Types of Solar Electric Systems
The modularity and flexibility of solar electricity allows users to have a system tailored to their specific needs and preferences. In addition to full or partial power for a home or business, solar electricity may serve as a power source for a specific job. This could be electricity for a well pump, patio or street lighting, or for a home security system or even a backyard waterfall. Typically, such systems consist of one or more modules and a charge controller accompanied by a battery or batteries.
Generally speaking, solar power systems may be categorized into three primary types: standalone, battery backup, and utility (grid) connected. Any of these types of systems may be designed to meet all or part of the user's electrical requirements.
Photovoltaic (PV) systems are composed of several individual components including arrays (multiple connected modules), inverters, controls, safety disconnects, and batteries. By assembling differing sizes of components together, systems can be built with varied power outputs to meet the demands of various loads.
Some applications need a system that includes a fuel power backup generator, wind turbine or water turbine. Typically, such "hybrid" systems share the load between the solar chargers and the back-up generator. Batteries are still required, plus the DC to AC inverter if regular AC loads will be powered.
Standalone DC System
Standalone type systems are usually a utility power substitute. They generally include solar charging modules, storage batteries and controls including a charge regulator. A small standalone DC system is an excellent replacement for kerosene lamps and noisy generators in a remote home, a recreational vehicle, or a boat. The actual sizing depends on the wattage of the loads and how often they are to be run.
In this system a photovoltaic (PV) array charges the battery during daylight hours and the battery supplies power to the loads when needed. The charge regulator terminates the charging when the battery reaches full charge.
Standalone AC-DC System
This system is the same as the previous system, except for the use of a DC to AC inverter. With the addition of an inverter, commonly available household appliances such as computers, power tools, vacuum cleaners, washing machines and kitchen appliances can be solar powered.
High quality DC to AC inverters are available with power outputs ranging from one hundred watts to ten kilowatts and more, and conversion efficiencies greater than 90 percent. Most larger inverters also have the ability to serve as battery chargers from a backup generator when more power is needed than can be supplied by the solar modules.
Backup AC System
A backup AC solar electric system will usually have a photovoltaic (PV) array of ten or more modules, a battery bank, and one or more inverters. The utility will backup the solar and run the loads when available and needed. If utility power fails, the power from the battery bank is available to the system.
Utility Interconnected System (Grid-tied)
These are the simplest systems and require no batteries because they are designed not for back-up power but to contribute power back into the existing power supply.
By lowering a building's power bills, these systems will pay for themselves over a number of years and reduce the air pollution produced by utility companies that burn coal. Contributing clean, green power from your own roof helps create jobs and in sunny states like Florida is the best alternative to buying electricity derived from fossil fuels.
Utility interconnected systems are generally designed to reduce power demands from the utility by 'net metering' power or in some cases to sell power back to the utility. A typical system might include solar modules, a mounting structure, and AC inverter/control for the power to be fed back through the building's 120/208/240 volt AC power distribution system.