Most of the excess was being used to charge a 100-kilowatt battery, which also drew from a natural-gas fired microturbine that doubles as a heater. An extra 2.5 kilowatts was being fed into utility power lines, although the project is too large to receive payment for excess generation.

“We’re very generous,” said Caramy Biederman, the project’s lead engineer.

With its combination of generation and storage — there’s a fuel cell, powered with hydrogen that is produced with excess solar power, and a backup natural gas generator — the grid is controlled by a central computer, which balances supply and demand in much the same way as the large grid.

The $3 million system, believed to be the first of its kind in Wisconsin, includes more generation than needed but it allows Faith to experiment with different configurations.

“We basically built several microgrids into one,” Biederman said.

For example, it might be more efficient to run the microturbine all-out and store the extra energy; or to use utility electricity at night when it’s cheaper and save the batteries for a cloudy afternoon.