CASE STUDY SYSTEM 4

Grid-connected system

Roof mounted grid connected PV array

System Sizing and Design

In Australia grid connect systems are typically used to offset the energy use of the household.  The power is exported to the utility grid, only when the household load is less than the inverter output.  The design of a grid connected PV system depends on several factors.  The system could be designed to replace all or part of the energy consumption of the household.  The proportion of the household load replaced by the PV system depends on the size of PV array.  The size of the PV array selected may be limited by the available roof space or the budget.    

The system should be designed according to Australian Standards (AS4777, AS5033, and AS3000) by an accredited designer.  A system is designed by first determining the size of the PV array then the grid-connect inverter is chosen to match the expected output of the chosen PV array. Because a household does not need to rely on the PV array to supply all its electricity requirements, a grid-connected system can be used purely to replace its electricity requirements from the utility grid.  However, if the budget and roof space permit, a large enough system can be installed, which can export power to the grid after supplying the household load.  For more information, see the Department of Environment, Water, Heritage & the Arts Grid Interactive Systems page.

System Installation and Specifications

The system was installed in the first week of December 2000.  The system has since been upgraded in late 2006 by replacing the inverter with a recent model from another manufacturer.  The system comprises the following major components:

Photovoltaic Modules The photovoltaic array absorbs energy from the sun and converts it directly into DC electricity.  This system has 12, 120Watt Sharp NE-H120EI type multi-crystalline PV modules giving a total PV array size of 1.44 kW.

Grid-Connect Inverter The PV modules are connected to the utility network through SMA - SB 1700, a grid connect inverter.  This inverter converts the DC electricity from the solar array to very high quality AC electricity suitable for use with standard appliances. The inverter interacts with the utility grid to export the excess power produced by the system. It disconnects the generation source (PV array) from the grid whenever the grid is tripped or turned off for repair, maintenance or troubleshooting purposes. The inverter was tested by RISE for compliance to Australian Guidelines for the grid connection of energy systems via inverters, in particular clause AS4777.2 and AS4777.3 of the Australian Standard..

DC Switchboard This box houses the DC circuit breaker. It allows the DC component of the system (PV array) to be isolated.

Energy Meter This meter is a Single Phase Watt-hour meter. It shows the total energy (AC kWh) that has been generated by the system.

Local Utility Grid The system is connected to the local utility grid which is owned and operated by Western Power.

 

System Performance

Since the installation, between December 2000 and June 2007, on average the array has produced 4.9 kWh of electricity per day.  The design energy output of the system (using sunny data software) is 6.0 kWh/day.  The shading of the PV array in the early morning due to the orientation limitations on the roof is a major contributing factor in this low energy yield.  In addition to that, the system was not connected to the grid for several days during the upgrade.

 

System costs

The cost of the various system components installed at RISE in September 2000 are given below. (Prices include GST.)

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