System Components

PV Electrical System Types

There are two general types of electrical designs for PV power systems for homes; systems that interact with the utility power grid and have no battery backup capability; and systems that interact and include battery backup as well.

Grid-Interactive Only (No Battery Backup)

This type of system only operates when the utility is available. Since utility outages are rare, this system will normally provide the greatest amount of bill savings to the customer per dollar of investment. However, in the event of an outage, the system is designed to shut down until utility power is restored.

Typical System Components

PV Array
A PV Array is made up of PV modules. The most common PV modules are 5-to-25 square feet in size and weighs about 3-4 lbs./ft2.
Balance of system equipment (BOS)
BOS includes mounting systems and wiring systems used to integrate the solar modules into the structural and electrical systems of the home. The wiring systems include disconnects for the dc and ac sides of the inverter, ground-fault protection, and overcurrent protection for the solar modules. Most systems include a combiner board of some kind since most modules require fusing for each module source circuit. Some inverters include this fusing and combining function within the inverter enclosure.
DC-AC inverter
This is the device that takes the dc power from the PV array and converts it into standard ac power used by the house appliances.
Metering
This includes meters to provide indication of system performance. Some meters can indicate home energy usage.
Grid-Interactive With Battery Backup
This type of system incorporates energy storage in the form of a battery to keep Òcritical loadÓ circuits in the house operating during a utility outage. When an outage occurs the unit disconnects from the utility and powers specific circuits in the home. These critical load circuits are wired from a subpanel that is separate from the rest of the electrical circuits. If the outage occurs during daylight hours, the PV array is able to assist the battery in supplying the house loads. If the outage occurs at night, the battery supplies the load. The amount of time critical loads can operate depends on the amount of power they consume and the energy stored in the battery system. A typical backup battery system may provide about 8kWh of energy storage at an 8-hour discharge rate, which means that the battery will operate a 1-kW load for 8 hours.

Typical additional system components include batteries and battery enclosures, a battery charge controller and separate subpanel(s) for critical load circuits.