Understanding The Technology Behind Solar PV Systems
A simple solar photovoltaic (PV) system consists of the following basic components:
- A solar cell: A solar cell is a solid-state electrical device (p-n junction) that converts the energy of light directly into electricity (DC) using the photovoltaic effect. A solar cell is categorized as a multi-junction cell, single-junction cell, crystalline cell, thin-film technology, or some of type of emerging PV cell (like organic cells, etc.).
- Solar module: Collections of a single solar cell are termed as solar modules. Solar cells are connected by a wire either in parallel or in series according to the desired output. If we wish to have more current, the cells are connected in parallel, and if we wish to have more voltage, the cells are connected in series.
- Solar module array: When solar modules are connected either in series or in parallel according to the desired output, the collection of the solar module is termed a solar module array.
- Solar charge controller: If we wish to charge the generated DC power from the solar array to a battery, as mostly seen in rooftop installation, a solar charge controller is inevitable. Through this controller, the battery life is elongated and maintains a constant output voltage for the battery input, which is normally either 12 volt or 24 volt. It uses the PWM (pulse width modulator) or MPPT (maximum power point tracker) technique for better charging performance.
- Combiner box: The combiner box is an electrical distribution box where the DC circuit breakers are placed. The combiner box combines the multiple DC inputs coming from the panel (either module or array) terminations and converts these into one DC output. The output of the combiner box is connected to the charge controller or the inverter, depending on the type of system installed.
- Solar array inverter: This inverter is also termed as a central inverter or string inverter. It converts the single DC output power from the combiner box into AC power which then can be connected to the power/electric grid. This inverter uses the MPPT (maximum power point tracker) technique for better optimized output. However, the problem of partial shading or shadowing — technically termed as potential induced degradation (PID) of the solar panel — is prominent with the use of such an inverter.
- Solar module inverter: This inverter is installed at the modular level. It converts the generated DC power to AC power using a micro inverter for each module. This inverter also uses the MPPT (maximum power point tracker) technique for better output. The advantages of an such inverter are that it has more reliability with better performance. And also it reduces the PID effect.
- Power cable: There are two types of power cables. Low-voltage power cables (solar panel to the combiner box, combiner box to the inverter, and inverter to the transformer) and medium-voltage power cables (transformer to the substation).
- Switch gears / protection: Switch gears are one of the most important components in a PV system. It allows protection of the components from any fault during the operation, such as over-current, over-voltage, temperature rises, lightening faults, switching faults, etc. For better reliability of the system, communication between each component is a must. A central monitoring computer allows checking the communication between each component and the execution of tripping the fault.
- Power quality issues: This has become one of the major topics in the utility sector for common consumers. Due to cabling, there is a higher chance for interference in the power signal, which leads to a reduction in generated output power. For such cases, a metal mesh encasing the cables improves shielding. Due to the use of power electronic switches in inverters, common mode (CM) disturbances are prominent. Because of CM disturbances, transience in the power is seen and the output power is distorted. A thorough understanding of EMC related to the PV system is important for better performance and high reliability for that given PV system.
With this basic intro on photovoltaics out of the way, we will next dive into articles more focused on each of these components.