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A Solar power system contains many different components besides the basic PV modules building block. For successfully planning a Solar PV system, it is crucial to understand the function of the basic components and to know their major functions. Further, it is important to know the effect on the location of the (expected) performance of a PV system whether you are planning this for your home or a small industrial concern or you simply want to power a single load. Understanding the different components in the Solar power system and their interrelationship with each other will help in making the right choice in terms of your financial outlay.
Solar PV systems can be very simple, consisting of just a few PV modules and load such as the direct powering of a water pump motor, which only needs to operate when the sun shines. However, when a whole house is required to be powered, the system must be operational day and night. It also may have to feed both AC and DC loads, have reserve power and may even include a back-up generator to charge batteries during hours of darkness or low sun light.
Types of PV Systems.
There are three main types of PV systems: stand-alone, grid-connected, and hybrid. The basic solar power system principles and elements remain the same. Systems are adapted to meet specific requirements by varying the type and quantity of the basic elements. One key advantage of the solar power system is that it is modular by nature. A modular system design allows easy expansion, when power demands change.
Stand-Alone Solar PV Power Systems
Stand-alone systems rely on solar power only. These systems can consist of the PV modules and a load only or they can include batteries for energy storage. When using batteries charge regulators are included, which switch off the PV modules when batteries are fully charged and may switch off the load to prevent the batteries from being discharged below a certain limit.
The batteries must have enough capacity to store the energy produced during the day to be used at night and during periods of poor weather. Below is shown below for the two commonly applied stand-alone systems: A simple DC Solar power system without a battery.
A large standalone Solar PV power system with both DC and AC loads
Grid Connected Solar PV Power Systems
Grid-connected Solar power systems are becoming increasingly popular for building integrated applications. As shown here, they are connected to the grid via inverters, which convert the DC power into AC electricity.
In small systems such as in residential homes, the inverter is connected to the distribution board, from where the PV-generated power is transferred into the electricity grid or to AC appliances in the house. These systems do not require batteries, since they are connected to the grid, which acts as a buffer such that an oversupply of PV electricity is transported while the grid also supplies the house with electricity in times of insufficient PV power generation.
Hybrid Solar Power PV Systems
Hybrid systems consist of combination of PV modules and a backup system for electricity generation such as a diesel, gas or wind generator. A schematic of an hybrid system shown below:
Hybrid systems typically require more sophisticated controls than stand-alone or grid-connected PV systems. As an example, in the case of an PV/diesel system, the diesel engine must be started when the battery reaches a given discharge level and stopped again when battery reaches an adequate state of charge. The back-up generator can be used to recharge batteries only or to supply the load as well.
