Grid Tie System

A Grid-Tie system has evolved primarily as a way to incorporate renewable energy sources into the existing grid in the developed world. The grid is highly reliable but dependant on traditional generation systems, primarily coal based power plants, which contribute to global warming. California and many other states in the US and countries like Germany, Spain, Canada and France support residential and large scale grid-tie systems and have mandated a portion of all electricity generated and used in their states and countries come from renewable energy systems. They also financially support these systems through a number of ways including rebates and SOCs (Standard Offer Contracts), buy back programs, accelerated depreciation for commercial systems, Performance based Initiatives and the like.

The key characteristic of a Grid-Tie system is that it does not provide any backup in the event of a grid power loss. The PV Grid-Tie system will shut down along with the grid and will not provide any backup capability.

A block diagram of a Grid-Tie system design is shown below:

The main components of a Grid-Tie system are:
PV Arrays and the Inverter. Other components include Fuses and Switches, Ground Fault protector devices, wiring, combiner boxes and other components also referred to as BOS (Balance of Systems).

The key missing component in this system compared to the other discussed in this website is the battery bank, which is why this system does not have any backup capability. This is a simpler system to design and maintain and less expensive compared to the other systems.

The main steps involved in designing a Grid Tie system are listed below:

Step 0: Determine the Solar Hours of your location
Solar PV systems depend on the Sun and sun light to generate electricity. Depending on the geographical location of the site, average number of hours of sun light has been recorded and is available at the National Renewable Energy Laboratories website (www.nrel.gov). Another link inside NREL's website that has a lot of information is www.nrel.gov/gis/solar.html. This is also referred to as "Solar Hours" and will be used in sizing the various components of the PV System.

Step 1: Select the size of the PV System in KW to be designed and pick a PV Module
The size of the PV system will determine the number of PV Modules in the array depending on the PV Module manufacturer and specifications of the module.

Step 2: Configure your PV Array
Determine the configuration of your PV Array, which determines the DC Voltage of your system.

Step 3: Select the right Inverter for your system
Select an appropriate Inverter that can support the PV system size. Also ensure that the inverter is capable of handling the input DC voltage and current as well as generate the required AC Voltage. The Inverter in a Grid-Tie system must be UL listed for Grid-Tie applications and must support a feature called "Islanding".

Step 4: Calculate and select BOS components
An important factor to keep in mind when selecting the main components of the system are to make sure they are rated for the application and certified by UL and/or appropriate local requirements for the application.

Step 0:	Determine the Solar Hours of your location Solar PV systems depend on the Sun and sun light to generate electricity. Depending on the geographical location of the site, average number of hours of sun light has been recorded and is available at the National Renewable Energy Laboratories website (www.nrel.gov). Another link inside NREL's website that has a lot of information is www.nrel.gov/gis/solar.html. This is also referred to as "Solar Hours" and will be used in sizing the various components of the PV System.
Step 1:	Select the size of the PV System in KW to be designed and pick a PV Module The size of the PV system will determine the number of PV Modules in the array depending on the PV Module manufacturer and specifications of the module.
Step 2:	Configure your PV Array Determine the configuration of your PV Array, which determines the DC Voltage of your system.
Step 3:	Select the right Inverter for your system Select an appropriate Inverter that can support the PV system size. Also ensure that the inverter is capable of handling the input DC voltage and current as well as generate the required AC Voltage. The Inverter in a Grid-Tie system must be UL listed for Grid-Tie applications and must support a feature called "Islanding".
Step 4:	Calculate and select BOS components An important factor to keep in mind when selecting the main components of the system are to make sure they are rated for the application and certified by UL and/or appropriate local requirements for the application.