The use of renewable energy is growing in the U.S., but its adoption has put pressure on old, overtaxed power grids. The intermittency of wind and solar power means that transmission systems need to find a way to store the energy generated from renewables to provide predictable power for grid operators. The latest company to try its hand at solving the problem for utilities is Ambri, which just raised $35 million in new capital from new investors KLP Enterprises.