Grid Interactive System

A Grid Interactive system, sometimes also referred to as Grid Interactive System with Batteries are ideal for locations that are connected to the grid, but where the grid is unreliable or the owner wants a backup source of power for critical loads. A block diagram of the Grid Interactive system design is shown below:

The main components of a Grid Interactive system are: PV Arrays, Battery Charge Controller, Battery Bank, Inverter. Other components include Fuses and Switches, Ground Fault protector devices, wiring, combiner boxes and meters where required, sometimes also referred to BOS (Balance of Systems).

When designing a Grid Interactive system it is important to identify the critical loads that must be supported by the system in the event the grid power goes down or is interrupted. Accurately estimating the critical load requirement can help size the system appropriately and reduce the overall cost of the system. As with all types of Solar PV systems, they are not the most economical way of powering all appliances in a typical house and when designing the system, wisely choosing which appliances are 'critical' is important to keep the overall costs down.

The main steps involved in designing a Grid Interactive 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: Estimate the critical loads that need to be supported

Step 2: Determine the days of Autonomy for the system
Define the duration of time the system should support the critical loads in the event of a grid failure. This is also sometime referred to as "Days of Autonomy". The longer the "days of autonomy" the larger the battery back up will need to be.

Step 3: Select a "Nominal" DC side voltage that the design will be based on

Step 4: Select the PV Panels to be used for the system
Depending on the manufacturer and model, the number of panels in the array can be calculated.

Step 5: Select the Battery manufacturer and model to be used in System
Depending on the characteristics of the model the Number of batteries required for the battery bank can be calculated.

Step 6: Select an appropriate Charge controller
The charge controller regulates the charging of the battery bank. You need to choose a charge controller that can support the DC nominal voltage and current required to charge the batteries.

Step 7: Select an appropriate Inverter
An Inverter converts DC power to AC power that is needed to power your loads. Select an Inverter that can support the power Requirements of the critical load as well as the power Surge requirements of the critical loads. Also ensure that the inverter is capable of handling the input DC voltage and current as well as generate the required AC Voltage.

Step 8: 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:	Estimate the critical loads that need to be supported
Step 2:	Determine the days of Autonomy for the system Define the duration of time the system should support the critical loads in the event of a grid failure. This is also sometime referred to as "Days of Autonomy". The longer the "days of autonomy" the larger the battery back up will need to be.
Step 3:	Select a "Nominal" DC side voltage that the design will be based on
Step 4:	Select the PV Panels to be used for the system Depending on the manufacturer and model, the number of panels in the array can be calculated.
Step 5:	Select the Battery manufacturer and model to be used in System Depending on the characteristics of the model the Number of batteries required for the battery bank can be calculated.
Step 6:	Select an appropriate Charge controller The charge controller regulates the charging of the battery bank. You need to choose a charge controller that can support the DC nominal voltage and current required to charge the batteries.
Step 7:	Select an appropriate Inverter An Inverter converts DC power to AC power that is needed to power your loads. Select an Inverter that can support the power Requirements of the critical load as well as the power Surge requirements of the critical loads. Also ensure that the inverter is capable of handling the input DC voltage and current as well as generate the required AC Voltage.
Step 8:	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.