The simplest type of stand-alone PV system is a direct-coupled system, where the DC output of a PV module or array is directly connected to a DC load. Since there is no electrical energy storage (batteries) in direct-coupled systems, the load only operates during sunlight hours, making these designs suitable for common applications such as ventilation fans, water pumps, and small circulation pumps for solar thermal water heating systems. Matching the impedance of the electrical load to the maximum power output of the PV array is a critical part of designing well-performing direct-coupled system. For certain loads such as positive-displacement water pumps, a type of electronic DC-DC converter, called a maximum power point tracker (MPPT) is used between the array and load to help better utilize the available array maximum power output.

A typical stand-alone photovoltaic power system with battery and battery charger arrangement

In stand-alone photovoltaic power systems, the electrical energy produced by the photovoltaic panels cannot always be used directly. Because the demand for energy does not always coincide with its production, electrical storage batteries are commonly used in PV systems. The primary functions of a storage battery in a stand-alone PV system are:

• Energy Storage Capacity and Autonomy: To store electrical energy when it is produced by the photovoltaic panels and to supply energy to electrical loads on demand.
• Voltage and Current Stabilization: To supply power to electrical loads at stable voltages and currents,
• Supply Surge Currents: To supply surge or high peak operating currents to electrical loads or appliances.

Stand alone systems will become increasingly important as the price of the system drops and the price of electricity rises. Please contact Bright Energy to discuss your plans.