Hybrid systems are perhaps the most complex of all PV systems in terms of equipment, system design, and installation. However, they offer the greatest flexibility with regard to configurations and control strategies. The contribution from each source can be optimized for the application while minimizing the initial and operating costs. For example, an array may be designed to power the loads only during the months with the highest insolation, with an engine generator supplying the balance of energy required at other times. With Interactive or bimodal inverter features, hybrid systems can be optimized load backup, utility rate management, and efficiency. For example, an engine generator can be loaded to its maximum output for meeting system loads and charging a battery bank, increasing its fuel efficiency. In addition, battery banks can be smaller in hybrid systems because auxiliary energy sources may also provide back-up or on-demand power.

Hybrid systems are classified by the way, in which the power outputs from the various sources are used. A DC bus hybrid system is a hybrid system that combines DC power output from any auxiliary energy sources with the DC power with the DC power array before the power is routed to batteries or any power conditioning equipment. When an engine generator, wind turbine, micro-hydroelectric turbine, or other AC power source is used, the AC output is rectified to DC power for battery charging.

An AC bus hybrid system is a hybrid system that supplies the loads with AC power from multiple energy sources, but does not combine them. Energy sources that output AC power such as inverters and engine generators will not be synchronized with each other, so they cannot be combined and must be isolated from one another through a bus transfer mechanism.

AC loads can be installed with a manual transfer switch that isolates that isolates the two AC power sources and allows switching between them, so the load operates from either the inverter or generator. This effectively changes the system between a DC-bus and AC-bus configuration. Many modern inverters are specifically designed to integrate and control multiple energy sources by including built-in battery chargers and automatic transfer switches. For example when a battery bank is discharged, the inverter control relays may start an engine generator and automatically transfer the loads to the output from the generator. The array power is then used to charge the battery bank.