Solar photovoltaic (PV) systems in essence allow solar panels to capture energy from the sun to generate electricity for a home or business. A solar PV system that operates in conjunction with utility power is called a ‘grid tie’. A utility-grid interconnected photovoltaic system typically has no battery backup. Consequently, it is less expensive and operates at a higher efficiency than battery-based off-grid systems. Although grid-tied PV systems are the less expensive to install, they will shut down when the utility’s grid power is interrupted. Grid tied systems are designed to shut down in the event of a utility power outage. This is for the safety of utility personnel working on power lines.
Solar panels generate electricity during the day for use in a home. When the PV system is producing more power than is being consumed by a home or business, excess power is fed into the utility grid and the meter spins backwards. Any surplus produced during a billing period may be credited to the following billing period. Spinning the meter backwards and accruing ‘banked power’ to be used by a home during times when solar is not available, such as at night is commonly referred to as “net-metering”.
Typical grid tie system components include: Solar panel array- Inverter to convert DC power into AC power- Circuit protection and utility disconnect switch
Grid-Tie with Battery Backup
Grid-tied solar electric (PV) systems with battery back-up produce power to meet the load demands of a home or business but also keep a battery bank charged to use in the event of a commercial power failure. Grid-tied systems with battery back-up realize the same net metering benefits of the more common and basic gird-tie PV system.
Grid-tied systems with battery back-up do however cost more than straight grid-tied systems. Estimates can reach as high as 40% more expensive. The added expense results from additional components i.e. batteries and charge controllers. Proper battery maintenance and charging can reduce costs by extending batter bank shelf life of to ten years. Photovoltaic electricity is used to charge a backup battery bank and also power household loads. When the battery bank is full, excess PV energy is sold back to the utility grid. During utility power failures, battery back-up can power critical loads such as lighting, pumps for heating systems, and communications.
Typical grid tie with battery backup system components include: Solar panel array – Inverter - Circuit protection and utility disconnect switch – Battery charge controller - Small battery bank and protective encasement
An off-grid solar system, otherwise known as a stand-alone or autonomous solar system, is the kind of solar system you would install in a remote location where traditional utility lines are not available or are not practical to access. The electricity generated by the panels is stored in a bank of rechargeable batteries as DC but in order to power household appliances an inverter is required to convert the stored DC to AC. This type of system does consequently allow for use of the energy both night and day. Although solar panels are the primary source of electricity, this type of system also often requires a generator for high power appliances & supplemental battery charging.
Typical off grid solar system components include: Solar panel array - Inverter - Circuit protection and disconnect switch- Battery bank and protective encasement- Battery charge control – Generator