Recently we had a workshop with our Chairman, Paschal Phelan, and our technical department to better understand the ins and outs of solar photovoltaic (PV) plants.
Have a read on the interesting insights shared by Paschal Phelan in this article.
According to Paschal Phelan, solar power is an internationally hot topic at the moment with Tesla’s takeover of Solar City, Perth leading a trial to let people with solar panels sell excess energy to each other, and the Havas Horizons study showing that solar power ranks as the most promising investment in Africa. South Africa has had its own success story with Solar Capital opening the largest solar farm in the Southern Hemisphere, Africa and the Middle East earlier this year. Despite this, Paschal Phelan concluded that the average man on the street does not understand how a solar PV panel converts sunlight into electrical energy. This is how it is achieved.
Paschal Phelan is passionate about solar power being a clean, green, free source of energy for the world to utilize. South Africa has one of the highest usable irradiation levels in the world and thus was the perfect choice for the installation of the 175MW solar farm located just outside of De Aar, Northern Cape.
Paschal Phelan explains that the photovoltaic effect is the conversion of light to electricity within some material. Photo means light and voltaic means electricity.
To break it down very simply, solar modules (another name for panels) hold photovoltaic cells. These cells are made up of two layers of semi-conducting material (usually silicon) which are then combined with other materials to give each layer a positive or negative charge.
The top layer of silicon is seeded with phosphorous which adds extra electrons and thus a negative charge. The bottom layer is combined with boron so that there are less electrons and a positive charge. As a result of these charges, an electric field is formed at the juncture where the layers join, says Paschal Phelan.
When a photon of sunlight hits these cells, electrons come lose and the electric field pushes the electron out of the junction. Conductive metal plates (called busbars) collect this energy and transfer them to cables.
The cables from multiple modules are joined together into strings. The number of strings will depend on the power rating of the particular module used in the installation. The strings are then joined into a string combiner in order to minimise the amount of cables used. It also provides a location in the installation where a switch is installed to assist in maintenance and where protective fuses are installed should there ever be any faults in the electrical installation. The electricity flowing through the cables at this stage is called Direct Current (DC).
The electrical network functions on Alternating Current (AC), which is what we get from the wall outlet in our homes. Thus in order to deliver the photovoltaic electricity to the grid the Direct Current must be converted to Alternating Current and this is achieved by a piece of equipment called an Inverter. In a home installation the solar panels are connected to the inverter which is normally mounted on a wall. In the case of large utility scale facilities like Solar Capital’s, several hundred modules are connected to each invertor, this is called the central inverter type installation.
Paschal Phelan, concluded this workshop by saying that the generated electricity that comes out of the inverter is normally at a low voltage that can either be used in the home environment, or must be increased in order to deliver it to the national power grid. At the Solar Capital Facility this is done in a two stage approach, firstly through a smaller transformer located next to each inverter, secondly the electricity is then transported from these transformers to what is called the power transformers where the final increase in voltage is established to match the grid voltage.
Solar Capital’s De Aar solar facility has approximately 430 invertors, 504 000 modules and 380 transformers. This may sound like a lot, and could have proven troublesome to put together, but the facility was constructed in just over three years and the 175MW can now power up to 75 000 homes.