Based on the attached quote, you can take the credit if you could generate electricity for your home, even though it wasn't connected to the grid. It must be functioning and providing the home with electricity.
"The system must be placed in service during the tax year and generate electricity for a home located in the United States. There is no bright-line test from the IRS on what constitutes “placed in service,” but the IRS has equated it with completed installation."
See middle column, second paragraph: Homeowner's Guide to the Federal Tax Credit for Solar Photovoltaics
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