Inverter and other fixed costs
The inverter is an electronic device which converts the direct current (DC) electricity that comes from the solar panels into alternating current (AC) electricity which matches the AC frequency of the power lines. The inverter also matches the AC voltage of the power lines, but sets its voltage slightly higher so that the energy from the solar cells is pumped back into the power grid. This runs the electric power meter backwards which gives the customer credit for the kilowatt-hours of energy produced by the solar panels.

The inverter must also be able to disconnect from the power grid at certain times. For example, if there is a power failure on the grid, it would be hopeless for your system to power everything else. So to protect your system, it must quickly disconnect. Also, if there are power company service people working on the power lines, they must be able to disconnect such a power source from the wiring so that it is safe to work on the power lines. The inverter has provisions for such remote control and also sends information back to the power company reporting how much energy has been generated.

Note that if you will produce more power than the input capacity of the inverter, you will need to buy more than one inverter or use a larger capacity model. In some instances, a fan can be attached to the inverter which will allow it to handle a slightly greater amount of power.

You should include the cost of the inverter(s) and any other fixed installation costs, including taxes, into the calculator at this point.

Here are some inverter models approved for grid use.
Cost Inverter Efficiency
$2500?? PV Powered StarInverter PVP2800 97.6%
$2500?? Sunny Boy 2500U 94%
$2500?? Xantrex STXR2500 91%