inverter. The purpose of an inverter is to
  • Change the direct current (DC) output of a solar module to an alternating current (AC), which is used by all appliances.
  • Transform the voltage from the module's voltage to voltage required.

In small-scale installations the AC output from the inverter is a 2-phase AC, which is common in households. The inverter output can be connected to the grid via a meter.

Maximum Power Point Tracker (MPP)

As described, the mpp- tracker ensures that the module operates at its maximum power point at all times. Most inverters also include the maxium power point tracker (mpp).

Where crystalline modules are used, partial shading of the entire roof (for instance caused by a tree or a chimney), the module will only generate as much current as its weakest string. In this instance, each string should have its own mpp- tracker to boos efficiency of the system.

Surge Protection

Some inverters may also provide surge protection. However, this may not be enough if the wires between the solar module and the inverter are longer than 10m, when additional surge protection devices ought to be considered.

Grid-connected, large-scale installation

PV stand-alone system

Junction Box

In large-scale installations, multiple modules are connected through a junction box, which is just that, but also provides surge protection.


DC Switch

In order to be able to undertake repair or general maintenance work, the solar generator must be separated from the inverter. This is achieved by a DC switch close to the inverter. As the modules continue to generate electricity as long as there is sufficient light, the DC switch must cope with the short-circuit current as well as the open-circuit voltage.

Just unplugging a string of modules may cause a corona with a risk of fire. Some mnaufacturers of inverters offer integrated DC switches.


Inverters used here will most likely produce a 3-phase AC, which is more common in industrial contexts.



An optional transformer may step up the voltage to very high voltage required by the grid.

AC Switch

An AC switch is required by grid operators to ensure safety. It automatically switches off the grid connection if error currents, changes in frequency or voltage are detected.


Off-grid, hybrid renewable system

Hybrid Renewable Energy System

Why Hybrid?

In a hybride system, several renewable energy sources are used in tandem. By doing so, the variability of a single source (i.e. wind or sun beam) can be softened. This is especially true in the Northern hemisphere where there is evidence of a inverse correlation between wind and sunshine. That is, on days with high wind speeds, there is probably less sunshine and vice versa.

Why Off-grid?

On small islands or in other remote areas, a grid connection is often not feasible. To avoid wasting surplus energy from the renewable sources (which would otherwise be fed back to the grid), a battery may be used for storage. In times when energy demand exceeds the supply from renewable energy sources, the battery may be discharged. As a last resort a diesel engine must be employed if supply is to be guaranteed.

A controller should be utilised to balance charging / discharging of the battery and starting / stopping of the diesel engine.

Despite the complexity of these systems, they can be economically viable for remote areas where diesel fuel is very costly due to high transport costs. The sizes of each component however, need to be considered very carefully.

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