Definitions
PhotoVoltaics (PV)
Is a technology that, by use of a variety of devices, converts energy from sun radiation (sunlight) into electricity.
Basics
Usually the device coverting light into electricity is a solar cell, packaged in PV modules (or solar panels), which are often installed in the form of PV arrays electrically interconnected. This energy conversion is typically not very efficient, with common values in the 10-15% range, depending on the specific technology adopted.
PV panels or PV arrays are generally configured in 4 different ways:
(1) stand-alone (off-grid)
(2) stand-alone with battery back-up (off-grid)
(3) stand-alone with battery back-up but grid-connected to feed battery
(4) stand-alone with battery back-up but grid-connected to dispose of excess power.
Since PV electricity is produced as Direct Current (DC) while that from the grid is Alternate Current (AC), in case (3) AC needs to be converted into DC by use of a rectifier while in case (4) DC needs to be converted into AC by use of an inverter.
Applications of PV
PV power stations
Existing PV power stations are in the 9 to 15 MW range. Bigger stations are under construction or planned, to reach a maximum to date of 154 MW in North-West Victoria (Australia) and 62 MW in Portugal. The Victoria power station utilises high performance solar cells originally developed to power satellites and capable of concentrating the sun energy by 500 times for ultra-high power output by use of a technology known as ‘Heliostat Concentrator Photovoltaic’ (HCPV) i.e. fields of heliostats (sun-tracking mirrors) focusing sunlight onto receivers. More details here.
PV installations near Olivenza, Extremadura (Spain)
PV in buildings
Building-integrated photovoltaics (BIPV) today are incorporated in new or retrofitted into existing roof or walls of residential, commercial and industrial buildings as a principal or auxiliary source of electrical power. Alternatively, the PV array could be installed away from the building but connected to it by cable.
Where a building is located at a considerable distance from the electricity supply grid, PV may be used for generating electricity alone or together with wind, hydro or diesel generators. Under these off-grid conditions, battery back-up packs are usually used to grant a continuous supply or to store the discontinous excess power produced. store the electric power.
PV in standalone devices
The is an increasing use of PV components in the design and installation of solar-powered remote fixed devices (e.g. rural or urban streetlighting, technical measurement or communication devices).
Standard streetlighting installation
Streetlighting. Solutions vary from standard industrial products to the artistic design of a recent installation.
A typical streetlinghting system includes the following components:
a) solar PV module
b) boxed battery
c) change controller c/w inverter
d) lamp fixture installed on
e) support post.
The system is designed so as to allow electricity produced by the PV panel to be accumulated in a battery storage unit capable of supplying enough power to lit the lamp for a maximum period of 12 hours/day. Power feeding is controlled by an automatic ON/OFF time switch for dusk to down operation. An overcharge / deep discharge prevention cut-off device is also included in the system to prevent damages to the battery or the lamp fixture.
The SPV modules are reported to have a service life of 15-20 years. Tubular Batteries provided with the solar street lighting system require lower maintenance; have longer life and give better performance as compared to pasted plate batteries used earlier.
Streetlight tree outside Museum für Angewandte Kunst, Vienna (Austria) (source)
More technical and calculation details are provided in Chapter 5 - SOLAR PHOTOVOLTAIC ENERGY of the ELREN Training Manual available in this website (here).