Grid tied systems, also known as on-grid or grid-interactive, can both feed excess power to the utility grid and pull electricity from the grid when demand exceeds generation. Grid tied renewable energy systems are easy to install and maintain since there are no battery back-ups involved. The main difference between grid tied systems and off-grid systems is the grid interactive inverter.
The inverter converts the DC current produced by the generated via the renewable energy source –solar, wind, biogas- to AC current. AC current is the same type of electricity that US utilities provide and the same type of electricity that the majority of home appliances require. In other words electricity flows freely between the renewable energy source system and the utility system, providing us with the “grid-interactive” name.
When the renewable power supply produces more than your house is consuming the excess electricity is directed to the utility. This connection enables the utility company to gain immediate access to the renewable energy directly from your roof. In most cases, you earn money by selling your excess power to the utility company. When your renewable energy system is not producing enough electricity for your needs the inverter pulls power from the utility grid.
Through this back and forth of sharing electricity the home owners utility bill is reduced. This savings over time allows for renewable energy system to “pay for themselves” through future savings. Most European companies are required to pay what is called a “feed in tariff” for the electricity they buy from consumers. In the US, some states require feed-in-tariffs, other states structure their pay back rates differently.
It should be noted that a grid-tied system should not be used as a back-up power in case of a grid blackout. In regions where temporary blackouts are common, grid tied systems are not the best solution.
[image credit: irisgroup]