Mounting Structures
Photovoltaic arrays must be mounted on a stable, durable structure that can support the array and withstand wind, rain, hail, and other adverse conditions. Sometimes, this mounting structure is designed to track the sun. However, stationary structures are usually used with flat-plate systems. These structures tilt the PV array at a fixed angle determined by the latitude of the site, the requirements of the load, and the availability of sunlight. Among the choices for stationary mounting structures, rack mounting may be the most versatile. It can be constructed fairly easily and installed on the ground or on flat or slanted roofs.
A typical PV array mounting rack.
Power Conditioners
Power conditioners process the electricity produced by a PV system so it will meet the specific demands of the load. Although most equipment is standard, it is very important to select equipment that matches the characteristics of the load. Power conditioners may have these functions:
- Limit current and voltage to maximize power output
- Convert DC power to AC
- Match the converted AC electricity to a utility's electrical network
- Have safeguards that protect utility personnel and the network from harm during repairs
Specific requirements of power conditioners depend on the type of PV system they are used with and the applications of that system. For DC applications, power conditioning is often done with regulators, which control output at some constant level of voltage and current to maximize output. For AC loads, power conditioning must include an inverter that converts the direct current generated by the PV array into alternating current. Many simple devices—for example, ones that run on batteries—use DC electricity. However, AC electricity, which is what is generated by utilities, is needed to run most modern appliances and electronic devices.
Workers install a 1-kilowatt PV/battery system at Camp Leakey in Kalimantan Tengah, Borneo, Indonesia. Part of the Solar in the Jungle project, this system supplies remote power for the Orangutan Foundation International.
Electricity Storage
We need electricity at night and on cloudy days as well as on the sunny days that are so perfect for PV power generation. If tapping into the utility grid is not an option, a battery backup system is necessary for energy storage. However, batteries do lower the efficiency of a PV system, because only about 80% of the energy that goes into them can be reclaimed. They usually need to be replaced every 5 to 10 years. Also, they take up considerable floor space, pose a few possible safety problems, and require periodic maintenance. Still, they provide one way to store PV electricity for later use.
Like PV cells, batteries are direct-current devices that are directly compatible only with DC loads. However, batteries can also serve as a power conditioner for these loads by regulating power. This allows the PV array to operate closer to its optimum power output.
Charge Controllers
An inverter (left) and charge controller (right) are known as the power conditioning components of a PV system.
An inverter converts the direct current (DC) electricity generated by the PV array into alternating current (AC) and the charge controller protects the battery (the electricity storage device) from overcharging and also excessive discharge. Most batteries must be protected from overcharge and excessive discharge, which can cause electrolyte loss and even damage or ruin the battery plates. Most charge controllers also have a mechanism that prevents current from flowing from the battery back into the array at night.
Tracking Structures
There are two basic kinds of tracking structures: one-axis and two-axis. The one-axis trackers are typically designed to track the sun from east to west. They are used with flat-plate systems and sometimes with concentrator systems. The two-axis type is used primarily with PV concentrator systems. These units track the sun's daily course, but also, its seasonal course between the northern and southern hemispheres. Naturally, the more sophisticated systems are the more expensive ones, and they usually require more maintenance.