Grid Tie Inverter
Most solar electric systems use inverters to convert direct current to alternating current, which is the type
compatible with our electrical appliances. However, some solar systems use special inverters with more
functionality and features.
A grid tie inverter is one that, on top of converting alternating current into direct current, feeds the current
on to an electrical grid.
They are typically used in systems where a renewable source is going to be ‘tied’ on to a grid to overcome
In technical terms, a grid inverter is called a ‘grid interactive inverter’, or at times known as synchronous
inverter. Grid inverters are cannot be used on a standalone application that is not connected to a utility
Types of solar systems
Solar energy can be used to power just about anything that requires electricity and it is now being used in a
number of applications. The type of solar system to be used depends on the type of application. There are basically
two types of solar electric systems:
Grid tie or grid connect solar system – this is a solar system that is also ‘tied’ or connected to another
electric system, usually a utility grid system.
Standalone solar system – these systems operate independent of another system. They are usually used to power
isolated electrical equipment, such as radio repeaters, street lighting and phone booths. Standalone solar systems
are also growing in popularity in the leisure caravan and boat market.
Grid tie systems
A number of states in the US, as well as countries elsewhere, allow grid-tied electrical systems where owners of
these systems are allowed to sell excess electricity to the utilities. There are several ways through which the
excess power supplied to the grid can be compensated.
The most widely used is net-metering, where the entity that owns the source of power receives compensation from
the utility company for the net outflow of power. For instance, if an entity supplies 300 kilowatt hours to the
utility grid and only uses 100 kilowatt hours from the grid, the net outflow would be 200 kilowatt hours and that
is the value of compensation it would receive, in form of credit at a retail or whole sale price, depending on
jurisdiction. Policies governing net-metering in the US vary by state.
Another type of compensation is based on a feed-in-tariff. In this system, a supplying entity is paid for each
kilowatt hour supplied to the utility grid using a special tariff based on an agreement with the utility company or
some other power authority.
In the US, there are particular requirements set for grid tied electric
systems, as stipulated by provisions in the National Electric Code.
Operation of a grid tie inverter
An inverter receives direct current and inverts it to alternating current so that it can be fed into the grid. A
grid tie inverter also synchronizes the grid’s frequency with its own by use of an oscillator and monitors voltage
changes, limiting it to the grid’s voltage.
In its design, a grid tie inverter will automatically disconnect from the grid once the grid goes down. This
particular feature is a NEC requirement that ensures safety of line workers who may be fixing the grid at the time
of a blackout.
In simple terms, a grid tie inverter enables a plug and play operation for homeowners who produce energy from
solar or wind