Varentec Inc., a maker of software and equipment to help utilities manage electric grids, completed its Series C funding round with investments from billionaire Bill Gates, Vinod Khosla and 3M Co.’s venture capital unit.

The Silicon Valley startup didn’t say how much it raised in the latest round, according to a statement Wednesday. Santa Clara, California-based Varentec began the round with a $13 million investment from the same three investors in November.

Varentec began working with Hawaiian Electric Co. in April to install and validate grid controls on the island of Oahu, which has seen a surge of rooftop solar power installations that can make grid management more difficult.

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